JP2008033062A - Optical scanner and image forming apparatus equipped with the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an optical scanner capable of preventing irregularity of output images while exposure properties are maintained, and to obtain an image forming apparatus equipped with the same. <P>SOLUTION: A part of the light beam emitted from a laser diode 26 reflects on the lens face 34A of an fθ lens 34, forms an image near the laser diode 26, and is further reflected on the light emitting face of the laser diode 26 to expose a photoreceptor drum 110 again, and stripes appear in the output image. However, since a cylindrical lens 30 is coated with a light quantity attenuation coating, the light beam reflected by the fθ lens 34 and returned is made to attenuate. As a result, no exposure defects are caused, and the irregularity of the output image is prevented while exposure properties are maintained. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an optical scanning apparatus that forms an electrostatic latent image by irradiating a photosensitive member with a light beam, and an image forming apparatus including the optical scanning apparatus.

  When an anti-reflection coating lens is used as the fθ lens that transmits the light beam emitted from the light source and forms an image on the photoreceptor, the amount of reflected light of the light beam reflected by the fθ lens to the light source increases. . The light beam reflected by the uncoated fθ lens affects the light beam emitted from the light source, which causes a problem in that exposure failure occurs and image unevenness such as white stripes and black stripes occurs in the output image. There is.

  Therefore, there is an optical scanning device that diffuses the light beam reflected by the fθ lens by changing the lens surface shape of the fθ lens. (Patent Document 1).

According to this, in order to diffuse the reflected light beam, the amount of reflected light of the light beam returning to the light source is attenuated. For this reason, the light beam emitted from the light source is not affected, thereby preventing exposure failure, so that unevenness of the output image can be prevented.
Japanese Patent Laid-Open No. 11-183816

  However, in this optical scanning device, it is conceivable that the exposure performance changes because the lens surface shape of the fθ lens is changed.

  In particular, when a single lens is used as the fθ lens, the exposure performance is greatly affected because curved surfaces are provided in the main scanning direction and the sub-scanning direction.

  An object of the present invention is to prevent unevenness of an output image while maintaining the exposure characteristics in consideration of the above facts.

  An optical scanning device according to a first aspect of the present invention includes a light source that emits a light beam, an optical system that shapes the light beam emitted from the light source, and light that deflects and scans the light beam shaped by the optical system. An optical scanning device comprising: a deflector; and an fθ lens that forms an image of a light beam deflected and scanned by the optical deflector on an exposure surface and is not coated with an antireflection coating. Is characterized in that a light quantity attenuating element is provided.

  According to the above configuration, since the anti-reflection coating is not applied to the fθ lens, the amount of reflected light of the light beam returned to the light source side by the fθ lens is increased compared to the case where the coating is applied.

  However, since the optical system is provided with a light amount attenuating element, the reflected light amount of the light beam reflected by the fθ lens and returning to the light source is attenuated by passing through the light amount attenuating element.

  In this way, since the amount of reflected light of the light beam returning to the light source is attenuated, the light beam emitted from the light source is not affected. For this reason, it is possible to prevent unevenness of the output image while maintaining the exposure characteristics without causing exposure failure.

  Further, even if the light beam emitted from the light source has a high light amount, it is attenuated by the light amount attenuating element, so that the appropriate light amount is obtained. In this way, since the light source can be used with a high light amount, there is also a droop suppression effect that occurs when emitting a low light amount.

  The optical scanning device according to a second aspect of the present invention is the optical scanning device according to the first aspect, wherein the light amount attenuating element is a cylindrical lens that is provided with an attenuation coating and forms an image of the light beam in the main scanning direction. .

  According to the above configuration, the light amount attenuating element is a cylindrical lens to which an attenuation coating is applied. In this way, by coating the existing parts constituting the optical system, it is not necessary to add another part, and unevenness of the output image can be prevented while maintaining the exposure characteristics.

  According to a third aspect of the present invention, in the optical scanning device according to the second aspect, the lens surface on the light source side of the cylindrical lens is provided with an attenuation coating.

  According to the above configuration, the attenuation coating is applied to the lens surface on the light source side of the cylindrical lens. For this reason, compared with the case where an attenuation coating is applied to the surface on the optical deflector side, the amount of light reflected from the light beam reflected from the cylindrical lens and directly returned to the light source can be attenuated. it can.

