JP2010224552A - Optical scanning device and image forming apparatus using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical scanning device by which ghost light can be removed more reliably or sufficiently reduced, and to provide an image forming apparatus using the optical scanner. <P>SOLUTION: The optical scanning device includes: an imaging optical system which deflects and scans a luminous flux emitted from a light source means on a deflecting surface of a deflecting means and images upon a surface to be scanned. In a sub scanning cross section, the luminous flux incident on the deflecting surface of the deflecting means is made incident on the deflecting surface from a diagonal direction with respect to the optical axis of the imaging optical system, a light-shielding member is disposed in an optical path between the deflecting surface and the surface to be scanned to shield the ghost light, the configuration of the light-shielding member and the shape of the light-shielding member in the sub-scanning direction are appropriately designed. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an optical scanning device and an image forming apparatus using the same, and is suitable for an image forming apparatus such as a laser beam printer, a digital copying machine, or a multi-function printer (multi-function printer) having an electrophotographic process.

  Conventionally, in a scanning optical system of a laser beam printer (LBP) or a digital copying machine, a light beam modulated and emitted from a light source means according to an image signal is periodically emitted by an optical deflector composed of a rotating polygon mirror (polygon mirror). It is deflected. The deflected light beam is focused in a spot shape on the surface of a photosensitive recording medium (photosensitive drum) by an imaging optical system having fθ characteristics, and image recording is performed by optically scanning the surface.

  In recent years, high image quality is desired in image forming apparatuses such as laser beam printers, digital copying machines, and multifunction printers. One cause of image deterioration is ghost light (reflected light) unnecessary for image formation.

  Conventionally, various optical scanning devices for removing the ghost light have been proposed (see Patent Document 1).

  In Patent Document 1, a ghost light reflected on a scanned surface is re-incident on a rotating polygon mirror (polygon mirror), and is deflected and reflected again to prevent incident on the scanned surface. The shading plate is provided.

  This light shielding plate does not shield the effective light beam (actual light beam) for forming an image, but shields only the ghost light, so that the effective light beam passes in the sub scanning direction with respect to the height in the sub scanning direction. It is located at a specific distance away.

  Moreover, the shape of the light-shielding plate disclosed in Patent Document 1 is a general linear shape (flat plate shape) or a curved shape.

  In this specification, “ghost light” is reflected by the deflecting surface of the optical deflector, is not reflected by the surface of the imaging optical system or other surfaces, passes through the imaging optical system, and is scanned. A light beam that is light other than the light beam incident thereon and that enters the effective scanning area of the surface to be scanned.

  Incidentally, when there are a plurality of optical scanning devices as shown in FIG. 1 of Example 1 of the present invention described later, the light flux in one optical scanning device is reflected by the surface of the imaging optical system or the other surface, Also included is a light beam that enters the other optical scanning device and enters the scanned surface of the other optical scanning device.

  The “effective light beam” refers to a light beam that is reflected by the deflecting surface of the deflecting unit, is not reflected by the surface of the imaging optical system, is transmitted, and enters the effective scanning area of the surface to be scanned.

JP 2000-193903 A

  In Patent Document 1, in the case of an optical system in which ghost light passes through a position closer to an effective light beam, the ghost light cannot be sufficiently shielded. The reason is described below.

  In Patent Document 1, in order to make the entire apparatus compact, a light beam incident on the deflecting surface of the deflecting means is incident in an oblique direction (obliquely incident) with respect to the normal line of the deflecting surface in the sub-scan section. . For this reason, the scanning locus of the effective light beam when passing over the flat plate-shaped light shielding plate has a curved shape.

  FIGS. 11A and 11B show the effective light beam passage area (scanning locus) (solid line) and ghost light passage area (dotted line) used for image formation on the light shielding plate when viewed from the optical axis direction of the imaging optical system. ), A graph (explanatory diagram) showing the shape of the end portion of the light shielding plate in the sub-scanning direction. FIG. 11A is an explanatory diagram when the light shielding plate 91 is disposed below (in the drawing, on the lower side) of the effective light flux passing region, and FIG. 11B is a light shielding plate 91 on the upper side (in the drawing, on the upper side) of the effective light flux. It is explanatory drawing when arrange | positioning.

  As shown in FIGS. 11A and 11B, when the ghost light passes through a position close to the effective light beam (passing region) whose scanning locus is curved (or a part of the passing region of the effective light beam), Patent Document 1 There are the following problems.

(1) With the light shielding plate 91 whose end in the sub-scanning direction is linear, no matter how the height of the light shielding plate 91 in the sub-scanning direction is changed, the effective light beam is shielded at the end in the main scanning direction. End up
(2) Ghost light cannot be shielded at the center in the main scanning direction.

  That is, in the light shielding plate 91 whose end in the sub-scanning direction is linear as in Patent Document 1, the ghost light is sufficiently shielded in the entire effective scanning area (printing area) without vignetting. There is a problem that can not be.

  The curved shape of the effective light beam when passing over the light shielding plate 91 is such that the oblique incident angle to the deflection surface in the sub-scanning section, the position of the light shielding plate 91 in the imaging optical system, and the deflection means more than the light shielding plate 91. It changes depending on the surface shape of the imaging optical element arranged on the side. However, Patent Document 1 does not mention what kind of curve the shape of the light shielding plate 91 in the sub-scan section is.

  Therefore, from Patent Document 1, it is not possible to obtain a shape of the light shielding plate that can sufficiently shield the ghost light without vignetting the effective light beam in the entire effective scanning region. That is, Patent Document 1 has a problem that when ghost light is implemented by an optical system that passes through a position closer to the effective light beam, the ghost light cannot be sufficiently shielded.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an optical scanning device capable of more reliably removing or sufficiently reducing ghost light and an image forming apparatus using the same.

The optical scanning device according to claim 1 is a light source unit, an incident optical system that guides a light beam emitted from the light source unit to a deflecting surface of the deflecting unit, and a light beam deflected and scanned by the deflecting surface of the deflecting unit. An optical scanning device having an imaging optical system that forms an image on a surface to be scanned,
In the sub-scan section, the light beam incident on the deflection surface of the deflection unit is incident on the deflection surface from an oblique direction with respect to the optical axis of the imaging optical system,
A light shielding member for shielding ghost light is disposed in an optical path between the deflection surface and the scanned surface; and
The end of the light shielding member in the sub-scanning direction is formed in a curved shape whose height in the sub-scanning direction changes according to the position in the main scanning direction, and
The curved shape includes an on-axis deflection point of a light beam incident on a deflecting surface of the deflecting unit as it goes off-axis in the main scanning direction when the intersection with the optical axis of the imaging optical system is the center. Curved in the direction in which the distance between the plane perpendicular to the rotation axis of the deflecting means and the end of the light shielding member in the sub-scanning direction is increased, and
The light-shielding member includes an upper light-shielding member having an upper end in the sub-scanning direction among end portions in the sub-scanning direction of the light-shielding member, and a lower sub-scanning among ends in the sub-scanning direction of the light-shielding member. Composed of a lower light-shielding member with an end in the direction,
The upper light shielding member and the lower light shielding member are integrally molded in an optical box that holds the optical scanning device,
The upper light-shielding member and the lower light-shielding member are arranged with their positions relative to the optical axis direction of the imaging optical system being shifted.

