Optical scanning device and image forming apparatus

A seal member is injection-molded with a simple structure that needs no complicated assembling process.An optical scanning device 21 includes a light source unit 202 from which a light beam is emitted; a rotating polygon mirror 203 that deflects the light beam such that the light beam emitted from the light source unit 202 is scanned over a photosensitive member; an optical component that directs the light beam deflected by the rotating polygon mirror 203 onto the photosensitive member; an optical housing 20 that contains the light source unit 202, the rotating polygon mirror 203, and the optical component; and a cover 30 that covers an opening of the optical housing 20. The cover 30 includes a seal member 31a molded such that the seal member 31a is sandwiched between the cover 30 and a side wall of the optical housing 20, a gate 31a from which hot melt is injected, and a channel through which the hot melt flows to form the seal member 31a such that the seal member 31a is sandwiched between the side wall of the optical housing 20 and the cover 30. The gate 31a is provided outside a light path area for the light beam when viewed in a direction of a rotational axis of the rotating polygon mirror 203.

TECHNICAL FIELD

The present invention relates to an optical scanning device with which an electrophotographic image forming apparatus, such as a copying machine, a printer, or a facsimile, is equipped and to the image forming apparatus equipped with the optical scanning device.

BACKGROUND ART

Electrophotographic image forming apparatuses, such as laser beam printers and digital copying machines, are provided with an optical scanning device that exposes a photosensitive member to light. The optical scanning device deflects a light beam emitted from a semiconductor laser by using a rotating polygon mirror that rotates and scans the light beam over the photosensitive member. An electrostatic latent image is thereby produced on the photosensitive member. Toner is attached to the electrostatic latent image for developing, so that a toner image is formed. The toner image is transferred to a sheet to form an image.

In recent years, the colorization of image forming apparatuses has been developed. For color image forming apparatuses, the so-called tandem-type, which includes photosensitive members that are each used for one color and collectively forms images in the respective colors on an intermediate transfer member, has been the mainstream type. In tandem-type color image forming apparatuses, the so-called four-in-one optical scanning devices, in which one rotating polygon mirror performs exposure for four colors, are widely used because of an advantageous unit size and cost.

Recent trends in image forming apparatuses that can be mentioned herein are an increase in speed and an increase in resolution, in addition to the colorization described above.

One measure to achieve the increase in speed and the increase in resolution is to rotate the rotating polygon mirror at a high speed. However, the rotation of the rotating polygon mirror at a high speed creates a high negative pressure near the rotating polygon mirror in the interior of the optical scanning device, so that it is easy for the optical scanning device to draw air from the exterior. The air drawn from the exterior of the optical scanning device may include fine dust and volatile matter in grease used in the image forming apparatus itself. When such air enters the optical scanning device, extraneous matter on the reflective surfaces of the rotating polygon mirror increases, and, within a period from several weeks to several months, an image failure may occur, for example, such that density is extremely decreased at part of the image due to a decrease in the amount of exposure light.

To prevent this, an elastic seal member made of synthetic rubber or polyurethane is attached to a cover for an optical housing at a junction that comes in contact with the outer periphery of the optical housing. The seal member is sandwiched between the cover and the optical housing to ensure the sealability of the interior of the optical housing. The seal member, as an independent component, is attached to the cover or the optical housing with a double-sided tape. For reliable sealing, however, it is necessary to carefully attach the seal member such that the seal member follows the shape of the cover or the optical housing. This operation is complicated.

In view of this, for example, PTL 1 discloses that an optical scanning device is configured such that a separated seal member is not attached, but an elastomeric seal member is injection-molded integrally on the optical housing or the cover so that an assembling process is simplified and the optical scanning device achieves sealability.

CITATION LIST

Patent Literature

SUMMARY OF INVENTION

Technical Problem

FIG. 7(a)is a perspective view showing the appearance of an optical scanning device21described later. As shown inFIG. 7(a), the optical scanning device21includes an optical housing20and a cover30that covers the opened side of the optical housing. A rotating polygon mirror, various lenses, reflection mirrors, and so on, which will be described later, are held together in the interior of the optical housing20. The cover30covers the opened side of the optical housing20and seals the interior of the optical housing20. The detail of the optical scanning device21will be described later.

