JP2013068698A - Optical scanner, and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical scanner that can be reduced in size without causing an increase in costs and a decrease in scanning accuracy.SOLUTION: A light source unit includes a light source, a driving chip, a circuit board, a polarization adjusting member 13, and a collimator lens. The polarization adjusting member 13 includes a phase-shifting element having an area 14a opposite to a light beam LB1 emitted from a light-emitting unit 101a of a semiconductor chip 101, and an area 14b opposite to a light beam LB2 emitted from a light-emitting unit 101b. The polarization direction of the light beam LB1 and the light beam LB2 are adjusted so as to be orthogonal to each other.

Description

  The present invention relates to an optical scanning device and an image forming apparatus, and more particularly to an optical scanning device that scans a plurality of scanned surfaces with light, and an image forming apparatus including the optical scanning device.

  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 scans laser light using an optical deflector (for example, a polygon mirror) in the axial direction of a photosensitive drum (hereinafter referred to as “photosensitive drum”). In general, a method of rotating the photosensitive drum to form a latent image on the surface of the photosensitive drum is common.

  In recent years, color formation and speeding-up have progressed in image forming apparatuses, and tandem type image forming apparatuses having a plurality (usually four) photosensitive drums have become widespread.

  An image forming apparatus having a plurality of photosensitive drums has a light source for each photosensitive drum. For example, when there are four photosensitive drums, four light sources are provided.

  In recent years, further downsizing and cost reduction of image forming apparatuses have been demanded, and accordingly, downsizing and cost reduction have been demanded for optical scanning apparatuses.

  Accordingly, attempts have been made to reduce the number of light sources in an optical scanning device used in an image forming apparatus having a plurality of photosensitive drums (see, for example, Patent Document 1 or Patent Document 2).

  In order to increase the resolution as well as the speed, an optical scanning device equipped with a surface emitting laser array in which a plurality of light emitting units are two-dimensionally arranged has been proposed (for example, see Patent Document 3).

  However, in the optical scanning devices disclosed in Patent Documents 1 to 3, it has been difficult to reduce the size without causing an increase in cost and a decrease in scanning accuracy.

  The present invention is an optical scanning device that optically scans a plurality of scanned surfaces along a main scanning direction, and includes a light source having a first light emitting unit and a second light emitting unit, and an emission from the first light emitting unit. A polarization adjusting member that makes the polarization direction of the emitted light and the polarization direction of the light emitted from the second light emitting unit orthogonal to each other, and the light emitted from the first light emitting unit as its polarization state Is divided into the first light and the second light while maintaining the light, and the light emitted from the second light emitting unit is divided into the third light and the fourth light while maintaining the polarization state An element and a plurality of reflection surfaces, wherein the first light and the third light are incident on the same reflection surface, and the second light and the fourth light are the same reflection surface. An optical deflector that is incident on the same different reflecting surface and deflects each light beam, and the first light and the third light deflected by the optical deflector A first polarization separating element that separates an optical scanning device and a second polarization separation element for separating the the deflected second light fourth light by the optical deflector.

  According to the optical scanning device of the present invention, the size can be reduced without increasing the cost and reducing the scanning accuracy.

1 is a diagram illustrating a schematic configuration of a color printer according to an embodiment of the present invention. FIG. 2 is a diagram (part 1) for explaining an optical scanning device 2010 in FIG. 1; FIG. 3 is a diagram (part 2) for explaining the optical scanning device 2010 in FIG. 1; It is a figure for demonstrating the light source unit LU in FIG. It is a figure for demonstrating the light source in light source unit LU. It is a figure for demonstrating a polarization preparation element. It is a figure for demonstrating the positional relationship of a semiconductor laser chip and a polarization preparation element, and the effect | action of a polarization preparation element. It is FIG. (1) for demonstrating a beam splitter. It is FIG. (2) for demonstrating a beam splitter. It is a figure for demonstrating the polarization separation surface of a polarization separation element. It is FIG. (1) for demonstrating the optical path of the two light beams deflected by the different deflection | deviation reflective surface of a polygon mirror. It is FIG. (2) for demonstrating the optical path of the two light beams deflected by the different deflection | deviation reflective surface of a polygon mirror. It is FIG. (3) for demonstrating the optical path of the two light beams deflected by the different deflection | deviation reflective surface of a polygon mirror. It is a timing chart for demonstrating operation | movement of a scanning control apparatus. It is a figure for demonstrating when image formation is performed in K station and C station. It is a figure for demonstrating when image formation is performed in the Y station and the M station. It is a figure for demonstrating the attachment method of a polarization preparation element. It is a figure for demonstrating the light-shielding part provided in the polarization preparation element. In order to describe a phase shift element having two regions including a transparent base material having an inclined surface formed with a period equal to or less than a wavelength and a plurality of dielectric layers laminated on the inclined surface of the transparent base material FIG. It is a figure for demonstrating the modification of a polarization preparation element. In the polarization adjusting element of FIG. 20, the transparent substrate having an inclined surface formed with a period equal to or shorter than the wavelength and a plurality of dielectric layers laminated on the inclined surface of the transparent substrate are divided into two regions. It is a figure for demonstrating the phase shift element which has. FIGS. 22A and 22B are diagrams for explaining the case where a surface emitting laser array is used instead of the edge emitting semiconductor laser.

