JP2013025003A - Optical scanner and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical scanner capable of remarkably lowering the height.SOLUTION: In the optical scanner, a scanning optical system is arranged between two polygon mirrors (2104A and 2104B) with respect to the X-axis direction, and has four polarization beam splitters (S1, S2, S3 and S4), three scanning lenses (L1, L2 and L3), two dichroic mirrors (D1 and D2), two quarter wave plates (W1 and W3), and two three-quarter wave plates (W2 and W4). Each of four light fluxes which have been deflected by the respective polygon mirrors moves in the same plane orthogonal to the Z-axis direction, and then moves toward a corresponding photoreceptor drum.

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 surface to be scanned with light and an image forming apparatus including the optical scanning device.

  In recent years, electrophotographic image forming apparatuses used in laser printers, laser plotters, digital copiers, laser facsimiles, or multi-function machines including these have become more colorized and faster, and photoconductor drums that are image carriers. Tandem type image forming apparatuses having a plurality of (usually four) are widely used.

  As an example, Patent Document 1 discloses an image forming apparatus including an optical scanning device for each photosensitive drum.

  As an example, Patent Document 2 discloses an optical scanning device including a two-stage polygon mirror.

  As an example, Patent Document 3 discloses an optical scanning device in which a plurality of light beams are obliquely incident on a one-stage polygon mirror.

  Currently, there is a great demand for miniaturization and weight reduction of image forming apparatuses for offices or personal use. In order to realize this, it is important to reduce the height of the optical scanning device (reduce the thickness).

  However, in the optical scanning devices disclosed in Patent Document 2 and Patent Document 3, it is difficult to further reduce the height.

  According to a first aspect of the present invention, there is provided an optical scanning device that individually scans a plurality of scanned surfaces with a light beam, and the first optical deflector that deflects the first light beam toward the first scanned surface. And a second optical deflector for deflecting the second light beam directed toward the second surface to be scanned, and a scanning optical system disposed between the first optical deflector and the second optical deflector. The scanning optical system includes one scanning lens having two optical surfaces, and the first light beam deflected by the first optical deflector is incident on an optical surface on one side of the scanning lens, The second light beam emitted from the other optical surface, guided to the first scanned surface, and deflected by the second optical deflector is incident on the other optical surface of the scanning lens. Then, the optical scanning device is characterized in that it is emitted from the optical surface on one side and guided to the second surface to be scanned.

  According to a second aspect of the present invention, there are provided a plurality of image carriers, and the optical scanning device of the present invention that scans the plurality of image carriers with a light beam modulated according to corresponding image information. An image forming apparatus provided.

  According to the optical scanning device of the present invention, the height can be significantly reduced.

  According to the image forming apparatus of the present invention, it is possible to reduce the size and weight.

