JP2012008579A - Optical scanning device and image-forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To uniform a light quantity among multiple light beams scanning a scanned surface.SOLUTION: When scanning a neighborhood of a central point O in a write area of a photosensitive drum, an optical scanning device activates VCSEL, VCSELand VCSELso that each intensity of two light beams LBand LBfarthest in a main scanning direction becomes greater than the intensity of a light beam LBat a center in the main scanning direction. To be more precise, each of peak values of two curves L1 and L3 showing the distributions of light quantities of the light beams LBand LBis made greater than the peak value of a curve L2 showing the distribution of light quantity of the light beam LBso that each light quantity of light beam entering a deflecting surface is uniformed among the beams.

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 a light beam and an image forming apparatus including the optical scanning device.

  Conventionally, as an image forming apparatus that forms an image using the Carlson process, for example, a surface of a rotating photosensitive drum is scanned with a light beam to form a latent image on the surface of the photosensitive drum. There is known an image forming apparatus that forms an image by fixing a toner image obtained by visualization on a sheet as a recording medium. In recent years, this type of image forming apparatus is often used for simple printing as an on-demand printing system, and demands for higher image density and faster image output are increasing.

  In general, as a method of speeding up image output, it is conceivable to increase the printing speed by increasing the number of rotations of a deflector for deflecting a light beam and the number of rotations of a photosensitive drum. However, when the rotation speed of the deflector is increased, noise and vibration from the drive system increase, power consumption increases, and the durability of the apparatus decreases. Further, since high-speed image output has a trade-off relationship with high-density images, there is a disadvantage that the image quality is lowered as the number of rotations of the deflector is increased.

  Therefore, as a method of simultaneously achieving higher image density and higher image output speed, an image forming apparatus has been proposed in which a light source is made into a multi-beam and a photosensitive drum is scanned with a plurality of light beams at a time. In this image forming apparatus, light emitted from a surface emitting laser array (VCSEL) having a plurality of light emitting sources as a light source of a light beam is collectively deflected by a deflector to be photosensitive. This is a device capable of simultaneously scanning a body drum with a plurality of light beams.

  Recently, an optical scanning device using an overfilled optical system in which the width of a deflecting surface of a deflector that deflects a plurality of light beams is smaller than an irradiation range of the plurality of light beams has been proposed (for example, Patent Document 1). reference). By using an overfilled optical system, the width of the deflecting surface can be reduced. Therefore, compared to a conventional deflector having the same diameter (the diameter of a circle in which the deflector is inscribed, with the rotation axis as the center), More deflection surfaces can be provided. For this reason, the scanning speed can be improved without increasing the rotational speed of the deflector.

  However, the optical scanning device using the overfilled optical system has a disadvantage that the light amount distribution of the light beam reflected by the deflecting surface is not uniform. Further, in the above-described surface-emitting laser array or the like, the light beam divergence angle is small, so that the light amount distribution of the light beam incident on the deflecting surface is slightly non-uniform compared to the edge-emitting laser or the like. For this reason, in order to combine both the surface-emitting light source and the overfilled optical system, a technique for making the light quantity distribution of the light beam uniform is required.

  According to a first aspect of the present invention, a light source unit having a plurality of light emitting sources arranged two-dimensionally in a plane parallel to a main scanning direction and a sub-scanning direction orthogonal to the main scanning direction, and the plurality of light emission A deflector that deflects a plurality of light beams respectively emitted from a source and scans a writing area of a surface to be scanned in a main scanning direction from a writing start position to a writing end position; In the optical scanning device in which the dimension in the main scanning direction is smaller than the light beam width in the main scanning direction of the plurality of light beams, each of the plurality of light beams is scanned when the vicinity of the center of the writing area is scanned. The intensity is increased from the light beam at the center in the main scanning direction to at least one of the light beam at the write start position side and the light beam at the write end position side. That is an optical scanning device.

  According to a second aspect of the present invention, a light source unit having a plurality of light emitting sources arranged two-dimensionally in a plane parallel to a main scanning direction and a sub scanning direction orthogonal to the main scanning direction, and the plurality of light emitting elements. A deflector that deflects a plurality of light beams respectively emitted from a source and scans a writing region of a surface to be scanned in a main scanning direction from a writing start position to a writing end position, and the deflection surface of the deflector is In the optical scanning device in which the dimension in the main scanning direction is smaller than the light beam width in the main scanning direction of the plurality of light beams, when scanning from the writing start position to the center of the writing area, the writing area The intensity of each of the plurality of light beams incident on the center is increased from the center light beam in the main scanning direction to the light beam on the writing end position side, and writing is performed from the center of the writing area. When scanning only to the end position, the intensity of each of the plurality of light beams incident on the writing area is increased from the light beam at the center in the main scanning direction to the light beam on the writing start position side. This is an optical scanning device.

  From a third aspect, the present invention provides a deflector that deflects a plurality of light beams and scans the plurality of light beams in a main scanning direction, and a coupling that couples the light beams incident on the deflector. An aperture member having openings through which the plurality of light beams coupled to the coupling lens pass, and the deflection surface of the deflector has a dimension in the main scanning direction, the plurality of light beams The aperture member is arranged such that the aperture is positioned in the vicinity of the focal position of the coupling lens and the aperture has a width in the sub-scanning direction. Is an optical scanning device characterized by being formed to increase from the central portion in the main scanning direction to the peripheral portion in the main scanning direction.

