JP2013020045A - Optical scanner and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical scanner that removes the influence of ghost light, and an image forming device.SOLUTION: The optical scanner includes: a first optical system for introducing light fluxes from a plurality of light sources to a second optical system; the second optical system for converging the light fluxes having passed through the first optical system in a sub scanning direction; deflection means having a plurality of reflection surfaces for deflecting the light flux having passed through the second optical system and made incident at a predetermined angle in the sub scanning direction; a third optical system for imaging the light fluxes deflected by the deflection means onto a plurality of scanned surfaces, respectively. When the diameter of the light flux in the sub scanning direction on a main plane of the second optical system is D, a focal distance of the second optical system is f, the distance between the incident surfaces of an optical element located closest to the reflection surface of the third optical system of two scanning optical systems is L, the distance from the reflection surface to the incident surface of the optical element closest to the deflection means is (a), and an incident angle in the sub scanning direction with respect to the reflection surface of the light flux having passed through the second optical system is β, (L+a)×tan(β-arctan(D/2f))-a×tan(β+arctan(D/2f))>0 is satisfied.

Description

  The present invention relates to an optical scanning apparatus and an image forming apparatus such as a digital copying machine, a printer, a plotter, a facsimile, and a digital copying machine using the optical scanning apparatus.

  Light that deflects the light beam by a deflecting means such as an optical deflector, forms an image of the deflected light beam as a fine spot light on the surface to be scanned by the scanning optical system, and scans the surface to be scanned at a constant speed in the main scanning direction. Scanning devices are conventionally known. This optical scanning device scans a surface to be scanned such as an image carrier by deflecting and reflecting, for example, laser light emitted from a laser light source by a polygon mirror which is an optical deflector, and also measures the intensity of the laser light. By modulating (for example, turning on and off) according to the signal, an image is written on the surface to be scanned.

  In the image forming apparatus, an image is formed on paper by attaching toner to the image carrier in accordance with the image written on the surface to be scanned using the optical scanning device described above, and transferring and fixing the toner image on the paper. I do. In the case of forming a color image, optical scanning is performed on an image carrier corresponding to a plurality of color toners, and each formed toner image is superimposed on one sheet of paper.

  As an example of the above-described image forming apparatus, as described in Patent Document 1, an image of a method in which scanning optical systems are arranged symmetrically across a single polygon mirror (hereinafter referred to as “opposing scanning method”). There is a forming device. Since a plurality of polygon mirrors are not used, control for adjusting the phase of the deflected light by each polygon mirror is not required, and a simple control configuration can be achieved, and power consumption and heat generation can be reduced. Further, the counter scanning method can reduce the number of polygon mirrors in half compared to a method in which a plurality of scanning optical systems are arranged on one side of one polygon mirror (hereinafter referred to as “one side scanning method”). High-speed rotation is possible, and power consumption and heat generation can be reduced.

  Patent Documents 2 and 3 describe image forming apparatuses in which the number of polygon mirrors is one. In the scanning optical system of these image forming apparatuses, the incident light beam is incident on the polygon mirror at a predetermined angle (oblique incidence angle) with respect to the rotation axis direction (sub-scanning direction) of the polygon mirror. It has become. The scanning optical systems described in Patent Documents 2 and 3 are single-sided scanning systems. However, by adopting the counter scanning system in the oblique incidence optical system, the oblique incidence angle can be reduced and the optical characteristics are good. Can be kept in.

  As a problem peculiar to the above-described scanning optical scanning apparatus, most of the scanning lenses constituting the scanning optical system, when the light beam is incident on the scanning lens disposed closest to the optical deflector, are mostly scanning lenses. However, some of the reflected light is reflected by the incident surface of the scanning lens, and the reflected light beam enters the other scanning optical system that faces the image, and reaches the image carrier made up of the photosensitive member that is the scanned surface. As a result, a so-called ghost image is created.

  Since the ghost image forms an image in an unfavorable place, the image quality is significantly deteriorated when the ghost image is formed. Usually, a light beam (ghost light) that forms a ghost image is a light beam reflected by a metal part or the like for holding a scanning lens or the like. In such a case, an extremely simple method is adopted in which the metal parts and the like are colored with a color that is difficult to reflect to prevent reflection and prevent a ghost image from being formed. However, since the reflected light flux as described above is generated on the optical surface that should originally be transmitted, it is not possible to adopt a simple method such as that used for metal parts.