1 is a diagram for describing a schematic configuration of a color printer according to an embodiment of the present invention. FIG. It is a figure for demonstrating the optical scanning device in FIG. It is a figure for demonstrating the scanning optical system of an optical scanning device. It is a figure for demonstrating a surface emitting laser array. FIG. 5A and FIG. 5B are diagrams for explaining the operation of the polarization beam splitter. It is a figure for demonstrating the shape of each optical surface of the scanning lens L1. FIG. 7A to FIG. 7C are diagrams for explaining the shape of the scanning lens L2. It is a figure for demonstrating the shape of each optical surface of the scanning lens L2. It is a figure for demonstrating the incident position of the light beam in each scanning lens. It is a figure for demonstrating the optical path of the light beam LBa in a scanning optical system. It is a figure for demonstrating the optical path of the light beam LBc in a scanning optical system. It is a figure for demonstrating the optical path of the light beam LBb in a scanning optical system. It is a figure for demonstrating the optical path of the light beam LBd in a scanning optical system. FIG. 14A is a diagram for explaining the imaging performance of the scanning optical system for the light beam LBa and the light beam LBd, and FIG. 14B is a diagram for explaining the fθ characteristics of the light beam LBa and the light beam LBd. It is. FIG. 15A is a diagram for explaining the imaging performance of the scanning optical system for the light beam LBb and the light beam LBc, and FIG. 15B is a diagram for explaining the fθ characteristics of the light beam LBb and the light beam LBc. It is. It is a figure for demonstrating the rotational deviation angle (phi) in two polygon mirrors. It is a figure for demonstrating drive control of the light source 2200A by a scanning control apparatus. It is a figure for demonstrating drive control of the light source 2200B by a scanning control apparatus. It is a figure for demonstrating the case where the shape of three scanning lenses is the same. FIGS. 20A and 20B are views (No. 1) for explaining the optical positional relationship between the light beam traveling toward the photosensitive drum and the two scanning lenses, respectively. FIGS. 21A and 21B are views (No. 2) for explaining the optical positional relationship between the light beam traveling toward the photosensitive drum and the two scanning lenses, respectively. It is a figure for demonstrating the optical scanning device corresponding to the case where there are two photoconductor drums. It is a figure for demonstrating the scanning optical system in the optical scanning device of FIG. It is a figure for demonstrating the optical path of the light beam which goes to the photosensitive drum B in the scanning optical system of FIG. It is a figure for demonstrating the optical path of the light beam which goes to the photosensitive drum A in the scanning optical system of FIG. It is a figure for demonstrating the modification of the optical scanning device corresponding to the case where there are two photoconductor drums.

  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 device 2050, paper feed roller 2054, registration roller pair 2056, paper discharge roller 2058, paper feed tray 2 60, the discharge tray 2070 includes a communication control unit 2080, and a printer controller 2090 for totally controlling the above elements.

  Here, in the XYZ three-dimensional orthogonal coordinate system, the direction along the longitudinal direction (rotation axis 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. explain.

  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 AD conversion circuit for converting the signal into digital data. Then, the printer control device 2090 notifies the optical scanning device 2010 of multi-color image information (black image information, cyan image information, magenta image information, yellow image information) received from the host device via the communication control device 2080. To do.

  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).

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

  The optical scanning device 2010 scans the surface of the corresponding charged photosensitive drum with a light beam modulated for each color based on multicolor image information from the printer control device 2090. 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 device as the photosensitive drum rotates. The configuration of the optical scanning device will be described later.

  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 the recording paper one by one from the paper feed tray 2060 and conveys it to the registration roller pair 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 paper on which the color image is transferred is sent to the fixing device 2050.

  In the fixing device 2050, heat and pressure are applied to the recording paper, thereby fixing the toner on the recording paper. The recording paper on which the toner is fixed is sent to the paper discharge tray 2070 via the 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 sources (2200A, 2200B), two coupling lenses (2201A, 2201B), a polarizing beam splitter 2205, a reflection mirror 2206, two A polygon mirror (2104A, 2104B), a scanning optical system, a scanning control device (not shown), and the like are provided.

  The light source 2200A emits linearly polarized light having a wavelength λ1 and inclined by 45 ° with respect to the incident surface of the polarization beam splitter 2205 in the −Y direction.

  The light source 2200B emits linearly polarized light having a wavelength λ2 (<λ1) and inclined by 45 ° with respect to the incident surface of the polarization beam splitter 2205 in the + X direction.

  Here, λ1 = 780 nm and λ2 = 655 nm.

  Each light source has a surface emitting laser array in which 40 light emitting units are two-dimensionally arranged as shown in FIG. 4 as an example.

  Returning to FIG. 2, the coupling lens 2201A is disposed on the optical path of the light beam emitted from the light source 2200A, and makes the light beam a substantially parallel light beam.

  The coupling lens 2201B is disposed on the optical path of the light beam emitted from the light source 2200B, and makes the light beam a substantially parallel light beam.

  The polarization beam splitter 2205 is disposed on the −Y side of the coupling lens 2201A and on the + X side of the coupling lens 2201B.

