JP6304476B2 - Optical scanning apparatus and image forming apparatus - Google Patents

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 electrophotographic image recording, an image forming apparatus using a laser is widely used. Generally, this image forming apparatus includes an optical scanning device for scanning the surface of a photosensitive drum with a laser beam and forming a latent image on the surface of the drum. The latent image is visualized with toner and transferred to a recording medium such as recording paper.

  For example, Patent Document 1 discloses an optical writing device that forms a latent image on the surface of a drum.

  Patent Documents 2 and 3 disclose optical scanning devices that define the shapes of a plurality of lenses that constitute scanning optical means.

  In recent years, with the development of information equipment, the demand for image forming apparatuses in small offices (small offices) and home offices has increased. Accordingly, further downsizing of the image forming apparatus is required. Also, the demand for image quality in the image forming apparatus is increasing year by year.

  However, in the optical scanning devices disclosed in Patent Document 2 and Patent Document 3, it has been difficult to further reduce the size without degrading the image quality.

The present invention provides an optical scanning device that scans a scanning area of a surface to be scanned with light along a main scanning direction. The scanning area includes a first area where an image is formed and the first area with respect to the main scanning direction. And the two second regions where the mark is formed, and the spot diameter of the light when scanning at least one of the two second regions scans the first region. The at least one second region is scanned , and the amount of light forming the mark in the one second region is a light that scans the first region. It is larger than the light quantity which performed the shading correction | amendment about the optical scanning apparatus characterized by the above-mentioned.

  According to the optical scanning device of the present invention, it is possible to further reduce the size without deteriorating the image quality.

1 is a diagram for describing a schematic configuration of a color printer according to an embodiment of the present invention. FIG. FIG. 2 is a diagram (part 1) for describing the optical scanning device in FIG. 1; It is FIG. (1) for demonstrating oblique incidence. It is FIG. (2) for demonstrating oblique incidence. FIG. 3 is a second diagram for explaining the optical scanning device in FIG. 1; It is a figure for demonstrating the shape of a 1st scanning lens. It is a figure for demonstrating the shape of a 2nd scanning lens. It is a figure for demonstrating D1-D4 and d1-d7. It is a figure for demonstrating the specific example of D1-D4. It is a figure for demonstrating the specific example of d1-d7. It is a figure for demonstrating image height and the scanning view angle (alpha). It is a figure for demonstrating an image formation area and a mark formation area. FIG. 13A is a diagram for explaining a scanning region in a conventional example, and FIG. 13B is a diagram for explaining a scanning region in the present embodiment. It is a figure for demonstrating the relationship between the spot diameter of a main scanning direction, and a defocus amount. It is a figure for demonstrating the relationship between the spot diameter of a subscanning direction, and a defocus amount. It is a figure for demonstrating the shape of the 1st scanning lens in a comparative example. It is a figure for demonstrating the shape of the 2nd scanning lens in a comparative example. It is a figure for demonstrating the specific value of D1-D4 in a comparative example. It is a figure for demonstrating the specific value of d1-d7 in a comparative example. It is a figure for demonstrating the relationship between the spot diameter of the main scanning direction and defocus amount in a comparative example. It is a figure for demonstrating the relationship between the spot diameter of the subscanning direction in a comparative example, and a defocus amount. It is a figure for demonstrating the influence of a sag. It is a figure for demonstrating the relationship between MTF and a spot diameter. FIG. 6 is a diagram for explaining a relationship between a toner adhesion state, a spot diameter, and a light amount. It is a figure for demonstrating the relationship between the exposure amount of the to-be-scanned surface in this embodiment, and image height.

  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), transfer A belt 2040, a transfer roller 2042, a fixing device 2050, a paper feed roller 2054, a paper discharge roller 2058, a paper feed tray 2060, a paper discharge tray 2070, a communication control device 2080, and a printer control device 209 that comprehensively controls the above-described units. And and the like.

  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 program written in a code decipherable by the CPU, a ROM storing various data used when executing the program, a RAM as a working memory, an analog signal An AD converter circuit for converting the signal into a digital signal. Then, the printer control device 2090 notifies the optical scanning device 2010 of multi-color image information from the host device received via the communication control device 2080.