  According to a second aspect of the present invention, there is provided an image forming apparatus comprising: the optical scanning device according to the first aspect; a photosensitive member disposed on the surface to be scanned; and a light beam scanned by the optical scanning device. A developing device that develops the electrostatic latent image formed on the toner image as a toner image, a transfer device that transfers the developed toner image to a transfer material, and a fixing device that fixes the transferred toner image to the transfer material. It is characterized by having.

  According to the present invention, there is provided a small optical scanning apparatus capable of forming a high-definition and high-quality image capable of more reliably removing or sufficiently reducing ghost light, and an image forming apparatus using the same. Can be achieved.

Main scanning sectional view of Embodiment 1 of the present invention Sub-scan sectional view of Embodiment 1 of the present invention An enlarged view of a portion of FIG. 2B FIG. 2 is a sub-scan sectional view of the incident optical system according to the first embodiment of the present invention. Explanatory drawing of the ghost light of Example 1 of this invention Explanatory drawing which showed the passage area of the effective light beam passage area ghost light on the upper side light shielding plate of Example 1 of this invention Explanatory drawing which showed the passage area of the effective light beam passage area ghost light on the lower side light-shielding plate of Example 1 of this invention Explanatory drawing which showed the shape on the upper side light shielding plate of Example 1 of this invention Explanatory drawing which showed the shape on the upper side light shielding plate of Example 1 of this invention Explanatory drawing showing the scanning locus | trajectory of the effective light beam on the light-shielding plate of Example 1 of this invention. Main scanning sectional view of Embodiment 2 of the present invention Sub-scan sectional view of Embodiment 2 of the present invention Explanatory drawing which showed the effective light beam passage area on the light-shielding plate of Example 2 of this invention, and the passage area of ghost light Explanatory diagram showing the effective light beam passing region ghost light passing region on the conventional upper light shielding plate Explanatory drawing showing the effective light beam passage region ghost light passage region on the conventional lower light shielding plate 1 is a schematic view of a main part of an image forming apparatus according to an embodiment of the invention. 1 is a schematic view of a main part of a color image forming apparatus according to an embodiment of the present invention.

  Embodiments of the present invention will be described below with reference to the drawings.

[Example 1]
FIG. 1 is a sectional view (main scanning sectional view) of a main part in the main scanning direction of Embodiment 1 of the present invention, and FIG. FIG. 2B is an enlarged explanatory view of a part of FIG. 2A.

  In the following description, the main scanning direction (Y direction) is a direction perpendicular to the rotation axis of the deflecting unit and the optical axis (X direction) of the imaging optical system (the light beam is deflected and reflected (deflected and scanned) by the deflecting unit). Direction). The sub-scanning direction (Z direction) is a direction parallel to the rotation axis of the deflecting unit. The main scanning section is a plane including the optical axis of the imaging optical system and the main scanning direction. The sub-scan section is a section that includes the optical axis of the imaging optical system and is perpendicular to the main scan section.

  The image forming apparatus of this embodiment has a plurality of image forming optical systems 15a and 15b arranged opposite to each other with an optical deflector (polygon mirror) 5 serving as a deflecting unit interposed therebetween, and two image forming optical systems 15a and 15b are provided. The four light beams are simultaneously deflected and reflected by one optical deflector 5. Then, the four light beams are guided to the photosensitive drum surfaces 8a, 8b, 8c, and 8d as the scanning surfaces corresponding to the four light beams, and the tandem type image is scanned on the photosensitive drum surfaces 8a, 8b, 8c, and 8d. Forming device.

  In the figure, S1 and S2 are first and second optical scanning devices (hereinafter also referred to as “station” or “scanning optical system”). The image forming apparatus of this embodiment has a plurality of optical scanning devices.

  Hereinafter, each member of the first and second optical scanning devices S1 and S2 will be described focusing on the first optical scanning device S1. Of the members of the second optical scanning device S2, the same members as those of the first optical scanning device S1 are shown in parentheses.

  The first (second) optical scanning device S1 (S2) has aperture stops 2a and 2c (2b and 2d) for regulating light beams from the light source means 1a and 1c (1b and 1d), respectively. Further, collimator lenses 3a and 3c (3b and 3d) for converting the light beams restricted by the aperture stops 2a and 2c (2b and 2d) into parallel light beams are provided. The light source means 1a and 1c form one light source unit.

  Furthermore, it has a cylindrical lens 4 that forms an image as a long line image in the main scanning direction, and an optical deflector 5 as a deflecting means. Further, it has an imaging optical system 15a (15b) for forming a light beam deflected and reflected by the optical deflector 5 in spots on the photosensitive drum surfaces 8a and 8c (8b and 8d) as scanning surfaces.

  In the present embodiment, the first and second optical scanning devices S1 and S2 use a common optical deflector 5 together. The first and second optical scanning devices S1 and S2 are arranged symmetrically with respect to a plane (XZ plane) including the rotation axis of the optical deflector 5 and parallel to the sub-scanning direction, and deflected and reflected by different deflection surfaces. Is used.

  In the first and second optical scanning devices S1 and S2, the light source means 1a, 1c, 1b, and 1d are each composed of a semiconductor laser. Each of the aperture stops 2a, 2c, 2b, and 2d shapes the beam shape of the light beam that has passed therethrough. The collimator lenses 3a, 3c, 3b, and 3d convert the light beams emitted from the light source means 1a, 1c, 1b, and 1d into parallel light beams (or divergent light beams or convergent light beams). The cylindrical lens 4 has a specific refractive power only in the sub-scanning direction (within the sub-scanning section).

  The light source means 1a, 1c (1b, 1d), aperture stops 2a, 2c (2b, 2d), collimator lenses 3a, 3c (3b, 3d), and the cylindrical lens 4 are elements of the incident optical system LA (LB). It constitutes one element.

  The optical deflector 5 is composed of a rotating polygon mirror (polygon mirror) having four deflection surfaces, and is rotated at a constant speed in the direction of arrow A in the figure by a motor driving means (not shown). In the present embodiment, as described above, the first and second optical scanning devices S1 and S2 use the optical deflector 5 in combination, and the first and second optical scanning devices S1 and S2 have the optical deflection. A light beam deflected and reflected by different deflecting surfaces 5a and 5b of the vessel 5 is used.

