Optical scanning device and image forming apparatus including same

An optical scanning device including a first housing including a rotating deflector configured to deflect a light beam from at least one light source to scan a surface to be scanned with a deflected light beam, a second housing including one or more reflecting mirrors, and three supporting members configured to support the second housing relative to an image forming apparatus. The first housing is mounted inside the second housing, and mounts to fix the first housing to the second housing are positioned substantially on or within sides of a triangle formed by the three supporting members.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present patent application is based on and claims priority pursuant to 35 U.S.C. §119 from Japanese Patent Application No. 2007-239714, filed on Sep. 14, 2007 in the Japan Patent Office, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Exemplary aspects of the present invention generally relate to an optical scanning device employed in a writing system in an image forming apparatus such as a digital copier and a laser printer, and an image forming apparatus including the optical scanning device.

2. Description of the Background

Related-art image forming apparatuses, such as a copier, a facsimile machine, a printer, or a multifunction printer having two or more of copying, printing, scanning, and facsimile functions, form a toner image on a recording medium (e.g., a sheet) according to image data using an electrophotographic method. In such a method, for example, a charger charges a surface of an image bearing member (e.g., a photoconductor); an optical scanning device emits a light beam onto the charged surface of the photoconductor to form an electrostatic latent image on the photoconductor according to the image data; the electrostatic latent image is developed with a developer (e.g., a toner) to form a toner image on the photoconductor; a transfer device transfers the toner image formed on the photoconductor onto a sheet; and a fixing device applies heat and pressure to the sheet bearing the toner image to fix the toner image onto the sheet. The sheet bearing the fixed toner image is then discharged from the image forming apparatus.

As described above, the image forming apparatus such as a laser printer, a digital copier, or a laser facsimile machine includes the optical scanning device to form the electrostatic latent image on the surface of the photoconductor. One example of the optical scanning device is configured to deflect a light beam emitted from a light source using a rotating deflector to scan the surface of the photoconductor with the deflected light beam.

To meet demand for high-quality images and high-speed image formation, a tandem-type image forming apparatus using multiple photoconductors is widely used as a full-color image forming apparatus in recent years. In the tandem-type image forming apparatus, higher accuracy in superposition of images respectively formed on the multiple photoconductors is required to achieve the high-quality images.

However, the above-described optical scanning device using the rotating deflector is susceptible to vibration due to high-speed rotation of a polygon mirror, possibly resulting in image deterioration such as color shift and uneven image density.

To prevent such image deterioration caused by the vibration from the optical scanning device, various methods and techniques have been proposed.

Published unexamined Japanese Patent Application No. (hereinafter referred to as JP-A-) 2006-323066 discloses an image forming system in which a vibration damping means is included in an optical scanning device to suppress vibration.

In another approach, JP-A-2002-341467 discloses an optical scanning device configured to suppress generation of vibration using a compact and lightweight configuration.

However, the image forming system disclosed in JP-A-2006-323066 requires higher cost to include the vibration unit and multiple detectors. Further, although a method for suppressing transmission of the vibration by improving rigidity of the optical scanning device is disclosed in JP-A-2002-341467, the range of available layouts of the optical scanning device is more limited because the optical scanning device needs to be fixed to a main frame of an image forming apparatus.

In the tandem-type image forming apparatus, in general, multiple optical scanning devices are included to perform exposure on multiple photoconductors. Alternatively, a single optical scanning device may be used to perform exposure on multiple photoconductors. When the single optical scanning device is used to emit four light beams onto surfaces of four photoconductors, for example, four optical paths are formed using multiple reflecting mirrors provided in the optical scanning device. A wide variety of arrangements of the reflecting mirrors is available depending on the layout of components in the image forming apparatus. To achieve such a wide variety of arrangements, one example of the optical scanning device includes a first optical housing and a second optical housing, with a rotating deflector, and an optical element such as a lens when needed, included in the first of these two optical housings while the multiple reflecting mirrors are included in the second optical housing.

