JP2011180168A - Optical scanning apparatus and image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical scanning apparatus which can be miniaturized without degrading its scanning accuracy. <P>SOLUTION: The optical scanning apparatus includes: a light source unit for emitting the light beam LBa which is the linearly polarized light with its electric field vector being directed in Z-axis direction, and the light beam LBb which is the linearly polarized light having the polarizing direction orthogonal to the polarizing direction of the light beam LBa; and an optical scanning system which includes a polarized light separation device 16<SB>1</SB>to transmit the p-polarized light and to reflect the s-polarized light, and individually converges a plurality of light beams polarized by a polygon mirror on the corresponding scanning surface. A wire grid element is used for the polarized light separation device 16<SB>1</SB>, having a structure in which the wire longitudinal direction is parallel to the polarized surface, the ghost beam intensity ratio when the light beam LBb is incident is smaller than that when the light beam LBa is incident, and its value is ≤1%. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an optical scanning apparatus and an image forming apparatus, and more particularly to an optical scanning apparatus having a polarization separation device and an image forming apparatus including the optical scanning apparatus.

  In electrophotographic image recording, an image forming apparatus using a laser is widely used. In this case, the image forming apparatus includes an optical scanning device, and the drum is rotated while scanning the laser beam using a deflector (for example, a polygon mirror) in the axial direction of the photosensitive drum, and the surface of the drum is hidden. A method for forming an image is common.

  2. Description of the Related Art In recent years, tandem image forming apparatuses having a plurality of photosensitive drums (usually four) have become widespread with the progress of colorization and speedup in image forming apparatuses.

  In the tandem system, the image forming apparatus tends to increase in size as the number of drums increases, and downsizing is required including the optical scanning apparatus. In order to make the optical scanning device smaller (thinner), it is effective to superimpose a plurality of optical paths of scanning light from the deflector toward each drum.

  For example, Patent Document 1 discloses two laser light sources that emit laser beams that are linearly polarized in directions perpendicular to each other and that are modulated by a signal to be recorded, and two laser beams that are emitted from these laser light sources. Polarized light combining means for combining, deflecting means for deflecting the combined laser light in the main scanning direction, and polarized light separating means for separating the combined laser light deflected by the deflecting means into separate spots on the scanning recording surface; A recording device is disclosed.

  Patent Document 2 discloses a single laser light source, information control means for giving different information to two polarized lights of laser light from the light source, and the amount of polarization based on information from the information control means. Light from the polarization control means, scanning means for scanning and irradiating the polarization-controlled light onto a predetermined irradiation surface, separation means for splitting the scanned light into two lights according to the polarization state, and light from the scanning means An optical scanning device having optical rotation control means for optically controlling laser light according to an incident angle incident on the separating means is disclosed.

  Patent Document 3 discloses a light source device that emits a plurality of light beams having different polarization directions, a single light deflecting unit that deflects and scans a plurality of light beams emitted from the light source device in the main scanning direction, A scanning image forming means for condensing a plurality of light beams toward a plurality of corresponding scanned surfaces, and an optical path from the light deflecting means to the scanned surface. An optical scanning device including an optical path branching unit that branches according to the polarization direction of a beam is disclosed. As the optical path branching means, an optical element in which a concavo-convex structure portion having a pitch equal to or less than the wavelength of the light beam is used.

  However, in the recording apparatus disclosed in Patent Document 1, the electric field vector of p-polarized light that should be transmitted through the polarized light separating unit may not be parallel to the incident surface of the polarized light separating surface. There is a disadvantage that a part of the light is reflected by the polarized light separating means.

  Further, the optical scanning device disclosed in Patent Document 2 has a disadvantage in that the cost increases when a magneto-optical element is used as the optical rotation control means. In addition, the power consumption increases with the optical rotation control, and heat is generated. Furthermore, the optical rotation angle is likely to change in an environment such as temperature, and it is difficult to stably manage the performance.

  Further, the optical scanning device disclosed in Patent Document 3 does not have any countermeasures against the possibility that light (ghost light) emitted in a direction other than a desired direction may be generated by the optical path branching unit. It was not mentioned.

  The present invention has been made under such circumstances, and a first object of the invention is to provide an optical scanning device that can be reduced in size without degrading scanning accuracy.

  A second object of the present invention is to provide an image forming apparatus that can be reduced in size without degrading image quality.

  From the first viewpoint, the present invention provides a first light beam whose polarization direction is the first polarization direction and a second light beam whose polarization direction is a second polarization direction different from the first polarization direction. A light source unit that emits a plurality of light fluxes including: a deflector that deflects the plurality of light fluxes from the light source unit; and transmits light in the first polarization direction and reflects light in the second polarization direction A scanning optical system that includes a polarization separation device and individually collects a plurality of light beams deflected by the deflector onto a corresponding scanned surface, and the polarization separation device transmits the first light beam. In the optical scanning device, the ratio of the light intensity of the reflected light to the light intensity of the light and the ratio of the light intensity of the transmitted light to the light intensity of the reflected light of the second light flux are different from each other.