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

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

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

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

  Each photosensitive drum has a photosensitive layer formed on the surface thereof. 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 is charged correspondingly with a light beam modulated for each color based on multicolor image information (black image information, cyan image information, magenta image information, yellow image information) from the printer control device 2090. The surface of the photosensitive drum is scanned. Thereby, a latent image corresponding to the image information is formed on the surface of each photosensitive drum. That is, here, the surface of each photosensitive drum is a surface to be scanned. Each photosensitive drum is an image carrier. Therefore, hereinafter, the surface of each photosensitive drum is also referred to as a “scanned surface” or an “image surface”. 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.

  By the way, in each photosensitive drum, an area scanned with light is called a “scanning area”, and an area in which image information is written in the scanning area is an “effective scanning area”, “image forming area”, “ This is called “effective image area”. In addition, the direction parallel to the rotation axis of each photosensitive drum is referred to as “main scanning direction”, and the rotation direction of the photosensitive drum is referred to as “sub-scanning direction”.

  As each developing roller rotates, toner from a corresponding toner cartridge (not shown) is thinly and uniformly applied to the surface thereof. Then, when the toner on the surface of each developing roller comes into contact with the surface of the corresponding photosensitive drum, the toner moves only to a portion irradiated with light on the surface and adheres to the surface. In other words, each developing roller causes toner to adhere to the latent image formed on the surface of the corresponding photosensitive drum so as to be visualized. Here, the toner-attached image (toner image) moves in the direction of the transfer belt 2040 as the photosensitive drum rotates.

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

  Recording paper is stored in the paper feed tray 2060. A paper feed roller 2054 is disposed in the vicinity of the paper feed tray 2060. The paper feed roller 2054 takes out the recording paper one by one from the paper feed tray 2060. The recording paper is sent out toward the gap between the transfer belt 2040 and the transfer roller 2042 at a predetermined timing. As a result, the color image on the transfer belt 2040 is transferred to the recording paper. 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.

  2 to 5 as an example, the optical scanning device 2010 includes four light sources (2200a, 2200b, 2200c, 2200d), four coupling lenses (2201a, 2201b, 2201c, 2201d), four openings. Plate (2202a, 2202b, 2202c, 2202d), four cylindrical lenses (2204a, 2204b, 2204c, 2204d), optical deflector 2104, two first scanning lenses (2105A, 2105B), and four second scanning lenses (2107a) 2107b, 2107c, 2107d), six folding mirrors (2106a, 2106b, 2106c, 2106d, 2108b, 2108c), a scanning control device (not shown), and the like.

  Here, in the XYZ three-dimensional orthogonal coordinate system, the direction parallel to the longitudinal direction (rotation axis direction) of each photosensitive drum is defined as the Y-axis direction, and the direction parallel to the rotation axis direction of the optical deflector 2104 is described as the Z-axis direction. .

  In the following, for convenience, in each optical member, a direction corresponding to the main scanning direction is abbreviated as “main scanning corresponding direction”, and a direction corresponding to the sub scanning direction is abbreviated as “sub scanning corresponding direction”.

  The light source 2200a, the coupling lens 2201a, the aperture plate 2202a, the cylindrical lens 2204a, the first scanning lens 2105A, the second scanning lens 2107a, and the folding mirror 2106a are optical members for forming a latent image on the photosensitive drum 2030a.

  The light source 2200b, the coupling lens 2201b, the aperture plate 2202b, the cylindrical lens 2204b, the first scanning lens 2105A, the second scanning lens 2107b, the folding mirror 2106b, and the folding mirror 2108b are optical for forming a latent image on the photosensitive drum 2030b. It is a member.

  The light source 2200c, the coupling lens 2201c, the aperture plate 2202c, the cylindrical lens 2204c, the first scanning lens 2105B, the second scanning lens 2107c, the folding mirror 2106c, and the folding mirror 2108c are optical for forming a latent image on the photosensitive drum 2030c. It is a member.

  The light source 2200d, the coupling lens 2201d, the aperture plate 2202d, the cylindrical lens 2204d, the first scanning lens 2105B, the second scanning lens 2107d, and the folding mirror 2106d are optical members for forming a latent image on the photosensitive drum 2030d.