  In the optical scanning device of the image forming apparatus described in Patent Document 2 described above, a condition is adopted in which the reflected light from the incident surface of the scanning lens, which is the first surface of the scanning optical system, does not re-enter the polygon mirror. However, if the above-described facing scanning method is employed in this optical scanning device, ghost light may pass over the polygon mirror and reach the facing scanning optical system.

  Further, in the image forming apparatus described in Patent Document 1, only ghost light is prevented from being condensed on the scanning surface on the opposite side, and the ghost light is prevented from reaching the scanning surface. Because it is not a thing, its influence cannot be completely removed. There is also a method of applying an antireflection coating to the scanning lens as in the image forming apparatus described in Patent Document 3, but this also requires a large number of coating layers in order to perform a coating that completely prevents reflection. The cost will be high.

  SUMMARY An advantage of some aspects of the invention is that it provides an optical scanning device capable of removing the influence of ghost light or an image forming apparatus including the optical scanning device.

The present invention provides a plurality of light source units, a first optical system that guides the respective light beams from the plurality of light source units to the second optical system, and a first optical system that converges the respective light beams that have passed through the first optical system in the sub-scanning direction. Two optical systems, a deflecting means having a plurality of reflecting surfaces for deflecting a light beam passing through the second optical system and incident at a predetermined angle in the sub-scanning direction, and a plurality of scanned light beams deflected by the deflecting means. And a third optical system that forms an image on each of the surfaces. At least two of the light beams from the plurality of light source units are incident on different reflecting surfaces of the deflecting unit, and are most commonly applied to the different deflecting units. Of the third optical system, the incident surface of the optical element closest to the deflecting means is parallel to the rotation axis of the deflecting means, and is the main plane in the sub-scanning direction of the second optical system. Light in the sub-scanning direction above The diameter is D, the focal length of the second optical system is f, the distance between the incident surfaces of the optical elements closest to the reflecting surface of the third optical system provided in each of the two scanning optical systems is L, and the deflection means from the reflecting surface When the distance to the incident surface of the optical element closest to is a and the incident angle in the sub-scanning direction with respect to the reflecting surface of the light beam that has passed through the second optical system is β,
(L + a) × tan (β-arctan (D / 2f)) − a × tan (β + arctan (D / 2f))> 0
Satisfying the most important feature.

  The present invention is also an image forming apparatus that forms an image by executing an electrophotographic process, and is characterized in that the above-described optical scanning device is mounted as an apparatus that executes an exposure process of an electrophotographic process. .

  According to the present invention, it is possible to provide an optical scanning device capable of removing the influence of ghost light, or an image forming apparatus including the optical scanning device.

It is a perspective view which shows the Example of the optical scanning device based on this invention. It is a model figure which shows the mode of condensing by the cylindrical lens provided in the optical scanning device of FIG. It is sectional drawing by the plane parallel to the subscanning direction of the optical scanning device of FIG. It is sectional drawing to which the polygon mirror vicinity of the optical scanning device of FIG. 1 was expanded. It is sectional drawing of the sub scanning direction of the polygon mirror vicinity in another Example of the optical scanning device based on this invention. FIG. 10 is an enlarged view of the vicinity of an aperture, a cylindrical lens, and a polygon mirror in still another embodiment of the optical scanning device according to the present invention. It is sectional drawing of the subscanning direction of the polygon mirror vicinity in another Example of the optical scanning device concerning this invention. It is sectional drawing of the subscanning direction of the aperture and polygon mirror vicinity in another Example of the optical scanning device based on this invention. 1 is a cross-sectional view showing a tandem type full-color laser printer as an embodiment of an image forming apparatus according to the present invention.

  Embodiments of an optical scanning device and an image forming apparatus according to the present invention will be described below with reference to the drawings.

[Example 1]
FIG. 1 is a schematic perspective view showing an embodiment of an optical scanning device according to the present invention. A light beam 201 emitted from a semiconductor laser (not shown), which is a light source, is converted into parallel light, or divergent or convergent light equivalent thereto by the coupling lens 102.