However, as described above, in the optical scanning device using the rotating deflector, the polygon mirror is rotated at high speed and vibration is transmitted from the optical housing including the rotating deflector to the other optical housing. Consequently, portions of the other optical housing cantilevered to the image forming apparatus are heavily susceptible to vibration, resulting in image deterioration.

SUMMARY

In view of the foregoing, exemplary embodiments of the present invention provide an optical scanning device including multiple optical housings configured to suppress transmission of vibration from one optical housing including a rotating deflector to another optical housing so as to prevent image deterioration and provide high-quality images, and an image forming apparatus including the optical scanning device.

In one exemplary embodiment, an optical scanning device includes a first housing including a rotating deflector configured to deflect a light beam from at least one light source to scan a surface to be scanned with a deflected light beam; a second housing including one or more reflecting mirrors; and three supporting members configured to support the second housing relative to an image forming apparatus. The first housing is mounted inside the second housing, and mounts to fix the first housing to the second housing are positioned substantially on or within sides of a triangle formed by the three supporting members.

Another exemplary embodiment provides an image forming apparatus including a latent image bearing member configured to bear an electrostatic latent image; a charging device configured to charge a surface of the latent image bearing member; an irradiating device configured to scan and irradiate a charged surface of the latent image bearing member with a light beam according to image data to form an electrostatic latent image thereon; a developing device configured to develop the electrostatic latent image with toner into a visible toner image; a transfer device configured to transfer the toner image onto a recording medium; and a fixing device configured to fix the toner image on the recording medium. The irradiating device includes the optical scanning device described above.

Additional features and advantages of the present invention will be more fully apparent from the following detailed description of exemplary embodiments, the accompanying drawings, and the associated claims.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Exemplary embodiments of the present invention are now described below with reference to the accompanying drawings.

In a later-described comparative example, exemplary embodiment, and exemplary variation, for the sake of simplicity the same reference numerals will be given to identical constituent elements such as parts and materials having the same functions, and redundant descriptions thereof omitted unless otherwise stated.

Typically, but not necessarily, paper is the medium from which is made a sheet on which an image is to be formed. It should be noted, however, that other printable media are available in sheets, and accordingly their use here is included. Thus, solely for simplicity, although this Detailed Description section refers to paper, sheets thereof, paper feeder, etc., it should be understood that the sheets, etc., are not limited only to paper but includes other printable media as well.

FIG. 1is a vertical cross-sectional view illustrating an example of a configuration of an optical scanning device according to exemplary embodiments.FIG. 2is an exploded perspective view illustrating configurations of a first housing and a second housing included in the optical scanning device.

Referring toFIGS. 1 and 2, it can be seen that an optical scanning device50includes an optical housing assembly53including a first housing51and a second housing52. The optical housing assembly53is covered with a cover member54to form a substantially enclosed space in the optical housing assembly53.

The first housing51includes light sources60and a polygon scanner61serving as a rotating deflector. According to exemplary embodiments, the first housing51further includes fθ lenses62. The optical scanning device50may be employed in a full-color image forming apparatus using four colors. Specifically, each of the two light sources60shown inFIG. 2includes a multi-beam light source unit in which two semiconductor lasers each serving as a light source are arranged one above the other so that four light beams in total are used for scanning. In order to handle the two light beams emitted from each of the light sources60, the polygon scanner61includes two polygon mirrors superimposed on each other, and each of the fθ lenses62also has a two-tiered structure.

The second housing52includes multiple reflecting mirrors63for reflecting the light beams passing through the fθ lenses62to change optical paths of the light beams. Reference numeral63is assigned only to some of the reflecting mirrors shown inFIGS. 1 and 2for the purpose of simplifying the drawings. The second housing52further includes a dustproof glass member, not shown, provided at a portion at which the light beam serving as scanning light is directed from the inside of the optical housing assembly53to the outside thereof.