  According to a fourth aspect of the present invention, there is provided the optical scanning device according to the first aspect, wherein the light amount attenuating element is a reflecting member that is provided with an attenuation coating and changes the direction of the light beam.

  According to the above configuration, the light amount attenuating element is a reflecting member to which an attenuation coating is applied. As described above, it is possible to prevent unevenness of the output image while maintaining the exposure characteristics only by changing the coating of the reflecting member to the attenuation coating.

  An optical scanning device according to a fifth aspect of the present invention is the optical scanning device according to any one of the first to fourth aspects, wherein the fθ lens is a single lens.

  According to the above configuration, since the fθ lens is a single lens, the R surface in the sub-scanning direction is provided on the surface on the optical deflector side. As a result, the light beam reflected by the fθ lens forms an image in the sub-scanning direction near the light source. For this reason, the light beam emitted from the light source is easily affected. However, since the light quantity attenuation element is provided in the optical system, it is possible to prevent unevenness in the output image while maintaining the exposure characteristics.

  An optical scanning device according to a sixth aspect of the present invention is the optical scanning device according to the fifth aspect, wherein the light beam reflected by the fθ lens forms an image in the vicinity of the light source in both the main scanning direction and the sub-scanning direction. It is characterized by having a curved surface.

  According to the above configuration, the light beam reflected by the fθ lens forms an image near the light source in both the main scanning direction and the sub-scanning direction. For this reason, the light beam emitted from the light source is easily affected. However, since the light amount attenuating element is provided in the optical system, it is possible to prevent unevenness in the output image while maintaining the exposure characteristics.

  An image forming apparatus according to a seventh aspect of the present invention includes the optical scanning device according to any one of the first to sixth aspects.

  According to the above configuration, since the image forming apparatus includes the optical scanning device according to any one of claims 1 to 6, unevenness of the output image can be prevented and image quality can be improved. it can.

  According to the present invention, it is possible to prevent unevenness of an output image while maintaining exposure characteristics.

  An image forming apparatus 100 equipped with the optical scanning device 20 of the first embodiment will be described with reference to FIGS.

  As shown in FIG. 9, a paper feed cassette 21 that can be pulled out from the image forming apparatus 100 is disposed in the lower part of the housing 102 of the image forming apparatus 100. Sheet materials P supplied to 100 image forming units 111 are stacked.

  The sheet materials P stacked on the sheet feeding cassette 21 are sequentially taken out by the pickup roll 104 and further conveyed one by one by a sheet feeding unit constituted by a sheet feeding roll 122 and a separation roll 112 that are rotationally driven. It has a configuration.

  In addition, a transport roll 106 is disposed at a predetermined position in the housing 102 and constitutes a transport path 108 for transporting the sheet material P. In addition, guide members 128 are disposed on both sides of the conveyance path 108, and the guide members 128 guide the sheet material P along the conveyance path 108. Hereinafter, simply “upstream” and “downstream” mean upstream and downstream in the transport direction, respectively.

  In the middle of the conveyance path 108, the photosensitive drum 110 is disposed so as to be in contact with the sheet material P, and rotates while being in contact with the sheet material P. The surface of the photosensitive drum 110 is charged by a charging device (not shown) and then irradiated with a light beam corresponding to image information by the optical scanning device 20 to form an electrostatic latent image. The electrostatic latent image is supplied with toner from the developing device 114 and visualized as a toner image. Details of the optical scanning device 20 will be described later.

  The image forming unit 111 includes a photosensitive drum 110 and a transfer roll 130, and the photosensitive drum 110 holds the sheet material P between the transfer roll 130 and is in close contact with the sheet material P. As a result, the toner image on the photosensitive drum 110 is transferred to the sheet material P, and an image is formed on the sheet material P.

  A fixing device 116 is disposed on the downstream side of the photosensitive drum 110. The fixing device 116 includes two rolls, and includes a heating roll 116H having a heater therein and a pressure roll 116N. The sheet material P is sandwiched and rotated by these two rolls to heat the sheet material P and fix the toner image of the sheet material P to the sheet material P.

  A discharge roll 118 is disposed on the downstream side of the fixing device 116, and the sheet material P on which the toner image is fixed is discharged to a discharge tray 126 provided on the side surface of the housing 102 by the discharge roll 118. It has become.

  A scanner 120 is provided above the housing 102 so that image information formed on a sheet or the like can be read.