  The light beam that has passed through the coupling lens 102 is shaped into a desired light beam diameter by passing through an aperture (not shown). The light beam 201 that has passed through the aperture enters the cylindrical lens 104 and forms an image only in the sub-scanning direction in the vicinity of the reflection surface of the polygon mirror 111 as a deflecting unit. In the lower right of FIG. 1, the main scanning direction and the sub-scanning direction are shown as orthogonal coordinate axes. The sub-scanning direction is a direction parallel to the rotation axis direction of the polygon mirror 111.

  The polygon mirror 111 is rotationally driven by a motor, has a plurality of reflecting surfaces in the rotational direction, and deflects the light beam 201 by rotating. The light beam 201 deflected to the polygon mirror 111 passes through the first scanning lens 121 and the second scanning lens 122, which are image forming means, and is reflected by the first folding mirror 131. Further, depending on the optical path, the second folding mirror may further be used. The light is also reflected by the light 132 and guided to the photoconductor 140 that is the surface to be scanned.

  Also, the light beam on the start end side of the light beam 201 that scans the photosensitive member is caused to enter the synchronization detection sensor 136 via the synchronization lens 135, and the light emission start timing of the effective scanning region is determined based on the generated synchronization detection signal. To do.

  Four photoconductors 140 are provided corresponding to black, cyan, magenta, and yellow toners, and are respectively denoted by symbols k, c, m, and y. Similarly, the light beams 201 that scan the respective photoreceptors 140 and the folding mirrors 131 and 132 are denoted by k, c, m, and y, respectively.

  The optical scanning device shown in FIG. 1 is a counter scanning system, and first scanning lenses 121a and 121b are arranged opposite to each other across the polygon mirror 111, and second scanning lenses 122a, 122b, first folding mirrors 131c, 131k, 131m, and 131y, and second folding mirrors 132c and 132m are arranged.

  The light sources corresponding to cyan and black and the light sources corresponding to magenta and yellow are arranged away from each other, and light beams 201c and 201k from the light sources corresponding to cyan and black are paired toward the reflecting surface of the polygon mirror 111. The light beams 201m and 201y from the light sources corresponding to magenta and yellow are combined to be directed to the reflection surface of the polygon mirror 111.

  Reference numerals 102c, 102k and 102m, 102y denote coupling lenses as the first optical system, and 104a, 114 denote cylindrical lenses as the second optical system. The cylindrical lens 104a passes light beams 201c and 201k corresponding to cyan and black, and the cylindrical lens 114 passes light beams 201m and 201y corresponding to magenta and yellow.

  The first scanning lenses 121a and 121b and the second scanning lenses 122a and 122b constitute a third optical system that forms an image of each light beam deflected by the polygon mirror 111 on a surface to be scanned corresponding to each light beam. Yes. The third optical system has an fθ characteristic in the main scanning direction in order to scan the light beam deflected at a constant angular velocity by the polygon mirror 111 on the surface to be scanned at a constant velocity.

  The light beam 201 has an incident angle β in the sub-scanning direction to the polygon mirror 111 with respect to a plane perpendicular to the rotation axis of the polygon mirror 111 (hereinafter referred to as a main scanning plane). The luminous fluxes 201k and 201c are symmetrical and equal with respect to the main scanning plane, the luminous fluxes 201m and 201y are symmetrical and equal with respect to the main scanning plane, and the luminous fluxes 201k and 201y and 201c and 201m have the same angle including the direction. ing.

  The cylindrical lens 104, the first scanning lens 121, and the second scanning lens 122 are shared by the light beams 201k and 201c or the light beams 201m and 201y, and of these configurations, the light beams 201k and 201c are passed or reflected. In contrast, a and b are attached to the configuration through which the light beams 201m and 201y pass or reflect.

  FIG. 2 is a diagram showing a state of light collection in the sub-scanning direction by the cylindrical lens 104. Here, for simplification, only the main plane of the cylindrical lens 104 having power only in the sub-scanning direction is shown. When a light beam close to a parallel light beam shaped into a desired light beam diameter by the aperture 103 is incident on the cylindrical lens 104, the sub-scanning direction is formed on the reflection surface of the polygon mirror 111 disposed at a distance substantially equal to the focal length f of the cylindrical lens 104. To form an image. At this time, if the light beam diameter in the sub-scanning direction on the main plane in the sub-scanning direction of the cylindrical lens 104 is D, the half angle θ obtained by looking into the cylindrical lens 104 from the imaging point, in other words, convergence in the sub-scanning direction by the cylindrical lens 104. The angle θ that is ½ of the angle is expressed by Equation 1.