The optical scanning device50according to exemplary embodiments is configured to direct each of the light beams downward. Alternatively, however, each of the light beams may be directed upward or sideward. Further, the number of the light beams is not limited to four. For example, a single light beam may be used for scanning in a monochrome image forming apparatus, or two or three light beams may be used for scanning in a multicolor image forming apparatus.

The second housing52is slightly larger than the first housing51and the first housing51is mounted within the second housing52. The optical scanning device50according to exemplary embodiments is provided with four mounts for fixing the first housing51to the second housing52. Each of the mounts includes a mounting member64provided on the first housing51and a positioning member65provided on the second housing52. The mounting member64provided on the first housing51is fitted into the positioning member65provided on the second housing52. Thereafter, both the mounting member64and the positioning member65are fixed together with a screw so that the first housing51is firmly fixed to the second housing52. Specifically, the mount including the mounting member64and the positioning member65functions as a positioning portion as well as a mount.

FIG. 3is a schematic perspective view illustrating the mounts provided on the first housing51and the second housing52, and supporting members provided on the second housing52. As illustrated inFIG. 3, the number of the positioning members65provided on the second housing52, which is four in exemplary embodiments, is the same as the number of the mounting members64provided on the first housing51. Each of the mounting members64is fixed to each of the positioning members65with a screw67.

Four or more mounts for fixing the first housing51to the second housing52are provided and arranged in a polygonal pattern. For example, when four mounts are provided, the mounts are arranged in a rectangular pattern, and when five mounts are provided, the mounts are arranged in a pentagonal pattern. In exemplary embodiments, the mounting members64included in the mounts are provided at outermost edges on the outline of the first housing51in a rectangular pattern.

The second housing52further includes three supporting members for attaching the optical scanning device50to the image forming apparatus. Supporting members66aand66bare provided at the front and back of the optical device50in a depth direction, that is, a longitudinal direction of the reflecting mirrors63, which is also a main scanning direction. A supporting member66cis provided on a side of the second housing52in a width direction perpendicular to the depth direction.

The mounts each including the mounting member64and the positioning member65are provided substantially on or within three sides of a triangle formed by the three supporting members66ato66c(hereinafter collectively referred to as supporting members66). It is to be noted that, in exemplary embodiments, positions of the supporting members66and the mounts in a vertical direction are not limited to any particular arrangement, and intersections of vertical lines drawn from each of the supporting members66and the mounts with a horizontal surface are defined. Specifically, the triangle formed by the supporting members66means a triangle formed by the intersections of the vertical lines drawn from each of the supporting members66in a plane of projection. Accordingly, the vertical lines drawn from each of the mounts are positioned substantially on or within the three sides of the triangle thus formed on the plane of projection. In exemplary embodiments, each of the positions of the supporting members66and the mounts indicates a center thereof. For example, when each of the mounts is tighten with the screw67as in the case of exemplary embodiments, each of the positions of the supporting members66and the mounts is indicated by a center of a screw hole. Therefore, when the mounts are positioned substantially on or within the three sides of the triangle formed by the supporting members66, it means that positions of vertical lines drawn from the center of each of the mounts, that is, the center of the screw hole in the case of exemplary embodiments, are positioned on or within the three sides of the triangle formed by the intersections of the vertical lines drawn from the supporting members66in the plane of projection.

FIGS. 4A to 4Eare schematic views illustrating examples of relative positions of the mounts and the supporting members66. In the following description, reference numeral68denotes the mount including the mounting member64and the supporting member65.

FIGS. 4A to 4Dillustrate exemplary embodiments of the relative positions of the mounts68and the supporting members66.FIG. 4Eillustrates a comparative example thereof.