  According to a fourth aspect of the present invention, there is provided an image forming apparatus for forming an image by fixing a toner image formed based on a latent image obtained from information relating to an image to a recording medium. An optical scanning device, a photosensitive member on which a latent image is formed by the optical scanning device, a developing unit that visualizes the latent image formed on the surface to be scanned of the photosensitive member, and a developing unit that visualizes the latent image And a transfer unit that fixes the toner image to the recording medium.

  According to a fifth aspect of the present invention, a multicolor image is formed by superimposing and fixing a toner image formed based on a latent image for each color obtained from information on a multicolor image on a recording medium. An optical scanning device according to the present invention, a plurality of photosensitive members on which latent images corresponding to respective colors are formed by the optical scanning device, and a plurality of scanned surfaces of the plurality of photosensitive members, respectively. An image forming apparatus comprising: a developing unit that visualizes the latent image that has been developed; and a transfer unit that superimposes and fixes the toner images for each color visualized by the developing unit on the recording medium.

  According to the optical scanning device of the present invention, when a surface-emitting light source is applied to an overfilled optical system, it is possible to improve the non-uniformity of the light amount distribution of the scanning light and scan the surface to be scanned with high accuracy. .

  According to the image forming apparatus of the present invention, an image can be formed with high accuracy.

1 is a diagram illustrating a schematic configuration of an image forming apparatus 200 according to the present embodiment. 1 is a diagram illustrating a schematic configuration of an optical scanning device 100. FIG. It is a figure which shows the light source. 2 is a cross-sectional view of a VCSEL formed in a light source 10. FIG. It is an enlarged view (the 1) of the active layer 24 of VCSEL. It is an enlarged view (the 2) of the active layer 24 of VCSEL. FIGS. 7A and 7B are views (No. 1 and No. 2) for explaining a method of equalizing the light amount of the light beam incident on the deflection surface. FIG. 8A and FIG. 8B are diagrams for explaining the incident position of the light beam on the deflection surface. FIGS. 9A and 9B are diagrams (No. 3 and No. 4) for explaining a method of equalizing the light amount of the light beam incident on the deflection surface. It is FIG. (1) for demonstrating the effect at the time of using the line image formation lens which has refractive power in the main scanning direction. FIG. 6 is a diagram (No. 2) for explaining an effect when a line image forming lens having a refractive power in the main scanning direction is used. It is a figure which shows the modification of the aperture member. 1 is a diagram illustrating a schematic configuration of a multicolor image forming apparatus 300. FIG. It is a perspective view which shows schematic structure of an optical scanning device. It is a side view which shows schematic structure of an optical scanning device.

  Hereinafter, an embodiment of the present invention will be described with reference to FIGS. FIG. 1 shows a schematic configuration of an image forming apparatus 200 according to the present embodiment.

  The image forming apparatus 200 is a printer that prints an image by transferring a toner image onto plain paper (paper) using a Carlson process. As shown in FIG. 1, the image forming apparatus 200 includes an optical scanning device 100, a photosensitive drum 201, a charging charger 202, a toner cartridge 204, a cleaning case 205, a paper feed tray 206, a paper feed roller 207, a registration roller pair. 208, a transfer charger 211, a fixing roller 209, a paper discharge roller 212, a paper discharge tray 210, and a housing 215 for housing them.

  The housing 215 has a substantially rectangular parallelepiped shape, and openings that communicate with the internal space are formed on the side walls on the + X side and the −X side.

  The optical scanning device 100 is disposed above the inside of the housing 215, and deflects the light beam modulated based on the image information in the main scanning direction (Y-axis direction in FIG. 1), thereby causing the surface of the photosensitive drum 201 to be deflected. Scan. The configuration of the optical scanning device 100 will be described later.

  The surface of the photosensitive drum 201 is a cylindrical member having a photosensitive layer having a property that becomes conductive when irradiated with a light beam. It is arranged with the axial direction as the longitudinal direction, and is rotated clockwise (in the direction indicated by the arrow in FIG. 1) in FIG. 1 by a rotation mechanism (not shown). In the vicinity thereof, the charging charger 202 is disposed at the 12 o'clock (upper) position in FIG. 1, the toner cartridge 204 is disposed at the 2 o'clock position, and the transfer charger 211 is disposed at the 6 o'clock position. A cleaning case 205 is disposed at the hour position.

  The charging charger 202 is disposed with a predetermined clearance with respect to the surface of the photosensitive drum 201, and charges the surface of the photosensitive drum 201 with a predetermined voltage.

  The toner cartridge 204 includes a cartridge main body filled with toner, a developing roller charged with a voltage having a polarity opposite to that of the photosensitive drum 201, and the toner charged in the cartridge main body passes through the developing roller. The drum 201 is supplied to the surface.

  The cleaning case 205 includes a rectangular cleaning blade whose longitudinal direction is the Y-axis direction, and is disposed so that one end of the cleaning blade is in contact with the surface of the photosensitive drum 201. The toner adsorbed on the surface of the photosensitive drum 201 is peeled off by the cleaning blade as the photosensitive drum 201 rotates, and is collected in the cleaning case 205.

  The transfer charger 211 is disposed with a predetermined clearance with respect to the surface of the photosensitive drum 201, and a voltage having a polarity opposite to that of the charging charger 202 is applied.

  The paper feed tray 206 is disposed in a state where the + X side end protrudes from an opening formed in the side wall on the + X side of the housing 215 and can accommodate a plurality of sheets 213 supplied from the outside. .