A seal member is formed on the cover30by injection molding in order to ensure the sealability of the interior of the optical housing20. The injection molding of the seal member on the cover30for the optical housing20requires a gate31afrom which molten material to form the seal member is injected. After the seal member has been injection-molded by injecting the molten material from the gate31a, as shown inFIG. 7(b), there is a residual runner portion31cthat protrudes from the gate31aand is in the form of the injection nozzle of an injection molding apparatus, as in typical injection-molded parts. Accordingly, there is a concern that, as shown inFIG. 7(b), the runner portion31cmay block a light path for synchronizing light that is to be incident on a synchronizing sensor, depending on a position at which the gate31ais provided, and the malfunction of the optical scanning device or a failure in images formed on a photosensitive member may occur. There is also a concern that the runner portion31cmay come in contact with the reflection mirror or lens and push away the lens and so on, and the position at which the photosensitive member is irradiated with the light beam may be out of position. Consequently, there is the problem in that prevention of this requires an extra work process such as cutting the runner portion31cprotruding from the gate31a.

The present invention has been accomplished in such circumstances, and an object of the present invention is to injection-mold the seal member with a simple structure that needs no complicated assembling process.

Solution to Problem

To solve the above problem, the present invention has the following features.

(1) An optical scanning device includes a light source from which a light beam is emitted, a rotating polygon mirror that deflects the light beam such that the light beam emitted from the light source is scanned over a photosensitive member, an optical component that directs the light beam deflected by the rotating polygon mirror onto the photosensitive member, an optical housing that contains the light source, the rotating polygon mirror, and the optical component, and a cover that covers an opening of the optical housing. The cover includes a dustproof member that is sandwiched between the cover and a side wall of the optical housing and molded on the cover so that the dustproof member protects an interior of the optical housing from dust, a gate from which melt of the dustproof member is injected, and a channel through which the melt of the dustproof member injected from the gate flows. The channel is formed in the cover such that the dustproof member is sandwiched between the side wall and the cover by attaching the cover to the optical housing. The gate is provided outside a light path area for the light beam when viewed in a direction of a rotational axis of the rotating polygon mirror.
(2) An optical scanning device includes a light source from which a light beam is emitted, a rotating polygon mirror that deflects the light beam such that the light beam emitted from the light source is scanned over a photosensitive member, an optical component that directs the light beam deflected by the rotating polygon mirror onto the photosensitive member, an optical housing that contains the light source, the rotating polygon mirror, and the optical component, and a cover that covers an opening of the optical housing. The cover includes a dustproof member that is sandwiched between the cover and a side wall of the optical housing and molded on the cover so that the dustproof member protects an interior of the optical housing from dust, a gate from which melt of the dustproof member is injected, and a channel through which the melt of the dustproof member injected from the gate flows. The channel is formed in the cover such that the dustproof member is sandwiched between the side wall and the cover by attaching the cover to the optical housing. The gate is formed at a position at which a virtual normal extending vertically with respect to the cover from the gate does not intersect a light path area for the light beam in the optical housing.
(3) An optical scanning device includes a light source from which a light beam is emitted, a rotating polygon mirror that deflects the light beam such that the light beam emitted from the light source is scanned over a photosensitive member, an optical component that directs the light beam deflected by the rotating polygon mirror onto the photosensitive member, an optical housing that contains the light source, the rotating polygon mirror, and the optical component, and a cover that covers an opening of the optical housing. The optical housing includes a wall extending vertically from a bottom of the optical housing such that the wall surrounds the rotating polygon mirror provided on the bottom of the optical housing. The cover includes a first cover that covers a first opening through which the rotating polygon mirror is caused to pass when the rotating polygon mirror is provided on the bottom and that is surrounded by the wall and a second cover that covers a second opening that is an opening of the optical housing other than the first opening. The first cover includes a dustproof member that is sandwiched between the first cover and the vertically extending wall and molded on the first cover so that the dustproof member protects an interior of the optical housing from dust, a gate from which melt of the dustproof member is injected, and a channel through which the melt of the dustproof member injected from the gate flows. The channel is formed in the first cover such that the dustproof member is sandwiched between the vertically extending wall and the first cover by attaching the first cover to the optical housing. The gate is provided outside a light path area for the light beam when viewed in a direction of a rotational axis of the rotating polygon mirror.
(4) An optical scanning device includes a light source from which a light beam is emitted, a rotating polygon mirror that deflects the light beam such that the light beam emitted from the light source is scanned over a photosensitive member, an optical component that directs the light beam deflected by the rotating polygon mirror onto the photosensitive member, an optical housing that contains the light source, the rotating polygon mirror, and the optical component, and a cover that covers an opening of the optical housing. The optical housing includes a wall extending vertically from a bottom of the optical housing such that the wall surrounds the rotating polygon mirror provided on the bottom of the optical housing. The cover includes a first cover that covers a first opening through which the rotating polygon mirror is caused to pass when the rotating polygon mirror is provided on the bottom and that is surrounded by the wall and a second cover that covers a second opening that is an opening of the optical housing other than the first opening. The first cover includes a dustproof member that is sandwiched between the first cover and the vertically extending wall and molded on the first cover so that the dustproof member protects an interior of the optical housing from dust, a gate from which melt of the dustproof member is injected, and a channel through which the melt of the dustproof member injected from the gate flows. The channel is formed in the first cover such that the dustproof member is sandwiched between the vertically extending wall and the first cover by attaching the first cover to the optical housing. The gate is formed at a position at which a virtual normal extending vertically with respect to the first cover from the gate does not intersect a light path area for the light beam in the optical housing.
(5) An image forming apparatus includes an optical scanning device described in (1) to (4), the photosensitive member on which an electrostatic latent image is formed by a light beam scanned from the optical scanning device, and a developing unit that develops the electrostatic latent image formed on the photosensitive member.