  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 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, paper discharge roller 2058, paper feed tray 2060, paper discharge tray 207 , A printer control device 2090 for controlling the communication control unit 2080, and the above units overall.

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

  The printer control device 2090 includes a CPU, a ROM described in a program written in code readable by the CPU, various data used when executing the program, a RAM as a working memory, an analog data An A / D converter or the like for converting the data into digital data. Then, the printer control device 2090 sends image information from the host device to the optical scanning device 2010.

  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. Configure.

  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. Configure.

  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. Configure.

  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. Configure.

  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).

  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.

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

  The optical scanning device 2010 is charged correspondingly by a light beam modulated for each color based on multicolor image information (black image information, cyan image information, magenta image information, yellow image information) from the printer control device 2090. Each surface of the photosensitive drum is scanned. Thereby, a latent image corresponding to the image information is formed on the surface of each photosensitive drum. The latent image formed here moves in the direction of the corresponding developing roller as the photosensitive drum rotates. The detailed configuration of the optical scanning device 2010 will be described later.

  By the way, a scanning area in which image information is written on each photosensitive drum is called an “effective scanning area”, an “image forming area”, an “effective image area”, or the like.

  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. The paper feed roller 2054 takes out the recording paper one by one from the paper feed tray 2060. The recording paper is sent out 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. Here, the recording sheet on which the color image is transferred 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. Here, the recording paper on which the toner is fixed 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 a light source unit LU, a beam splitter 30, two cylindrical lenses (12 ₁ , 12 ₂ ), a polygon mirror 14, and two scanning lenses (15 ₁ , 15 ₂ ), two polarization separation elements (16 ₁ , 16 ₂ ), four reflection mirrors (M1, M2, 17 ₁ , 17 ₂ ), four folding mirrors (18a, 18b, 18c, 18d), and A scanning control device (not shown) is included. These are assembled at predetermined positions of the optical housing 2300 (not shown in FIG. 2, see FIG. 3).

  The optical housing 2300 is provided with four slit-shaped exit windows (19a, 19b, 19c, 19d) through which a light beam directed to each photosensitive drum passes. Each exit window is covered with dust-proof glass.

  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”.

The light source unit LU, as shown in FIG. 4 as an example, the light source 10 _1, the light source 10 driving chip 10 ₂ containing ₁ light source driving circuit for driving the light source 10 ₁ and the driving chip 10 ₂ is mounted Circuit board 10 ₃ , polarization adjusting member 13, collimating lens 11, and the like.

Light source 10 _1, as shown in FIG. 5, includes one of the semiconductor laser chip 101. The semiconductor laser chip 101 includes an edge-emitting semiconductor laser having two light emitting portions (101a and 101b), and linearly polarized light is emitted from each light emitting portion. The polarization direction of the linearly polarized light emitted from each light emitting unit (the vibration plane of the electric field vector) is substantially the same, and is usually parallel to the straight line connecting the two light emitting units. Instead of the edge emitting semiconductor laser, a surface emitting laser array in which a plurality of light emitting units are two-dimensionally arranged may be used.

  Hereinafter, the light beam emitted from the light emitting unit 101a is referred to as “light beam LB1”, and the light beam emitted from the light emitting unit 101b is referred to as “light beam LB2”. In FIG. 4, the chief ray of each light beam is shown.

Light source 10 _1, so that the distance between the two light emitting portions in the Z-axis direction becomes a predetermined value, it may be rotationally adjusted about an axis parallel to the principal ray of the light beams. In this case, the polarization direction of linearly polarized light emitted from the light emitting portion becomes a direction that depends on the rotation angle of the light source 10 _1, not necessarily the direction parallel or perpendicular to the Z-axis direction. In the following, linearly polarized light whose polarization direction is parallel to the Z-axis direction is referred to as “longitudinal polarized light”, and linearly polarized light in a direction orthogonal thereto is referred to as “laterally polarized light”.

Polarization adjustment member 13, the polarization direction of the light beam LB1 and flux LB2 from the light source 10 _1, to adjust the polarization directions perpendicular to each other.

  As an example, the polarization adjusting member 13 includes a phase shift element 14 having two regions (14a, 14b) individually corresponding to the light beam LB1 and the light beam LB2 from the semiconductor laser chip 101, as shown in FIG. .

  Here, as shown in FIG. 7 as an example, it is assumed that longitudinally polarized light is emitted from each light emitting unit.