  Next, FIG. 3 and FIG. 4 show how the ghost light generated on the first surface of the scanning optical system passes through the polygon mirror 111 to the opposite side. 3 is a sectional view of the optical scanning device shown in FIG. 1 in the sub-scanning direction, and FIG. 4 is an enlarged view of the vicinity of the polygon mirror 111 of the optical scanning device.

  In this embodiment, the first surface of the scanning optical system is the incident surface of the first scanning lens 121, and the shape in the sub-scanning direction is designed to be parallel to the rotation axis of the polygon mirror 111. That is, the shape in the sub-scanning direction is a surface that is not inclined with respect to the rotation axis of the polygon mirror 111 and has no curvature. Although this embodiment has such a configuration, it may be a parallel plate having no inclination with respect to the rotation axis of the polygon mirror 111. If this parallel plate is fitted into a window hole in the casing surrounding the polygon mirror 111 to seal the inside of the casing, wind noise of the polygon mirror 111 can be reduced and contamination of the reflecting surface of the polygon mirror 111 can be prevented. .

  Here, attention is focused on the light beam 201k in FIG. A light beam 201k emitted from the polygon mirror 111 at an oblique incident angle β with respect to the main scanning plane enters the first scanning lens 121a. Most of the light intensity is transmitted and guided to the desired photoconductor 140k, but a part of the light intensity is reflected on the surface of the incident surface of the first scanning lens 121a and becomes ghost light 201kg indicated by a broken line in FIG. If this passes through an optical path that reaches the opposite side, for example, a photoreceptor for yellow toner, image deterioration occurs such that the yellow toner is developed at the timing of developing the black toner, and the image quality is lowered. I will invite you. In order to prevent this, it is necessary to prevent the ghost light 201 kg from passing through the effective range of the first scanning lens 121 b through which the light beam 201 y that visualizes yellow toner passes.

  After forming an image in the sub-scanning direction on the reflection surface of the polygon mirror 111, the deflected and scanned light beam diverges. The outermost light beam on the lower side of the page in FIG. 4 of the light beam 201k is emitted at an angle of β−θ (refer to FIG. 2 for θ). Since the incident surface of the first scanning lens 121a is parallel to the rotation axis of the polygon mirror 111 as described above, the outermost light ray on the lower side of the drawing in FIG. 4 of the ghost light 201kg is also an angle of β-θ. . The distance in the sub-scanning direction from the main scanning plane through which the ghost light 201 kg passes at the position of the incident surface of the opposing first scanning lens 121b is expressed by Formula 2.

  Here, L represents the distance between the first scanning lenses 121a and 121b included in the facing scanning optical system, and a represents the distance from the reflection point of the polygon mirror 111 to the first scanning lens 121.

  Regarding the light beam 201y, the outermost light beam on the upper side in FIG. 4 is emitted at an angle of β + θ. The distance in the sub-scanning direction from the main scanning plane through which this light beam passes at the position of the incident surface of the first scanning lens 121b is expressed by Equation 3.

  As shown in FIG. 4, in order to prevent the light beam 201k from entering the effective range of the optical path of the light beam 201y, it is sufficient that the number 2 is larger than the number 3. Therefore, the optical scanning device is preferably configured to satisfy the condition of Equation 4.

  Since the incident surface of the scanning lens 121a has a known fθ characteristic as an aspherical shape in the main scanning direction, L and a differ depending on the main scanning position. At this time, the expression 4 may be satisfied for only a part of the incident surface, but it is more preferable to satisfy the whole area, because the influence of the ghost light 201 kg can be completely removed.

  Also, the light beam shaped by the aperture 103 and incident on the cylindrical lens 104 is substantially parallel light, but sub-scanning on the main plane of the cylindrical lens 104 having power only in the sub-scanning direction represented by D in FIG. Since the light beam diameter in the direction is substantially equal to the aperture diameter of the aperture 103 in the sub-scanning direction, it may be configured to satisfy the condition of Equation 5.