Advantageous Effects of Invention

The present invention enables the seal member to be injection-molded with a simple structure that needs no complicated assembling process.

DESCRIPTION OF EMBODIMENTS

Embodiments of the present invention will hereinafter be described in detail with reference to the drawings.

First Embodiment

An embodiment of the present invention will be described below with reference to the drawings. In the following description, the direction of the rotational axis of a rotating polygon mirror203, described later, corresponds to a Z-axis direction, a main scanning direction that is the scanning direction of a light beam or the longitudinal direction of a reflection mirror corresponds to an X-axis direction, and the direction perpendicular to the X-axis and the Z-axis corresponds to a Y-axis direction.

[Outline of Image Forming Apparatus]

FIG. 1is a sectional schematic view of an electrophotographic image forming apparatus100in the first embodiment. The image forming apparatus100shown inFIG. 1includes four image forming units101Y,101M,101C, and101Bk that form respective toner images that are each colored in yellow (Y), magenta (M), cyan (C), and black (Bk) The symbols Y, M, C, and Bk, which represent the colors, are omitted in the following description unless necessary. The image forming units101include respective photosensitive drums102that are photosensitive members. The image forming units also include respective charging devices103that charge the corresponding photosensitive drums102, and respective developing devices104that develop electrostatic latent images on the corresponding photosensitive drums with toner. The image forming units also include respective cleaning devices111that remove residual toner on the corresponding photosensitive drums from the photosensitive drums (photosensitive members).

The image forming units are configured as process cartridges in which the respective photosensitive drums102, charging devices103, developing devices104, and cleaning devices111are integrated. The process cartridges are replacement units that are attachable to and detachable from the image forming apparatus100. The image forming units101Y,101M,101C, and101Bk are referred to as the process cartridges101Y,101M,101C, and101Bk below.

The main body of the image forming apparatus100is provided with the optical scanning device21, transfer rollers105Y,105M,105C, and105Bk, an intermediate transfer belt106, a paper feeding unit109, a paper discharging unit110, a transfer roller107, and a fixing device108. The intermediate transfer belt106rotates in the direction of an arrow shown in the figure (counterclockwise direction). The optical scanning device21is disposed below the photosensitive drums102in the direction of gravity (−Z-axis direction). The optical scanning device21may be disposed so as to expose the photosensitive drums102to light from the upper side in direction of gravity (+Z-axis direction).

A process of forming an image will next be described. The optical scanning device21emits light beams LY, LM, LC, and LBk to which the photosensitive drums102Y,102M,102C, and102Bk that are charged by the respective charging devices103Y,103M,103C, and103Bk are exposed. An electrostatic latent image is formed on each of the photosensitive drums102Y,102M,102C, and102Bk by the exposure to the light beam.

The developing device104Y develops the electrostatic latent image formed on the photosensitive drum102Y with yellow toner. The developing device104M develops the electrostatic latent image formed on the photosensitive drum102M with magenta toner. The developing device104C develops the electrostatic latent image formed on the photosensitive drum102C with cyan toner. The developing device104Bk develops the electrostatic latent image formed on the photosensitive drum102Bk with black toner.