  Reference numeral 15a (15b) denotes an imaging optical system (fθ lens system) having a condensing function and an fθ characteristic, and the first and second connections having positive refractive power (power) in the main scanning and sub-scanning sections. It consists of image lenses (optical elements) 6a, 7a (6b, 7b). The imaging optical system 15a (15b) images the two light beams deflected and reflected by the optical deflector 5 onto the corresponding scanned surfaces 8a and 8c (8b and 8d) in a spot shape. The imaging optical system 15a (15b) has a conjugate relationship between the deflecting surface 5a (5b) of the optical deflector 5 and the scanned surfaces (on the scanned surface) 8a, 8c (8b, 8d) in the sub-scan section. By doing so, compensation for face down is performed.

  The first imaging lens 6a (6b) in this embodiment is disposed in the optical path between the optical deflector 5 and a light shielding plate (upper and lower light shielding plates) described later, and is only in the main scanning direction. It has a refractive power (power), and the refractive power in the sub-scanning direction is 0 (non-power).

  Here, the refractive power being 0 may be substantially 0, and may be 1/50 or less of the refractive power in the main scanning direction of the imaging optical system 15a (15b).

  10aU (10bU) is a light-shielding plate as a light-shielding member, and sandwiches a normal line including the deflection point of the deflection surface 5a in the sub-scanning direction above the effective light beam passing through the imaging optical system, that is, in the sub-scanning section. It is provided on the side opposite to the photosensitive drum. The light shielding plate 10aU (10bU) is arranged at a position away from the axial deflection point O by a distance LU [mm] so as to be perpendicular to the main scanning section and parallel to the main scanning direction, and the imaging optical system 15a ( The ghost light generated in 15b) is shielded. Hereinafter, the light shielding plate 10aU (10bU) is also referred to as an upper light shielding plate (upper light shielding plate).

  10aL (10bL) is a light shielding plate as a light shielding member, and sandwiches a normal line including the deflection point of the deflection surface 5a in the lower side of the effective light beam passing through the imaging optical system, that is, in the sub scanning section. And provided on the photosensitive drum side. The light shielding plate 10aL (10bL) is disposed at a position away from the on-axis deflection point O by a distance LL [mm] so as to be perpendicular to the main scanning section and parallel to the main scanning direction. The ghost light generated in 15b) is shielded. Hereinafter, the light shielding plate 10aL (10bL) is also referred to as a lower light shielding plate (lower light shielding plate).

  The upper and lower light shielding plates 10aU, 10aL (10bU, 10bL) are effective light beams deflected and reflected from the optical deflector 5 over the entire effective scanning area on the scanned surfaces 8a, 8c (8b, 8d), respectively. It is made of a shape that does not block light.

  In the present embodiment, the end portions in the sub-scanning direction of the upper and lower light shielding plates 10aU and 10aL (10bU and 10bL) have curved shapes in which the height in the sub-scanning direction changes according to the position in the main scanning direction. It is formed with. Here, the intersection with the optical axis of the imaging optical system 15a (15b) is the center with respect to the main scanning direction. At this time, the curved shape is as follows from the center to the periphery (as it goes off-axis). A plane (XY plane) perpendicular to the rotation axis of the optical deflector 5 including the on-axis deflection point O, and end portions in the sub-scanning direction of the light shielding plates (upper and lower light shielding plates 10aU, 10aL (10bU, 10bL)). Is curved in the direction in which the interval between

  The upper and lower light shielding plates 10aU, 10aL (10bU, 10bL) each have a planar shape (linear shape) in the main scanning direction.

  Reference numerals 20a, 21a, and 22a (20b, 21b, and 22b) are reflection mirrors as light beam separation means, and corresponding photosensitive drum surfaces 8a and 8c (8b and 8d) are light beams that have passed through the imaging optical system 15a (15b). Folded to the side.

  In the present embodiment, first, in the first optical scanning device S1, two light beams emitted after being light-modulated from the light source means 1a and 1c in accordance with image information pass through the aperture stops 2a and 2c (partially shielded from light). ) Then, the two light beams that have passed through the aperture stops 2 a and 2 c are converted into parallel light beams by the collimator lenses 3 a and 3 c and are incident on the cylindrical lens 4. Out of the light beam incident on the cylindrical lens 4, the light beam is emitted as it is in the main scanning section. In the sub-scanning section, the light beams converge and enter (obliquely incident) at different angles with respect to the deflecting surface 5a of the optical deflector 5 to form a line image (a line image that is long in the main scanning direction).

  The two light beams deflected and reflected by the deflecting surface 5a of the optical deflector 5 are spot-formed on the photosensitive drum surfaces 8a and 8c via the corresponding reflecting mirrors 20a, 21a and 22a by the imaging optical system 15a. Is done. Then, by rotating the optical deflector 5 in the direction of arrow A, optical scanning is performed on the photosensitive drum surfaces 8a and 8c in the direction of arrow B (main scanning direction) at a constant speed. Thus, image recording is performed on the photosensitive drum surfaces 8a and 8c which are recording media.

  In the second optical scanning device S2, the two light beams emitted from the light source means 1b and 1d are at different angles with respect to the deflecting surface 5b of the optical deflector 5 from the same direction as the incident direction of the first optical scanning device S1. Is incident (oblique incidence). The two light beams deflected and reflected by the deflecting surface 5b are imaged in spots on the photosensitive drum surfaces 8b and 8d via the corresponding reflecting mirrors 20b, 21b and 22b by the imaging optical system 15b, and optically scanned. The

  As described above, in this embodiment, one scanning line is formed on each of the four photosensitive drum surfaces 8a, 8b, 8c, and 8d to perform image recording.

  FIG. 3 is a sub-scan sectional view of the incident optical system LA of the first optical scanning device S1 shown in FIG. In FIG. 3, the same elements as those shown in FIG. The configuration and optical action of the incident optical system LB of the second optical scanning device S2 are the same as those of the incident optical system LA of the first optical scanning device S1.

  As shown in FIG. 3, two incident optical systems LA (LB) are arranged on the upper and lower sides in the drawing, and in the sub-scan section, the deflecting surface 5a (5b) is projected from the incident optical system LA (LB). Light beams are incident (obliquely incident) on the normal 5c from obliquely upward and obliquely downward. The two light beams obliquely incident on the deflecting surface 5a (5b) are conically scanned by the optical deflector 5 in the upward, downward and downward directions, respectively. Then, the light beam reflected upward (upper oblique incident light beam) and the light beam reflected downward (lower oblique incident light beam) pass through the upper and lower sides of the same first imaging lens 6a (6b). Are reflected by the corresponding reflecting mirrors 20a, 21a, 22a (20b, 21b, 22b). Then, the two reflected light beams are scanned as imaging spots on two different photosensitive drum surfaces 8a and 8c (8b and 8d), respectively.