  In this embodiment, the ghost light 201 kg is not re-incident on the polygon mirror 111. With this configuration, the ghost light 201 kg is re-reflected by the polygon mirror, re-enters the first scanning lens 121a, and is prevented from reaching the photoconductor 140k for black toner. In this embodiment, as shown in FIG. 4, the incident position of each light beam 201 on the reflecting surface of the polygon mirror 111 in the sub-scanning direction is substantially the center of the outer shape of the polygon mirror 111. Thereby, the size of the polygon mirror 111 can be made small. When the height of the polygon mirror 111 is P and the condition of Equation 6 is satisfied, the ghost light 201 kg does not re-enter the polygon mirror 111 and the ghost light 201 kg does not reach the black toner photoconductor 140 k. can do. As described above, the ghost light 201kg derived from the light beam 201k is configured not to re-enter the polygon mirror 111, but the ghost light derived from the light beam 201y is also configured not to re-enter the polygon mirror 111. It has become.

[Example 2]
In the previous embodiment, the ghost light 201 kg is configured not to re-enter the polygon mirror 111. However, even if the ghost light 201 kg re-enters the polygon mirror 111 and re-reflects, if the light beam does not enter the effective range of the first scanning lens again, it reaches the photoconductor and forms an unnecessary image. Can be prevented.

  FIG. 5 is an enlarged sub-scanning sectional view in the vicinity of the polygon mirror 111 in the present embodiment. Of the light beam 201k, the ghost light 201kg reflected by the surface of the first scanning lens 121a incident surface, a part of which is re-reflected by the polygon mirror 111, and again the light beam 201kgp toward the first scanning lens 121a. think about. Since the light beam 201 kgp re-enters the polygon mirror 111, the scanning optical system satisfies the condition of Expression 7 in which the inequality sign is opposite to the conditional expression Expression 6 re-entering the polygon mirror 111.

Further, the scanning optical system has a configuration satisfying Expression 8 as a condition that the outermost light beam on the lower side of FIG. 5 is not incident on the first scanning lens 121a with respect to the luminous flux 201 kgp.

  As described above, the ghost light 201kg derived from the light beam 201k is not incident on the effective range of the first scanning lens. However, the ghost light derived from the light beam 201y is also effective for the first scanning lens. It is configured not to enter the range.

[Example 3]
FIG. 6 shows an enlarged view around the aperture 103, the cylindrical lens 104, and the polygon mirror 111 of this embodiment. Other configurations are the same as those in the previous embodiments. A light beam 201 emitted from a light source in a direction perpendicular to the rotation axis of the polygon mirror 111 is allowed to enter the polygon mirror 111 at an oblique incident angle β by passing outside the optical axis of the cylindrical lens 104. The optical axis of the cylindrical lens 104 refers to an axis that vertically connects the apex of the cylindrical surface that is the incident surface and the plane that is the exit surface.

  In addition, the light beams 201k and 201c directed to the two photoconductors pass through the common cylindrical lens 104. By causing the light beams 201k and 201c to enter the sub-scanning position symmetrical to the optical axis of the cylindrical lens 104, an equal oblique incident angle β opposite to the main scanning plane is set. At this time, when the center of the outer shape of the polygon mirror 111 in the sub-scanning direction is aligned with the optical axis of the cylindrical lens 104, the effective range and outer size of the polygon mirror 111 can be reduced.

  Here, let S be the distance in the sub-scanning direction when the two light beams 201k and 201c passing through the cylindrical lens 104 pass through the central portion of the aperture 103. At this time, the equations 9 and 10 can be derived in the same manner as the equation 1 is derived from FIG.

At this time, in order to satisfy Equation 1, β-θ is positive. Equation 11 is derived from Equations 9 and 10.

[Example 4]
FIG. 7 shows an enlarged sub-scanning sectional view in the vicinity of the polygon mirror 111 of this embodiment. In this embodiment, the oblique incident angle of the light beams 201c and 201m deflected to the installation surface G side of the polygon mirror 111 on the lower side of the paper surface in FIG. 7 is deflected to β2, which is opposite to the main scanning plane. The oblique incident angles of the emitted light beams 201k and 201y are β1. That is, two light beams 201c and 201m are incident from both sides across a plane perpendicular to the rotation axis R direction of the polygon mirror 111. The oblique incident angles β1 and β2 have a magnitude relationship shown in Equation 12.