The yellow toner image formed on the photosensitive drum102Y is transferred to the intermediate transfer belt106, which is an intermediate transfer member, by the transfer roller105Y at a transfer unit Ty. The cleaning device111Y collects the residual toner on the photosensitive drum102Y that is not transferred to the intermediate transfer belt106at a portion in the rotation direction of the photosensitive drum102Y between the transfer unit Ty and a charge unit of the charging device103Y. The magenta toner image formed on the photosensitive drum102M is transferred to the intermediate transfer belt106by the transfer roller105M at a transfer unit Tm. The cleaning device111M collects the residual toner on the photosensitive drum102M that is not transferred to the intermediate transfer belt106at a portion in the rotation direction of the photosensitive drum102M between the transfer unit Tm and a charge unit of the charging device103M.

The cyan toner image formed on the photosensitive drum102C is transferred to the intermediate transfer belt106by the transfer roller105C at a transfer unit Tc. The cleaning device111C collects the residual toner on the photosensitive drum102C that is not transferred to the intermediate transfer belt106at a portion in the rotation direction of the photosensitive drum102C between the transfer unit Tc and a charge unit of the charging device103C. The black toner image formed on the photosensitive drum102Bk is transferred to the intermediate transfer belt106by the transfer roller105Bk at a transfer unit TBk. The cleaning device111Bk collects the residual toner on the photosensitive drum102Bk that is not transferred to the intermediate transfer belt106at a portion in the rotation direction of the photosensitive drum102Bk between the transfer unit TBk and a charge unit of the charging device103Bk.

The cleaning devices111in the embodiment include a blade that comes into contact with the respective photosensitive drums102. The residual toner on each of the photosensitive drums is scraped and collected by the blade. At a transfer unit T2, the transfer roller107transfers, to recording paper fed from the paper feeding unit109, the toner images in the respective colors that have been transferred to the intermediate transfer belt106. The toner images transferred to the recording paper at the transfer unit T2are subjected to a fixing process with the fixing device108and discharged to the paper discharging unit110after the fixing process.

With regard to the structures described below, the image forming apparatus100described above may be a monochrome image forming apparatus with one photosensitive drum or an image forming apparatus that transfers toner images formed on photosensitive drums directly to recording medium.

[Outline of Optical Scanning Device]

The optical scanning device21will next be described.FIG. 2(a)is a perspective view of the structure of the optical scanning device21.FIG. 2(b)is a sectional view of the optical scanning device21. As shown inFIG. 2(a), light source units202Y,202M,202C, and202Bk are attached to the outer wall of the optical housing20of the optical scanning device21. The light source unit202Y emits a light beam LY to which the photosensitive drum102Y is exposed. The light source unit202M emits a light beam LM to which the photosensitive drum102M is exposed. The light source unit202C emits a light beam LC to which the photosensitive drum102C is exposed. The light source unit202Bk emits a light beam LBk to which the photosensitive drum102Bk is exposed.

The light source units202Y,202M,202C, and202Bk are disposed so as to be close to each other. A plane that cuts across the rotating polygon mirror203such that the rotation axis of the rotating polygon mirror203is a normal is defined here as a virtual plane. The light beam LY emitted from the light source unit202Y and the light beam LBk emitted from the light source unit202Bk are incident diagonally on the virtual plane from the upper side in the direction of gravity (+Z-axis direction) and are incident on one of the reflective surfaces of the rotating polygon mirror203. In contrast, the light beam LC emitted from the light source unit202C and the light beam LM emitted from the light source unit202M are incident diagonally on the virtual plane from the lower side in the direction of gravity (−Z-axis direction) and are incident on one of the reflective surfaces of the rotating polygon mirror203. As shown inFIG. 2(a), the rotating polygon mirror203with four reflective surfaces is disposed at a central portion of the optical housing20. The rotating polygon mirror203rotates in the direction R1about the rotation axis shown by a dotted line inFIG. 2(a)when an image is formed.

The light beam LY emitted from the light source unit202Y is incident on one of the reflective surfaces of the rotating polygon mirror203. The light beam LY is deflected (reflected) to the A side shown inFIG. 2(a)by the reflective surface of the rotating polygon mirror203. The light beam LM emitted from the light source unit202M is incident on the same reflective surface as the reflective surface of the rotating polygon mirror203on which the light beam LY is incident. The light beam LM is deflected to the same side (A side) as the light beam LY by the reflective surface of the rotating polygon mirror203.