Referring toFIG. 4Aillustrating a first exemplary embodiment, the four mounts68are arranged on the first housing51in a square or a rectangular pattern, and the supporting members66are provided on outer surfaces of the second housing52. As illustrated inFIG. 4A, each of the mounts68is positioned substantially on or within the triangle formed by the supporting members66.

Referring toFIG. 4Billustrating a second exemplary embodiment, the four mounts68are arranged on the first housing51in a trapezoidal pattern, and the supporting members66are provided on inner surfaces of the second housing52. In the second exemplary embodiment, each of the mounts68is positioned substantially on or within the triangle formed by the supporting members66.

Referring toFIG. 4Eillustrating a first comparative example, the supporting members66aand66bare provided on an outer surface of the second housing52in a width direction. As a result, an acute triangle is formed by connecting the supporting members66, and the two mounts68arranged closer to the supporting member66care positioned outside the acute triangle. To solve such a problem, the two mounts68arranged closer to the supporting member66care arranged as illustrated inFIGS. 4C and 4D.

Referring toFIG. 4Cillustrating a third exemplary embodiment, the four mounts68are arranged on the first housing51. Because the triangle formed by the supporting members66has an acute angle, a distance between the two mounts68arranged closer to the supporting member66cis reduced such that the two mounts68are positioned substantially on the triangle. The other two mounts68are positioned substantially on or within the triangle.

Referring toFIG. 4Dillustrating a fourth exemplary embodiment, only one mount68is arranged closer to the supporting member66csuch that all of the three mounts68are positioned substantially on or within the acute triangle formed by the supporting members66.

FIGS. 5A and 5Bare schematic views illustrating examples of relative positions of the mounts68and the supporting members66when the triangle formed by the supporting members66is small in a width direction of the second housing52.

Referring toFIG. 5Billustrating a second comparative example, the two mounts68arranged closer to the supporting members66aand66bare positioned outside of a side of the triangle between the supporting members66aand66bwhen the triangle formed by the supporting members66is small in a width direction of the second housing52. To solve such a problem, the mounts68are arranged as illustrated inFIG. 5A.

Referring toFIG. 5Aillustrating a fifth exemplary embodiment, the four mounts68are arranged on the first housing51in a rectangular pattern. The two mounts68arranged closer to the supporting members66aand66bare positioned slightly close to the supporting member66cso as to be positioned substantially on the side of the triangle between the supporting members66aand66b. Alternatively, the two mounts68may be arranged so as to be positioned within the triangle.

A description is now given of the first and second comparative examples respectively illustrated inFIG. 4EandFIG. 5Bwith reference toFIGS. 6A and 6B.FIG. 6Ais a schematic view illustrating cantilevered portions in the configuration according to the first comparative example.FIG. 6Bis a schematic view illustrating cantilevered portions in the configuration according to the second comparative example.

An inner portion of the triangle formed by the supporting members66provided on the second housing52is firmly supported by the three supporting members66a,66b, and66c. Accordingly, when the mounts68are arranged within the triangle, the second housing52can tolerate the vibration mainly transmitted from the rotating deflector61through the mounts68. However, as illustrated inFIGS. 6A and 6B, portions exterior to the triangle formed by the supporting members66, that is, shaded portions inFIGS. 6A and 6B, are cantilevered. Specifically, the shaded portions illustrated inFIG. 6Aare supported only by two sides of the triangle between the supporting members66aand66cand the supporting members66band66c, and the shaded portion illustrated inFIG. 6Bis supported only by one side of the triangle between the supporting members66aand66b. When the mounts68are positioned within the shaded portions which are cantilevered as described above, the shaded portions are vibrated heavily compared to the inner portion of the triangle due to the vibration transmitted through the mounts68, possibly degrading image quality.

However, as described in the foregoing exemplary embodiments with reference toFIGS. 4A to 4Dand5A, the optical scanning device50according to exemplary embodiments prevents an increase in the vibration transmitted from the first housing51to the second housing52by arranging the mounts68substantially on or within the triangle formed by the supporting members66. As a result, high-quality image can be obtained by preventing image deterioration.