  As described above, in this embodiment, the incident optical systems LA and LB of the first and second optical scanning devices S1 and S2 are arranged obliquely, and the first and second optical scanning devices S1 and S2 are opposed to each other. As a result, the optical parts are shared, and the entire apparatus is made compact.

  However, in such an image forming apparatus using the first and second optical scanning devices S1 and S2 arranged to face each other, ghost light generated in the first and second optical scanning devices S1 and S2 is scanned. The light is incident on the surfaces 8a, 8c, 8b, and 8d. As a result, there is a problem that the image is deteriorated.

  4A, 4B, and 4C are explanatory diagrams showing examples of ghost light generated in the optical scanning device. 4 (A), (B), and (C), the same elements as those shown in FIG. 2B are denoted by the same reference numerals.

  FIGS. 4A, 4B, and 4C are sub-scan sectional views showing the main parts of the first and second optical scanning devices S1 and S2 arranged to face each other, and ghost light called a face-to-face reflection ghost is shown. The generation principle is shown.

  That is, in FIG. 4A, when the light beam deflected and reflected by the optical deflector 5 passes through the first imaging lens 6b, a part of the light beam does not pass through the first imaging lens 6b. Reflected by the first surface (incident surface) 6b1. In FIG. 4B, when the light beam deflected and reflected by the optical deflector 5 passes through the first imaging lens 6a, a part of the light beam is reflected by the second surface (outgoing surface) 6a2. In FIG. 4C, a part of the light beam incident on the deflecting surface 5a of the optical deflector 5 is reflected by the deflecting surface 5a.

  The luminous flux reflected by each surface is called a face-to-face reflected ghost light, and the ghost light from the second optical scanning device S2 is the first optical scanning device on the right side that is disposed to face the optical deflector 5. Incident into the optical path of S1. If this face-to-face reflected ghost light reaches the scanned surfaces 8a and 8c, there is a problem that streaks and color unevenness occur in the formed image.

  Therefore, in this embodiment, the upper and lower light shielding plates 10aU and 10aL (10bU and 10bL) are provided in the imaging optical system 15a (15b) to shield the facing reflection ghost. The upper light shielding plate (upper light shielding member) 10aU (10bU) shields the reflected ghost light passing through the upper side in the drawing of the optical deflector 5, and the lower light shielding plate (lower light shielding member) 10aL (10bL). Shields the reflection ghost that passes through the lower side of the optical deflector 5 in the drawing.

  Here, the shapes of the upper and lower light shielding plates 10aU and 10aL (10bU and 10bL) will be described with reference to FIGS.

  FIGS. 5A and 5B show the effective light beam passage area (scanning locus) (solid line) used for image formation on the light shielding plate when viewed from the optical axis direction of the imaging optical system in this embodiment, and the ghost light. It is a graph (descriptive drawing) showing the passage region (dotted line) and the end shape of the light shielding plate of the present embodiment in the sub-scanning direction.

  FIG. 5A is an explanatory diagram when the upper light shielding plate 10aU (10bU) is disposed on the upper side of the effective light beam in the sub-scanning direction, and FIG. 5B is a lower light shielding plate 10aL (10bL) on the lower side of the effective light beam in the sub-scanning direction. It is explanatory drawing when arrange | positioning.

  5A and 5B, the horizontal axis in the graph is the position Y (mm) in the main scanning direction on the light shielding plate, which coincides with the main scanning direction, and Y = 0 is the imaging optical system 15a (15b). This is the intersection of the optical axis and the light shielding plate. In this embodiment, since the on-axis deflection point O is on the extension line of the optical axis of the imaging optical system 15a (15b), it coincides with the position of Y = 0 in the graph. The vertical axis in the graph is the height Z (mm) in the sub-scanning direction, and the height in the sub-scanning direction from the plane (XY plane) including the on-axis deflection point O and perpendicular to the rotation axis of the optical deflector 5. It represents.

  As can be seen from FIGS. 5A and 5B, the ghost light passage area and the effective light flux passage area (scanning trajectory) are very close to each other. Further, since the present embodiment is an oblique incidence optical system, the effective light beam is conical scanned, and the scanning locus of the effective light beam moves from the optical axis of the imaging optical system 15a (15b) to the periphery in the main scanning direction. Curved to be higher.

  As described above, when the scanning locus of the effective light beam is curved, the ghost light cannot be sufficiently shielded by the conventional light shielding plate 91 whose end portion in the sub-scanning direction is linear. This will be described below with reference to FIGS. 11A and 11B described above. 11A and 11B also show a case where a conventional light shielding plate 91 is used in this embodiment for comparison with this embodiment.

  Since the conventional light shielding plate 91 is a flat plate having an end in the sub-scanning direction, as shown in FIGS. 11A and 11B, the end of the light shielding plate 91 is a straight line extending in the main scanning direction.

  At this time, in order to prevent the effective light beam from being vignetted by the light shielding plate 91, the end portion of the light shielding plate 91 is aligned with the highest position through which the effective light beam passes, that is, the effective light beam passing region in the peripheral portion in the main scanning direction. Had to set the height of. For this reason, at the center position in the main scanning direction, the end portion of the light shielding plate 91 is disposed above the drawing more than necessary, and the ghost light cannot be sufficiently shielded.

  Therefore, in this embodiment, the end portions of the upper and lower light shielding plates 10aU and 10aL (10bU and 10bL) are curved along the scanning locus of the effective light beam.

  That is, in this embodiment, as can be seen from FIGS. 5A and 5B, the end shapes of the upper and lower light shielding plates 10aU and 10aL (10bU and 10bL) are each changed from the center to the periphery in the main scanning direction. Is curved in the direction in which the height Z increases.

  6A is an explanatory diagram showing the shape of the upper light shielding plate 10aU (10bU), and FIG. 6B is an explanatory diagram showing the shape of the lower light shielding plate 10aL (10bL).

  In this embodiment, the position in the main scanning direction on the light shielding plate (upper and lower light shielding plates 10aU, 10aL (10bU, 10bL)) is Y [mm] (the optical axis of the imaging optical system and the light shielding plate). And Y = 0). Further, at any position Y in the main scanning direction, a plane (XY plane) perpendicular to the rotation axis of the optical deflector 5 including the on-axis deflection point O and light shielding plates (upper and lower light shielding plates 10aU, 10aL ( 10bU, 10bL)) is defined as h (Y) [mm]. Further, the interval at the position Y = 0 in the main scanning direction is h (0) [mm].

  Further, the difference of the interval h (Y) with respect to the interval h (0) is defined as the amount of curvature Δh (Y) of the light shielding plates (upper and lower light shielding plates 10aU, 10aL (10bU, 10bL)). Further, an oblique incident angle of the optical axis in the sub-scanning direction is α [rad] (an angle formed between a plane perpendicular to the rotation axis of the optical deflector 5 and a light beam incident on the deflecting surface). Further, the distance from the on-axis deflection point O to the light shielding plates (upper and lower light shielding plates 10aU, 10aL (10bU, 10bL)) in the plane (in the XZ plane) is L (corresponding to LU or LL in FIG. 2B). [mm]. At that time, the amount of curvature Δh (Y) of the light shielding plates (upper and lower light shielding plates 10aU, 10aL (10bU, 10bL)) is the entire effective scanning region.