  According to this, it is possible to reduce the size without reducing the scanning accuracy.

  According to a second aspect, the present invention comprises: a plurality of image carriers; and the optical scanning device according to the present invention that individually scans the plurality of image carriers with a light beam, and the light source unit of the optical scanning device comprises: The light beam A modulated by the black image information and the light beam B having a polarization direction different from that of the light beam A are emitted, and the polarization separation device of the optical scanning device goes to the corresponding image carrier for the light beam A. Light intensity Is1 of light, light intensity Ig1 of light toward other than the corresponding image carrier, light intensity Is2 of light toward the corresponding image carrier, and light intensity of light toward other than the corresponding image carrier for the light flux B An image forming apparatus using Ig2 having separation characteristics satisfying a relationship of (Ig1 / Is1)> (Ig2 / Is2).

  According to this, it is possible to reduce the size without degrading the image quality.

1 is a diagram illustrating a schematic configuration of a color printer according to an embodiment of the present invention. It is FIG. (1) for demonstrating an optical scanning device. It is FIG. (2) for demonstrating an optical scanning device. It is a figure for demonstrating light source unit LU1. It is a figure for demonstrating the light source in light source unit LU1. It is a figure for demonstrating light source unit LU2. It is a figure for demonstrating the light source in light source unit LU2. FIG. 8A to FIG. 8C are diagrams for explaining wire grid elements, respectively. It is a figure for demonstrating the effect | action of a wire grid element. It is a diagram for explaining a polarization splitting device 16 _1. It is a diagram for explaining a polarization splitting device 16 _2. It is FIG. (1) for demonstrating the relationship between the height of the wire in a wire grid element, and a ghost light intensity ratio. It is FIG. (2) for demonstrating the relationship between the height of the wire in a wire grid element, and a ghost light intensity ratio. FIG. 14A and FIG. 14B are diagrams for explaining wire grid elements corresponding to FIG. It is a figure for demonstrating addition of a polarizer. It is a figure for demonstrating the modification of a scanning optical system.

  Hereinafter, an embodiment of the present invention will be described with reference to FIGS. FIG. 1 shows a schematic configuration of a color printer 2000 as an image forming apparatus according to an embodiment.

  The color printer 2000 is a tandem multi-color printer that forms a full-color image by superimposing four colors (black, cyan, magenta, and yellow), and includes an optical scanning device 2010, four photosensitive drums (2030a, 2030b, 2030c, 2030d), four cleaning units (2031a, 2031b, 2031c, 2031d), four charging devices (2032a, 2032b, 2032c, 2032d), four developing rollers (2033a, 2033b, 2033c, 2033d), 4 Toner cartridges (2034a, 2034b, 2034c, 2034d), transfer belt 2040, transfer roller 2042, fixing roller 2050, paper feed roller 2054, registration roller pair 2056, paper discharge roller 2058, paper feed tray 060, paper ejection tray 2070 includes a communication control unit 2080, and a printer controller 2090 for totally controlling the above elements.

  In the following description, in the XYZ three-dimensional orthogonal coordinate system, the direction along the longitudinal direction of each photosensitive drum is defined as the Y-axis direction, and the direction along the arrangement direction of the four photosensitive drums is defined as the X-axis direction.

  The communication control device 2080 controls bidirectional communication with a host device (for example, a personal computer) via a network or the like.

  Each photosensitive drum has a photosensitive layer formed on the surface thereof. That is, the surface of each photoconductive drum is a surface to be scanned. Each photosensitive drum is rotated in the direction of the arrow in the plane of FIG. 1 by a rotation mechanism (not shown).

  A charging device 2032a, a developing roller 2033a, and a cleaning unit 2031a are disposed in the vicinity of the surface of the photosensitive drum 2030a along the rotation direction of the photosensitive drum 2030a.

  The photosensitive drum 2030a, the charging device 2032a, the developing roller 2033a, the toner cartridge 2034a, and the cleaning unit 2031a are used as a set and form an image forming station (hereinafter also referred to as “K station” for convenience) that forms a black image. Constitute.

  A charging device 2032b, a developing roller 2033b, and a cleaning unit 2031b are arranged in the vicinity of the surface of the photosensitive drum 2030b along the rotation direction of the photosensitive drum 2030b.

  The photosensitive drum 2030b, the charging device 2032b, the developing roller 2033b, the toner cartridge 2034b, and the cleaning unit 2031b are used as a set and form an image forming station (hereinafter also referred to as “C station” for convenience) that forms a cyan image. Constitute.

  A charging device 2032c, a developing roller 2033c, and a cleaning unit 2031c are arranged in the vicinity of the surface of the photosensitive drum 2030c along the rotation direction of the photosensitive drum 2030c.

  The photosensitive drum 2030c, the charging device 2032c, the developing roller 2033c, the toner cartridge 2034c, and the cleaning unit 2031c are used as a set, and form an image forming station (hereinafter also referred to as “M station” for convenience) that forms a magenta image. Constitute.