Further, as illustrated inFIG. 7, an elastic or viscoelastic member69may be provided between the optical scanning device50and the image forming apparatus, not shown, by attaching the elastic or viscoelastic member69to a bottom surface of the second housing52. As a result, vibration transmitted from the image forming apparatus to the optical device50can be further suppressed.

The elastic or viscoelastic member69is preferably contacted against a member of the image forming apparatus placed immediately below the elastic or viscoelastic member69. Accordingly, an increase in vibration in the portions exterior to the triangle formed by the supporting members66of the second housing52is prevented. When a main body of the image forming apparatus is placed immediately below the elastic or viscoelastic member69, the elastic or viscoelastic member69is preferably contacted against the main body. Alternatively, when a developing device is placed immediately below the elastic or viscoelastic member69, the elastic or viscoelastic member69may be contacted against the developing device. Vibration transmitted from the image forming apparatus to the optical device50can be suppressed by providing the elastic or viscoelastic member69therebetween, regardless of whether the optical scanning device50is fixed or not fixed to the image forming apparatus.

Vibration or impact may be transmitted to the image forming apparatus including the optical scanning device50through an installation surface of the image forming apparatus that necessarily contacts a supporting desk, a shelf, a floor, or the like. To prevent image deterioration due to such vibration and impact, it is preferable to provide a viscoelastic member81on the installation surface of the image forming apparatus.FIG. 8Bis a cross-sectional view illustrating a structure of a vibration absorbing member80, in which the viscoelastic member81is sandwiched between two structural materials82and83. The vibration absorbing member80having the above-described structure is provided on the installation surface of an image forming apparatus100as illustrated inFIG. 8A, which is a perspective view illustrating an example in which the two generally rectangular vibration absorbing members80are provided on the installation surface of the image forming apparatus100. The vibration absorbing member80may be sized and shaped as required. For example, the four vibration absorbing members80may be provided at four corners on the bottom of the image forming apparatus100, respectively. As a result, transmission of vibration and impact from outside of the image forming apparatus100to the optical scanning device50can be prevented by providing the vibration absorbing member80including the viscoelastic member81on the installation surface of the image forming apparatus100. Additionally, a rubber foot often provided on a bottom surface of the image forming apparatus is preferably provided under the vibration absorbing member80.

FIG. 9is a schematic plan view illustrating an arrangement of optical elements in the optical scanning device50.

Referring toFIG. 9, the optical scanning device50includes the polygon scanner61serving as a common rotating deflector. A set of optical elements is provided on each side of the polygon scanner61in a substantially symmetrical manner in order to scan images of four colors. Reference numeral71denotes a semiconductor laser serving as a light source and corresponds to the light source60illustrated inFIG. 2. Reference numeral72denotes a collimating lens; reference numeral73denotes an aperture; reference numeral74denotes a cylindrical lens; and reference numeral75denotes a synchronization detector including an imaging lens76, a photodiode77, and a substrate78. Reference numeral79denotes a reflecting mirror for guiding the light beam to the synchronization detector75. The reflecting mirror79guides the light beam to the synchronization detector75placed outside of a writing area in a main scanning direction during scanning to control a timing of writing. The synchronization detector75is provided on the second housing52.

A description is now given of the image forming apparatus100including the optical scanning device50according to exemplary embodiments.

FIG. 10is a vertical cross-sectional view illustrating a configuration of a full-color printer serving as the image forming apparatus100including the optical scanning device50. The image forming apparatus100includes an intermediate transfer belt11at a substantially center portion of the main body thereof. The intermediate transfer belt11is stretched across multiple rollers. Four imaging units10are arranged along an upper traveling surface of the intermediate transfer belt11.