  The polarization separation surface of the polarization beam splitter 2205 transmits linearly polarized light whose polarization direction is parallel to the Z-axis direction (referred to as “s-polarized light”) with respect to light having the wavelength λ1, and the polarization direction is orthogonal to the s-polarized light. It has the characteristics of reflecting linearly polarized light (referred to as “p-polarized light”), transmitting p-polarized light, and reflecting s-polarized light with respect to light of wavelength λ2.

  Therefore, the light beam having the wavelength λ1 via the coupling lens 2201A is divided into s-polarized light (referred to as “light flux LBa”) and p-polarized light (referred to as “light flux LBd”) by the polarization beam splitter 2205, and the light flux LBa 2205 is transmitted, and the light beam LBd is reflected in the + X direction by the polarization beam splitter 2205 (see FIG. 5A).

  Further, the light beam having the wavelength λ2 via the coupling lens 2201B is divided into s-polarized light (referred to as “light flux LBc”) and p-polarized light (referred to as “light flux LBb”) by the polarization beam splitter 2205. 2205 is transmitted, and the light beam LBc is reflected in the −Y direction by the polarization beam splitter 2205 (see FIG. 5B).

  That is, the light beam LBa and the light beam LBc travel from substantially the same optical path toward the polygon mirror 2104A from the polarization beam splitter 2205.

  Further, the light beam LBb and the light beam LBd travel from substantially the same optical path toward the reflection mirror 2206 from the polarization beam splitter 2205.

  The reflection mirror 2206 reflects the light beam LBb and the light beam LBd in the direction toward the polygon mirror 2104B.

  The polygon mirror 2104A has a rotating four-sided mirror. Each mirror is a deflecting reflecting surface. The polygon mirror 2104A deflects the light beam LBa and the light beam LBc to the + X side.

  The polygon mirror 2104B has a rotating four-sided mirror. Each mirror is a deflecting reflecting surface. Polygon mirror 2104B deflects light beam LBb and light beam LBd to the -X side.

  The polygon mirror 2104A and the polygon mirror 2104B are arranged apart from each other in the X-axis direction, and are arranged at substantially the same position in the Y-axis direction and the Z-axis direction.

  Polygon mirror 2104A and polygon mirror 2104B are rotated so that none of the deflecting and reflecting surfaces of polygon mirror 2104B is parallel to one deflecting and reflecting surface of polygon mirror 2104A.

  The scanning optical system is disposed between the polygon mirror 2104A and the polygon mirror 2104B in the X-axis direction.

  The scanning optical system includes four polarizing beam splitters (S1, S2, S3, S4), three scanning lenses (L1, L2, L3), two dichroic mirrors (D1, D2), and two quarter-wave plates ( W1, W3) and two 3/4 wave plates (W2, W4).

  The polarization beam splitter S1 is disposed on the optical path of the light beam deflected by the polygon mirror 2104A. The polarization beam splitter S1 transmits s-polarized light and reflects p-polarized light.

  The scanning lens L1 is disposed on the + X side of the polarization beam splitter S1.

The shape of the cross section (main scanning cross section) orthogonal to the Z-axis direction of each optical surface of the scanning lens L1 is a non-arc shape expressed by the following equation (1). Here, x is a so-called depth in the X-axis direction. Further, y is a distance from the optical axis in the main scanning corresponding direction. K is a conic constant, and A ₁ , A ₂ , A ₃ , A ₄ , A ₅ , A ₆ ,... Are high-order coefficients. Furthermore, Cm = 1 / Ry, where Ry is the paraxial radius of curvature.

  The shape of the cross section (sub-scanning cross section) orthogonal to the Y-axis direction of each optical surface of the scanning lens L1 is expressed by the following equation (2).

Rz (0) in the above equation (2) is a radius of curvature on the optical axis in the sub-scanning section. B ₁ , B ₂ , B ₃ , B ₄ , B ₅ , B ₆ ,... Are higher-order coefficients.

  A specific example is shown in FIG. Here, the optical surface on the −X side is a surface on one side, and the optical surface on the + X side is a surface on the other side.

  Returning to FIG. 3, the quarter-wave plate W1 is disposed on the + X side of the scanning lens L1, and gives an optical phase difference of a quarter wavelength to the incident light beam.