Light beam LB1 from the light source 10 _1, incident on the area 14a of the phase shift element 14, the polarization direction is emitted from region 14a in a state rotated 90 degrees. Light beam LB2 from the light source 10 _1, incident on the area 14b of the phase shift element 14, is emitted from the left region 14b maintaining the polarization direction.

  The polarization adjusting member 13 may rotate the polarization directions of the linearly polarized light by different angles to adjust the polarization directions to be orthogonal to each other. For example, when the polarization direction of each linearly polarized light emitted from the semiconductor laser chip 101 is inclined with respect to the Z-axis direction, the polarization of each linearly polarized light is such that the light beam LB1 is longitudinally polarized light and the light beam LB2 is laterally polarized light. The direction may be adjusted.

  Returning to FIG. 4, the collimating lens 11 is disposed on the optical path of the light beams LB <b> 1 and LB <b> 2 from the polarization adjusting member 13, and makes each light beam substantially parallel light. The light beam that has passed through the collimating lens 11 is a light beam emitted from the light source unit LU.

  Returning to FIG. 2, the beam splitter 30 is disposed on the optical path of the light beams LB1 and LB2 from the light source unit LU.

  The beam splitter 30 has a beam splitting surface that emits while maintaining the polarization state of incident light with the same transmittance and reflectance with respect to incident longitudinally polarized light and transversely polarized light. That is, the beam splitting surface is a half mirror.

  The beam splitter 30 includes a light beam LB1 (longitudinal polarization) having a polarization direction perpendicular to an incident surface (see FIG. 8) including a normal line of the beam splitting surface and a principal ray of incident light, and a parallel light beam LB2. (Laterally polarized light) is incident (see FIG. 9).

  The light beam LB1 and the light beam LB2 are split by the beam splitter 30 with the same light intensity as the reflected light and the transmitted light. Hereinafter, the reflected light of the light beam LB1 is referred to as “light beam LBa”, the transmitted light is referred to as “light beam LBd”, the reflected light of the light beam LB2 is referred to as “light beam LBb”, and the transmitted light is referred to as “light beam LBc”. The direction of polarization of each light beam is maintained. That is, the light beam LBa and the light beam LBd are vertically polarized light, and the light beam LBb and the light beam LBc are horizontally polarized light.

  If the polarization direction of the light incident on the beam splitter 30 is not perpendicular or parallel to the incident surface, the phase difference between the p-polarized light and the s-polarized light on the beam splitting surface is accurately set to 0 in order to maintain the polarization direction. It is necessary to set the angle to 180 ° or 180 °, which is not preferable because the structure of the beam splitting surface becomes complicated.

  In addition, each light beam emitted from the beam splitter 30 becomes a light beam (vertical polarization) whose polarization direction is perpendicular to the deflection surface of the polygon mirror 14 and a parallel light beam (lateral polarization). In this case, it is possible to prevent each light beam deflected by the polygon mirror 14 from having a different polarization direction depending on the deflection angle, and to suppress adverse effects on polarization separation in the subsequent stage.

The cylindrical lens 12 ₁ is disposed on the optical path of the light beam LBa and flux LBb, each light beam through the reflecting mirror M1, 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 is disposed on the optical path of the light beam LBc and flux LBd, each light beam through the reflecting mirror M2, and forms an image with respect to the Z-axis direction on the deflecting reflection surface near the polygon mirror 14.

  The optical system disposed between each light source and the polygon mirror 14 is called a pre-deflector optical system.

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 constant speed about an axis parallel to the Z-axis direction, from the cylindrical lens 12 _1, light beams LBa and light beams LBb, from the cylindrical lens 12 _2, the light beam LBc and the light beam LBd, Z Deflection at a constant angular velocity in a plane perpendicular to the axis.

  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 Japanese Patent Application Laid-Open No. 11-202252). Here, the deflection surface is parallel to the XY plane.

  The light beam LBa and the light beam LBb are incident on the deflection reflection surface located on the −X side of the rotation axis of the polygon mirror 14, and the light beam LBc and the light beam LBd are incident on the deflection reflection surface located on the + X side of the rotation axis.

  In a plane perpendicular to the Z axis, the angle formed by the light beam LBa and the light beam LBb and the light beam LBc and the light beam LBd when entering the polygon mirror 14 is approximately 90 ° (see FIG. 2). Therefore, the light beam LBa and the light beam LBd do not simultaneously scan the effective scanning area on the corresponding photosensitive drum. Similarly, the light beam LBb and the light beam LBc do not simultaneously scan the effective scanning area on the corresponding photosensitive drum.

  The light beam LBa and the light beam LBb are deflected to the −X side of the polygon mirror 14, and the light beam LBc and the light beam LBd are deflected to the + X side of the polygon mirror 14.

Returning to Figure 3, the scanning lens 15 ₁ is a -X side of the polygon mirror 14 is disposed on an optical path of the light beam LBa and flux LBb deflected by the polygon mirror 14.