The imaging units10include photoconductors1M,1C,1Y, and1Bk (hereinafter collectively referred to as photoconductors1) each serving as an image bearing member, respectively. A charger2, a developing device3, and a cleaning device4are provided around each of the photoconductive drums1. A transfer roller12serving as a primary transfer unit is provided at an inner portion of the intermediate transfer belt11, facing each of the photoconductors1. According to exemplary embodiments, each of the four imaging units10has the same configuration, except that a color of a developer, that is, magenta, cyan, yellow, and black, used in each of the developing devices3is different from one another. In the image forming apparatus100, the imaging units10are arranged in order of magenta, cyan, yellow, and black from the left side inFIG. 10. Each of the imaging units10is detachably attached to the image forming apparatus100as a process cartridge.

The optical scanning device50is provided above the imaging units10. As described above, the optical scanning device50includes the polygon scanner61and the group of mirrors to direct modulated laser beams onto the surfaces of the photoconductors1in the imaging units10.

A paper feed cassette15is provided at the bottom of the image forming apparatus100. In addition, a paper feed roller16configured to feed a recording medium such as a transfer sheet (hereinafter referred to as a sheet) from the paper feed cassette15is provided. A pair of registration rollers18is provided diagonally above the paper feed roller16on a downstream side relative to a paper feed direction. A transfer roller19is provided above the pair of registration rollers18, facing a transfer facing roller13serving as one of the rollers across which the intermediate transfer belt11is stretched to form a secondary transfer unit.

A fixing device20is provided above the secondary transfer unit. A discharge tray30is provided on an upper surface of the image forming apparatus100, and a pair of discharge rollers29configured to discharge the sheet to the discharge tray30is provided above the fixing device20.

A description is now given of image formation performed by the image forming apparatus100having the above-described configuration.

The photoconductors1in the imaging units10are rotated in a clockwise direction by a driving unit, not shown, and surfaces of each of the photoconductors1are evenly charged to a predetermined polarity by the chargers2. A laser beam is directed onto each of the surfaces of the photoconductors1thus charged from the optical scanning device50to form an electrostatic latent image on each of the surfaces of the photoconductors1. Image data exposed on each of the surfaces of the photoconductors1at this time is monochrome image data obtained by separating a full-color image into color data of magenta, cyan, yellow, and black. Toner of each color is applied to each of the electrostatic latent images thus formed from the developing device3to form toner images.

The intermediate transfer belt11is driven in a counterclockwise direction inFIG. 10, and the toner images of each color are sequentially transferred onto the intermediate transfer belt11from each of the photoconductors1by the primary transfer rollers12. Accordingly, the intermediate transfer belt11bears a full-color toner image on the surface thereof.

Alternatively, a monochrome toner image may be formed by any one of the imaging units10, or a toner image using two or three colors may be formed by the appropriate imaging units10. When the monochrome toner image is formed, the imaging unit10using black toner provided on the far right side in the image forming apparatus100illustrated inFIG. 10is used to perform image formation.

Residual toner particles which are not transferred onto the intermediate transfer belt11but remain on the surfaces of each of the photoconductors1are removed by the cleaning devices4. Thereafter, a neutralizing device, not shown, neutralizes the potential charge on the surface of each of the photoconductors1to prepare for a subsequent image formation.

Meanwhile, the sheet is fed from the paper feed cassette15to the secondary transfer unit by the pair of registration rollers18in synchronization with entry of the full-color toner image borne on the intermediate transfer belt11. In the image forming apparatus100, a transfer voltage having a polarity opposite to the polarity of the toner in the full-color toner image is applied to the transfer roller19. As a result, the full-color toner image on the intermediate transfer belt11is transferred onto the sheet all at once. Heat and pressure are applied to the sheet having the full-color toner image thereon when the sheet passes through the fixing device20to fix the full-color toner image to the sheet. The sheet having the fixed toner image thereon is then discharged to the discharge tray30provided on the upper surface of the image forming apparatus100by the pair of the discharge rollers29.