In contrast, the light beam LBk emitted from the light source unit202Bk is incident on one of the reflective surfaces that differs from the reflective surface on which the light beams LY and LM are incident. The light beam LBk is deflected to the B side shown inFIG. 2(a)by the reflective surface of the rotating polygon mirror203. The light beam LC emitted from the light source unit202C is incident on the same reflective surface as the reflective surface of the rotating polygon mirror203on which the light beam LBk is incident. The light beam LC is deflected to the same side (B side) as the light beam LBk by the reflective surface of the rotating polygon mirror203.

The light beams LY and LM deflected by the rotating polygon mirror203become light beams that move in the +X direction. In other words, the light beam LY becomes a light beam that is scanned over the photosensitive drum102Y in the +X direction and the light beam LM becomes a light beam that is scanned over the photosensitive drum102M in the +X direction, as a result of being deflected by the rotating polygon mirror203that rotates.

In contrast, the light beams LBk and LC deflected by the rotating polygon mirror203become light beams that move in the −X direction. In other words, the light beam LBk becomes a light beam that is scanned over the photosensitive drum102Bk in the −X direction and the light beam LC becomes a light beam that is scanned over the photosensitive drum102C in the −X direction, as a result of being deflected by the rotating polygon mirror203that rotates.

Light paths for the light beams LY, LM, LC, and LBk deflected by the rotating polygon mirror203will next be described with reference toFIG. 2(b). As shown inFIG. 2(b), optical components such as the rotating polygon mirror203, lenses206,207,208,209,210, and211, reflection mirrors212,213,214,215,216, and217are contained in the interior of the optical housing20and disposed on the bottom (bottom surface) of the optical housing20. The cover30that protects the rotating polygon mirror203, the above lenses, and the reflection mirrors from dust is attached at an opening of an upper portion of the optical housing20that is an opened side.

The light beam LY deflected by the rotating polygon mirror203is incident on the reflection mirror212after passing the lens206and lens207. The reflection mirror212reflects the incident light beam LY toward the photosensitive drum102Y. An opening219that allows the light beam LY reflected by the reflection mirror212to pass is formed in the cover30. The opening219is covered by a dustproof window223that is a transparent window that allows the light beam LY to pass. The light beam LY that has passed the dustproof window223forms an image on the photosensitive drum102Y.

The light beam LM deflected by the rotating polygon mirror203is incident on the reflection mirror213after passing the lens206. The reflection mirror213reflects the incident light beam LM toward the reflection mirror214. The light beam LM reflected by the reflection mirror213is incident on the reflection mirror214via the lens208. The reflection mirror214reflects the incident light beam LM toward the photosensitive drum102M. An opening220that allows the light beam LM reflected by the reflection mirror214to pass is formed in the cover30. The opening220is covered by a transparent dustproof window224that allows the light beam LM to pass. The light beam LM that has passed the dustproof window224forms an image on the photosensitive drum102M.

The light beam LBk deflected by the rotating polygon mirror203is incident on the reflection mirror215after passing the lens209and the lens210. The reflection mirror215reflects the incident light beam LBk toward the photosensitive drum102Bk. An opening222that allows the light beam LBk reflected by the reflection mirror215to pass is formed in the cover30. The opening222is covered by a transparent dustproof window226that allows the light beam LBk to pass. The light beam LBk that has passed the dustproof window226forms an image on the photosensitive drum102Bk.

The light beam LC deflected by the rotating polygon mirror203is incident on the reflection mirror216after passing the lens209. The reflection mirror216reflects the incident light beam LC toward the reflection mirror217. The light beam LC reflected by the reflection mirror216is incident on the reflection mirror217via the lens211. The reflection mirror217reflects the incident light beam LC toward the photosensitive drum102C. An opening221that allows the light beam LC reflected by the reflection mirror217to pass is formed in the cover30. The opening221is covered by a transparent dustproof window225that allows the light beam LC to pass. The light beam LC that has passed the dustproof window225forms an image on the photosensitive drum102C.

FIG. 3(a)shows the structure of the cover30in the embodiment and is a perspective view of the cover30when viewed from the side of the optical housing20. InFIG. 3(a), the cover30is provided with plural hooks32that are engaged with projections provided on the outer wall of the optical housing20and provide a snap-fit structure. The cover30is also provided with the dustproof windows223,224,225, and226. When the cover30is attached to the optical housing20, a seal member31that is a dustproof member is formed by injection molding along the entire portion of the cover30that faces the outer periphery formed by the side wall of the optical housing20. InFIG. 3(a), the gates31afrom which a hot melt adhesive (referred to as “hot melt” below) of molten polyolefin, which is a molding material, is injected during injection molding are provided at two positions such that the entire length of the seal member31is substantially halved. Although the gates31aare provided at the two positions in the embodiment, the number of the gates31acan be increased or decreased in accordance with actual moldability, and it is sufficient to provide at least one gate.