Polarization separation element 16 ₁ is a -X side of the scanning lens 15 ₁ is disposed on an optical path of the light beam LBa and flux LBb through the scanning lens 15 _1.

Polarization separation element 16 ₁ transmits light of vertical polarization toward the effective scanning region of the corresponding photosensitive drum, a polarization separation element for reflecting light horizontally polarized light (see FIG. 10). As the polarization separation element, for example, a wire-grid polarization element disclosed in JP 2010-134411 A can be used. Therefore, the light beam LBa is transmitted through the polarization separation element 16 _1, the light beam LBb is reflected by the polarization separation element 16 _1.

Light beam LBa passing through the polarization separating element 16 ₁ is guided to the surface of the photosensitive drum 2030a via the folding mirror 18a and exit window 19a.

Further, the light beam LBb reflected by the polarization separation element 16 ₁ is guided to the surface of the photosensitive drum 2030b via the reflecting mirror 17 _1, folding mirrors 18b and the exit window 19b.

Scanning lens 15 _2, a + X side of the polygon mirror 14 is disposed on an optical path of the light beam LBc and flux LBd deflected by the polygon mirror 14.

Polarization separating element 16 ₂ is a scanning lens 15 ₂ + X side, it is disposed on the optical path of the light beam LBc and flux LBd through the scanning lens 15 _2.

Polarization separating element 16 ₂ is a polarization separation element similar to the polarization separation element 16 _1. Therefore, the light beam LBd is transmitted through the polarization separating element 16 _2, the light beam LBc is reflected by the polarization separation element 16 _2.

Light beam LBd transmitted through the polarization separating element 16 ₂ is guided to the surface of the photosensitive drum 2030d via a folding mirror 18d and the exit window 19d.

Further, the light beam LBc that has been reflected by the polarization separating element 16 _2, reflection mirror 17 _2, is guided to the surface of the photosensitive drum 2030c via the folding mirror 18c and the exit window 19c.

  The light spot on each photosensitive drum moves in the longitudinal direction of the photosensitive drum as the polygon mirror 14 rotates. The moving direction of the light spot at this time is the “main scanning direction”, and the rotation direction of the photosensitive drum is the “sub scanning direction”.

Mirrors 18a folded and the scanning lens 15 ₁ and the polarization beam splitter 16 ₁ is a scanning optical system of the "K station". The mirror 18b folded and the scanning lens 15 ₁ and the polarization beam splitter 16 ₁ and the reflection mirror 17 ₁ is a scanning optical system of the "C station".

Thus, the scanning lens 15 ₁ and the polarization beam splitter 16 ₁ is shared by two image forming stations.

Mirror 18c folded between the scanning lens 15 ₂ and the polarization separating element 16 ₂ and the reflecting mirror 17 ₂ is a scanning optical system of the "M station". The mirror 18d folded and the scanning lens 15 ₂ and the polarization separating element 16 ₂ is a scanning optical system of the "Y station".

Thus, the scanning lens 15 ₂ and the polarization separating element 16 ₂ is shared by the two image forming stations.

  Here, the number of deflecting and reflecting surfaces in the polygon mirror 14 is four, and the light beams (light beam LBa and light beam LBb) that pass through the reflection mirror M1 and the light beams (light beam LBc and light beam LBd) that pass through the reflection mirror M2 are mutually different. It is incident on a different deflecting reflecting surface. The angle formed between the light beam that has entered the polygon mirror 14 via the reflection mirror M1 and the light beam that has passed through the reflection mirror M2 is set to be approximately 90 ° in plan view.

  Therefore, the light beam LBa and the light beam LBd, and the light beam LBb and the light beam LBc do not simultaneously scan the effective scanning areas on the corresponding photosensitive drums.

  For example, as shown in FIG. 11, when the light beam LBa reflected by the deflection reflection surface of the polygon mirror 14 goes to the writing start position on the photosensitive drum 2030a, the light beam LBd reflected by the deflection reflection surface of the polygon mirror 14. Is directed to a position on the + Y side of the writing end position on the photosensitive drum 2030d.

  Also, as shown in FIG. 12, when the light beam LBa reflected by the deflecting reflection surface of the polygon mirror 14 is directed to the center (image height 0) position of the effective scanning area of the photosensitive drum 2030a, the deflection of the polygon mirror 14 is performed. The light beam LBd reflected by the reflecting surface is directed in the + Y direction.

  When the light beam LBa reflected by the deflecting / reflecting surface of the polygon mirror 14 exceeds the center (image height 0) position of the effective scanning region on the photosensitive drum 2030a, the deflecting / reflecting surface of the polygon mirror 14 that reflects the light beam LBd is formed. The direction in which the light beam LBd reflected by the deflecting reflection surface of the polygon mirror 14 is switched from the + Y direction to the −Y direction.