  The light source 2200a and the light source 2200d are disposed at positions separated from each other in the X-axis direction (see FIG. 2). The light source 2200b is disposed on the −Z side of the light source 2200a (see FIG. 3). The light source 2200c is arranged on the −Z side of the light source 2200d (see FIG. 4).

  From each light source, a light beam modulated based on the image information is emitted toward the optical deflector 2104. The wavelength of the light emitted from each light source is the same (here, 655 nm). Each light source has a drive circuit (not shown). Each drive circuit is controlled by a scanning control device. Hereinafter, the light beam emitted from the light source 2200a is referred to as “light beam La”, and the light beam emitted from the light source 2200b is referred to as “light beam Lb”. Further, a light beam emitted from the light source 2200c is referred to as “light beam Lc”, and a light beam emitted from the light source 2200d is referred to as “light beam Ld”.

  Each coupling lens makes a light beam emitted from a corresponding light source a substantially parallel light beam. Here, the focal length of each coupling lens is 14.4 mm.

  Each aperture plate has an opening, and regulates the size of the light beam through the corresponding coupling lens. Each aperture plate is arranged so that the center of the aperture is located at or near the focal position of the corresponding coupling lens. Here, the opening has a rectangular or elliptical shape with a size in the main scanning corresponding direction of 3.3 mm and a size in the sub scanning corresponding direction of 1.56 mm.

  Each cylindrical lens is disposed on the optical path of the light beam that has passed through the opening of the corresponding aperture plate, and condenses the light beam in the Z-axis direction. The light beam that has passed through each cylindrical lens enters the optical deflector 2104.

  By the way, when the light beam is incident on the optical deflector 2104, the incident from a direction inclined with respect to the plane orthogonal to the rotation axis of the optical deflector 2104 is called “oblique incidence”, and the inclination angle is “oblique incidence”. It ’s called a “horn”. On the other hand, when light enters the optical deflector 2104, it is referred to as “horizontal incidence” when it enters from a direction parallel to a plane perpendicular to the rotation axis of the optical deflector 2104. An optical system corresponding to oblique incidence is called “oblique incidence optical system”, and an optical system corresponding to horizontal incidence is called “horizontal incidence optical system”.

  In this embodiment, as shown in FIG. 3 as an example, the light beam La is obliquely incident on the optical deflector 2104 at an inclination angle + δ, and the light beam Lb is obliquely incident on the optical deflector 2104 at an inclination angle −δ. Has been. As an example, as shown in FIG. 4, the light beam Lc is obliquely incident on the optical deflector 2104 at an inclination angle −δ, and the light beam Ld is obliquely incident on the optical deflector 2104 at an inclination angle + δ. . Here, δ = 2.3 °.

  The optical system disposed on the optical path between each light source and the optical deflector 2104 is also referred to as “pre-deflector optical system”.

  The optical deflector 2104 has a rotating polygon mirror, and each mirror surface becomes a deflection reflection surface. This rotary polygon mirror rotates at a constant speed around an axis parallel to the Z-axis direction, and deflects the light flux through each cylindrical lens at a constant angular velocity. Here, the rotating polygon mirror has five mirror surfaces, and when viewed from the Z-axis direction, the outer shape of the rotating polygon mirror is a pentagon, and the radius of a circle inscribed in the pentagon is 9 mm.

  The light beam La and the light beam Lb are deflected to the + X side of the optical deflector 2104, and the light beam Lc and the light beam Ld are deflected to the −X side of the optical deflector 2104.

  The first scanning lens 2105A is disposed on the optical path of the light beam La and the light beam Lb deflected by the optical deflector 2104. The first scanning lens 2105B is disposed on the optical path of the light beam Lc and the light beam Ld deflected by the optical deflector 2104.

  The light beam La that has passed through the first scanning lens 2105A is irradiated onto the photosensitive drum 2030a through the folding mirror 2106a and the second scanning lens 2107a.

  The light beam Lb that has passed through the first scanning lens 2105A is applied to the photosensitive drum 2030b through the folding mirror 2106b, the folding mirror 2108b, and the second scanning lens 2107b.

  Thus, the first scanning lens 2105A is shared by the two light beams, the light beam La and the light beam Lb.

  The light beam Lc that has passed through the first scanning lens 2105B is applied to the photosensitive drum 2030c through the folding mirror 2106c, the folding mirror 2108c, and the second scanning lens 2107c.