Is set to satisfy the following conditional expression.

  In the above conditional expression (1), the curve amount Δh (Y) of the light shielding plates (upper and lower light shielding plates 10aU, 10aL (10bU, 10bL)) is set so as to satisfy the conditional expression (1) over the entire effective scanning region. Thus, the ghost light can be sufficiently shielded without vignetting the effective light beam.

  The reason why the ghost light can be sufficiently shielded without vignetting the effective light beam if the conditional expression (1) is satisfied is described below.

  The oblique incident angle of the optical axis in the sub-scanning direction is α [rad] as described above, and the angle between the scanning light beam and the optical axis of the imaging optical system 15a (15b) in the main scanning section is an arbitrary scanning angle θ [rad]. ], The on-axis deflection point (deflection point when θ = 0) is defined as point O. Further, a deviation amount of the deflection point from the on-axis deflection point O at an arbitrary scanning angle θ is ΔX [mm].

  In this image forming apparatus, light shielding plates (upper and lower light shielding plates 10aU, 10aL (10bU, 10bL)) are perpendicular to the main scanning section at a position separated from the on-axis deflection point O by L (LU or LL) [mm]. And arranged so as to be parallel to the main scanning direction. Here, it is assumed that no optical element is disposed between the on-axis deflection point O and the light shielding plates (upper and lower light shielding plates 10aU, 10aL (10bU, 10bL)).

  At an arbitrary scanning angle θ, the distance L ′ in the main scanning section until the light beam deflected and scanned reaches the light shielding plate (upper and lower light shielding plates 10aU, 10aL (10bU, 10bL)) from the deflection point. Can be expressed as a function of θ as follows.

L ′ (θ) = L / cos (θ) + ΔX (3)
Here, ΔX ≠ 0 when a rotating polygonal mirror (polygon mirror) is used as the deflecting means, but since the deviation amount ΔX is sufficiently small with respect to L / cos (θ), equation (3) is expressed as follows: It is replaced with an approximate expression.

L '(θ) ≒ L / cos (θ) ... (4)
Further, at the scanning angle θ, the height H in the sub-scanning direction where the light beam reaches the light shielding plates (upper and lower light shielding plates 10aU, 10aL (10bU, 10bL)) (the axial deflection point O is set to zero). Is
H (θ) = L ′ (θ) × tan (α) (5)
And substituting equation (4) into equation (5),
H (θ) ≒ L / cos (θ) x tan (α) (6)
It can be expressed.

Here, the position in the main scanning direction where the light beam reaches the light shielding plates (upper and lower light shielding plates 10aU, 10aL (10bU, 10bL)) at the scanning angle θ is Y [mm], and the scanning angle θ = 0. When the position in the main scanning direction reaching the light shielding plate is Y = 0 [mm]
Y = L x tan (θ) ... (7)
When converted, θ = ATAN (Y / L) (8)
It becomes.

  Here, substituting equation (8) into equation (6)

  FIG. 7 shows the scanning locus R on the light shielding plate on the upper side of the light beam represented by the equation (9). FIG. 7 shows a scanning trajectory R on the upper light shielding plate of the effective light beam when the light beam subjected to conical scanning reaches the upper light shielding plate.

  As shown in FIG. 7, the scanning locus R on the light shielding plate 10aU (10bU) on the upper side of the light beam subjected to the conical scanning has an axial deflection point as it moves from the optical axis of the imaging optical system to the periphery in the main scanning direction. It is curved in a direction away from a plane (XY plane) perpendicular to the rotation axis of the included optical deflector.

  Here, as shown in FIG. 7, when the curvature amount ΔH (Y) of the scanning locus R of the light beam in an arbitrary main scanning direction Y on the light shielding plate is Y = 0, the light beam reaches the light shielding plate. It is defined as the height H (Y) in the sub-scanning direction at an arbitrary scanning angle θ with respect to the height H (0) in the sub-scanning direction. Then, the bending amount ΔH (Y) can be expressed as follows.

  As described above, if there is no optical element in the optical path between the on-axis deflection point O and the light shielding plate (upper and lower light shielding plates 10aU, 10aL (10bU, 10bL)), The effective light beam scanning trajectory R is obtained by an approximate expression of Expression (12). Even if optical elements such as lenses and mirrors are arranged between the axial deflection point and the light shielding plates (upper and lower light shielding plates 10aU, 10aL (10bU, 10bL)), the sub-scanning of these optical elements is provided. If the power is small in the direction, the influence on the bending amount ΔH (Y) is sufficiently small. Therefore, the approximate expression (12) holds.

  In this embodiment, the first imaging lens 6a (6b) is provided in the optical path between the light shielding plates (upper and lower light shielding plates 10aU, 10aL (10bU, 10bL)) and the optical deflector 5. ing. However, since the first imaging lens 6a (6b) has power only in the main scanning direction and is non-powered in the sub-scanning direction as described above, the light beam passes through the first imaging lens 6a (6b). The angle in the sub-scanning direction hardly changes before and after. Therefore, also in the present embodiment, the bending amount of the effective light beam on the light shielding plates (upper and lower light shielding plates 10aU, 10aL (10bU, 10bL)) is approximated by Expression (12).

  In the present embodiment, the shape of the end portion in the sub-scanning direction of the light shielding plates (upper and lower light shielding plates 10aU, 10aL (10bU, 10bL)) in order to sufficiently shield the ghost light without shielding the effective light beam. Is set to follow the scanning locus of the effective luminous flux.

  Specifically, the amount of curvature Δh (Y) of the end shape of the light shielding plate (upper and lower light shielding plates 10aU, 10aL (10bU, 10bL)) is set so as to satisfy the following conditional expression (13). Yes. As a result, the amount of bending of the light shielding plates (upper and lower light shielding plates 10aU, 10aL (10bU, 10bL)) is kept within a range of ± 50% with respect to the amount of effective luminous flux obtained by the approximate expression (12). ing.

That is, in this embodiment, the ratio of the bending amount Δh (Y) and the bending amount ΔH (Y) is set so as to satisfy the following conditional expression (13).
0.5 ≦ Δh (Y) / ΔH (Y) ≦ 1.5 (13)
Here, the following conditional expression (1) is obtained by substituting the expression (12) into the expression (13).

  More preferably, the bending amount Δh (Y) of the end shape of the light shielding plate (upper and lower light shielding plates 10aU, 10aL (10bU, 10bL)) is the curvature of the effective luminous flux obtained by the approximate expression (12). It is better to be within a range of ± 20% with respect to the amount. That is, the shape of the light shielding plates (upper and lower light shielding plates 10aU, 10aL (10bU, 10bL)) may be set so as to satisfy the following conditional expression (14).