  A charging device 2032d, a developing roller 2033d, and a cleaning unit 2031d are arranged in the vicinity of the surface of the photosensitive drum 2030d along the rotation direction of the photosensitive drum 2030d.

  The photosensitive drum 2030d, the charging device 2032d, the developing roller 2033d, the toner cartridge 2034d, and the cleaning unit 2031d are used as a set, and form an image forming station (hereinafter also referred to as “Y station” for convenience) that forms a yellow image. Constitute.

  By the way, in a tandem type color printer, the K-station photosensitive drum is usually placed at the leading end or trailing end of the photosensitive drum array for ease of color synthesis and easy handling of high-speed monochrome printing. It is arranged.

  Each charging device uniformly charges the surface of the corresponding photosensitive drum.

  Based on the multicolor image information (black image information, cyan image information, magenta image information, yellow image information) from the higher-level device, the optical scanning device 2010 charges the light flux modulated for each color correspondingly. Irradiate each surface of the photosensitive drum. As a result, on the surface of each photoconductive drum, the charge disappears only in the portion irradiated with light, and a latent image corresponding to the image information is formed on the surface of each photoconductive drum. The latent image formed here moves in the direction of the corresponding developing roller as the photosensitive drum rotates. The configuration of the optical scanning device 2010 will be described later.

  The toner cartridge 2034a stores black toner, and the toner is supplied to the developing roller 2033a. The toner cartridge 2034b stores cyan toner, and the toner is supplied to the developing roller 2033b. The toner cartridge 2034c stores magenta toner, and the toner is supplied to the developing roller 2033c. The toner cartridge 2034d stores yellow toner, and the toner is supplied to the developing roller 2033d.

  As each developing roller rotates, the toner from the corresponding toner cartridge is thinly and uniformly applied to the surface thereof. Then, when the toner on the surface of each developing roller comes into contact with the surface of the corresponding photosensitive drum, the toner moves only to a portion irradiated with light on the surface and adheres to the surface. In other words, each developing roller causes toner to adhere to the latent image formed on the surface of the corresponding photosensitive drum so as to be visualized. Here, the toner-attached image (toner image) moves in the direction of the transfer belt 2040 as the photosensitive drum rotates.

  The yellow, magenta, cyan, and black toner images are sequentially transferred onto the transfer belt 2040 at a predetermined timing, and are superimposed to form a color image.

  Recording paper is stored in the paper feed tray 2060. A paper feed roller 2054 is disposed in the vicinity of the paper feed tray 2060, and the paper feed roller 2054 takes out recording sheets one by one from the paper feed tray 2060 and conveys them to a pair of registration rollers 2056. The registration roller pair 2056 feeds the recording paper toward the gap between the transfer belt 2040 and the transfer roller 2042 at a predetermined timing. As a result, the color image on the transfer belt 2040 is transferred to the recording paper. The recording sheet transferred here is sent to the fixing roller 2050.

  In the fixing roller 2050, heat and pressure are applied to the recording paper, whereby the toner is fixed on the recording paper. The recording paper fixed here is sent to a paper discharge tray 2070 via a paper discharge roller 2058 and is sequentially stacked on the paper discharge tray 2070.

  Each cleaning unit removes toner (residual toner) remaining on the surface of the corresponding photosensitive drum. The surface of the photosensitive drum from which the residual toner has been removed returns to the position facing the corresponding charging device again.

  Next, the configuration of the optical scanning device 2010 will be described.

As shown in FIG. 2 and FIG. 3 as an example, the optical scanning device 2010 includes two light source units (LU1, LU2), two cylindrical lenses (12 ₁ , 12 ₂ ), a polygon mirror 14, and two fθ lenses. (15 ₁ , 15 ₂ ), two polarization separation devices (16 ₁ , 16 ₂ ), two reflection mirrors (17 ₁ , 17 ₂ ), a plurality of folding mirrors (18a, 18b ₁ , 18b ₂ , 18c ₁ , 18c ₂ , 18d), four anamorphic lenses (19a, 19b, 19c, 19d), four exit windows (21a, 21b, 21c, 21d) and a scanning control device (not shown). These are assembled at predetermined positions of the optical housing 2300 (not shown in FIG. 2, see FIG. 3).

Here, "w1 direction" optical axis direction of the cylindrical lenses 12 _1, the optical axis direction of the cylindrical lens 12 _2, "w2 direction". In addition, a direction orthogonal to both the w1 direction and the Z-axis direction is referred to as “m1 direction”, and a direction orthogonal to both the w2 direction and the Z-axis direction is referred to as “m2 direction”.

  In the following, for convenience, the direction corresponding to the main scanning direction is abbreviated as “main scanning corresponding direction”, and the direction corresponding to the sub scanning direction is abbreviated as “sub scanning corresponding direction”.

Further, when there is no need to distinguish between the fθ lens 15 ₁ and fθ lens 15 ₂ are collectively referred to as "fθ lens 15 '. Similarly, when there is no need to distinguish between the polarization splitting device 16 ₁ and the polarization splitting device 16 ₂ are collectively referred to as "polarization splitting device 16".