  The sheet feeding roller 207 takes out the sheets 213 one by one from the sheet feeding tray 206, and a gap formed between the photosensitive drum 201 and the transfer charger 211 via a registration roller pair 208 including a pair of rotating rollers. To derive.

  The fixing roller 209 is composed of a pair of rotating rollers, overheats and pressurizes the paper 61, and guides it to the paper discharge roller 212.

  The paper discharge roller 212 is composed of a pair of rotating rollers and the like, and with respect to the paper discharge tray 210 disposed with the −X side end protruding from the opening formed in the −X side side wall of the housing 215, The sheets 213 sent from the fixing roller 209 are sequentially stacked.

  Next, the configuration of the optical scanning device 100 will be described. FIG. 2 is a diagram showing a schematic configuration of the optical scanning device 100. As shown in FIG. 2, the optical scanning device 100 includes a light source 10, a coupling lens 11, an aperture member 12, a line image forming lens 13, and a reflection mirror 14 that are sequentially arranged from the light source 10 in the −Y direction. , A polygon mirror 15 disposed on the −X side of the reflection mirror 14, and a first scanning lens 16 and a second scanning lens 17 sequentially disposed on the + X side of the reflection mirror 14.

The light source 10 is a surface-emitting type semiconductor laser array in which, for example, VCSELs are two-dimensionally arranged as light emitting sources. As shown in FIG. 3, 40 VCSELs are formed on the light emitting surface (the surface on the −X side). They are arranged in a matrix of 8 rows and 5 columns with the direction parallel to the straight line L forming the angle θ with the Y axis as the row direction and the direction parallel to the Z axis as the column direction. Each VCSEL has a near-field pattern diameter of 4 μm, and a light beam having a wavelength of 780 nm is emitted with a divergence angle of 7 ± 1 degrees in the main scanning direction and the sub-scanning direction. In this embodiment, the row interval Dz is 24.0 μm, the column interval Dy is 23.9 μm, and the interval dz between adjacent VCSELs in the Z-axis direction (sub-scanning direction) of each VCSEL is 4.8 μm. (= Dz / 5). In the following description, as shown in FIG. 3, the VCSEL located in the mth row and the nth column is expressed as VCSEL _mn for convenience.

FIG. 4 is a schematic view showing a cross-sectional structure of the VCSEL, and FIG. 5 is an enlarged view around the active layer in FIG. Each VCSEL is a 780 nm band VCSEL, and as can be understood from FIG. 4 and FIG. 5 together, a quantum consisting of Al _0.12 Ga _0.88 As is formed on the n-GaAs substrate 21 on which the n-side electrode 20 is formed. The active layer 24 includes a well layer 24a and a barrier layer 24b made of Al _0.3 Ga _0.7 As, and includes an active layer 24 and spacer layers 23 and 25 made of Al _0.6 Ga _0.4 As. The resonator region of the wavelength optical thickness is divided into 40.5 pairs of n-Al _0.3 Ga _0.7 As high refractive index layers with an optical thickness of each layer λ / 4, and n-Al _0.9 Ga _{0. From the} lower reflecting mirror 22 composed of a low refractive index layer of ₁ As, 24 pairs of p-Al _0.3 Ga _0.7 As high refractive index layer and p-Al _0.9 Ga _0.1 As low refractive index layer The upper reflecting mirror 27 is sandwiched. An AlAs selectively oxidized layer 30 surrounded by the AlxOy current confinement layer 26 is provided on the upper reflecting mirror 27 that is λ / 4 away from the resonator region. Between each layer of the reflecting mirrors 22 and 27, there is included a composition gradient layer (not shown) whose composition gradually changes in order to reduce the resistance value.

  Here, a method for forming a VCSEL provided in the light source 10 will be described. First, each of the above layers is formed by a crystal growth method using a metal organic chemical vapor deposition method (MOCVD method) or a molecular beam crystal growth method (MBE method).

  Next, a mesa shape is formed by forming a groove having a depth of, for example, 4.5 μm around the region to be an element region by dry etching. In general, the etching bottom surface is provided at least beyond the AlAs selective oxidation layer 30.

Next, the AlAs selectively oxidized layer 30 whose side surface is exposed by the groove forming process by etching is heat-treated in water vapor to oxidize the periphery to an Al _x O _y insulator layer, and the element driving current path is formed at the center. A current confinement structure is formed that limits only to the unoxidized AlAs region.

Next, a SiO ₂ protective layer (not shown) having a thickness of 150 nm, for example, is provided except for the region where the upper electrode 31 is formed on each element region and the light emitting portion 32, and the etched portion is embedded with polyimide 29. Flatten.

Next, the polyimide and SiO ₂ protective layer (not shown) on the upper reflecting mirror having the p contact layer 28 and the light emitting portion in each element region are removed, and the upper electrode other than the light emitting portion 32 on the p contact layer 28 is removed. 31 is formed, and an n-side electrode is formed on the lower surface of the n-GaAs substrate 21.

  In the case of this embodiment, the mesa portion formed by the dry etching method becomes each surface emitting laser element. The method of forming the arrangement of the light source of the light source 10 can be formed by forming a photomask along the arrangement of the light source of the present invention, forming an etching mask by a normal photolithography process, and etching. For electrical and spatial separation of each element of the array, it is preferable to provide a groove of about 4 to 5 μm or more between the elements. This is because if it is too narrow, it becomes difficult to control etching. In addition to the circular shape as in the present embodiment, the mesa portion can have an arbitrary shape such as an elliptical shape, a square shape, or a rectangular shape. Further, the size (diameter or the like) is preferably about 10 μm or more. This is because if it is too small, heat will be accumulated during device operation and the characteristics will deteriorate.