  That is, the incident angles of the light beams 201c and 201m in the sub-scanning direction are different from the incident angles of the light beams 201k and 201y in the sub-scanning direction. Since the light beams 201c and 201m deflected to the installation surface G side of the polygon mirror 111 enter the installation surface of the polygon mirror before entering the facing scanning optical system, there is no image deterioration. On the other hand, the light beams 201k and 201y deflected to the side opposite to the installation surface G of the polygon mirror 111 are not shielded unlike the polygon mirror 111, but by increasing the oblique incident angle β1. The ghost light 201 kg is effectively prevented from entering the effective range of the first scanning lens 121 and the polygon mirror 111, thereby preventing the ghost light 201 kg from reaching the photoconductor 140. When the installation surface G side of the polygon mirror 111 is on the same side as the side on which the light beams 201k and 201y are deflected in the sub-scanning direction, the magnitude relationship between the oblique incident angles β1 and β2 may be reversed.

  In the present embodiment, the incident angles of the light beams 201c and 201m in the sub-scanning direction and the incident angles of the light beams 201k and 201y in the sub-scanning direction are asymmetric with respect to the main scanning plane. When the cylindrical lens 104 is configured to give an oblique incident angle as in the previous embodiment, the luminous fluxes 201k and 201c are at asymmetrical sub-scanning positions with respect to the optical axis of the cylindrical lens 104 indicated by the chain line in FIG. It is good to make it incident.

  At this time, as shown in FIG. 3, one folding mirror 131 is provided for the light beams 201k and 201y having a large oblique incident angle, and for the light beams 201c and 201m having a small oblique incident angle. Two folding mirrors 131 and 132 are provided. When the oblique incidence angle is large, the imaging characteristics of the light beam are likely to deteriorate. However, by reducing the number of folding mirrors, variations such as fluctuations in tolerance are reduced.

[Example 5]
An embodiment of an image forming apparatus using an optical scanning device according to the present invention will be described with reference to FIG. This embodiment is an example in which the optical scanning device according to the present invention is applied to a tandem full-color laser printer. In FIG. 9, a transport belt 906 that transports transfer paper (not shown) fed from a paper feed cassette 907 disposed in the horizontal direction is provided on the lower side in the apparatus. Four photosensitive members 901 for yellow (Y), magenta (M), cyan (C), and black (K) are arranged on the conveyance belt 906 at regular intervals in order from the upstream side in the conveyance direction of the transfer paper. ing. The four photoconductors 901 are all formed to have the same diameter, and process members for executing each process according to the electrophotographic process are sequentially arranged around the four photoconductors 901. A charging charger 902, an optical scanning optical system 100, a developing device 904, a transfer charger (not shown), a cleaning device 905, and the like are sequentially arranged. In the present embodiment, a corresponding light beam is imaged from the optical scanning device on each color photoconductor. The optical scanning device is a counter scanning system, the optical deflector is shared by a single color, and the scanning lens is shared by two stations. A fixing device 910 is provided downstream of the belt separation charger (not shown) in the transfer paper conveyance direction, and is connected to a paper discharge tray 911 by a paper discharge roller 912.

  In such a schematic configuration, for example, in the full color mode (multiple color mode), each optical scanning device 100 uses each color image signal for Y, M, C, and K for each photoconductor 901. An electrostatic latent image corresponding to each color signal is formed on the surface of each photoconductor by optical scanning of the light beam. These electrostatic latent images are developed with color toners by the corresponding developing devices to become toner images, which are superposed by being sequentially transferred onto transfer paper that is electrostatically attracted onto the transport belt 906 and transported. As a result, a full-color image is formed on the transfer paper. This full-color image is fixed by the fixing device 910 and then discharged onto a discharge tray 911 by a discharge roller 912.

  By using the optical scanning optical system 100 of this image forming apparatus as the optical scanning apparatus according to the above-described embodiment, an image forming apparatus capable of achieving the object of the present invention can be obtained.