  The light source unit LU1 and the light source unit LU2 are arranged at positions separated from each other in the X-axis direction.

  In the light source unit LU1, the m1 direction is the main scanning corresponding direction, and the direction parallel to the Z axis is the sub scanning corresponding direction. In the light source unit LU2, the m2 direction is the main scanning corresponding direction, and the direction parallel to the Z axis is the sub scanning corresponding direction.

  The light source unit LU1 has two light sources (10a, 10b) and two collimating lenses (11a, 11b) as shown in FIG. 4 as an example.

  Both the light source 10a and the light source 10b are light sources having equivalent semiconductor lasers. As shown in FIG. 5 as an example, the light source 10a and the light source 10b are arranged on the circuit board so that the polarization directions of the light beams emitted from these semiconductor lasers are orthogonal to each other. That is, one of the two light sources is arranged in a posture orthogonal to the other light source.

  Here, it is assumed that polarized light whose electric field vector is directed in the Z-axis direction is emitted from the light source 10a, and polarized light orthogonal to the polarized light from the light source 10a is emitted from the light source 10b.

  Returning to FIG. 4, the collimator lens 11 a is disposed on the optical path of the light beam emitted from the light source 10 a, and makes the light beam substantially parallel light. Hereinafter, the light beam emitted from the light source 10a is also referred to as “light beam LBa”. Therefore, the light beam LBa is linearly polarized light whose electric field vector is oriented in the Z-axis direction.

  The collimating lens 11b is disposed on the optical path of the light beam emitted from the light source 10b, and makes the light beam substantially parallel light. Hereinafter, the light beam emitted from the light source 10b is also referred to as “light beam LBb”. Therefore, the light beam LBb is linearly polarized light having a polarization direction orthogonal to the polarization direction of the light beam LBa.

  As shown in FIG. 6 as an example, the light source unit LU2 includes two light sources (10c, 10d) and two collimating lenses (11c, 11d).

  Both the light source 10c and the light source 10d are light sources having an equivalent semiconductor laser. As shown in FIG. 7 as an example, the light source 10c and the light source 10d are arranged on the circuit board so that the polarization directions of the light beams emitted from these semiconductor lasers are orthogonal to each other. That is, one of the two light sources is arranged in a posture orthogonal to the other light source.

  Here, it is assumed that polarized light whose electric field vector is directed in the Z-axis direction is emitted from the light source 10d, and polarized light orthogonal to the polarized light from the light source 10d is emitted from the light source 10c.

  Returning to FIG. 6, the collimating lens 11 c is disposed on the optical path of the light beam emitted from the light source 10 c and makes the light beam substantially parallel light. Hereinafter, the light beam emitted from the light source 10c is also referred to as “light beam LBc”. Therefore, the light beam LBc is linearly polarized light whose electric field vector is oriented in the Z-axis direction.

  The collimating lens 11d is disposed on the optical path of the light beam emitted from the light source 10d, and makes the light beam substantially parallel light. Hereinafter, the light beam emitted from the light source 10d is also referred to as “light beam LBd”. Therefore, the light beam LBd is linearly polarized light having a polarization direction orthogonal to the polarization direction of the light beam LBc.

Returning to Figure 2, the cylindrical lens 12 _1, each of the light beams from the light source unit LU1 (LBa, LBb) and forms an image with respect to the Z-axis direction on the deflecting reflection surface near the polygon mirror 14.

The cylindrical lens 12 _2, each of the light beams from the light source unit LU2 (LBc, LBd) and forms an image with respect to the Z-axis direction on the deflecting reflection surface near the polygon mirror 14.

  The polygon mirror 14 has a four-sided mirror as an example, and each mirror serves as a deflection reflection surface. The polygon mirror 14 rotates at a constant speed around an axis parallel to the Z-axis direction, and deflects the light beam from each cylindrical lens at a constant angular velocity in a plane parallel to the XY plane.

Here, the light beam from the cylindrical lens 12 ₁ is deflected to the -X side of the polygon mirror 14, the light beam from the cylindrical lens 12 ₂ are deflected in the + X side of the polygon mirror 14. The beam bundle surface formed with time by the light beam deflected by the deflecting / reflecting surface of the polygon mirror 14 is called a “deflecting surface” (see JP-A-11-202252). Here, the deflection surface is parallel to the XY plane.

fθ lens 15 ₁ is a -X side of the polygon mirror 14 is disposed on the optical path of the light beam from the cylindrical lens 12 ₁ deflected by the polygon mirror 14.

fθ lens 15 _2, a + X side of the polygon mirror 14 is disposed on the optical path of the light beam from the cylindrical lens 12 ₂ deflected by the polygon mirror 14.

Polarization splitting device 16 ₁ is an fθ lens 15 ₁ on the -X side, it is disposed on the optical path of the light beam through the fθ lens 15 ₁ (light beam LBa and the light beam LBb).

Polarization splitting device 16 ₂ is a fθ lens 15 ₂ + X side, is disposed on the optical path of the light beam through the fθ lens 15 ₂ (light beam LBc and the light beam LBd).