An upper cover31including the discharge tray30on an upper surface thereof is configured to be pivotally openable/closable about a shaft32. In the image forming apparatus100, the optical scanning device50is provided on the upper cover31and is not fixed to the main body of the image forming apparatus100, such that the optical scanning device50is opened/closed together with the upper cover31relative to the main body of the image forming apparatus100. Such a configuration makes it possible to reduce the effect of vibration from the main body of the image forming apparatus100, thereby achieving high-quality writing and scanning, and preventing image deterioration caused by such vibration. Further, a range of possible layouts of the optical scanning device50in the image forming apparatus100can be increased, and operation of the optical scanning device50is improved.

In the image forming apparatus100according to exemplary embodiments, a vibration sensor, not shown, is provided in the optical scanning device50. Accordingly, vibration and impact applied to the optical scanning device50can be detected by the vibration sensor. When a signal output from the vibration sensor exceeds a predetermined value during image formation, the vibration sensor notifies the user of the image forming apparatus100that image deterioration may occur due to the vibration.

For example, the vibration sensor may generate an audio alarm to notify the user that image deterioration may occur due to vibration during image formation. Alternatively, a warning light may be turned on or flashed on a control panel or the like of the image forming apparatus100. In the above-described configurations, it is very important that the alarm or light notifying the user of vibration is distinguishable from other sounds or lights notifying the user of other malfunctions of the image forming apparatus100. However, the user may not identify a difference in the alarm sounds or light. Further, such a notification may not be conveyed to the user by the audio alarm or the warning light. To solve such problems, a text or a pictorial symbol for notifying the user of vibration may be displayed on the control panel. Alternatively, a warning message indicating that the amount of the vibration or impact exceeds a predetermined value may be sent to a device issuing a print request such as a personal computer to display such a warning message on a screen of the personal computer. For example, a message indicating possible image deterioration due to unexpected vibration or impact from outside of the image forming apparatus may be displayed on the screen of the personal computer. When the user finds irregularities in a printed image because of the message displayed on the screen, printing may be performed again to obtain a proper image.

It is to be noted that the present invention is not limited to the above-described configuration. Thus, for example, the first housing51and the second housing52may have any appropriate shape. The shape of the second housing52is not limited to a rectangle, but may be another polygon. The number of the mounts68to fix the first housing51to the second housing52is not limited to four as described in the foregoing exemplary embodiments, but may be three as illustrated in the fourth exemplary embodiment, or may be five or more.

The first housing51may include an optical element such as a lens in addition to the light source60and the polygon scanner61serving as a deflector. The second housing52may include an arbitrary optical element. The optical scanning device50may scan the surface of the photoconductor1with a single light beam so as to be employed in a monochrome image forming apparatus.

In the image forming apparatus100according to the foregoing exemplary embodiments, a configuration of each unit such as the imaging units10may be arbitrarily set. For example, a transfer method applied to the image forming apparatus100is not limited to an indirect transfer method, but may be a direct transfer method. The arrangement order of the imaging units10in the tandem-type image forming apparatus may be arbitrarily set. Not only the tandem-type image forming apparatus but also an image forming apparatus in which multiple developing devices are provided around a single photoconductor or a revolver-type developing device is provided may be used. Further, the present invention may be applied to a full-color image forming apparatus using three toner colors, a multicolor image forming apparatus using two toner colors, and a monochrome image forming apparatus. Needless to say, the image forming apparatus100according to the foregoing exemplary embodiments is not limited to a printer, but may be a copier, a facsimile machine, and a multifunction apparatus that combines the functions of the copier, the printer, and the facsimile machine.

Elements and/or features of different exemplary embodiments may be combined with each other and/or substituted for each other within the scope of this disclosure and appended claims.

The number of constituent elements, locations, shapes and so forth of the constituent elements are not limited to any of the structure for performing the methodology illustrated in the drawings.