  In the image forming apparatus 100 configured as described above, an image is formed as follows.

  First, a charger (not shown) to which a voltage is applied uniformly charges the surface of the photosensitive drum 110 with a predetermined potential.

  Subsequently, based on the image information read by the scanner 120, the optical scanning device 20 forms an electrostatic latent image on the charged photosensitive drum 110.

  That is, based on image data supplied from a control device (not shown), an electrostatic latent image corresponding to the image data is formed on the photosensitive drum 110 by the optical scanning device 20. Further, the electrostatic latent image is visualized as a toner image by toner supplied from the developing device 114.

  Therefore, the sheet material P taken out from the paper feed cassette 21 by the pickup roll 104 is sent out one by one along the guide 124 by the paper feed roll 122 and the separation roll 112 to the conveyance path 108 and is nipped and conveyed by the conveyance roll 106. Then, the toner image passes between the photosensitive drum 110 and the transfer roll 130 and is transferred to the sheet material P. The transferred toner image is fixed to the sheet material P by passing between a heating roll 116H and a pressure roll 116N provided in the fixing device 116, and the sheet material P is discharged to the discharge tray 126 by the discharge roll 118. Is done.

  Next, the optical scanning device 20 will be described in detail.

  As shown in FIGS. 1 and 2, the optical scanning device 20 includes a box-shaped housing 22 and a cover 24 (see FIG. 3) that closes the opening of the housing 22. 1 and 2, the cover 24 is not shown in order to make the mechanism in the housing 22 easier to see.

  A laser diode (LD) 26 as a light source is disposed in the housing 22. A collimator lens 28, a slit 29, a cylindrical lens 30, an optical deflector 32, an fθ lens 34, and a reflection mirror 40 are disposed in the optical path from the laser diode (LD) 26 to the photosensitive drum 110. Yes. The surface configuration of the cylindrical lens 30 is a convex R surface on the light source side.

  The optical deflector 32 includes a polygon mirror 36 and a motor 38 that rotates the polygon mirror 36. The light beam emitted from the laser diode 26 is converted into parallel light by the collimator lens 28. The cylindrical lens 30 forms an image on the polygon mirror 36 so as to be linear in the main scanning direction of the light beam. The light beam imaged in a linear form is main-scanned (deflected) in a predetermined direction by the rotation of the polygon mirror 36, and after the scanning speed is corrected by the fθ lens 52 not coated with anti-reflection, the reflection mirror The photosensitive drum 110 (see FIG. 3) is exposed by being reflected by 40.

  As shown in FIG. 3, the cover 24 is provided with a dustproof glass 42 in the opening 24 </ b> A of the cover 24 that transmits the light beam reflected by the reflecting mirror 40.

  Here, since the fθ lens 34 of the present embodiment is a single lens having a single lens configuration, the lens surface 34A on the polygon mirror 36 side of the fθ lens 34 has an R-surface shape in both the main scanning direction and the sub-scanning direction. Yes. Further, since the anti-reflection coating is not applied to the fθ lens 34, the amount of reflected light of the light beam returned to the laser diode 26 side by the fθ lens is larger than when the anti-reflection coating is applied. Become.

  Specifically, the light beam emitted from the laser diode 26 is reflected by about 4% toward the polygon mirror 36 by the lens surface 34A of the plastic material fθ lens 34.

  As shown in FIG. 4A, a part of the light beam emitted from the laser diode 26 is reflected by the lens surface 34 </ b> A of the fθ lens 34. Further, the reflected light beam is reflected by the polygon mirror 36, passes through the cylindrical lens 30 and the collimator lens 28, and forms an image in the main scanning direction in the vicinity of the laser diode 26 as shown in FIG. .

  Further, as shown in FIG. 6, a part of the light beam emitted from the laser diode 26 (see FIG. 5) is reflected by the lens surface 34A of the fθ lens 34, reflected by the polygon mirror 36, and further, As shown in FIG. 5A, the light passes through the cylindrical lens 30 and the collimator lens 28 and forms an image in the sub-scanning direction near the laser diode 26 as shown in FIG. 5B.

  The light beam formed in the vicinity of the laser diode 26 is reflected by the light emitting surface 26A of the laser diode 26 shown in FIG. 7, is reflected again toward the fθ lens 34 shown in FIG. 1, and is scanned by the fθ lens 34. After the speed correction, the photosensitive drum 110 (see FIG. 3) is exposed by being reflected by the reflecting mirror 40.