Note that the above-described surface-emitting laser in the 780 nm band can be manufactured using another material. FIG. 6 shows an enlarged view around the active layer made of another material. As shown in FIG. 6, the active layer has a compressive strain composition and Ga _0.6 In ₀ having a tensile strain of four layers lattice-matched with the three layers of GaInPAs quantum well active layer 24c having a band gap wavelength of 780 nm. _.4 P barrier layer 24d and clad layers 23 and 25 for confining electrons (spacer layer in this embodiment) having a wide band gap (Al _0.7 Ga _0.3 ) _0.5 In _{0 .5} P is used. The band gap difference between the cladding layer and the quantum well active layer can be made extremely large as compared with the case where the carrier confinement cladding layer is formed of AlGaAs.

  Table 1 below shows an AlGaAs (spacer layer) / AlGaAs (quantum well active layer) system 780 nm, 850 nm surface emitting semiconductor laser, and an AlGaInP (spacer layer) / GaInPAs (quantum well active layer) system 780 nm surface emitting semiconductor. The band gap difference between the spacer layer and the well layer and the barrier layer and the well layer at the typical material composition of the laser is shown. Note that the spacer layer is a layer between the active layer and the reflecting mirror in the case of a normal configuration, and indicates a layer having a function as a cladding layer for confining carriers.

  As shown in the following Table 1, according to the AlGaInP (spacer layer) / GaInPAs (quantum well active layer) system 780 nm surface emitting semiconductor laser, not only the AlGaAs / AlGaAs system 780 nm surface emitting semiconductor laser but also the AlGaAs / AlGaAs system It can be seen that the band gap difference can be made larger than that of the 850 nm surface emitting semiconductor laser. Specifically, the band gap difference between the cladding layer and the active layer is 767 meV, which is very large, compared to 466 meV (when the Al composition is 0.6) when the cladding layer is formed of AlGaAs. Similarly, the band gap difference between the barrier layer and the active layer also has a dominant difference, resulting in good carrier confinement.

  In addition, since the active layer has compressive strain, the increase in gain is increased by band separation of heavy holes and light holes. Because of these high gains, the output was high at a low threshold. Note that this effect cannot be obtained with a surface-emitting laser having a wavelength of 780 nm or 850 nm manufactured using an AlGaAs system having substantially the same lattice constant as the GaAs substrate. Furthermore, by lowering the threshold by improving carrier confinement and increasing the gain by the strained quantum well active layer, it is possible to reduce the reflectivity of the light extraction side DBR and further increase the output.

  In addition, the active layer and the barrier layer are made of a material that does not contain Al, and are formed as an Al-free active region (a quantum well active layer and a layer adjacent thereto). Formation of a non-radiative recombination center can be suppressed, and a long life can be achieved. Thereby, the writing unit or the light source unit can be reused.

  Returning to FIG. 2, the coupling lens 11 is a lens having a focal length of 47.7 mm, and shapes the light beam from the light source 10 into substantially parallel light.

  The aperture member 12 has a rectangular or elliptical opening having a size in the Y-axis direction (main scanning direction) of 5.44 mm and a size in the Z-axis direction (sub-scanning direction) of 2.10 mm. The center of the aperture is arranged so as to be located at or near the focal position of the coupling lens 11.

  The line image forming lens 13 is a cylindrical lens having a focal length of 107.0 mm and having a refractive power in the Z-axis direction (sub-scanning direction). The light beam that has passed through the aperture member 12 passes through the reflection mirror 14. Thus, an image is formed in the vicinity of the reflection surface of the polygon mirror 15 in the sub-scanning direction.

  The polygon mirror 15 is a regular polygonal columnar member whose upper surface is a regular dodecagon inscribed in a circle having a radius of 7 mm. Deflection surfaces for deflecting the incident light beam are formed on the 12 side surfaces of the polygon mirror 15, and are rotated at a constant angular velocity around an axis parallel to the Z axis by a rotation mechanism (not shown). Thereby, the light beam incident on the polygon mirror 15 is scanned in the Y-axis direction.

  The first scanning lens 16 and the second scanning lens 17 are scanning lenses made of, for example, resin having thicknesses at the centers (on the optical axis) of 13.5 mm and 3.5 mm, respectively.

  In the optical scanning device 100 described above, the sub-scanning lateral magnification of the optical scanning device 100 as a whole is 2.18 times, and the sub-scanning lateral magnification of the optical system (scanning optical system) after the polygon mirror 15 is 0.97 times. ing. Further, the focal length in the main scanning direction of the scanning optical system is 237.8 mm, the focal length in the sub-scanning direction is 71.4 mm, and the width of the writing area of the photosensitive drum 201 is the point O shown in FIG. Is in the range of ± 105.0 mm in the main scanning direction (Y-axis direction). Note that point O is a point where a straight line passing through the rotation center of the polygon mirror 15 and parallel to the X axis in FIG. 2 intersects the surface to be scanned of the photosensitive drum 201. The aim of the spot diameter of the light beam on the surface of the photosensitive drum 201 is 52 μm in the main scanning direction and 55 μm in the sub scanning direction. As shown in FIG. 2, the optical distances d1, d2, d3, d4, d5, d6, d7, d8 between the light source 10 and each optical element, and the dimensions D1, D2 of each element in the optical axis direction. , D3, and D4 are as shown in Tables 2 and 3 as an example.