In the upper light shielding plate 10aU (10bU) of this embodiment, α = 3 deg, and the distance LU from the on-axis deflection point O to the upper light shielding plate 10aU (10bU) is 31 mm. In the effective scanning region, the effective light beam passes through the region in the main scanning direction Y = −21 mm to +21 mm on the upper light shielding plate 10aU (10bU), and satisfies the conditional expression (1) in the entire effective scanning region. Where Y = 19mm
ΔH (Y) = 0.34 [mm], Δh (Y) = 0.44 [mm], Δh (Y) / ΔH (Y) = 1.3
This satisfies the conditional expression (1).

In the lower light shielding plate 10aL (10bL) of this embodiment, α = 3 deg, and the distance LL from the on-axis deflection point O to the lower light shielding plate 10aL (10bL) is 26 mm. In the effective scanning region, the effective light beam passes through the region in the main scanning direction Y = −19 mm to +19 mm on the lower light shielding plate 10aL (10bL), and satisfies the conditional expression (1) in the entire effective scanning region. Where Y = 19 mm
ΔH (Y) = 0.33 [mm], Δh (Y) = 0.39 [mm], Δh (Y) / ΔH (Y) = 1.2
This satisfies the conditional expression (1).

  In this embodiment, in order to simplify the shape of the end portions of the light shielding plates (upper and lower light shielding plates 10aU, 10aL (10bU, 10bL)) and to reduce the difficulty in forming the light shielding plates, the sub-scanning of the light shielding plates is performed. The end shape in the direction is set to an arc (arc shape).

  The upper light shielding plate 10aU (10bU) has an arc shape with a radius of 500 mm, and is set so that the height in the sub-scanning direction increases as the distance from the optical axis increases with respect to the scanning direction.

  The lower light-shielding plate 10aL (10bL) has an arc shape with a radius of 460 mm, and is set such that the height in the sub-scanning direction decreases as the distance from the optical axis increases with respect to the scanning direction.

  In this embodiment, the spatial separation interval between the effective light beam and the end portion in the sub-scanning direction of the light shielding plates (upper and lower light shielding plates 10aU, 10aL (10bU, 10bL)) is the entire effective scanning region. Is 0.3 mm or more. Further, even when the effective light beam passing position is shifted due to the mounting tolerance of the optical components, the light shielding plates (upper and lower light shielding plates 10aU, 10aL (10bU, 10bL)) are set so that the effective light flux is not vignetted. .

  As can be seen from FIGS. 4A, 4B, and 4C, in the oblique incidence optical system, the effective light beam scanned on the right side of the optical deflector 5 and the counter-reflection ghost are sub-scanned. The interval in the scanning direction tends to become the largest on the side closest to the optical deflector 5. Further, the distance tends to become narrower as the distance from the optical deflector 5 increases. For this reason, the light shielding plates (upper and lower light shielding plates 10aU, 10aL (10bU, 10bL)) are placed as close to the optical deflector 5 as possible in order to reliably shield only ghost light without vignetting the effective light beam used for image formation. It is desirable to arrange.

  On the other hand, if the light shielding plates (upper and lower light shielding plates 10aU, 10aL (10bU, 10bL)) are too close to the optical deflector 5, there is a problem that noise increases.

  Therefore, in this embodiment, the light shielding plates (upper and lower light shielding plates 10aU, 10aL (10bU, 10bL)) are provided between the first imaging lens 6a (6b) and the second imaging lens 7a (7b). And is disposed at a position closest to the first imaging lens 6a (6b) that can be disposed. As a result, the above two conflicting conditions are satisfied.

  However, the upper light shielding plate 10aU (10bU), the lower light shielding plate 10aL (10bL), or both light shielding plates are arranged in the optical path between the optical deflector 5 and the first imaging lens 6a (6b). Even so, if the conditional expression (1) is satisfied, the effects of the present invention can be sufficiently obtained.

  In this embodiment, the optical box for holding the optical scanning device and the light shielding plates (upper and lower light shielding plates 10aU, 10aL (10bU, 10bL)) are integrally formed (molded) for compactness. It is composed.

  At this time, the light shielding plates (upper and lower light shielding plates 10aU, 10aL (10bU, 10bL)) shift the position of the imaging optical system 15a (15b) with respect to the optical axis direction by 3 mm so that the mold can be easily removed. Are arranged.

  In the present embodiment, the optical box and the light shielding plates (upper and lower light shielding plates 10aU, 10aL (10bU, 10bL)) are integrally formed.

  In the present embodiment, the upper light shielding plate 10aU (10bU) and the lower light shielding plate 10aL (10bL) are configured as separate members. However, the present invention is not limited to this, and may be configured by integral molding.

  In this embodiment, the lower light-shielding plate 10aL (10bL) is arranged closer to the light deflector 5 than the upper light-shielding plate 10aU (10bU). However, the upper light-shielding plate 10aU (10bU) is not limited to this. You may arrange | position to the optical deflector 5 side rather than the lower light-shielding plate 10aL (10bL).

  In this embodiment, the imaging optical system 15a (15b) is composed of two lenses, but it may be composed of three or more lenses. In the present embodiment, the first imaging lens 6a (6b) is constituted by one lens, but may be constituted by two or more lenses.

  In this embodiment, the refractive power of the first imaging lens 6a (6b) in the sub-scanning direction is non-power (the curvature radius R of the first surface in the sub-scanning direction R = -1000 mm, the second surface in the sub-scanning direction). It is composed of a toric lens with a radius of curvature R = -1000 mm and a non-arc shape in the main scanning direction. As a result, the scanning locus of the effective light beam after passing through the first imaging lens 6a (6b) is not complicated, and the fθ performance is satisfied.

  In the present embodiment, the first and second optical scanning devices S1 and S2 are disposed to face each other for the purpose of more compactness. However, the present embodiment is not limited to this, and the present embodiment is not limited to this. Alternatively, a light shielding plate may be used. Even in such an image forming apparatus, it is possible to satisfactorily shield various ghost lights such as a lens internal reflection ghost and a light deflector rereflection ghost, and the effects of the present invention can be sufficiently obtained. It is done.

  In this embodiment, in order to simplify the shape of the light shielding plates (upper and lower light shielding plates 10aU, 10aL (10bU, 10bL)), the shape in the main scanning section is a straight line. However, not limited to this, as long as conditional expression (1) is satisfied, the shape of the light shielding plates (upper and lower light shielding plates 10aU, 10aL (10bU, 10bL)) in the main scanning section may be curved. The effect of the present invention can be sufficiently obtained.