  Then, as shown in FIG. 13, when the light beam LBa reflected by the deflecting / reflecting surface of the polygon mirror 14 goes to the writing end position of the effective scanning area of the photosensitive drum 2030a, it is reflected by the deflecting / reflecting surface of the polygon mirror 14. The emitted light beam LBd is directed to a position on the −Y side of the writing start position on the photosensitive drum 2030d.

  As described above, when the light beam LBa reflected by the deflecting / reflecting surface of the polygon mirror 14 scans the effective scanning area of the photosensitive drum 2030a, the light beam LBd reflected by the deflecting / reflecting surface of the polygon mirror 14 is photosensitive. It does not go into the effective scanning area of the body drum 2030d.

  On the other hand, when the light beam LBd reflected by the deflection reflection surface of the polygon mirror 14 scans the effective scanning area of the photosensitive drum 2030d, the light beam LBa reflected by the deflection reflection surface of the polygon mirror 14 is It does not go into the effective scanning area of the drum 2030a.

  Similarly, when the light beam LBb reflected by the deflecting / reflecting surface of the polygon mirror 14 scans the effective scanning area of the photosensitive drum 2030b, the light beam LBc reflected by the deflecting / reflecting surface of the polygon mirror 14 is It does not go into the effective scanning area of the drum 2030c.

  Further, when the light beam LBc reflected by the deflecting / reflecting surface of the polygon mirror 14 scans the effective scanning area of the photosensitive drum 2030c, the light beam LBb reflected by the deflecting / reflecting surface of the polygon mirror 14 is changed to the photosensitive drum. It does not go into the effective scanning area in 2030b.

  Therefore, at the timing when the light beam LBa scans the effective scanning region on the photosensitive drum 2030a, the light beam LB1 is modulated according to the black image information, and at the timing when the light beam LBd scans the effective scanning region on the photosensitive drum 2030d, The light beam LB1 is modulated in accordance with yellow image information.

  Similarly, at the timing when the light beam LBb scans the effective scanning area on the photosensitive drum 2030b, the light beam LB2 is modulated according to the cyan image information, and at the timing when the light beam LBc scans the effective scanning area on the photosensitive drum 2030c. The light beam LB2 is modulated in accordance with magenta image information.

  It should be noted that the angle formed between the light beam that has entered the polygon mirror 14 through the reflection mirror M1 and the light beam through the reflection mirror M2 may slightly deviate from 90 ° in plan view.

  Next, the operation of the scanning control device when a latent image is formed on each photosensitive drum will be described with reference to the timing chart of FIG.

(1) When a synchronization detection sensor (not shown) detects light and the synchronization detection signal output from the synchronization detection sensor changes from a high level to a low level, the count value of the timer is reset to zero.
(2) Perform APC (Auto Power Control).
(3) When the count value of the timer is tB, so that the light flux modulated according to image information of black is emitted from the light emitting unit 101a, and controls the light source driving circuit of the light source 10 _1. As a result, the effective scanning area on the photosensitive drum 2030a is scanned with the light beam LBa (see FIG. 15). Similarly, when the count value of the timer is tC, so that the light flux modulated according to image information of cyan is emitted from the light emitting portion 101b, and controls the light source driving circuit of the light source 10 _1. As a result, the effective scanning area on the photosensitive drum 2030b is scanned with the light beam LBb (see FIG. 15).

  Ideally, tB and tC have the same value, but color shift may occur due to temperature distribution or the like. In that case, tB and tC may be set to different values.

(4) Next, when the synchronization detection signal changes from the high level to the low level, the timer count value is reset to zero.
(5) Perform APC.
(6) When the count value of the timer is tY, so that the light flux modulated according to image information of yellow is emitted from the light emitting unit 101a, and controls the light source driving circuit of the light source 10 _1. As a result, the effective scanning area on the photosensitive drum 2030d is scanned with the light beam LBd (see FIG. 16). Similarly, when the count value of the timer is tM, so that the light flux modulated according to image information of magenta is ejected from the light emitting portion 101b, and controls the light source driving circuit of the light source 10 _1. As a result, the effective scanning area on the photosensitive drum 2030c is scanned with the light beam LBc (see FIG. 16).

  Ideally, tY and tM take the same value, but color misregistration may occur due to temperature distribution or the like. In that case, tY and tM may be set to different values.

  Thereafter, the operations (1) to (6) are repeated.

Thereby, it is possible to write in four photosensitive drums with a single light source 10 _1. By the way, tB, tC, tY, and tM are obtained in advance as appropriate values for each optical scanning device and stored in the memory of the scanning control device.

  In FIG. 14, the light amount of the light beam emitted from the light source (hereinafter abbreviated as “emitted light amount”) is constant, but actually, the transmittance and reflectance of each optical element are relatively different. For this reason, the amount of light flux reaching each photosensitive drum may be different. In this case, the amount of emitted light may be adjusted for each photosensitive drum to be scanned so that the amount of light beams reaching each photosensitive drum is substantially the same.