  Here, as each polarization separation device, as shown in FIGS. 8A to 8C, a wire grid is formed on a plate-like substrate as a fine structure grating whose grating pitch is smaller than the wavelength of incident light. The wire grid element in which is formed is used. 8B is a cross-sectional view taken along the line AA in FIG. 8A, and FIG. 8C is a cross-sectional view taken along the line BB in FIG. 8A.

  The surface on which the wire grid is formed is a polarization separation surface, and the length direction of the wire is parallel to the deflection surface. The material of the wire is aluminum, and a transparent material such as glass or hard plastic is selected as the substrate. The wire grid element is designed to transmit linearly polarized light (p-polarized light) whose electric field vector is oriented in the Z-axis direction and reflect other light (see FIG. 9).

  However, actually, even if the light to be transmitted enters the wire grid element, a part of the light is reflected by the wire grid element. Even if light to be reflected is incident on the wire grid element, a part of the light is transmitted through the wire grid element.

  Here, when the light to be transmitted is incident on the wire grid element, the intensity of the light reflected by the wire grid element with respect to the intensity of the light transmitted through the wire grid element, and the light to be reflected are The intensity of the light transmitted through the wire grid element with respect to the intensity of the light reflected by the wire grid element when incident on is referred to as a “ghost light intensity ratio”.

  That is, when light to be transmitted enters the wire grid element, assuming that the intensity of the light transmitted through the wire grid element is Is1, and the intensity of the light reflected by the wire grid element is Ig1, the ghost light intensity ratio R1 ( (Unit:%) is expressed by the following equation (1).

R1 = (Ig1 / Is1) × 100 (1)

  Further, when the light to be reflected is incident on the wire grid element, if the intensity of the light reflected by the wire grid element is Is2, and the intensity of the light transmitted through the wire grid element is Ig2, the ghost light intensity ratio R2 ( (Unit:%) is expressed by the following equation (2).

R2 = (Ig2 / Is2) × 100 (2)

Polarization splitting device 16 _1, as shown in FIG. 10 as an example, the polarization splitting surface is disposed in a state inclined by 45 ° with respect to the deflection plane. Therefore, the light reflected by the polarization splitting device 16 ₁ is directed in the -Z direction.

Here, the layout of the optical system, with respect to the polarization separating device 16 _1, the light to be transmitted is a light beam LBa, light to be reflected is the light beam LBb. Therefore, most of the light beams LBa is transmitted through the polarization splitting device 16 _1, the majority of the light beam LBb is reflected in the -Z direction by the polarization splitting device 16 _1.

Returning to Figure 3, the light beam transmitted through the polarization splitting device 16 _1, the folding mirror 18a, is irradiated to the anamorphic lens 19a and the surface of the photosensitive drum 2030a via the exit window 21a, the light spot is formed. This light spot moves in the longitudinal direction of the photosensitive drum 2030a as the polygon mirror 14 rotates. That is, the photosensitive drum 2030a is scanned. The moving direction of the light spot at this time is the “main scanning direction” on the photosensitive drum 2030a, and the rotational direction of the photosensitive drum 2030a is the “sub-scanning direction” on the photosensitive drum 2030a.

On the other hand, the light flux by the polarization splitting device 16 ₁ is reflected in the -Z direction is reflected in the -X direction by the reflection mirror 17 _1, folding mirrors 18b _1, folding mirror 18b _2, the anamorphic lens 19b and the exit window 21b Then, the surface of the photosensitive drum 2030b is irradiated to form a light spot. This light spot moves in the longitudinal direction of the photosensitive drum 2030b as the polygon mirror 14 rotates. That is, the photosensitive drum 2030b is scanned. The moving direction of the light spot at this time is the “main scanning direction” on the photosensitive drum 2030b, and the rotational direction of the photosensitive drum 2030b is the “sub-scanning direction” on the photosensitive drum 2030b.

Polarization splitting device 16 _2, as shown in FIG. 11 as an example, the polarization splitting surface is disposed in a state inclined by 45 ° with respect to the deflection plane. Therefore, the light reflected by the polarization separation device 16 ₂ is directed in the -Z direction.

Here, with respect to the polarization separating device 16 _2, the light to be transmitted is a light beam LBd, light to be reflected is the light beam LBc. Therefore, most of the light beam LBd is transmitted through the polarization splitting device 16 _2, most of the light beam LBc is reflected in the -Z direction by the polarization splitting device 16 _2.

Returning to Figure 3, the light beam reflected in the -Z direction by the polarization splitting device 16 ₂ is reflected in the + X direction by the reflection mirror 17 _2, the folding mirror 18c _1, folding mirror 18c _2, anamorphic lens 19c and the exit window The light spot is formed by irradiating the surface of the photosensitive drum 2030c through 21c. This light spot moves in the longitudinal direction of the photosensitive drum 2030c as the polygon mirror 14 rotates. That is, the photosensitive drum 2030c is scanned. The moving direction of the light spot at this time is the “main scanning direction” on the photosensitive drum 2030c, and the rotational direction of the photosensitive drum 2030c is the “sub-scanning direction” on the photosensitive drum 2030c.