  The light beam Ld that has passed through the first scanning lens 2105B is applied to the photosensitive drum 2030d through the folding mirror 2106d and the second scanning lens 2107d.

  Thus, the first scanning lens 2105B is shared by the two light beams, the light beam Lc and the light beam Ld.

  The light spot on each photosensitive drum moves along the main scanning direction as the rotary polygon mirror rotates.

  The optical system disposed on the optical path between the optical deflector 2104 and each photosensitive drum is also called a “scanning optical system”.

  Each first scanning lens is a resin scanning lens having a thickness of 7.1 mm at the center (on the optical axis). Each second scanning lens is a resin scanning lens having a center (on the optical axis) thickness of 4.1 mm.

The shape of the cross section (main scanning cross section) orthogonal to the sub-scanning corresponding direction of each optical surface of each scanning lens is a non-arc shape expressed by the following equation (1). Here, x is a so-called depth in a direction orthogonal to both the main scanning corresponding direction and the sub-scanning corresponding 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 coefficients. Furthermore, Cm = 1 / Ry, where Ry is the paraxial radius of curvature.

  Further, the shape of the cross section (sub-scanning cross section) orthogonal to the main scanning corresponding direction of each optical surface of each scanning lens 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 coefficients.

  Specific examples of the surface shape on the incident side and the surface shape on the exit side of each first scanning lens are shown in FIG. Further, FIG. 7 shows specific examples of the surface shape on the incident side and the surface shape on the exit side of each second scanning lens.

  In the present embodiment, the lateral magnification of the scanning optical system in the sub-scanning corresponding direction is −1.61 times. Further, the focal length in the main scanning corresponding direction of the scanning optical system is 198.9 mm, and the focal length in the sub scanning corresponding direction is 55.05 mm. The aim of the spot diameter of the light spot in the image forming area of each photosensitive drum is 60 μm in the main scanning direction and 80 μm in the sub scanning direction.

  Also, the size of the main optical member in the optical axis direction (D1, D2, D3, D4) and the optical distance between the main optical members (d1, d2, d3, d4, d5, d6, d7) (FIG. 8) is shown in FIG. 9 and FIG. That is, the optical path length from the center of the rotary polygon mirror to the image plane is 240 mm. In FIG. 8, the optical path is set to be parallel to the paper surface for easy understanding.

  The position in the main scanning direction in the scanning area on the surface to be scanned is called the image height. In the following, with respect to the main scanning direction, the center position of the scanning region is also referred to as “center image height”, and both ends of the scanning region are also referred to as “peripheral image height”. In general, the image height is expressed by coordinates where the central image height is 0 mm. In the present embodiment, the length of the scanning region in the main scanning direction is 327 mm, the central image height is 0 mm, the peripheral image height on one side is +163.5 mm, and the peripheral image height on the other side is −163.5 mm ( (See FIG. 11). Further, the half field angle which is ½ times the scanning field angle α (see FIG. 11) is 47.40 °.

  Therefore, the color printer 2000 can cope with paper having a width wider than the A3 size (297 mm × 420 mm), for example, a special A3 size (328 mm × 453 mm) as the recording paper. Here, as an example, as shown in FIG. 12, an area where an image height is −148.5 mm to +148.5 mm and an A3 size image is formed in the scanning area on the surface to be scanned is formed. An area surrounding the image forming area is called a mark forming area. A cutting mark such as a registration mark is formed in the mark formation region. That is, the scanning area includes an image forming area (first area) where an image is formed, and two mark forming areas (second areas) where the image forming area is sandwiched between the image forming area in the main scanning direction. Including.

  By the way, with respect to the main scanning corresponding direction, the light beam that has passed near the end of the scanning lens has a larger spot diameter on the surface to be scanned than the light beam that has passed through the central part of the scanning lens. Therefore, conventionally, as an example, as shown in FIG. 13A, an area having a substantially uniform spot diameter is used as a scanning area. That is, the spot diameter when scanning the image forming area and the spot diameter when scanning the mark forming area are substantially the same.

  On the other hand, in this embodiment, as shown in FIG. 13B as an example, an area having a substantially uniform spot diameter is set as an image forming area, and an area having a large spot diameter is set as a mark forming area. That is, the spot diameter when scanning the mark forming area is larger than the spot diameter when scanning the image forming area.