  Also, here, a case has been described in which each scanning light corresponding to black, yellow, cyan, and magenta is composed of one light beam, but each scanning light may be composed of a plurality of light beams.

  Next, the polarization adjusting member 13 will be described.

  In the phase shift element 14 of the polarization adjusting member 13, the fast axis direction of the region 14a and the fast axis direction of the region 14b are set at different angles.

  The phase shift amount in the phase shift element 14 is an amount corresponding to ½ of the wavelength of the light beam, and the phase shift element 14 is a so-called half wavelength element.

  In this case, by setting the angle formed by the fast axis direction of the region 14a and the fast axis direction of the region 14b to 45 degrees, the incident light beam is emitted from the region 14a regardless of the direction of polarization. And the polarization direction emitted from the region 14b can be adjusted to be surely orthogonal.

  In particular, the fast axis direction of the region 14a is set to a direction in which the polarization direction of light emitted from the region 14a is orthogonal to the main scanning corresponding direction, and the fast axis direction of the region 14b is output from the region 14b. The polarization direction of the emitted light is a direction parallel to the main scanning corresponding direction. This facilitates light beam separation at each polarization separation element.

  For example, the polarization direction of light emitted from each light emitting unit is inclined by an angle φ (0 ° <φ <90 °) with respect to the Z-axis direction, and the light beam LB1 emitted from the polarization adjusting member 13 is vertically polarized. When the light beam LB2 is transversely polarized light, the angle of the fast axis of the region 14a may be set to φ / 2, and the angle of the fast axis of the region 14b may be set to (90 + φ) / 2.

By the way, the light beam emitted from each light emitting portion is a divergent light beam, and in the case of a surface emitting laser array, the divergence angle is generally about 10 ° at the full width at half maximum. Further, the distance between the two light emitting portions (distance between the centers) is generally around 50 μm. In this case, the distance from the light emitting part to the phase shift element 14 may be within 285 μm (= 50 (μm) / 2 / tan (10 ° / 2)). If this distance is D, as shown in FIG. 17, as the distance to the light emitting portion and the phase shift element is as D, the polarization adjustment member from the surface of the light source 10 ₁ of the semiconductor laser chip 101 through spacer 13 may be bonded.

  Lamination via a spacer is a technique that is often incorporated in liquid crystal elements, and can be performed as follows as an example.

First, the adhesive of the ultraviolet curable before curing as a spacer, a plurality of locations of the light sources 10 ₁ before the phase shift element is bonded, it is added dropwise with a dispenser or the like.

  The distance between each light emitting unit and the phase shift element 14 is D while aligning the phase shift element 14 so that the region 14a faces the light emitting unit 101a and the region 14b faces the light emitting unit 101b. As described above, the polarization adjusting member 13 is brought close to the semiconductor laser chip 101.

  Thereafter, the adhesive is cured by irradiating ultraviolet rays.

  Of the luminous flux from the light emitting part, divergent light outside the full width at half maximum is incident on an adjacent region and may behave as noise light (ghost light). In this case, as shown in FIG. 18 as an example, a light shielding portion may be provided at the boundary between two regions in the phase shift element 14.

  As shown in FIG. 19, the phase shift element 14 includes a transparent base material having an inclined surface formed with a period equal to or less than a wavelength, and a plurality of dielectric layers stacked on the inclined surface of the transparent base material. The ridge line direction of the inclined surface is different between the region 14a and the region 14b.

  In this case, for example, the film can be designed so that the direction parallel to the ridge line direction is the slow axis direction and the direction orthogonal to the ridge line direction is the fast axis direction. Specifically, the angle formed by the ridge line direction of the inclined surface in the region 14a and the ridge line direction of the inclined surface in the region 14b is set to 45 °, and the polarization component parallel to the ridge line direction and the polarization component orthogonal to the ridge line direction And a dielectric layer may be formed so that a half-wave phase difference is generated.

  Further, the phase shift amount in the phase shift element 14 may be an amount corresponding to ¼ of the wavelength of the light beam. This phase shift element is a so-called quarter wavelength element.

In this case, as shown in FIG. 20 as an example, the polarization adjusting member 13 has a quarter wavelength element 14 ₁ having two regions (14 ₁ a, 14 ₁ b) individually corresponding to the light beam LB1 and the light beam LB2. When configured by combining a 1/4 wavelength element 14 ₂ which is not divided into regions.

For example, when the polarization direction of light emitted from each light emitting unit is inclined by an angle φ (0 ° <φ <90 °) with respect to the Z-axis direction, the region 14 ₁ a of the quarter wavelength element 14 ₁ is used. The fast axis direction is set to φ + 45 °, and the fast axis direction of the region 14 ₁ b is set to φ-45 °. Thus, 1/4 light beam LB1 passing through the wavelength element 14 ₁ in the right-handed circularly polarized light, the light beam LB2 is converted into left-handed circularly polarized light.