On the other hand, the light beam transmitted through the polarization splitting device 16 _2, the folding mirror 18 d, is irradiated to the anamorphic lens 19d and the surface of the photosensitive drum 2030d via the exit window 21d, the light spot is formed. This light spot moves in the longitudinal direction of the photosensitive drum 2030d as the polygon mirror 14 rotates. That is, the photosensitive drum 2030d is scanned. The moving direction of the light spot at this time is the “main scanning direction” on the photosensitive drum 2030d, and the rotational direction of the photosensitive drum 2030d is the “sub-scanning direction” on the photosensitive drum 2030d.

Light beam LBa is the light to be transmitted to the polarization separating device 16 _1, some of which is reflected by the polarization splitting device 16 _1, the ghost light. This ghost light scans the photosensitive drum 2030b through the same optical path as the light beam LBb.

Light beam LBb is the light to be reflected to the polarization separating device 16 _1, a portion is transmitted through the polarization splitting device 16 _1, the ghost light. The ghost light scans the photosensitive drum 2030a through the same optical path as the light beam LBa.

  For example, if the light intensity of the ghost light of the light beam LBa is strong, an image that should originally be formed with black toner is formed with cyan toner. Further, for example, when the light intensity of the ghost light of the light beam LBb is strong, an image that should originally be formed with cyan toner is formed with black toner.

Light beam LBc is the light to be reflected to the polarization separating device 16 _2, a portion is transmitted through the polarization splitting device 16 _2, the ghost light. The ghost light scans on the photosensitive drum 2030d through the same optical path as the light beam LBd.

Light beam LBd is the light to be transmitted to the polarization separating device 16 _2, some of which is reflected by the polarization separation device 16 _2, the ghost light. The ghost light scans the photosensitive drum 2030c through the same optical path as the light beam LBc.

  For example, if the light intensity of the ghost light of the light beam LBc is strong, an image that should originally be formed with magenta toner is formed with yellow toner. Further, for example, when the light intensity of the ghost light of the light beam LBd is strong, an image that should originally be formed with yellow toner is formed with magenta toner.

  The inventors conducted various experiments while changing the ghost light intensity ratio in the wire grid elements of the light beam LBa, the light beam LBb, the light beam LBc, and the light beam LBd, and the ghost light intensity ratio and the ghost light on the surface of each photosensitive drum. The relationship with the visibility of the toner image (hereinafter also referred to as “ghost image” for the sake of convenience) formed by the above was investigated. As a result, it has been found that even if the ghost light intensity ratio is the same, the visibility of the ghost image varies greatly depending on the photosensitive drum, that is, the color of the toner.

  Specifically, a black ghost image was most visually recognizable, and was visually recognized even when the ghost light intensity ratio was around 1%. On the other hand, ghost images of toner colors other than black were not visually recognized when the ghost light intensity ratio was around 1%.

  By the way, the transmission / reflection characteristics (separation characteristics) of the wire grid element can be adjusted by changing the structure (grating pitch, wire height, wire width, etc.).

  FIG. 12 shows the relationship between the wire height and the ghost light intensity ratio in a wire grid element in which the wire length direction is parallel to the deflection surface, the grating pitch is 100 nm, and the wire width is 50 nm. . Note that the parameter “phi” in FIG. 12 indicates the deflection angle (in deg) of incident light. For example, phi20 indicates a case where the deflection angle of incident light is 20 (deg). In addition, “0T” in FIG. 12 means that light to be transmitted is incident on the wire grid element, and “0R” means that light to be reflected is incident on the wire grid element. ing.

  According to FIG. 12, when the wire height is less than 0.04 μm, the ghost light intensity ratio when the light to be transmitted is incident is more than the ghost light intensity ratio when the light to be reflected is incident. Although the wire height is within a range of 0.04 μm to 0.2 μm, the ghost light intensity ratio when the light to be reflected is incident is larger than the ghost light when the light to be transmitted is incident. Greater than intensity ratio.

  FIG. 13 shows, as a comparative example, a wire grid element (see FIGS. 14A and 14B) in which the wire arrangement direction is parallel to the deflection surface, the grating pitch is 100 nm, and the wire width is 50 nm. The relationship between the wire height and the ghost light intensity ratio is shown. In this case, there is no condition that can suppress the ghost light intensity ratio to a sufficiently small value (1% or less). Note that FIG. 14B is a cross-sectional view taken along the line AA of FIG.

  In addition to the polarization separation performance of the wire grid element itself, the ghost light intensity ratios R1 and R2 are reduced to 1% or less at the same time due to the degradation of the linear polarization of the light beam before entering the wire grid element. It is difficult to suppress.

  Therefore, in the present embodiment, the ghost light intensity ratio of the light beam LBb in the wire grid element is set to 1% or less in order to reduce the ghost light that forms the black ghost image that is most visible. In this case, even if the ghost light intensity ratio of the light beam LBa at the wire grid element is not 1% or less, the visibility of the cyan ghost image is low, and thus the output image quality is not adversely affected.