  The dichroic mirror D1 is disposed on the + X side of the quarter wavelength plate W1. The dichroic mirror D1 reflects light having a wavelength longer than the wavelength λt and transmits light having a wavelength shorter than the wavelength λt. Here, λt = 700 nm is set.

  The 3/4 wavelength plate W2 is disposed on the + X side of the dichroic mirror D1, and gives an optical phase difference of 3/4 wavelength to the incident light beam.

  The polarizing beam splitter S2 is disposed on the + X side of the 3/4 wavelength plate W2. The polarization beam splitter S2 transmits s-polarized light and reflects p-polarized light in the + Z direction.

  The scanning lens L2 is disposed on the + X side of the polarization beam splitter S2.

  As an example, as shown in FIGS. 7A to 7C, the scanning lens L2 includes a two-fold symmetry axis A1 parallel to the Y-axis direction and a two-fold symmetry axis A2 parallel to the X-axis direction. Have. Therefore, in the scanning lens L2, the + X side optical surface and the −X side optical surface have the same shape.

  A specific example of each optical surface of the scanning lens L2 is shown in FIG. Further, the scanning lens L2 has a center thickness of 19 mm and a refractive index with respect to light having a wavelength of 655 nm is 1.52396.

  The polarization beam splitter S3 is disposed on the + X side of the scanning lens L2. The polarization beam splitter S3 transmits p-polarized light and reflects s-polarized light in the + Z direction.

  The 3/4 wavelength plate W4 is disposed on the + X side of the polarization beam splitter S3, and gives an optical phase difference of 3/4 wavelength to the incident light beam.

  The dichroic mirror D2 is disposed on the + X side of the 3/4 wavelength plate W4. Similar to the dichroic mirror D1, the dichroic mirror D2 reflects light having a wavelength longer than the wavelength λt and transmits light having a wavelength shorter than the wavelength λt.

  The quarter wavelength plate W3 is disposed on the + X side of the dichroic mirror D2, and gives an optical phase difference of a quarter wavelength to the incident light beam.

  The scanning lens L3 is a scanning lens having the same shape as the scanning lens L1, and is disposed on the + X side of the quarter-wave plate W3. Here, the + X side optical surface is the one side surface, and the −X side optical surface is the other side surface.

  Here, as an example, as shown in FIG. 9, in each scanning lens, the center of gravity of the incident position of a plurality of incident light beams is set so as to be positioned on the two-fold symmetry axis A2.

  The polarization beam splitter S4 is disposed on the + X side of the scanning lens L3. The polarization beam splitter S4 transmits p-polarized light and reflects s-polarized light in the + Z direction.

  Therefore, as shown in FIG. 10, the light beam LBa deflected by the polygon mirror 2104A passes through the polarization beam splitter S1, passes through the scanning lens L1, and enters the quarter-wave plate W1. The light beam LBa that has passed through the quarter-wave plate W1 is reflected by the dichroic mirror D1, and is incident on the quarter-wave plate W1 again. Accordingly, the light beam LBa that passes through the quarter-wave plate W1 and travels (returns) toward the scanning lens L1 becomes p-polarized light. The light beam LBa passes through the scanning lens L1 again, is reflected in the + Z direction by the polarization beam splitter S1, and travels toward the photosensitive drum 2030a.

  Further, as shown in FIG. 11, the light beam LBc deflected by the polygon mirror 2104A passes through the polarization beam splitter S1, passes through the scanning lens L1, and enters the quarter-wave plate W1. The light beam LBc that has passed through the quarter-wave plate W1 passes through the dichroic mirror D1 and enters the ¾-wave plate W2. The light beam LBc that has passed through the ¾ wavelength plate W2 remains s-polarized light. The light beam LBc passes through the polarization beam splitter S2 and enters the −X side optical surface of the scanning lens L2. The light beam LBc emitted from the + X side optical surface of the scanning lens L2 is reflected in the + Z direction by the polarization beam splitter S3 and travels toward the photosensitive drum 2030c.