By setting 1/4 fast axis direction of the wavelength element 14 ₂ in a direction -45 ° inclined with respect to the Z-axis direction, the light beam LB1 emitted from the polarization adjustment member 13 and the vertically polarized light, the light beam LB2 Can be laterally polarized.

1/4 fast axis direction of each region of the wavelength elements 14 _1, designed and arranged in accordance with the polarization direction of light emitted from the light source, 1/4 fast axis direction of the wavelength element 14 _2, the optical scanning By designing and arranging according to the polarization direction handled by the device, even if the light source is rotated, it is not necessary to prepare a phase shift element corresponding to the rotation angle, and it is excellent in adapting to design changes .

In this case, as shown in FIG. 21, the angle formed by the ridge line direction of the inclined surface in the region 14 ₁ a and the ridge line direction of the inclined surface in the region 14 ₁ b is set to 90 ° and is parallel to the ridge line direction. The dielectric layer may be formed such that a phase difference of ¼ wavelength is generated between the polarization component and the polarization component orthogonal to the ridge line direction. In this case, linearly polarized light having an angle of ± 45 ° with respect to the ridge line direction is incident on each region of the quarter wavelength element 14 ₁ , so that circularly polarized light having different rotation directions in the region 14 ₁ a and the region 14 ₁ b. Can be obtained.

  In each quarter wavelength element, the phase can be adjusted by the refractive index and film thickness of the dielectric material.

  22A and 22B show a case where a surface emitting laser array in which a plurality of light emitting portions are two-dimensionally arranged is used instead of the edge emitting semiconductor laser. .

  In this case, the phase shift element has a plurality of regions individually corresponding to the plurality of light emitting units. Further, since the phase shift element easily sets a desired distance from the light emitting unit, the size of the outer shape of the phase shift element is the size included in the region surrounded by the extraction electrode when viewed from the light emission direction. It is preferable.

  The surface emitting laser array and the phase shift element can be bonded as follows as an example.

(A) An ultraviolet curable adhesive before curing as a spacer is dropped onto a plurality of portions of the surface emitting laser array using a dispenser or the like (four locations in FIG. 22A).
(B) While aligning a plurality of regions corresponding to each light emitting portion with the phase shift element, the polarization adjusting member is used as a surface emitting laser array so that the distance between each light emitting portion and the phase shift element becomes D. Close to.
(C) Irradiate ultraviolet rays to cure the adhesive.

  Each light beam emitted from the plurality of light emitting units passes through a corresponding region of the phase shift element and is adjusted to have a predetermined polarization direction. For example, if the number of light emitting units is 32, 16 light sources are adjusted to vertically polarized light and horizontally polarized light. In this case, multi-beam writing with 16 beams can be performed for each station.

  By the way, in the surface emitting laser array, the polarization direction of the emitted light beam can be adjusted by the shape of the metal minute opening provided in each light emitting portion. As this technique, for example, “surface plasmon surface emitting laser using a metal microhole array”, Onishi, Tanikawa, Ueda, Ueda, O plus E, Vol. 29, no. 4, (2007).

  In this case, if the shape of the metal micro-aperture of each light emitting unit is set so that the polarization direction of the light beam emitted from one light emitting unit and the polarization direction of the light beam emitted from the other light emitting unit are orthogonal to each other, There is no need to provide a separate shift element, and a small and highly reliable light source can be realized at low cost.

As described above, according to the optical scanning device 2010 according to the present embodiment, the light source unit LU, the beam splitter 30, the two cylindrical lenses (12 ₁ , 12 ₂ ), the polygon mirror 14, the two scanning lenses (15 ₁ , 15 ₂ ), two polarization separation elements (16 ₁ , 16 ₂ ), four reflection mirrors (M1, M2, 17 ₁ , 17 ₂ ), four folding mirrors (18a, 18b, 18c, 18d), and scanning control I have a device.

The light source unit LU includes a light source 10 ₁ , a driving chip 10 ₂ , a circuit board 10 ₃ , a polarization adjusting member 13, a collimating lens 11, and the like.

  The polarization adjusting member 13 includes a phase shift element 14 having a region 14a facing the light beam LB1 emitted from the light emitting unit 101a of the semiconductor laser chip 101 and a region 14b facing the light beam LB2 emitted from the light emitting unit 101b. The polarization directions of the light beam LB1 and the light beam LB2 are adjusted to the polarization directions orthogonal to each other.

Thus, the polarization separation element 16 ₁ is capable of separating the light beams LBa and the light beam LBb correctly. The polarization separating element 16 _2, it is possible to separate the light beam LBc and the light beam LBd correctly.

  Thus, the optical scanning device 2010 can be reduced in size without increasing the cost and reducing the scanning accuracy.

  Since the color printer 2000 includes the optical scanning device 2010, as a result, it is possible to reduce the size without degrading the image quality.