  In this embodiment, the light shielding plates (upper and lower light shielding plates 10aU, 10aL (10bU, 10bL)) are formed in a straight line shape in the main scanning section in order to simplify the shape and reduce the difficulty of molding. However, the present invention is not limited thereto, and the effect of the present invention can be sufficiently obtained if the end shape in the sub-scanning direction is curved so as to follow the scanning locus of the effective light beam even in the main scanning section.

  In the present embodiment, the optical axis of the imaging optical system 15a (15b) is set to coincide with the on-axis deflection point O. However, the present invention is not limited to this, and the optical axis of the imaging optical system 15a (15b) is shifted by several mm in the main scanning direction with respect to the axial deflection point O in order to correct the left-right asymmetry of the optical characteristics. May be. For example, it may be shifted from 1 mm to 5 mm.

  Even at this time, the main axis of the optical axis of the imaging optical system 15a (15b) is larger than the width in the main scanning direction of the light beam passing over the light shielding plates (upper and lower light shielding plates 10aU, 10aL (10bU, 10bL)). The shift amount in the scanning direction is sufficiently small. Therefore, if the light shielding plates (upper and lower light shielding plates 10aU, 10aL (10bU, 10bL)) are set so as to satisfy the conditional expression (1), the shape of the end portion of the light shielding plate is reduced to an effective light flux to a level where there is no problem. It is possible to follow the scanning trajectory, and the effect of the present invention can be sufficiently obtained.

  Next, Table 1 shows the configuration of the optical scanning device according to the first embodiment. Table 2 shows the configuration of the incident optical system (R (curvature radius), D (lens spacing and lens thickness), N (refractive index of material)) in Example 1. Table 3 shows the aspheric shape of the cylindrical lens in Example 1.

  The numerical examples in Tables 1, 2, and 3 show the first optical scanning device S1, and the numerical examples of the second optical scanning device S2 are the same.

[Example 2]
FIG. 8 is a sectional view (main scanning sectional view) of the main part in the main scanning direction according to the second embodiment of the present invention, and FIG. is there. 8 and 9, the same elements as those shown in FIGS. 1 and 2A are denoted by the same reference numerals.

  The difference between the present embodiment and the first embodiment is that the arrangement and shape of the light shielding plate 11 are different. Other configurations and optical functions are the same as those in the first embodiment, and the same effects are obtained.

  That is, in the figure, 11 is a light shielding plate as a light shielding member, and is constructed by integrally molding the upper light shielding plate 11U and the lower light shielding plate 11L, and is generated in the imaging optical system 15a (15b). To block ghost light.

  The light-shielding plate 11 in this embodiment is provided in the imaging optical system 15a, has an opening, and is provided from the optical deflector 5 over the entire effective scanning area on the scanned surfaces 8a and 8b. The shape is such that the effective light beam deflected and reflected is not shielded.

  The upper and lower light shielding plates in the first embodiment are formed in a linear shape (that is, a flat plate) in the main scanning section. On the other hand, in the present embodiment, the shape of the light shielding plate 11 is formed in a curved shape in the main scanning section. As a result, the shape of the end portion of the light shielding plate 11 is aligned with the effective light beam that is conically scanned.

  In other words, in this embodiment, the shape of the light shielding plate 11 in the main scanning section is curved in a direction approaching the optical deflector 5 as it is away from the optical axis of the imaging optical system 15a, thereby blocking light at any position in the main scanning section. The distance between the plate 11 and the on-axis deflection point O is matched.

  Specifically, the shape of the light shielding plate 11 is an arc (arc shape) having a radius R = 31 mm with the on-axis deflection point O as the center of the circle in the main scanning section.

  In this embodiment, the end shape of the light shielding plate 11 in the sub-scanning direction is a straight line (linear shape).

  FIG. 10 shows the upper and lower passing areas (scanning trajectory) (solid line) of the effective light beam used for image formation on the light shielding plate when viewed from the optical axis direction of the imaging optical system in this embodiment, and the ghost. It is the graph (description figure) showing the passage region (dotted line) of light, and the opening shape of the light-shielding plate of a present Example.

  In FIG. 10, reference numeral 11 denotes a light shielding plate, which is configured by integrally molding an upper light shielding plate 11U and a lower light shielding plate 11L. Reference numeral 12 denotes an opening having a shape that allows the upper and lower effective light beams to pass therethrough.

  As can be seen from FIG. 10, in this embodiment, the effective light beam passage area is made straight by curving the shape of the light shielding plate 11 in the main scanning section as described above. As a result, the end shape of the light shielding plate 11 can remain along the effective light beam passage region in the entire scanning region, and the ghost light can be sufficiently shielded without shielding the effective light beam.

  In this embodiment, the end of the light shielding plate 11 in the sub-scanning direction is set at a height of 0.6 mm away from the effective light flux in the entire effective scanning region. Thus, even when the effective light beam is displaced in the sub-scanning direction due to attachment tolerance or the like, the light shielding plate 11 prevents the effective light beam from vignetting.

  The light shielding plate 11 in this embodiment is made compact by integrally molding the upper light shielding plate and the lower light shielding plate. However, the present invention is not limited to this. You may comprise with a member.

  In the present embodiment, the end shape is set to be a straight line in the sub-scanning section in order to reduce the difficulty of forming the light shielding plate 11, but the present invention is not limited to this, and the present invention is sufficient even if it is set to a curve. The effect is obtained.

  In the present embodiment, the light shielding plate 11 is provided in the first optical scanning device S1, but not limited thereto, it may be provided in the second optical scanning device S2, or in both the optical scanning devices S1 and S2. It may be provided.

  In each of the embodiments, the color image forming apparatus having a plurality of optical scanning devices has been described. However, the present invention is not limited to this, and the present invention can also be applied to an image forming apparatus that forms a monochrome image composed of a single optical scanning device. Needless to say.

[Image forming apparatus]
FIG. 12 is a cross-sectional view of the main part in the sub-scanning direction showing an embodiment of the image forming apparatus of the present invention. In the figure, reference numeral 104 denotes an image forming apparatus. Code data Dc is input to the image forming apparatus 104 from an external device 117 such as a personal computer. The code data Dc is converted into image data (dot data) Di by a printer controller 111 in the apparatus. This image data Di is input to the optical scanning device 100. The light scanning device 100 emits a light beam 103 modulated in accordance with the image data Di, and the light beam 103 scans the photosensitive surface of the photosensitive drum (photosensitive member) 101 in the main scanning direction.

  The photosensitive drum 101 as an electrostatic latent image carrier (photosensitive drum) is rotated clockwise by a motor 115. With this rotation, the photosensitive surface of the photosensitive drum 101 moves in the sub-scanning direction perpendicular to the main scanning direction with respect to the light beam 103. Above the photosensitive drum 101, a charging roller 102 for uniformly charging the surface of the photosensitive drum 101 is provided so as to contact the surface. The surface of the photosensitive drum 101 charged by the charging roller 102 is irradiated with a light beam 103 scanned by the optical scanning device 100.