  Further, as shown in FIG. 12, the light beam LBb deflected by the polygon mirror 2104B passes through the polarization beam splitter S4, passes through the scanning lens L3, and enters the quarter-wave plate W3. The light beam LBb that has passed through the quarter-wave plate W3 passes through the dichroic mirror D2 and enters the ¾-wave plate W4. The light beam LBb that has passed through the ¾ wavelength plate W4 remains p-polarized light. This light beam LBb passes through the polarization beam splitter S3 and enters the + X side optical surface of the scanning lens L2. The light beam LBb emitted from the −X side optical surface of the scanning lens L2 is reflected in the + Z direction by the polarization beam splitter S2 and travels toward the photosensitive drum 2030b.

  Further, as shown in FIG. 13, the light beam LBd deflected by the polygon mirror 2104B passes through the polarization beam splitter S4, passes through the scanning lens L3, and enters the quarter-wave plate W3. The light beam LBd that has passed through the quarter-wave plate W3 is reflected by the dichroic mirror D2, and is incident on the quarter-wave plate W3 again. Therefore, the light beam LBd passing through the quarter wavelength plate W3 and returning (returning) to the scanning lens L3 becomes s-polarized light. The light beam LBd passes through the scanning lens L3 again, is reflected in the + Z direction by the polarization beam splitter S4, and travels toward the photosensitive drum 2030d.

  As described above, in the scanning optical system, the optical paths of the respective light beams exist in the same plane orthogonal to the Z-axis direction until they are reflected in the + Z direction by the polarization beam splitter.

  FIG. 14A shows imaging performance in the main scanning direction (broken line) and sub-scanning direction (solid line) of the scanning optical system with respect to the light beam LBa and the light beam LBd. Note that x = 0 corresponds to the surface positions of the photosensitive drum 2030a and the photosensitive drum 2030d. FIG. 14B shows a deviation from a uniform linear motion when scanning the surfaces of the photosensitive drum 2030a and the photosensitive drum 2030d. This is called the fθ characteristic.

  FIG. 15A shows the imaging performance in the main scanning direction (broken line) and the sub-scanning direction (solid line) of the scanning optical system with respect to the light beam LBb and the light beam LBc. Note that x = 0 corresponds to the surface positions of the photosensitive drum 2030b and the photosensitive drum 2030c. FIG. 15B shows a deviation from the uniform linear motion when scanning the surfaces of the photosensitive drum 2030b and the photosensitive drum 2030c.

  As shown in FIG. 16 as an example, the polygon mirror 2104A and the polygon mirror 2104B are formed by one deflection reflection surface of the polygon mirror 2104A and one deflection reflection surface of the polygon mirror 2104B when viewed from the Z-axis direction. It is rotating so that the angle (shift angle) becomes φ. Here, the deviation angle φ is set to be approximately 45 °.

  In general, when two polygon mirrors are evenly shifted, the shift angle φ is φ = (360 ° ÷ M) / 2, that is, 180 ° ÷ M, where M is the number of polygon mirror surfaces. However, when the shift is not uniform, when the smaller shift angle is φ1, the larger shift angle φ2 is 360 ° / M−φ1.

  In the present embodiment, during the period in which the light beam LBa deflected by the polygon mirror 2104A scans the photosensitive drum 2030a, the light beam LBd deflected by the polygon mirror 2104B does not travel toward the photosensitive drum 2030d. On the other hand, during the period in which the light beam LBd deflected by the polygon mirror 2104B scans the photosensitive drum 2030d, the light beam LBa deflected by the polygon mirror 2104A does not travel toward the photosensitive drum 2030a.

  Therefore, the scanning control device controls the light source 2200A based on the black image information during the period in which the light beam LBa scans the photosensitive drum 2030a, and based on the yellow image information during the period in which the light beam LBd scans the photosensitive drum 2030d. Then, the light source 2200A is controlled (see FIG. 17).