  As described above, the reflected light beam reflected by the lens surface 34A of the fθ lens 34 is reflected by the light emitting surface 26A of the laser diode 26 to expose the photosensitive drum 110 (see FIG. 3), as shown in FIG. A streak appears in the output image and a so-called ghost is generated. In particular, this streak appears prominently when a halftone color (light color) is used for the background of the output image. Since the reflected light from the lens surface 34A of the fθ lens 34 is also scanned, the photosensitive drum 110 is exposed only during the time when it is reflected by the light emitting surface 26A of the laser diode 26. Therefore, the exposure width is short (about 2 mm). It looks like a shape.

However, as shown in FIG. 1, the lens surface 30A on the laser diode 26 side of the cylindrical lens 30 of this embodiment is coated with a titanium dioxide (TiO ₂ ) film as an attenuation coating that attenuates the amount of light beam. Therefore, the transmittance of the light beam is 50%.

With this configuration, the light beam emitted from the laser diode 26 passes through the titanium dioxide (TiO ₂ ) film on the lens surface 30A, so that the light amount of the light beam is attenuated by 50%. A part of the light beam transmitted through the titanium dioxide (TiO ₂ ) film is reflected by the lens surface 34 A of the fθ lens 34, further reflected by the polygon mirror 36, and returned from the polygon mirror 36 to the laser diode 26. Passes through the lens surface 30A coated with the titanium dioxide (TiO ₂ ) film of the cylindrical lens 30 again and is attenuated by 50% again to form an image in the vicinity of the laser diode. As described above, when the light beam emitted from the laser diode 26 is reflected by the fθ lens 34 and returns to the laser diode 26, it passes through the lens surface 30 </ b> A of the cylindrical lens 30 twice to return to the laser diode 26. The reflected light amount of the light beam is 1% (50% × 4% × 50%) of the emitted light amount. That is, since the relative light quantity with respect to the main beam on the photosensitive drum 110 is 1%, no image defect occurs.

  In this way, by attenuating the light amount of the light beam returning to the laser diode 26, the light beam returning to the laser diode 26 is reflected by the light emitting surface 26A (see FIG. 7) of the laser diode 26, and the photosensitive drum 110 (FIG. 3). It is possible to prevent unevenness of the output image generated by exposing (see).

Further, in the present embodiment, since the laser diode 26 side of the lens surface 30A on the titanium dioxide (TiO ₂₎ film of the cylindrical lens 30 is subjected, titanium dioxide polygon mirror 36 side of the lens surface 30B (TiO ₂₎ film Compared with the case where the laser beam is applied, the amount of reflected light of the light beam that is emitted from the laser diode 26 is reflected by the cylindrical lens 30 and returns directly to the laser diode 26 can be attenuated. For this reason, unevenness of the output image can be effectively prevented.

  Further, by changing the lens surface shape of the fθ lens 34, the light beam returning to the laser diode 26 is diffused, and compared with the method of attenuating the reflected light amount of the light beam returning to the laser diode 26, the lens surface shape is changed. Since no change is made, unevenness of the output image can be prevented while maintaining the exposure characteristics.

  Further, even if the light beam emitted from the laser diode 26 has a high amount of light, it is attenuated by the cylindrical lens 30 so that an appropriate amount of light is obtained. Thus, since the laser diode 26 can be used with a high light amount, there is also a droop suppression effect that occurs when a low light amount is emitted. Droop refers to a phenomenon in which a decrease in light output (droop) within one bit pulse begins to become apparent as the pulse width increases.

Although the present invention has been described in detail with respect to specific embodiments, the present invention is not limited to such embodiments, and various other embodiments are possible within the scope of the present invention. It is clear to the contractor. For example, in the above embodiment, in order to attenuate the amount of reflected light beam, a titanium dioxide (TiO ₂ ) film, which is a dielectric film, is applied as an attenuation coat, but other dielectric films may be applied, The amount of reflected light may be attenuated by applying a metal film or the like.

In this embodiment, the titanium dioxide (TiO ₂ ) film is applied to the lens surface 30A of the cylindrical lens 30, but the reflected light quantity may be attenuated by applying a titanium dioxide (TiO ₂ ) film to the other lens surface. .