  Next, the operation of the image forming apparatus 200 configured as described above will be described. When image information is received from the host device, the optical scanning device 100 is driven by the modulation data based on the image information, and 50 light beams modulated based on the image information are emitted from the light source 10. After these light beams are coupled by the coupling lens 11, the spot diameters are adjusted by passing through the aperture member 12. Each light beam that has passed through the aperture member 12 is condensed on the deflection surface of the polygon mirror 15 by the line image forming lens 13 via the reflection mirror 14.

FIG. 7A is located at the center of the first row of the VCSELs formed on the light source 10 assuming a plane parallel to the deflection surface of the polygon mirror 15 (hereinafter simply referred to as the incident surface). a VCSEL _13, emitted from each _VCSEL 11, VCSEL ₁₅ is located in the main scanning direction both ends of the row faces a diagram showing the intensity of the light beam incident on the incident surface. Note that the horizontal axis in FIG. 7A is the position coordinate in the main scanning direction on the incident surface, and the vertical axis is the intensity of the light beam. Y2 is a position coordinate in the center of the deflection surface of the polygon mirror 15 in the main scanning direction, and y1 and y3 are position coordinates of both ends of the deflection surface in the main scanning direction. For convenience, the light beams from VCSEL ₁₁ , VCSEL ₁₃ , and VCSEL ₁₅ are expressed as light beams LB ₁₁ , LB ₁₃ , and LB ₁₅ , respectively.

When the light beams LB ₁₁ , LB ₁₃ , and LB ₁₅ having the same intensity are scanned near the center point O of the writing area of the photosensitive drum 201, the light beams LB ₁₁ , LB ₁₃ , and LB ₁₅ are substantially on the ZY plane. Since the light beams are deflected to the parallel deflection surfaces, the intensity distributions on the incident surfaces of the light beams LB ₁₁ , LB ₁₃ , and LB ₁₅ are indicated by curves L 1, L 2, and L 3 shown in FIG. Of the three light beams LB ₁₁ , LB ₁₃ , and LB ₁₅ , only two of the two light beams LB ₁₁ and LB ₁₅ are incident on the deflection surface, and therefore the amount of light after being reflected on the deflection surface is a curve. Proportional to the area of areas A1 and A3 (areas colored in FIG. 7A) defined by L1 or L3, a straight line passing through position y1 or position y2 and orthogonal to the Y axis, and the Y axis It becomes the light quantity. On the other hand, since all of the light beam LB ₁₃ is incident on the deflection surface, the amount of light after being reflected by the deflection surface becomes a light amount proportional to the area of the area A2 defined by the curve L2 and the Y axis. . That is, the light quantity ratio of each of the light beams LB ₁₁ , LB ₁₃ , and LB ₁₅ reflected by the deflection surface is equal to the area ratio of the regions A1, A2, and A3, and the light beam incident on the center of the deflection surface increases. The light beam incident near the edges at both ends of the main scanning direction becomes smaller.

Therefore, in the optical scanning device 100 according to the present embodiment, when the vicinity of the center point O of the writing area of the photosensitive drum 201 is scanned, the intensity of the two light beams LB ₁₁ and LB ₁₅ is higher than the intensity of the light beam LB _13. The VCSEL ₁₁ , the VCSEL ₁₃ , and the VCSEL ₁₅ are driven so as to become stronger. For example, as shown in FIG. 7B, the areas of the regions A1 and A3 and the region A2 are almost equal so that the peak values of the two curves L1 and L3 are larger than the peak values of the curve L2. The VCSEL ₁₁ , the VCSEL ₁₃ , and the VCSEL ₁₅ are driven so as to be equal. As a result, the light amounts of the three light beams LB ₁₁ , LB ₁₃ , and LB ₁₅ reflected by the deflection surface are equalized.

Similarly, the VCSEL ₁₂ and the VCSEL ₁₄ arranged in the first row of the light source 10 are also controlled so that the intensity of the emitted light beam is higher than the intensity of the light beam LB ₁₃ and reflected by the deflection surface. The light amount of each of the light beams is made equal to the light amount of the light beam LB ₁₃ reflected by the deflecting surface, and the VCSEL ₂₁ to VCSEL ₈₅ from the second row to the eighth row are also the first row VCSEL. Similarly, the intensity of the light beam emitted from the VCSEL arranged at both ends in the main scanning direction is larger than the intensity of the light beam emitted from the VCSEL _m3 arranged at the center in the main scanning direction. Control the VCSEL. Thereby, the light quantity of each light beam emitted from each VCSEL of the light source 10 and deflected by the deflecting surface of the polygon mirror 15 becomes substantially equal.

  As described above, the movement speed of the light beam spot in the main scanning direction of each light beam deflected by the deflecting surface of the rotating polygon mirror 15 is adjusted by the first scanning lens 16 and the second scanning lens 17. In this state, the light is condensed on the surface of the photosensitive drum 201.

  On the other hand, the surface of the photosensitive drum 201 is charged with a predetermined voltage by the charging charger 202, so that charges are distributed with a constant charge density. Then, when the photosensitive drum 201 is scanned by the light beam deflected by the polygon mirror 15, carriers (charges) are generated in the photosensitive layer where the light beam is incident. descend. Therefore, when the photosensitive drum 201 rotating in the direction of the arrow in FIG. 1 is scanned with a light beam modulated based on image information, an electrostatic latent image defined by the distribution of charges is formed on the surface. It is formed.