  Similarly, during the period in which the light beam LBc deflected by the polygon mirror 2104A scans the photoconductor drum 2030c, the light beam LBb deflected by the polygon mirror 2104B does not travel toward the photoconductor drum 2030b. On the other hand, during the period in which the light beam LBb deflected by the polygon mirror 2104B scans the photoconductor drum 2030b, the light beam LBc deflected by the polygon mirror 2104A does not travel toward the photoconductor drum 2030c.

  Therefore, the scanning control device controls the light source 2200B based on the magenta image information during a period in which the light beam LBc scans the photosensitive drum 2030c, and based on the cyan image information during a period in which the light beam LBb scans the photosensitive drum 2030b. Then, the light source 2200B is controlled (see FIG. 18).

  As described above, according to the optical scanning device 2010 according to the present embodiment, the two light sources (2200A, 2200B), the two coupling lenses (2201A, 2201B), the polarization beam splitter 2205, the reflection mirror 2206, and the two polygons. A mirror (2104A, 2104B), a scanning optical system, a scanning control device, and the like are provided.

  The light source 2200A emits linearly polarized light having a wavelength of 780 nm and inclined by 45 ° with respect to the incident surface of the polarizing beam splitter 2205. The light source 2200B has a wavelength of 655nm and inclined by 45 ° with respect to the incident surface of the polarizing beam splitter 2205. Emits linearly polarized light.

  Polarization beam splitter 2205 divides the light beam from light source 2200A into s-polarized light beam LBa and p-polarized light beam LBd, and divides the light beam from light source 2200B into p-polarized light beam LBb and s-polarized light beam LBc. To do. The light beam LBa and the light beam LBc enter the polygon mirror 2104A through the same optical path, and the light beam LBb and the light beam LBd enter the polygon mirror 2104B through the same optical path.

  The scanning optical system is disposed between two polygon mirrors with respect to the X-axis direction, and includes four polarizing beam splitters (S1, S2, S3, S4), three scanning lenses (L1, L2, L3), and two dichroic. It has mirrors (D1, D2), two quarter wave plates (W1, W3), and two 3/4 wave plates (W2, W4).

  All optical elements constituting the scanning optical system are arranged so that their centers substantially coincide with each other in the Z-axis direction.

  The light beam LBa deflected by the polygon mirror 2104A passes through the polarization beam splitter S1, the scanning lens L1, the quarter wavelength plate W1, the dichroic mirror D1, the quarter wavelength plate W1, the scanning lens L1, and the polarization beam splitter S1. Light is guided to the photosensitive drum 2030a.

  The light beam LBc deflected by the polygon mirror 2104A is a polarization beam splitter S1, a scanning lens L1, a quarter wavelength plate W1, a dichroic mirror D1, a 3/4 wavelength plate W2, a polarization beam splitter S2, a scanning lens L2, and a polarization beam. The light is guided to the photosensitive drum 2030c via the splitter S3.

  The light beam LBb deflected by the polygon mirror 2104B is a polarization beam splitter S4, a scanning lens L3, a ¼ wavelength plate W3, a dichroic mirror D2, a 3/4 wavelength plate W4, a polarization beam splitter S3, a scanning lens L2, and a polarization beam. The light is guided to the photosensitive drum 2030b via the splitter S2.

  The light beam LBd deflected by the polygon mirror 2104B passes through the polarization beam splitter S4, the scanning lens L3, the quarter wavelength plate W3, the dichroic mirror D2, the quarter wavelength plate W3, the scanning lens L3, and the polarization beam splitter S4. Light is guided to the photosensitive drum 2030d.

  In this case, the four light beams (light beam LBa, light beam LBb, light beam LBc, and light beam LBd) deflected by the respective polygon mirrors all move in the same plane orthogonal to the Z-axis direction, and then the corresponding photosensitive drum. Head for. In other words, the scanning optical system does not require a three-dimensional light beam swirling by a conventional folding mirror. Therefore, the height of the optical scanning device 2010 can be significantly reduced.

  The color printer 2000 includes the optical scanning device 2010. As a result, the color printer 2000 can be reduced in size and weight.

  In the above embodiment, as shown in FIG. 19 as an example, the shapes of the three scanning lenses (L1, L2, L3) may be the same.