  In the scanning lens, it is possible to reduce the difference between the spot diameter on the surface to be scanned of the light beam that has passed near the end and the spot diameter on the surface to be scanned of the light beam that has passed through the center of the scanning lens. The change in linearity becomes large, and the change in lateral magnification in the sub-scanning direction becomes large, so that it becomes difficult to ensure the scanning position accuracy.

  In order to form a high-quality image, the curvature of field is well corrected over the entire image forming area so that the spot diameters are uniform, and constant speed is maintained when optically scanning the surface of the photosensitive drum. It is important that the horizontal magnification in the sub-scanning direction is corrected uniformly over the entire image forming area and the spot diameters in the sub-scanning direction are uniform. In a multi-beam optical scanning device using a light source that emits a plurality of light beams, the lateral magnification in the sub-scanning direction is uniformly corrected over the entire image forming area, and the scanning line pitch (interval) is kept constant. It is important to.

  For the main image height Y, the relationship between the spot diameter and the defocus amount in the main scanning direction of the light spot is shown in FIG. 14, and the relationship between the spot diameter and the defocus amount in the sub-scanning direction is shown in FIG. Yes.

  As a comparative example, FIG. 16 shows the surface shape on the incident side and the surface shape on the exit side of the conventional first scanning lens. FIG. 17 shows the surface shape on the incident side and the surface shape on the exit side of the conventional second scanning lens.

  In this comparative example, the size (D1, D2, D3, D4) of the main optical member in the optical axis direction and the optical distance (d1, d2, d3, d4, d5, d6) between the main optical members. , D7) is shown in FIGS. That is, the optical path length from the center of the rotary polygon mirror to the scanned surface is 255 mm.

  In this case, the half angle of view that is 1/2 times the scanning angle of view is 43.35 °. Further, for the main image height Y, the relationship between the spot diameter and the defocus amount in the main scanning direction of the light spot is shown in FIG. 20, and the relationship between the spot diameter and the defocus amount in the sub scanning direction is shown in FIG. Has been.

  In this embodiment, since the scanning angle of view α can be made larger than that of the comparative example, the optical path length from the center of the rotary polygon mirror to the surface to be scanned can be made shorter than that of the comparative example. Specifically, the scanning field angle can be about 10% higher than that of the comparative example, and the optical path length from the center of the rotary polygon mirror to the scanned surface can be made about 6% shorter than that of the comparative example. did it. In addition, the relationship between the spot diameter and the defocus amount in the image forming area is almost the same between this embodiment and the comparative example. That is, in the present embodiment, it is possible to reduce the size without reducing the image quality.

  By the way, in this embodiment, the beam diameter is extremely large only when the image height is -163.5 mm. One of the factors is the effect of so-called sag on a rotating polygon mirror. This sag means that the incident position of the light beam incident on the deflecting / reflecting surface differs depending on the deflection direction. In FIG. 22, the optical path length between the cylindrical lens and the deflecting / reflecting surface, and the optical path length between the deflecting / reflecting surface and the first scanning lens are respectively the light flux toward the central image height and the light flux toward each peripheral image height. It is shown. Thus, since the influence of the sag is not symmetric with respect to the image height, if the spot diameter at one peripheral image height is to be reduced, the spot diameter at the other peripheral image height is increased. Therefore, in the main scanning direction, the spot diameter when scanning one of the two mark forming areas sandwiching the image forming area may be larger than the spot diameter when scanning the image forming area.

  FIG. 23 also shows the relationship between the MTF (modulation transfer function) of the pattern of 8 cycles / mm and the spot diameter. Generally, in order to reproduce a 3 pt (point) character, the MTF of a pattern of 8 cycles / mm needs to be 0.3 or more. In this embodiment, in order to reliably reproduce 3pt characters in consideration of variations, the target value of the spot diameter is set to 60 μm in the main scanning direction and 80 μm in the sub scanning direction in the image forming area. On the other hand, since a high resolution is not required in the mark formation region, the target value of the spot diameter is set to 80 μm in the main scanning direction and 100 μm in the sub-scanning direction for ease of design. Hereinafter, for convenience, a spot diameter of 60 μm in the main scanning direction and 80 μm in the sub scanning direction is also referred to as “first spot diameter”, and a spot diameter of 80 μm in the main scanning direction and 100 μm in the sub scanning direction is referred to as “second spot”. Also called “diameter”.