  When an electrostatic latent image is formed on the surface of the photosensitive drum 201, toner is supplied to the surface of the photosensitive drum 201 by the developing roller of the toner cartridge 203. At this time, since the developing roller of the toner cartridge 203 is charged with a voltage having a polarity opposite to that of the photosensitive drum 201, the toner attached to the developing roller is charged with the same polarity as that of the photosensitive drum 201. Accordingly, toner does not adhere to the portion of the surface of the photoconductive drum 201 where the electric charges are distributed, and the toner adheres only to the scanned portion, so that an electrostatic latent image is formed on the surface of the photoconductive drum 201. A visualized toner image is formed. The toner image is attached to the sheet 213 by the transfer charger and then fixed by the fixing roller 209, thereby forming an image on the sheet 213. The paper 213 on which the image is formed in this manner is discharged by the paper discharge roller 212 and sequentially stacked on the paper discharge tray 210.

  As described above, in the optical scanning device 100 according to the present embodiment, the light amount of each light beam deflected to the deflection surface is substantially uniform. Of light beam. Therefore, it is possible to scan the entire writing area without unevenness.

  As an example, as shown in FIG. 3, the 40 VCSELs formed in the light source 10 have a distance (= 148.0 μm) between the VCSELs farthest apart in the sub-scanning direction (Z-axis direction). It is two-dimensionally arranged on a plane parallel to the ZY plane so as to be larger than the distance (= 95.6 μm) between the most distant VCSELs in the (Y-axis direction). Therefore, it is possible to avoid the light quantity distribution of the plurality of light beams deflected to the deflection surface of the polygon mirror 15 from being uneven, and it is possible to scan the surface to be scanned with high accuracy.

  In the optical scanning device 100 according to the above-described embodiment, when scanning the writing region on the −Y side from the central portion of the writing region of the photosensitive drum 201 (near the center point O), for example, FIG. As shown in FIG. 2, the incident position of the light beam on the deflection surface moves in the + Y direction. For this reason, the light quantity of the light beam not incident on the deflection surface increases as the light quantity of the light beam on the + Y side increases. In this case, the intensity of the light beam incident near the + Y side edge of the deflecting surface is made larger than the light beam L2 as shown in FIG. 9A, for example, as the light beam L3 shown in FIG. The VCSEL of the light source 10 may be driven so that the area of the region A2 is substantially equal. This makes it possible to scan the writing area on the −Y side from the center of the writing area with a light beam having a uniform amount of light.

  Further, when scanning the writing region on the + Y side from the central portion of the writing region (near the center point O), for example, as shown in FIG. 8B, the incident position of the light beam on the deflection surface is −Y. Move in the direction. For this reason, the light quantity of the light beam not incident on the deflection surface increases as the light quantity of the light beam on the −Y side increases. In this case, the intensity of the light beam incident near the −Y side edge of the deflection surface is made larger than the light beam L2 as shown in FIG. The VCSEL of the light source 10 may be driven so that the area of A1 and the area A2 is substantially equal. This makes it possible to scan the writing area on the −Y side from the center of the writing area with a light beam having a uniform amount of light.

  Alternatively, an anamorphic lens having refractive power in the main scanning direction may be used as the line image forming lens 13 so that the spots of the light beams overlap on the deflection surface of the polygon mirror 15. As an example, if the line image forming lens 13 of the optical system shown in FIG. 3 is an anamorphic lens having a focal length of 107.0 mm in the sub-scanning direction and a focal length of 54 mm in the main scanning direction, for example, FIG. As shown in FIG. 4, the light beam from the light source 10 is condensed near a certain point in the deflection surface formed on the polygon mirror 15. In this case, the curves indicating the intensity distributions of the respective light beams almost overlap as shown in FIG. 11 as an example. Therefore, by emitting a plurality of light beams with uniform intensity from the light source 10, the photosensitive drum The writing area 201 can be scanned with a light beam having a uniform amount of light.

  In the present embodiment, the aperture member 12 has a rectangular or elliptical shape with a size in the Y-axis direction (main scanning direction) of 5.44 mm and a size in the Z-axis direction (sub-scanning direction) of 2.10 mm. Although the case of having an opening has been described, the present invention is not limited to this, and the aperture member 12 is disposed at a position slightly shifted in the X-axis direction from the focal position of the coupling lens 11 and the shape of the opening is, for example, FIG. As shown in the figure, the size in the sub-scanning direction may increase from the center in the main scanning direction toward both ends. As a result, the light amount of the light beam incident near the edges of both ends of the polygon mirror 15 in the main scanning direction can be made larger than the light amount of the light beam incident on the center of the deflecting surface in the main scanning direction. It becomes possible to make the light quantity of the light beam reflected on the surface uniform.

  In addition, since the image forming apparatus 200 according to the present embodiment includes the optical scanning device 100, a final image is generated based on a latent image formed on the photosensitive drum 201 by a light beam having a uniform light amount. It is formed. Accordingly, it is possible to form an image on the paper with high accuracy.

  In the above embodiment, the case where the optical scanning device 100 is used in the single-color image forming apparatus 200 has been described. However, the image forming apparatus corresponds to a color image and is a tandem color machine including a plurality of photosensitive drums. Also good.