The seal member31is formed on the cover30in a manner in which polyolefin hot melt is injected into a space between the formed cover30and a mold in contact with the cover30.FIG. 3(b)is a J-J sectional view of the cover30that is taken along J-J (a dashed line) shown by an outlined arrow inFIG. 3(a)and shows the relation between the cover30and the seal member31. InFIG. 3(b), the cover30is provided with a groove30athrough which the hot melt injected from the gates31aflows. The groove30ais filled with the hot melt and the seal member31is thereby formed. The groove30ais formed such that the seal member31is sandwiched between the side wall of the optical housing20and the cover30by attaching the cover30to the optical housing20. A narrow, shallow anchor groove30cis provided in the interior of the groove30a, so that a contact area between the cover30and the seal member31is increased. This ensures adhesion between the cover30and the seal member31in order to prevent the seal member, which is a dustproof member, from being unintentionally detached from the cover30. A depressed groove is formed on the surface of the seal member31. The outer periphery formed by the side wall of the optical housing20is inserted into this groove, so that the interior of the optical housing20is protected from dust and the sealability of the optical housing20is ensured.

FIG. 3(c)is an enlarged view of part (a portion around the gate31a) of the cover30that is encircled inFIG. 3(a). When the seal member31is formed by injection molding, the hot melt is injected from the gates31athrough injection nozzles. Accordingly, as shown inFIG. 3(c), the molding materials that remain in the injection nozzles are solidified after the injection of the hot melt is finished, and the runner portions31care formed into the forms of the nozzles at the gates31a. When the runner portions31care formed at the gates31a, there is a concern that, as shown inFIG. 7(b), the runner portions31cmay block the light paths for the light beams in the optical housing20or the runner portions31cmay come in contact with the optical components disposed in the optical housing20so that the posture or the position of the optical components may be changed.

In view of this, the gates31aare disposed such that there is no problem with the light paths for the light beams and so on even when the runner portions31cgreatly protrude in the optical scanning device21in the embodiment, and the areas at which the gates31aare disposed will be described with reference toFIG. 4.FIG. 4is a diagram of the optical scanning device21in the embodiment when viewed from the lower side (−Z-axis direction) and shows, for example, the cover30and the optical components (such as the lenses and the reflection mirrors), other than the optical housing20, that are disposed in the interior of the optical scanning device21.

InFIG. 4, each of the light beams emitted from the light source units202(Y, M, C, and Bk) propagates along one of incident light paths L1and is incident on the rotating polygon mirror (not shown inFIG. 4) driven by a polygon motor232. InFIG. 4, the light source units202that are disposed on the A side are the light source units202Y and202M described above. The light source units202that are disposed on the B side are the light source units202C and202Bk described above. Each of the light beams incident on the rotating polygon mirror that rotates in the direction of an arrow (counterclockwise direction) is deflected to the reflection mirror212or215along one of scanning light paths L2or scanning light paths L3. In the figure, the scanning direction represents a direction in which each of the light beams deflected by the rotating polygon mirror is scanned. The light beams emitted from the light source units202Y and202M are deflected to the A side in the figure (right hand direction in the figure). The scanning light paths L2represent scanning light paths through which the light beam emitted from the light source unit202Y propagates to the reflection mirror212. The light beams emitted from the light source units202C and202Bk are deflected to the B side in the figure (left hand direction in the figure). The scanning light paths L3represent scanning light paths through which the light beam emitted from the light source unit202Bk propagates to the reflection mirror215. The scanning light paths L2represent light paths for the light beam propagating toward the reflection mirror212when the scanning is started and when the scanning is finished. The scanning light paths L3likewise represent light paths for the light beam propagating toward the reflection mirror215when the scanning is started and when the scanning is finished. In the optical scanning device21, the light beams emitted from the light source units202are deflected by the rotating polygon mirror (not shown inFIG. 4) and are incident on a synchronizing sensor231along synchronizing light paths L4via an anamorphic lens230. The synchronizing sensor231makes, on the basis of timing of the incident light beams, synchronous signals that indicate scan-start timing with which the light beams are emitted from the light source units202. The other symbols inFIG. 4have been described inFIG. 2, and the description is accordingly omitted here.