  By the way, as the spot diameter increases, the energy density of the light spot decreases and the amount of toner adhesion decreases, and as a result, the density of the toner image decreases. FIG. 24 shows the toner adhesion state on the formed toner image when the spot diameter is the first spot diameter and the second spot diameter. When the amount of light is the same, the toner image at the second spot diameter has a smaller toner adhesion amount and a lower density than the toner image at the first spot diameter. When the light amount is increased for the second spot diameter, the amount of toner attached to the formed toner image increases and the density increases. The toner adhesion amount in the toner image formed at the second spot diameter when the light amount is 120% is the toner adhesion amount in the toner image formed at the first spot diameter when the light amount is 100%. It becomes almost equal to the amount of adhesion.

  Therefore, in the present embodiment, the light amount when scanning the mark formation region is set to 120% of the light amount when scanning the image formation region. The exposure amount on the scanned surface at this time is shown in FIG. In this case, the reproducibility of the mark formed in the mark formation area can be improved. This light amount control is performed by the scanning control device and added to the conventional shading correction (for example, see Japanese Patent Application Laid-Open No. 2010-0669668).

  In recent years, image forming apparatuses are required to support various paper sizes. The so-called A3 printer market is also required to support a wide range of paper sizes. This means that there is an increasing need to print a cutting mark such as a registration mark using paper having a width wider than A3 size. Further, there is a demand for downsizing of the image forming apparatus, and accordingly, further downsizing of the optical scanning device is required.

  The optical scanning device 2010 of the present embodiment shortens the optical path length from the center of the rotary polygon mirror to the surface to be scanned by increasing the scanning field angle, thereby reducing the size of the optical scanning device.

  As described above, according to the optical scanning device 2010 according to the present embodiment, an image forming area provided on the surface of each photosensitive drum on which an A3 size image is formed, and surrounding the image forming area, a registration mark, etc. It is possible to optically scan the mark forming region where the cutting mark is formed.

  The spot diameter of the light spot when scanning the image forming area is set to the first spot diameter, and the spot diameter of the light spot when scanning the mark forming area is set to the second spot diameter. ing. Thereby, the scanning angle of view can be made larger than before. Therefore, the optical path length from the center of the rotary polygon mirror to the surface to be scanned becomes shorter than before, and the optical scanning device can be downsized.

  In this case, since the image forming area is scanned with a small spot diameter as in the conventional case, it is possible to ensure the same image quality as in the conventional case. In the mark formation region, the spot diameter may be large because a line pattern constituting the mark may be formed.

  Therefore, further downsizing can be achieved without degrading the image quality.

  In the above-described embodiment, the amount of light when scanning the mark formation region is larger than the amount of light when scanning the image formation region. In this case, the reproducibility of the mark formed in the mark formation area can be improved.

  In the above embodiment, the MTF in the image forming area is set to be larger than the MTF in the mark forming area. In this case, the quality of the image formed in the image forming area can be improved.

  In the above embodiment, the light from the light source is set so as to be obliquely incident on the rotary polygon mirror. In this case, it is possible to reduce the size of the rotary polygon mirror, and it is possible to achieve high-speed image formation, low cost, and further downsizing.

  In the above embodiment, the spot diameter of light when scanning the image forming area is 60 μm in the main scanning direction and 80 μm in the sub-scanning direction. In this case, the MTF in the image forming area is 0.3 or more, and three-point characters can be reliably reproduced in the image forming area. Note that the same effect can be obtained if the spot diameter of light when scanning the image forming region is 70 μm or less in the main scanning direction and 90 μm or less in the sub-scanning direction.

  Since the color printer 2000 includes the optical scanning device 2010, as a result, the size of the output image can be further reduced without degrading the image quality.

  In the above embodiment, the case where the spot diameter of the light spot when scanning the image forming region is 60 μm in the main scanning direction and 80 μm in the sub scanning direction has been described, but the present invention is not limited to this. Any spot diameter corresponding to the required image quality may be used.