  Hereinafter, a multicolor image forming apparatus 300 corresponding to a color image and including a plurality of photosensitive drums will be described with reference to FIGS. The multicolor image forming apparatus 300 shown in FIG. 13 includes a photosensitive drum K1 for black (K), a charger K2, a developing device K4, a cleaning unit K5, a transfer charging unit K6, and cyan (C). Photosensitive drum C1, charging device C2, developing device C4, cleaning device C5, transfer charging device C6, magenta (M) photosensitive drum M1, charging device M2, developing device M4, cleaning device M5, and transfer Charging unit M6, yellow (Y) photosensitive drum Y1, charger Y2, developing unit Y4, cleaning unit Y5, transfer charging unit Y6, optical scanning device 900, transfer belt 901, fixing unit 902 etc. are provided.

  Each photosensitive drum rotates in the direction of the arrow in FIG. 13, and a charging device, a developing device, a transfer charging device, and a cleaning device are arranged in the order of rotation. Each charger uniformly charges the surface of the corresponding photosensitive drum. The surface of the photosensitive drum charged by the charger is irradiated with a beam by the optical scanning device 900, and an electrostatic latent image is formed on the photosensitive drum. Then, a toner image is formed on the surface of the photosensitive drum by the corresponding developing device. Further, the toner images of the respective colors are transferred onto the recording paper by the corresponding transfer charging means, and finally the image is fixed on the recording paper by the fixing means 902.

  Next, the optical scanning device 900 will be described with reference to FIGS.

  The optical scanning device 900 includes four light source units 10K, 10C, 10M, and 10Y, and the coupling lens 11 and the aperture member 12 in the same manner as the optical scanning device 100 described above. An optical system (not shown) that guides the light beams from 10C, 10M, and 10Y to the polygon mirror 230, the polygon mirror 230, the four first scanning lenses 218a, 218b, 218c, and 218d, and the eight folding mirrors 224a, 224b, 224c, 224d, 227a, 227b, 227c, 227d, four second scanning lenses 220a, 220b, 220c, 220d, and the like. 14 and 15, only a part of the optical scanning device 900 is shown for convenience.

  The four light source units 10K, 10C, 10M, and 10Y are all light source units configured to include the light source 10.

  The light source unit 10K emits a laser beam (hereinafter also referred to as a black beam) modulated according to black image information. The light source unit 10C emits a laser beam (hereinafter also referred to as a cyan beam) modulated according to cyan image information. The light source unit 10M emits a laser beam (hereinafter also referred to as a magenta beam) modulated according to magenta image information. The light source unit 10Y emits a laser beam (hereinafter also referred to as a yellow beam) modulated according to yellow image information.

  The first scanning lens 218a, the folding mirror 224a, the second scanning lens 220a, and the folding mirror 227a each correspond to a black beam.

  The first scanning lens 218b, the folding mirror 224b, the second scanning lens 220b, and the folding mirror 227b each correspond to a cyan beam.

  The first scanning lens 218c, the folding mirror 224c, the second scanning lens 220c, and the folding mirror 227c each correspond to a magenta beam.

  The first scanning lens 218d, the folding mirror 224d, the second scanning lens 220d, and the folding mirror 227d each correspond to a yellow beam.

  The laser beam emitted from each light source unit is converged in the sub-scanning direction so as to be linear on the deflection surface of the polygon mirror 230, and is focused on the deflection point of the polygon mirror 230 and the surface of the corresponding photosensitive drum. The point is conjugate with the sub-scanning direction.

  The polygon mirror 230 is composed of a six-sided mirror having a two-stage structure. A black beam from the light source unit 10K and a yellow beam from the light source unit 10Y are deflected in the first-stage six-sided mirror, respectively, and a cyan beam from the light source unit 10M and magenta from the light source unit 10C in the second-stage six-sided mirror. Each beam is deflected. That is, all the laser beams are deflected by the single polygon mirror 230.

  The first scanning lens 218a and the first scanning lens 218b are arranged on one side (here, + X side) of the polygon mirror 230, and the first scanning lens 218c and the first scanning lens 218d are on the other side of the polygon mirror 230 ( Here, it is arranged on the −X side). The first scanning lens 218a and the first scanning lens 218b, and the first scanning lens 218c and the first scanning lens 218d are stacked in a direction corresponding to the sub-scanning direction (here, the Z-axis direction).

  The black beam from the first scanning lens 218a forms a spot image on the photosensitive drum K1 via the folding mirror 224a, the second scanning lens 220a, and the folding mirror 227a.

  The cyan beam from the first scanning lens 218b forms a spot image on the photosensitive drum C1 via the folding mirror 224b, the second scanning lens 220b, and the folding mirror 227b.

  The magenta beam from the first scanning lens 218c forms a spot image on the photosensitive drum M1 via the folding mirror 224c, the second scanning lens 220c, and the folding mirror 227c.

  The yellow beam from the first scanning lens 218d forms a spot image on the photosensitive drum Y1 via the folding mirror 224d, the second scanning lens 220d, and the folding mirror 227d.

  The folding mirrors are arranged so that the optical path lengths from the polygon mirror 230 to the photosensitive drums coincide with each other, and the incident position and the incident angle of the laser beam on each photosensitive drum are equal to each other. Has been.

  In the multi-color image forming apparatus 300 configured as described above, a line image is formed on each of the photosensitive drums K1, C1, M1, and Y1 by a light beam whose light amount is uniformly adjusted. Therefore, it is possible to form a high-definition multicolor image with high accuracy on the recording medium.

  In each of the above embodiments, the case where the optical scanning device of the present invention is used in a printer has been described. However, the image forming device other than the printer, for example, a copier, a facsimile, or a multifunction machine in which these are integrated. Is preferred.