That is, in this embodiment, as a polarization separation device 16 _1, the length direction of the wire is parallel to the deflecting surface, ghost light intensity ratio R2 when the light to be reflected (light beams LBb) is incident, transmitted The structure (grating pitch, wire height, wire width, etc.) so that it is smaller than the ghost light intensity ratio R1 when the light to be performed (light beam LBa) is incident and the value is 1% or less. ) Is used. That is, the relationship of (Ig1 / Is1)> (Ig2 / Is2) is satisfied.

  As a result, the light intensity of the ghost light that scans the photosensitive drum 2030a can be reduced, and a black toner image with high visibility can be formed with high quality.

  In order to reduce the ghost light included in the light reflected by the wire grid element, only s-polarized light is transmitted through the optical path of the light beam reflected by the wire grid element as shown in FIG. 15 as an example. It has been proposed to provide a polarizer. However, the addition of a polarizer causes an increase in size, complexity, and cost of the apparatus, so it is preferable to avoid it as much as possible. In this embodiment, it is not necessary to provide such a polarizer.

Further, as a polarization separation device 16 _2, the polarization separating device 16 ₁ may be equivalent wire grid element is used and but, because of lower both the visibility of ghost images and yellow ghost image of magenta, the polarization separating device as 16 _2, the length direction of the wire is parallel to the deflection plane, the ghost light intensity ratio R2 when the light to be reflected (light beam LBc) is incident, transmitted by to a light (light beam LBd) is incident A wire grid element in which the structure (grid pitch, wire height, wire width, etc.) is set so that the ghost light intensity ratio R1 at that time is substantially the same may be used.

Here, the mirror 18a and the anamorphic lens 19a folded fθ lens 15 ₁ and the polarization splitting device 16 ₁ is a scanning optical system K stations.

The mirror 18b ₂ and the anamorphic lens 19b folded fθ lens 15 ₁ and the polarization splitting device 16 ₁ and the reflection mirror 17 ₁ and the folding mirror 18b ₁ is a scanning optical system C station.

fθ lens 15 ₁ is provided between the polarized light separation device 16 ₁ and the polygon mirror 14. Then, the optical path of the light beams LBa and flux LBb is, since the substantially overlap with respect to the Z-axis direction, it is possible to share the fθ lens 15 ₁ in two image forming stations.

The mirror 18c ₂ and the anamorphic lens 19c folding mirror 18c ₁ folded and fθ lens 15 ₂ and the polarization separating device 16 ₂ and the reflecting mirror 17 ₂ is a scanning optical system M stations.

The mirror 18d and the anamorphic lens 19d folded and fθ lens 15 ₂ and the polarization separating device 16 ₂ is a scanning optical system in the Y station.

fθ lens 15 ₂ is provided between the polarized light separation device 16 ₂ and the polygon mirror 14. Then, the optical path of the light beam LBc and flux LBd is, since the substantially overlap with respect to the Z-axis direction, it is possible to share the fθ lens 15 ₂ at two image forming stations.

  Each folding mirror is provided so that the optical path lengths at the respective image forming stations are equal to each other.

  The scanning control device has a light source control circuit corresponding to each light source. The light source control circuit corresponding to the light source 10a and the light source 10b is mounted on the circuit board of the light source unit LU1. The light source control circuit corresponding to the light source 10c and the light source 10d is mounted on the circuit board of the light source unit LU2.

  As is clear from the above description, in the color printer 2000 according to the present embodiment, the optical scanning device 2010 constitutes the optical scanning device of the present invention.

  The light beam LBa forms the first light beam in the optical scanning device of the present invention and the light beam A in the image forming device of the present invention, and the light beam LBb forms the second light beam in the optical scanning device of the present invention and the book. The light beam B in the image forming apparatus of the invention is configured.

In addition, the fθ lens (15 ₁ , 15 ₂ ), the polarization separation device (16 ₁ , 16 ₂ ), the reflection mirror (17 ₁ , 17 ₂ ), and the folding mirror (18a, 18b ₁ , 18b ₂ , 18c ₁ , 18c ₂ , 18d) and the anamorphic lenses (19a, 19b, 19c, 19d) constitute a scanning optical system in the optical scanning device of the present invention.

As described above, according to the optical scanning device 2010 according to the present embodiment, the linearly polarized light having the polarization direction orthogonal to the polarization direction of the light beam LBa and the linearly polarized light beam LBa whose electric field vector is oriented in the Z-axis direction. a light source unit LU1 for emitting a light beam LBb is, a polygon mirror 14 for deflecting the plurality of light beams from the light source unit LU1, by transmitting p-polarized light, wherein the polarization separation device 16 ₁ which reflects s-polarized light, a polygon mirror 14 And a scanning optical system for individually condensing a plurality of light beams deflected in step (b) on the corresponding scanned surface.

Then, as a polarization separation device 16 _1, the length direction of the wire is parallel to the deflecting surface, ghost light intensity ratio R2 when the light beam LBb is incident, ghost light intensity ratio when the light beam LBa is incident R1 The wire grid element in which the structure (grid pitch, wire height, wire width, etc.) is set so that the value is 1% or less is used. In this case, generation of a black ghost image with the highest visibility can be suppressed.