DESCRIPTION OF SYMBOLS 100 Scanning optical system 102 Coupling lens 103 Aperture 104 Cylindrical lens 111 Polygon mirror 121 1st scanning lens 122 2nd scanning lens 131 1st folding mirror 132 2nd folding mirror 135 Synchronous lens 136 Synchronization detection sensor 140 Photoconductor 201 Light beam 901 Photosensitive Body 902 Charger 904 Developing device 905 Cleaning device 906 Conveying belt 907 Feed cassette 910 Fixing device 911 Discharge tray 912 Discharge roller

JP 2006-133517 A Japanese Patent No. 4430855 Japanese Patent No. 4191562

Claims (10)

A plurality of light source units;
A first optical system for guiding each light beam from the plurality of light source units to a second optical system;
A second optical system that converges each light beam that has passed through the first optical system in a sub-scanning direction;
Deflecting means having a plurality of reflecting surfaces for deflecting a light beam passing through the second optical system and incident at a predetermined angle in the sub-scanning direction;
A third optical system for imaging each of the light beams deflected by the deflecting means on a plurality of scanned surfaces;
In an optical scanning device comprising:
At least two of the light beams from the plurality of light source units are incident on different reflecting surfaces of the deflecting unit, and are deflected so as to be incident on optical elements closest to the different deflecting units,
Of the third optical system, the incident surface of the optical element closest to the deflecting means is parallel to the rotation axis of the deflecting means,
The third optical system is provided with D as the beam diameter in the sub-scanning direction on the main plane in the sub-scanning direction of the second optical system, f as the focal length of the second optical system, respectively. L is the distance between the incident surfaces of the optical elements closest to the reflecting surface of the system, a is the distance from the reflecting surface to the incident surface of the optical element closest to the deflecting means, and the light flux that has passed through the second optical system When the incident angle in the sub-scanning direction with respect to the reflecting surface is β,
(L + a) × tan (β-arctan (D / 2f)) − a × tan (β + arctan (D / 2f))> 0
An optical scanning device that satisfies the requirements.   2. The optical scanning device according to claim 1, wherein an incident surface of an optical element closest to the deflecting unit is opposed to the deflecting unit. The first optical system converts a light beam from the light source unit into a substantially parallel light beam, and includes an aperture member that defines a diameter of the light beam between the first optical system and the second optical system, When the diameter of the aperture member in the sub-scanning direction is Dapt,
(L + a) × tan (β-arctan (Dapt / 2f)) − a × tan (β + arctan (Dapt / 2f))> 0
The optical scanning device according to claim 1, wherein: When the thickness of the deflecting means in the sub-scanning direction is P,
2.times.a.times.tan (.beta.-arctan (Dapt / 2f))> P / 2
The optical scanning device according to claim 1, wherein: When the thickness of the deflecting means in the sub-scanning direction is P,
2 * a * tan ([beta] -arctan (Dapt / 2f)) <P / 2
While satisfying
3 * a * tan ([beta] -arctan (Dapt / 2f))-a * tan ([beta] + arctan (Dapt / 2f))> 0
The optical scanning device according to claim 1, wherein: Of the light beams from the plurality of light source units, two light beams incident on the same reflecting surface of the deflecting unit are emitted in parallel from the light source unit at a distance S in the sub-scan section,
The two light beams pass through the common second optical system,
The incident angle of the two light beams to the deflecting unit in the sub-scanning direction is an angle that is substantially symmetric and substantially equal to a main scanning plane orthogonal to the rotation axis of the deflecting unit.
S> Dapt
The optical scanning device according to claim 1, wherein:   7. The optical scanning device according to claim 1, wherein two light beams are incident from both sides of a plane perpendicular to the rotation axis direction of the deflecting unit.   8. The incident angle in the sub-scanning direction of a light beam incident from one side of the plane where the deflecting unit is disposed is smaller than an incident angle in the sub-scanning direction of a light beam incident from the other side of the plane. Optical scanning device.   The number of reflecting members that guide the light beam incident from the one surface side of the plane to the scanned surface is greater than the number of reflecting members that guide the light beam incident from the other surface side of the plane to the scanned surface. The optical scanning device according to claim 8, wherein the optical scanning device is less. An image forming apparatus for forming an image by executing an electrophotographic process, wherein the image forming apparatus includes the optical scanning device according to claim 1 as an apparatus for performing an exposure process of the electrophotographic process. .

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