  Next, a second embodiment of the image forming apparatus 100 employing the optical scanning device 20 of the present invention will be described with reference to FIGS.

  In addition, about the same member as 1st Embodiment, the same code | symbol is attached | subjected and the description is abbreviate | omitted.

In this embodiment, the cylindrical lens 30 is not provided with a titanium dioxide (TiO ₂ ) film as in the first embodiment. Instead, as shown in FIGS. 10 and 11, the collimator lens 28 and A titanium dioxide (TiO ₂ ) film is applied to a reflecting mirror 50 as a reflecting member provided between the cylindrical lens 30.

  As shown in FIG. 12, the light beam emitted from the laser diode 26 is reflected by the reflection mirror 50, and reflected by the fθ lens 34 through the cylindrical lens 30 and the polygon mirror 36. The light beam reflected by the fθ lens 34 and returning to the laser diode 26 is reflected again by the reflection mirror 50 and forms an image near the laser diode 26.

In this way, by reflecting the light beam with the reflection mirror 50 to which the titanium dioxide (TiO ₂ ) film is applied, the amount of reflected light of the light beam returning to the laser diode 26 can be attenuated.

Further, since the amount of light can be attenuated simply by adding a titanium dioxide (TiO ₂ ) film to the surface protective coating of the reflection mirror 50, the structure is inexpensive. Alternatively, since the amount of reflected light is attenuated only by changing the aluminum coating specification of the reflection mirror 50 (number of films, etc.), the structure is inexpensive.

It is a top view of the optical scanning device concerning a 1st embodiment of the present invention. 1 is a perspective view of an optical scanning device according to a first embodiment of the present invention. It is a side view of the optical scanning device concerning a 1st embodiment of the present invention. 1 illustrates an optical scanning device according to a first embodiment of the present invention, in which a light beam emitted from a laser diode and a light beam reflected by an fθ lens are viewed from the main scanning direction. 1 shows an optical scanning device according to a first embodiment of the present invention, in which a light beam emitted from a laser diode and a light beam reflected by an fθ lens are viewed from the sub-scanning direction. 1 is a diagram illustrating an optical scanning device according to a first embodiment of the present invention, in which a light beam reflected by a polygon mirror and a light beam reflected by an fθ lens are viewed from the sub-scanning direction. 1 is a perspective view showing a laser diode according to a first embodiment of the present invention. 4 is a diagram illustrating streaks of an output image improved by the optical scanning device according to the first embodiment of the present invention. 1 is a schematic configuration diagram of an image forming apparatus according to a first embodiment of the present invention. It is a top view of the optical scanning device concerning a 2nd embodiment of the present invention. It is a perspective view of the optical scanning device concerning a 2nd embodiment of the present invention. FIG. 6 shows an optical scanning device according to a second embodiment of the present invention, and is a view of a light beam emitted from a laser diode and a reflected light beam reflected from an fθ lens, as viewed from the main scanning direction.

Explanation of symbols

20 Optical scanning device 26 Laser diode (light source)
30 Cylindrical lens 30A Lens surface
32 Optical deflector 50 Reflection mirror (reflection member)
100 Image forming apparatus

Claims (7)

A light source that emits a light beam, an optical system that shapes the light beam emitted from the light source, an optical deflector that deflects and scans the light beam shaped by the optical system, and deflected and scanned by the optical deflector In an optical scanning device having an image of a light beam on an exposure surface and an fθ lens not coated with an antireflection coating,
An optical scanning device characterized in that a light amount attenuating element is provided in the optical system.   2. The optical scanning device according to claim 1, wherein the light amount attenuating element is a cylindrical lens that is provided with an attenuation coating and forms an image of the light beam in the main scanning direction.   3. The optical scanning device according to claim 2, wherein an attenuation coating is applied to a lens surface on the light source side of the cylindrical lens.   2. The optical scanning device according to claim 1, wherein the light amount attenuating element is a reflecting member that is provided with an attenuation coating and changes the direction of the light beam.   5. The optical scanning device according to claim 1, wherein the fθ lens is a single lens. 6.   The optical scanning device according to claim 5, wherein the fθ lens has a curved surface on which the light beam reflected by the fθ lens forms an image in the vicinity of the light source in both a main scanning direction and a sub-scanning direction. An image forming apparatus comprising the optical scanning device according to claim 1.

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