As shown inFIG. 4, the optical components (such as the lenses206to211and the reflection mirrors212,213,215, and216), mechanical components that secure the lenses and mirrors, and so on are disposed in the interior of the optical scanning device21. Electrical components such as the polygon motor232, the synchronizing sensor231, and so on are also disposed in the interior of the optical scanning device21. There are the incident light paths L1, the scanning light paths L2and L3, and the synchronizing light paths L4, through which the light beams propagate, in spaces in the optical scanning device21. InFIG. 4, the light paths L1to L4are each shown by two solid lines, and the light beams propagate within light path areas that are the spaces occupied between the two solid lines. The light path areas occupied by the scanning light paths L2, L3are largest in the optical scanning device21. InFIG. 4, there are areas, surrounded by dashed lines, in which there is no component or light path. These areas are referred to as “disposed gate areas”. In the disposed gate areas, the gates31aare formed at positions at which a virtual normal extending vertically with respect to the cover30from each gate31adoes not intersect the light path areas of the light beams in the optical housing20. Accordingly, when the gates31aare provided in the disposed gate areas, the light paths are not blocked by the runner portions31cformed at the gates31a, and the posture of the components is not changed due to the contact with the runner portions31c. In the embodiment, the disposed gate areas are provided at four positions, and the gates31afor the seal member31are disposed at two positions of these positions. Accordingly, the protruding runner portions31cat the gates31ado not affect the exposure performance of the optical scanning device21.

In the optical scanning device21, as shown inFIG. 4, the reflection mirrors (for example, the reflection mirrors212,215) and the scanning lenses (for example, the lenses207,210) are disposed in parallel with the scanning direction of a scan optical system (X-axis direction). In many cases, the reflection mirrors and the scanning lenses are disposed near the outer periphery (short sides in the figure) of the optical housing20that is parallel with the scanning direction (X-axis direction) in order to effectively use the spaces in the optical housing. Accordingly, the gates are preferably disposed at positions other than the sides of the optical scanning device21that are parallel with the scanning direction (X-axis direction), i.e., positions on the outer peripheral sides (long sides) that are sides in the direction (Y-axis direction) perpendicular to the scanning direction.

Providing the seal member31integrally on the cover30by injection molding, as described above, enables the process of attaching a separated seal member to the cover to be eliminated and the additional work process of cutting the runner portions31cof the seal member31to also be eliminated. Consequently, the process of making the cover including the seal member can be simplified and the cost of the components can be reduced. In addition, the effect of the molding is to make the shape of the seal member31uniform, and hence good sealability can be stably ensured.

Because the hot melt adhesive hardens relatively quickly after being injected, it is desirable that, when a plurality of the gates31aare provided, the gates be disposed such that the entire flow path is substantially equally divided. It is of course necessary to dispose the gates31aat the disposed gate areas, in which there is no light path or component. According to the embodiment, the seal member can be injection-molded with a simple structure that needs no complicated assembling process, as described above.

Second Embodiment

In the optical scanning device, the rotation of the polygon motor creates a negative pressure in the interior of the apparatus, and it may be easy for the optical scanning device to draw air from the exterior into the interior. For this reason, there is an optical scanning device in which the polygon motor is placed on a portion of the optical scanning device that is in an independent space divided by, for example, a partition. In this embodiment, the disposed gate area of the cover, when the space in which the polygon motor is disposed is sealed by the cover that is sealed by the seal member, will be described.

[Structure of Image Forming Apparatus]

A laser beam printer will be described as an example of an electrophotographic image forming apparatus in a second embodiment.FIG. 5shows the schematic structure of a laser beam printer300. The laser beam printer300is a monochrome image forming apparatus including one photosensitive drum. The laser beam printer300includes a photosensitive drum311on which an electrostatic latent image is formed by an optical scanning device42, a charging device317that uniformly charges the photosensitive drum311, and a developing device312that develops the electrostatic latent image formed on the photosensitive drum311with toner. A toner image developed on the photosensitive drum311is transferred to recording paper supplied from a cassette316with a transfer unit318. The toner image transferred to the recording paper is fixed with a fixing device314and the recording paper is then discharged to a tray315. The photosensitive drum311, the charging device317, the developing device312, and the transfer unit318constitute an image forming unit. The laser beam printer300also includes a controller, not shown, that controls the action of forming an image by the image forming unit and the action of feeding recording paper.