  Further, the fθ lens and the polarization separation device are shared by the two image forming stations.

  Therefore, it is possible to achieve downsizing (thinning) without reducing the scanning accuracy.

  Further, in each light source unit, one of the two light sources is arranged in a posture orthogonal to the other light source, so that an optical element for obtaining the orthogonal state of polarized light is not required, and the cost is reduced. Can be planned.

  Since the color printer 2000 according to the present embodiment includes the optical scanning device 2010, it is possible to reduce the size without degrading the image quality.

  In the above embodiment, in each light source unit, instead of providing two light sources orthogonal to each other, one light source may be provided, and the polarization direction of the light source may be switched over time. In this case, an optical element including a liquid crystal or the like that actively generates an optical phase difference of λ / 2 may be provided on the optical path from the light source to the polygon mirror 14. As a result, the number of light sources is reduced, and the size and cost can be reduced.

  In the above embodiment, as shown in FIG. 16 as an example, a polarization separation device may be disposed between the polygon mirror 14 and the fθ lens. However, the fθ lens 15a for the light beam LBa, the fθ lens 15b for the light beam LBb, the fθ lens 15c for the light beam LBc, and the fθ lens 15d for the light beam LBd are required. In this case, each fθ lens can have a lens shape suitable for the polarization state of the light beam, the optical path length, the imaging position, and the scanning length.

  Moreover, although the said embodiment demonstrated the case where each light source had one light emission part, it is not limited to this. For example, each light source may have a plurality of semiconductor lasers. Each light source may have a semiconductor laser array having a plurality of light emitting portions.

  In the above embodiment, the color printer 2000 having four photosensitive drums as the image forming apparatus has been described. However, the present invention is not limited to this. For example, a printer having two photosensitive drums (2030a, 2030b) may be used. In this case, one light source unit LU1 is used.

  As described above, the optical scanning device of the present invention is suitable for downsizing without reducing the scanning accuracy. The image forming apparatus of the present invention is suitable for downsizing without deteriorating image quality.

14 ... polygon mirror (deflector), 15 ₁ , 15 ₂ ... fθ lens (part of scanning optical system), 16 ₁ , 16 ₂ ... polarization separation device, 17 ₁ , 17 ₂ ... reflection mirror (one of scanning optical system) Part), 18a, 18b ₁ , 18b ₂ , 18c ₁ , 18c ₂ , 18d ... folding mirror (part of scanning optical system), 19a to 19d ... anamorphic lens (part of scanning optical system), 2000 ... color printer ( Image forming apparatus), 2030a to 2030d ... photosensitive drum (image carrier), 2010 ... optical scanning device, LU1 ... light source unit, LU2 ... light source unit.

JP-A-60-32019 JP-A-7-144434 JP 2008-70599 A

Claims (5)

A light source unit that emits a plurality of light beams including a first light beam whose polarization direction is a first polarization direction and a second light beam whose polarization direction is a second polarization direction different from the first polarization direction; ;
A deflector for deflecting a plurality of light beams from the light source unit;
A polarization separation device that transmits light in the first polarization direction and reflects light in the second polarization direction, and individually collects a plurality of light beams deflected by the deflector on a corresponding scanned surface. An optical scanning optical system;
In the polarization separation device, the ratio of the light intensity of the reflected light to the light intensity of the transmitted light for the first light flux is different from the ratio of the light intensity of the transmitted light to the light intensity of the reflected light for the second light flux. An optical scanning device. A plurality of image carriers;
The optical scanning device according to claim 1, wherein the plurality of image carriers are individually scanned with a light beam.
The light source unit of the optical scanning device emits a light beam A modulated by black image information and a light beam B having a polarization direction different from that of the light beam A,
The polarization separation device of the optical scanning device includes a light intensity Is1 of light toward the corresponding image carrier, a light intensity Ig1 of light toward other than the corresponding image carrier, and a corresponding image of the light beam B with respect to the light flux B. Using the light intensity Is2 of the light toward the carrier and the light intensity Ig2 of the light other than the corresponding image carrier, it has a separation characteristic that satisfies the relationship of (Ig1 / Is1)> (Ig2 / Is2). An image forming apparatus.   For the luminous flux A, the light traveling toward the corresponding image carrier is light transmitted through the polarization separation device, and the light traveling toward other than the corresponding image carrier is light reflected by the polarization separation device. The image forming apparatus according to claim 2. The light beam A and the light beam B are linearly polarized light whose polarization directions are orthogonal to each other,
The image forming apparatus according to claim 2, wherein the polarization separation device is a wire grid element. The polarization direction of the light flux A incident on the wire grid element is a direction orthogonal to the deflection surface,
The polarization direction of the light beam B incident on the wire grid element is a direction parallel to the deflection surface,
The image forming apparatus according to claim 4, wherein the wire grid element has a wire length direction parallel to the deflection surface.