  FIG. 20A shows a relationship between the optical path and the scanning lens when the optical path of the light beam LBa is a single straight line. FIG. 20B shows the relationship between the optical path and the scanning lens when the optical path of the light beam LBc is a single straight line. The second scanning lens through which the light beam LBa passes is the scanning lens L1, and the second scanning lens through which the light beam LBc passes is the scanning lens L2. Therefore, if the scanning lens L1 and the scanning lens L2 have the same shape, the optical position of the second scanning lens through which the light beam LBa passes and the optical position of the second scanning lens through which the light beam LBc passes are determined. Can be substantially matched.

  FIG. 21A shows the relationship between the optical path and the scanning lens when the optical path of the light beam LBb is a single straight line. FIG. 21B shows a relationship between the optical path and the scanning lens when the optical path of the light beam LBd is a single straight line. The second scanning lens through which the light beam LBb passes is the scanning lens L2, and the second scanning lens through which the light beam LBd passes is the scanning lens L3. Therefore, if the scanning lens L2 and the scanning lens L3 have the same shape, the optical position of the second scanning lens through which the light beam LBb passes and the optical position of the second scanning lens through which the light beam LBd pass are determined. Can be substantially matched.

  As described above, the scanning lens L1, the scanning lens L2, and the scanning lens L3 have the same shape, so that the scanning lenses can be easily assembled. Moreover, cost reduction can be achieved.

  In the above embodiment, the case where the image forming apparatus has four photosensitive drums has been described. However, the present invention is not limited to this. For example, the image forming apparatus has two photosensitive drums (photosensitive drum A, photosensitive drum A, It may have a photoreceptor drum B).

  In this case, as shown in FIG. 22 as an example, the light source 2200B and the coupling lens 2201A are unnecessary. As an example, as shown in FIG. 23, the polarization beam splitter S1, the polarization beam splitter S4, the two dichroic mirrors (D1, D2), the two quarter-wave plates (W1, W3), and The two 3/4 wavelength plates (W2, W4) are also unnecessary.

  In this case, the light beam deflected by the polygon mirror 2104A is guided to the photosensitive drum B through the scanning lens L1, the polarizing beam splitter S2, the scanning lens L2, and the polarizing beam splitter S3 as shown in FIG. .

  Further, as shown in FIG. 25, the light beam deflected by the polygon mirror 2104B is guided to the photosensitive drum A via the scanning lens L3, the polarization beam splitter S3, the scanning lens L2, and the polarization beam splitter S2.

  In this case, as shown in FIG. 26 as an example, the scanning lens L1 and the scanning lens L3 may be omitted.

  Moreover, although the said embodiment demonstrated the case where each light source had 40 light emission parts, it is not limited to this.

  In the above embodiment, the case of the image forming apparatus in which the toner image is transferred from the photosensitive drum to the recording paper via the transfer belt has been described. However, the present invention is not limited to this, and the toner image is directly transferred to the recording paper. An image forming apparatus may be used.

  Further, an image forming apparatus using a silver salt film as the image carrier may be used. In this case, a latent image is formed on the silver salt film by optical scanning, and this latent image can be visualized by a process equivalent to a developing process in a normal silver salt photographic process. Then, it can be transferred to a photographic paper as a transfer object by a process equivalent to a printing process in a normal silver salt photographic process. Such an image forming apparatus can be implemented as an optical plate making apparatus or an optical drawing apparatus that draws a CT scan image or the like.

  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 of a color printer is described as the image forming apparatus. 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.

  2000 ... color printer (image forming apparatus), 2010 ... optical scanning device, 2030a-2030d ... photosensitive drum (image carrier), 2104A, 2104B ... polygon mirror (optical deflector), 2200a-2200d ... light source, 2205 ... polarized light Beam splitter, D1, D2 ... Dichroic mirror, L1, L2, L3 ... Scan lens, W1, W3 ... 1/4 wavelength plate, W2, W4 ... 3/4 wavelength plate.