  In the above embodiment, the toner image is transferred from the photosensitive drum to the recording paper via the transfer belt. However, the present invention is not limited to this, and the toner image is directly transferred to the recording paper. Also good.

  Further, an image forming apparatus using a color developing medium (positive photographic paper) that develops color by the heat energy of a beam spot as an image carrier may be used. In this case, a visible image can be directly formed on the image carrier by optical scanning.

  In the above embodiment, the case where the optical scanning device is used in a printer has been described. However, the present invention is also suitable for an image forming apparatus other than a printer, for example, a copier, a facsimile, or a multifunction machine in which these are integrated.

10 1 _... light source, 10 2 _... driving chip, 10 3 _... circuit board, 11 ... collimator lens, ₁₂ 1, 12 2 _... cylindrical lens, 13 ... polarization adjustment member, 14 ... phase shift elements, 14a, 14b ... area, 14 ... Polygon mirror (light deflector), 15 ₁ , 15 ₂ ... Scanning lens (part of scanning optical system), 16 ₁ ... Polarization separation element (first polarization separation element), 16 ₂ ... Polarization separation element (first) 2 polarization separation elements), 17 ₁ , 17 ₂ ... Reflection mirror (part of the scanning optical system), 18a, 18b, 18c, 18d ... folding mirror (part of the scanning optical system), 19a to 19d ... exit window, DESCRIPTION OF SYMBOLS 30 ... Beam splitter, 101 ... Semiconductor laser chip, 101a, 101b ... Light emission part, 2000 ... Color printer (image forming apparatus), 2030a-2030d ... Photosensitive drum (image) Carrier), 2010... Optical scanning device, LU... Light source unit, M1, M2.

JP 2009-139039 A JP 2006-284822 A JP 2006-350167 A

Claims (8)

An optical scanning device that optically scans a plurality of scanned surfaces along a main scanning direction,
A light source having a first light emitting part and a second light emitting part;
A polarization adjusting member that makes the polarization direction of the light emitted from the first light emitting unit and the polarization direction of the light emitted from the second light emitting unit orthogonal to each other;
The light emitted from the first light emitting unit is divided into the first light and the second light while maintaining the polarization state, and the light emitted from the second light emitting unit is maintained in the polarization state. A light splitting element that splits the third light and the fourth light as they are;
A plurality of reflecting surfaces, wherein the first light and the third light are incident on the same reflecting surface, and the second light and the fourth light are different from the same reflecting surface; An optical deflector that enters the reflecting surface and deflects each light beam;
A first polarization separation element that separates the first light and the third light deflected by the light deflector;
An optical scanning device comprising: the second light deflected by the optical deflector; and a second polarization separation element that separates the fourth light. The polarization adjusting member includes a phase shift element having a first region where light emitted from the first light emitting unit is incident and a second region where light emitted from the second light emitting unit is incident. Including
2. The optical scanning device according to claim 1, wherein the fast axis direction of the first region and the fast axis direction of the second region are different from each other. The phase shift element generates a half-wave phase difference,
3. The optical scanning device according to claim 2, wherein an angle formed by the fast axis direction of the first region and the fast axis direction of the second region is 45 degrees. The fast axis direction of the first region is a direction in which the polarization direction of light emitted from the first region is a direction orthogonal to the main scanning direction,
The fast axis direction of the second region is a direction in which the polarization direction of light emitted from the second region is parallel to the main scanning direction. Optical scanning device.   The phase shift element is composed of a transparent base material having an inclined surface formed with a period equal to or less than a wavelength, and a plurality of dielectric materials laminated on the inclined surface of the transparent base material, and the first region and the The optical scanning device according to claim 2, wherein a ridge line direction of the inclined surface is different from that of the second region. The light source includes a surface emitting laser array,
The said phase shift element is adhere | attached on the said surface emitting laser array in the state in which the space | gap was provided between the emission surfaces of the said surface emitting laser array. The optical scanning device according to 1. The polarization adjusting member has a first phase having a first region where light emitted from the first light emitting unit is incident and a second region where light emitted from the second light emitting unit is incident. A shift element; and a second phase shift element that is incident on the light that has passed through the first phase shift element and is not divided into regions,
The fast axis direction of the first region is a direction in which light emitted from the first region becomes circularly polarized light, and the fast axis direction of the second region is emitted from the second region. The direction of the circularly polarized light is opposite to the circularly polarized light emitted from the first region,
The fast axis direction of the second phase shift element is such that the light passing through the first region becomes linearly polarized light in a direction orthogonal to the main scanning direction, and the light passing through the second region is The optical scanning device according to claim 1, wherein the optical scanning device has a direction of linearly polarized light parallel to the main scanning direction. A plurality of image carriers;
An image forming apparatus comprising: the optical scanning device according to claim 1 that scans the plurality of image carriers with light modulated according to image information.