  DESCRIPTION OF SYMBOLS 10 ... Light source, 11 ... Coupling lens, 12 ... Aperture member, 13 ... Line image formation lens, 14 ... Reflection mirror, 15 ... Polygon mirror, 16 ... 1st scanning lens, 17 ... 2nd scanning lens, 20 ... P side Electrode, 21 ... n-GaAs substrate, 22 ... Lower reflector, 23, 25 ... Spacer layer, Lower reflector 24 ... Active layer, 26 ... AlxOy current confinement layer, 27 ... Upper reflector, 28 ... p contact layer, 29 DESCRIPTION OF SYMBOLS ... Polyimide, 30 ... AlAs selective oxidation layer, 31 ... Upper electrode, 32 ... Light emission part, 100 ... Optical scanning device, 200 ... Image forming apparatus, 201 ... Photosensitive drum, 202 ... Charger charger, 204 ... Toner cartridge, 205 ... Cleaning case, 206 ... Paper feed tray, 207 ... Paper feed roller, 208 ... Registration roller pair, 209 ... Fixing roller, 210 ... Paper discharge tray, 2 DESCRIPTION OF SYMBOLS 11 ... Transfer charger, 212 ... Discharge roller, 213 ... Paper, 215 ... Housing, 300 ... Multicolor image forming apparatus, 900 ... Optical scanning device.

JP 2003-270777 A

Claims (7)

A light source unit having a plurality of light emitting sources arranged two-dimensionally in a plane parallel to a main scanning direction and a sub scanning direction orthogonal to the main scanning direction, and a plurality of light beams respectively emitted from the plurality of light emitting sources. And a deflector that deflects and scans the writing area of the surface to be scanned from the writing start position to the writing end position in the main scanning direction, and the deflection surface of the deflector has a dimension in the main scanning direction, In an optical scanning device smaller than the light beam width in the main scanning direction of a plurality of light beams,
When scanning the vicinity of the center of the writing area, the intensity of each of the plurality of light beams is changed from the light beam at the center in the main scanning direction to the light beam at the write start position and the light beam at the write end position. An optical scanning device characterized in that it is enlarged over at least one of them. A light source unit having a plurality of light emitting sources arranged two-dimensionally in a plane parallel to a main scanning direction and a sub scanning direction orthogonal to the main scanning direction, and a plurality of light beams respectively emitted from the plurality of light emitting sources. And a deflector that deflects and scans the writing area of the surface to be scanned in the main scanning direction from the writing start position to the writing end position, and the deflection surface of the deflector has a dimension in the main scanning direction of the plurality In the light scanning device smaller than the light beam width in the main scanning direction of the light beam,
When scanning from the writing start position to the center of the writing area, the intensity of each of the plurality of light beams incident on the writing area is changed from the light beam at the center in the main scanning direction to the light beam on the writing end position side. To increase the size,
When scanning from the center of the writing area to the writing end position, the intensity of each of the plurality of light beams incident on the writing area is changed from the light beam at the center in the main scanning direction to the light beam at the writing start position side. An optical scanning device characterized in that it increases in size. A coupling lens for coupling a plurality of light beams incident on the deflector, and the plurality of light beams coupled by the coupling lens are condensed on the deflection surface of the deflector in the sub-scanning direction. An optical element,
3. The optical element according to claim 1, wherein the optical element has a positive power also in the main scanning direction and is disposed at a position closer to the deflector than a focal position of the coupling lens. The optical scanning device described. A deflector that deflects a plurality of light beams and scans the plurality of light beams in a main scanning direction, a coupling lens that couples a light beam incident on the deflector, and a coupling lens coupled to the coupling lens. An aperture member having openings through which the plurality of light beams pass, and the deflecting surface of the deflector is light whose dimension in the main scanning direction is smaller than the beam width of the plurality of light beams in the main scanning direction. In the scanning device,
The aperture member is disposed so that the opening is positioned in the vicinity of the focal position of the coupling lens, and the width of the opening in the sub-scanning direction is changed from the central part in the main scanning direction to the peripheral part in the main scanning direction. An optical scanning device characterized by being formed so as to increase in size. An optical element for condensing the plurality of light beams coupled by the coupling lens in the sub-scanning direction on a deflection surface of the deflector;
5. The optical element according to claim 4, wherein the optical element has positive power also in the main scanning direction, and is disposed at a position closer to the deflector than a focal position of the coupling lens. Optical scanning device. An image forming apparatus that forms an image by fixing a toner image formed based on a latent image obtained from information about an image to a recording medium,
An optical scanning device according to any one of claims 1 to 5,
A photoreceptor on which a latent image is formed by the optical scanning device;
Developing means for visualizing a latent image formed on the scanned surface of the photoreceptor;
An image forming apparatus comprising: a transfer unit that fixes the toner image visualized by the developing unit to the recording medium. An image forming apparatus for forming a multicolor image by superimposing and fixing a toner image formed on the basis of a latent image for each color obtained from information on a multicolor image on a recording medium,
An optical scanning device according to any one of claims 1 to 5,
A plurality of photosensitive members on which latent images corresponding to the respective colors are formed by the optical scanning device;
Developing means for visualizing latent images formed on the scanned surfaces of the plurality of photoconductors,
An image forming apparatus comprising: a transfer unit configured to superimpose and fix the toner images of the respective colors visualized by the developing unit on the recording medium.