JP-A-2003-75753 Japanese Patent No. 4476047 Japanese Patent No. 3869701

Claims (10)

An optical scanning device that individually scans a plurality of scanned surfaces with a light beam,
A first optical deflector for deflecting a first light beam directed toward the first scanned surface;
A second optical deflector for deflecting the second light beam traveling toward the second scanned surface;
A scanning optical system disposed between the first optical deflector and the second optical deflector,
The scanning optical system includes one scanning lens having two optical surfaces, and the first light beam deflected by the first optical deflector is incident on an optical surface on one side of the scanning lens, and the other. The second light beam emitted from the optical surface on the side, guided to the first surface to be scanned, and deflected by the second optical deflector enters the optical surface on the other side of the scanning lens. An optical scanning device, wherein the optical scanning device is emitted from the optical surface on one side and guided to the second surface to be scanned.   The optical scanning device according to claim 1, wherein the scanning lens has two two-fold symmetry axes.   The scanning optical system includes the scanning lens as a first scanning lens, and further includes a second scanning lens disposed between the first scanning lens and the first optical deflector, and the second scanning lens. The optical scanning device according to claim 1, further comprising a third scanning lens having the same shape as the scanning lens and disposed between the first scanning lens and the second optical deflector. . The first optical deflector further deflects the third light flux toward the third scanned surface,
The second optical deflector further deflects the fourth light beam toward the fourth surface to be scanned,
The scanning optical system includes a first beam separating unit disposed between the first optical deflector and the second scanning lens, and between the second scanning lens and the first scanning lens. The second beam separating means arranged in the first, the third beam separating means arranged between the first scanning lens and the third scanning lens, the second optical deflector and the third And a fourth beam separating means disposed between the scanning lens and
The first light beam deflected by the first optical deflector includes the first beam separating unit, the second scanning lens, the second beam separating unit, the first scanning lens, and the first beam. 3 is guided to the first surface to be scanned through the beam separation means 3,
The second light beam deflected by the second optical deflector includes the fourth beam separation unit, the third scanning lens, the third beam separation unit, the first scanning lens, and the first beam. Guided to the second surface to be scanned through two beam separating means,
The third light beam deflected by the first optical deflector includes the first beam separation unit, the second scanning lens, the second beam separation unit, the second scanning lens, and the first beam. Guided to the third surface to be scanned through one beam separating means,
The fourth light beam deflected by the second optical deflector includes the fourth beam separating means, the third scanning lens, the third beam separating means, the third scanning lens, and the 4. The optical scanning device according to claim 1, wherein the light is guided to the fourth surface to be scanned through four beam separation units. The first light beam and the second light beam are both light beams having a first wavelength,
The third light beam and the fourth light beam are both light beams having a second wavelength different from the first wavelength,
5. The optical scanning device according to claim 4, wherein the second beam separation unit and the third beam separation unit include a dichroic mirror. The first light flux and the fourth light flux are both linearly polarized light in the first polarization direction,
The second light flux and the third light flux are both linearly polarized light in a second polarization direction orthogonal to the first polarization direction,
6. The optical scanning device according to claim 4, wherein each of the first to fourth beam separation units includes a polarization beam splitter.   The optical scanning device according to claim 3, wherein the first scanning lens, the second scanning lens, and the third scanning lens have the same shape. The first optical deflector and the second optical deflector rotate so that none of the reflective surfaces of the second optical deflector is parallel to one reflective surface of the first optical deflector,
The light source includes a first light source that emits the first light flux and the second light flux, and a second light source that emits the third light flux and the fourth light flux. The optical scanning device according to claim 4. A common polarization separation element disposed on an optical path of a light beam emitted from the first light source and the second light source;
The light beam emitted from the first light source and the second light source is circularly polarized light or linearly polarized light whose polarization direction is inclined by approximately 45 ° with respect to the incident surface of the polarization separation element. 9. The optical scanning device according to 8. A plurality of image carriers;
An image forming apparatus comprising: the optical scanning device according to claim 1, wherein the plurality of image carriers are scanned with light beams modulated according to corresponding image information.

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