  In the above-described embodiment, the case where the spot diameter of the light spot when scanning the mark formation region is 80 μm in the main scanning direction and 100 μm in the sub-scanning direction is described, but the present invention is not limited to this. In short, it is only necessary that the spot diameter of the light spot when scanning the mark forming area is larger than the spot diameter of the light spot when scanning the image forming area.

  In the above embodiment, the case where the amount of light when scanning the mark formation region is 120% of the amount of light when scanning the image formation region has been described, but the present invention is not limited to this. Note that the amount of light when scanning the mark formation region is preferably 110% or more of the amount of light when scanning the image formation region.

  In the above embodiment, the case where the light from the light source is obliquely incident on the rotating polygonal mirror has been described. However, the present invention is not limited to this, and the light from the light source may be incident on the rotating polygonal mirror horizontally. . Even in this case, the scanning angle of view can be made larger than the conventional one.

  In addition, the shape of the first scanning lens in the above embodiment is an example, and the present invention is not limited to this. Similarly, the shape of the second scanning lens in the above embodiment is an example, and the present invention is not limited to this.

  Further, in the above embodiment, the case where the recording paper is compatible with the special A3 size (328 mm × 453 mm) as the paper having a width wider than the A3 size (297 mm × 420 mm) has been described, but 12 inches × 19 inches. It is also possible to cope with paper having a size (304.8 mm × 482.6 mm), SRA3 size (320 mm × 450 mm), and so-called A3 Nobi (329 mm × 483 mm).

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

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

  Moreover, in the said embodiment, each light source may have one light emission part, and may have a some light emission part. When each light source has a plurality of light emitting portions, so-called “multi-beam scanning” is possible in which one photosensitive drum is simultaneously scanned with a plurality of light spots.

  In the above-described embodiment, the case of a tandem multi-color printer that forms a full-color image by superimposing four colors (black, cyan, magenta, and yellow) has been described as an image forming apparatus. Is not to be done. For example, a multi-color printer that further uses auxiliary colors may be used.

  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.

  2000 ... Color printer (image forming apparatus), 2010 ... Optical scanning device, 2030a to 2030d ... Photosensitive drum (image carrier), 2104 ... Optical deflector, 2105A ... First scanning lens, 2105B ... First scanning lens, 2106a ˜2106d: folding mirror, 2107a to 2107d, second scanning lens, 2108b, 2108c, folding mirror, 2200a to 2200d, light source, 2201a to 2201d, coupling lens, 2202a to 2202d, aperture plate, 2204a to 2204d, cylindrical lens.

Japanese Patent Laid-Open No. 11-237572 Japanese Patent No. 4402126 Japanese Patent No. 4388053

Claims (8)

In an optical scanning device that scans a scanning area of a surface to be scanned with light along a main scanning direction,
The scanning region includes a first region in which an image is formed, and two second regions in which the mark is formed with the first region in between with respect to the main scanning direction,
The spot diameter of light when scanning at least one of the two second regions is larger than the spot diameter of light when scanning the first region,
The at least one second region is scanned , and the amount of light that forms the mark in the one second region is greater than the amount of light that has undergone shading correction for the light that scans the first region. An optical scanning device characterized by the above.   2. The optical scanning device according to claim 1, wherein an MTF (modulation transfer function) in the first region is larger than an MTF in the at least one second region. 3. A light source that emits the light, and a rotating polygon mirror that deflects the light from the light source;
3. The optical scanning device according to claim 1, wherein light from the light source is incident obliquely on the rotary polygon mirror.   The spot diameter of light when scanning the first region is 70 μm or less with respect to the main scanning direction and 90 μm or less with respect to the sub-scanning direction orthogonal to the main scanning direction. 4. The optical scanning device according to claim 3.   The spot diameter of the light when scanning the at least one second region is 70 μm or more with respect to the main scanning direction, and is 90 μm or more with respect to the sub-scanning direction orthogonal to the main scanning direction. Item 5. The optical scanning device according to any one of Items 1 to 4.   The amount of light when scanning the at least one second region is 10% or more larger than the amount of light when scanning the first region. The optical scanning device according to one item.   The optical scanning device according to claim 1, wherein a length of the first region in the main scanning direction is equal to a length of a short side of the A3 size paper. An image carrier;
An image forming apparatus comprising: the optical scanning device according to claim 1, wherein the image carrier is scanned with a light beam modulated by image information.

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