[Outline of Optical Scanning Device]

FIG. 6(a)is a perspective view showing the appearance of the optical scanning device42in this embodiment. An optical housing33includes a first opening that is an opened side and defined by partition walls43a,43b,43c, and43ddescribed later, and a second opening that is the opened side of the optical housing other than the first opening. The optical housing33is sealed such that the first opening is sealed by a cover34that is a second cover and the second opening is sealed by a cover35that is a first cover. In the figure, the upper portion of the cover35is represented by C, and the lower portion of the cover35is represented by D. A space sealed by the cover35is surrounded by the partition walls43a,43b,43c, and43dmolded integrally with the optical housing33in the optical scanning device42. The partition walls43a,43b,43c, and43dare provided so as to extend vertically from the bottom surface of the optical housing33. The adjacent partition walls are connected. The partition wall43ais provided with an opening portion39through which a light beam passes. A polygon motor36and a rotating polygon mirror37that is rotated by the polygon motor36are placed on the bottom surface of the optical housing33surrounded by the partition walls43a,43b,43c, and43d. A light beam emitted from a light source unit38is reflected by a reflection mirror, not shown, that is provided in the interior of the optical scanning device42sealed by the cover34, and the light beam is then incident on the rotating polygon mirror37via the opening portion39(shown by a dashed arrow in the figure). The light beam incident on the rotating polygon mirror37is deflected and again incident on the side sealed by the cover34via the opening portion39.

In this embodiment, as shown inFIG. 6(a), the cover35, which covers only the opened side above the independent space in which the polygon motor36is placed on the bottom, is provided.FIG. 6(b)is a diagram of the cover35when viewed from the side of the polygon motor36(bottom surface side of the optical scanning device42). The external shape of the polygon motor36is overlapped so that positional relations with a seal member40molded at the outer periphery of the cover35can be seen. Scanning light paths L5(shown by dashed lines) represent light paths through which the light beam incident on the rotating polygon mirror37is reflected and the deflected light beam (reflected light) propagates. The light beam propagates within a light path area that is a space occupied between the two dashed lines. The cover35includes the seal member40, a gate40a, and a channel through which hot melt injected from the gate40aflows. The seal member40is a dustproof member that is sandwiched between the cover35and the vertically extending partition walls43a,43b,43c, and43dand molded on the cover35in order to protect the interior of the optical housing from dust. The gate40ais used to inject the hot melt to form the seal member40. When the cover35is attached to the optical housing33, the injected hot melt is caused to flow through the channel and the seal member40is thereby formed so as to be sandwiched between the partition walls43a,43b,43c, and43dand the cover35. The seal member40is consequently injection-molded along the periphery of the cover35over the entire circumference. The gate40ais provided for this molding.

In this embodiment, the gate40ais formed at a position at which a virtual normal extending vertically with respect to the cover35from the gate40adoes not intersect the light path area for the light beam that is surrounded by the partition walls43ato43din the optical housing33, as in the first embodiment. Accordingly, the gate40ais provided at a position away from the polygon motor36and the scanning light paths L5in this embodiment. However, a plurality of the gates40amay be provided. The same effects as the first embodiment can be consequently achieved in this embodiment. Specifically, providing the seal member40integrally on the cover35by injection molding enables the process of attaching a separated seal member to the cover to be eliminated and the process of cutting the runner portion of the seal member40to also be eliminated. Consequently, the process of making the cover including the seal member can be simplified and the cost of the components can be reduced. In addition, the effect of the molding is to make the shape of the seal member40uniform, and hence good sealability can be ensured. With regard to the cover34, the same effects as the first embodiment can be achieved, when the gate is provided at a position apart from the optical components disposed in the interior of the optical housing33covered by the cover34, the incident light path, the scanning light path, and the synchronizing light path, through which the light beam propagates, as in the first embodiment. According to this embodiment, the seal member can be injection-molded with a simple structure that needs no complicated assembling process, as described above.

The present invention is not limited to the above embodiment, and various variations and modifications are available without departing from the concept and scope of the present invention. Accordingly, the following claims are attached to publish the scope of the present invention.

This application claims the benefit of Japanese Patent Application No. 2013-212157, filed Oct. 9, 2013, which is hereby incorporated by reference herein in its entirety.

REFERENCE SIGNS LIST