  As described above, the light beam 103 is modulated based on the image data Di, and by irradiating the light beam 103, an electrostatic latent image is formed on the surface of the photosensitive drum 101. This electrostatic latent image is developed as a toner image by a developing device 107 disposed so as to abut on the photosensitive drum 101 further downstream in the rotation direction of the photosensitive drum 101 than the irradiation position of the light beam 103.

  The toner image developed by the developing unit 107 is transferred onto a sheet 112 as a transfer material by a transfer roller 108 disposed below the photosensitive drum 101 so as to face the photosensitive drum 101. The paper 112 is stored in the paper cassette 109 in front of the photosensitive drum 101 (on the right side in FIG. 12), but can be fed manually. A paper feed roller 110 is provided at the end of the paper cassette 109, and feeds the paper 112 in the paper cassette 109 into the transport path.

  As described above, the sheet 112 on which the unfixed toner image has been transferred is further conveyed to a fixing device behind the photosensitive drum 101 (left side in FIG. 12). The fixing device includes a fixing roller 113 having a fixing heater (not shown) therein and a pressure roller 114 disposed so as to be in pressure contact with the fixing roller 113. Then, the unfixed toner image on the sheet 112 is fixed by heating the sheet 112 conveyed from the transfer unit (transfer unit) while being pressed by the pressure roller 114 and the pressure roller 114. Further, a paper discharge roller 116 is disposed behind the fixing roller 113, and the fixed paper 112 is discharged out of the image forming apparatus.

  Although not shown in FIG. 12, the print controller 111 controls not only the data conversion described above but also each part in the image forming apparatus including the motor 115 and a motor in the optical scanning apparatus described later. Do.

[Color image forming device]
FIG. 13 is a sub-scan sectional view of the color image forming apparatus of the present invention.

  In the figure, 60 is a color image forming apparatus, 201 is an image forming apparatus having the configuration shown in the first or second embodiment, 21, 22, 23, and 24 are photosensitive drums as image carriers, 31, 32, and 33, respectively. , 34 are developing devices. 51 is a conveyor belt, 52 is an external device such as a personal computer, and 53 is a printer controller that converts color signals input from the external device 52 into image data of different colors and inputs them to the image forming apparatus 201.

  In the figure, the color image forming apparatus 60 receives R (red), G (green), and B (blue) color signals from an external device 52 such as a personal computer. These color signals are converted into C (cyan), M (magenta), Y (yellow), and B (black) image data (dot data) by a printer controller 53 in the apparatus. These image data are input to the image forming apparatus 201. The image forming apparatus 201 emits light beams (light beams) 41, 42, 43, and 44 that are modulated according to each image data, and the photosensitive surfaces of the photosensitive drums 21, 22, 23, and 24 are emitted by these light beams. Are scanned in the main scanning direction.

  The color image forming apparatus in this embodiment emits light beams corresponding to C (cyan), M (magenta), Y (yellow), and B (black) from one image forming apparatus 201. Then, image signals (image information) are recorded on the photosensitive drums 21, 22, 23, and 24, and a color image is printed at high speed.

  In the color image forming apparatus according to the present embodiment, as described above, the latent image of each color is formed on the corresponding photosensitive drums 21, 22, 23, and 24 using the light beams based on the respective image data by one image forming apparatus 201. Forming. After that, multiple transfer is performed on the recording material on the conveyance belt 51 to form one full-color image, and the full-color image is transferred to a sheet member (paper).

  As the external device 52, for example, a color image reading device including a CCD (line sensor) may be used. In this case, the color image reading apparatus and the color image forming apparatus 60 constitute a color digital copying machine.

1a, 1b, 1c, 1d Light source means 2a, 2b, 2c, 2d Aperture (aperture stop)
3a, 3b, 3c, 3d Collimator lens lens 4 Cylindrical lens 5 Deflection means 5a Deflection surfaces 15a, 15b Imaging optical system 6a, 6b First imaging lens 7a, 7b Second imaging lens 8a, 8b, 8c, 8d Scanned surface (photosensitive drum surface)
21a, 22a, 23a Light beam separating means (reflection mirror)
21b, 22b, 23b Light beam separating means (reflection mirror)
10aU, 10bU Upper light shielding plate 10aL, 10bL Lower light shielding plate 11 Light shielding plate 12 Opening 201 Image forming apparatus 21, 22, 23, 24 Image carrier (photosensitive drum) 31, 32, 33, 34 Developer 41, 42, 43, 44 Light beam 71 Conveying belt 72 External device 73 Printer controller 60 Color image forming device 100 Optical scanning device 101 Photosensitive drum 102 Charging roller 103 Light beam 104 Image forming device 107 Developing device 108 Transfer roller 109 Paper cassette 110 Paper feed Roller 111 Printer controller 112 Transfer material (paper) 113 Fixing roller 114 Pressure roller 115 Motor 116 Paper discharge roller 117 External device

Claims (2)

A light source means, an incident optical system for guiding the light beam emitted from the light source means to the deflection surface of the deflection means, and an image forming an image of the light beam deflected and scanned by the deflection surface of the deflection means on the surface to be scanned An optical scanning device having an optical system,
In the sub-scan section, the light beam incident on the deflection surface of the deflection unit is incident on the deflection surface from an oblique direction with respect to the optical axis of the imaging optical system,
A light shielding member for shielding ghost light is disposed in an optical path between the deflection surface and the scanned surface; and
The end of the light shielding member in the sub-scanning direction is formed in a curved shape whose height in the sub-scanning direction changes according to the position in the main scanning direction, and
The curved shape includes an on-axis deflection point of a light beam incident on a deflecting surface of the deflecting unit as it goes off-axis in the main scanning direction when the intersection with the optical axis of the imaging optical system is the center. Curved in the direction in which the distance between the plane perpendicular to the rotation axis of the deflecting means and the end of the light shielding member in the sub-scanning direction is increased, and
The light-shielding member includes an upper light-shielding member having an upper end in the sub-scanning direction among ends in the sub-scanning direction of the light-shielding member, and a lower sub-scanning among ends in the sub-scanning direction of the light-shielding member. Composed of a lower light-shielding member with an end in the direction,
The upper light shielding member and the lower light shielding member are integrally molded in an optical box that holds the optical scanning device,
The optical scanning device according to claim 1, wherein the upper light shielding member and the lower light shielding member are arranged so as to be shifted in a position with respect to an optical axis direction of the imaging optical system. An electrostatic latent image formed on the photosensitive member by a light beam scanned by the optical scanning device according to claim 1, the photosensitive member disposed on the surface to be scanned, and the optical scanning device, and a toner image. An image forming apparatus comprising: a developing device that develops the toner image; a transfer device that transfers the developed toner image onto a transfer material; and a fixing device that fixes the transferred toner image onto the transfer material.