JP2008015140A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a compact image forming apparatus capable of obtaining an image high in quality. <P>SOLUTION: The image forming apparatus includes: incident optical systems LA and LB by which luminous fluxes emitted from light source means 1a and 1b are guided to the same deflecting face 5a of a deflecting means 5 at different angles in a sub-scanning cross-section; and imaging optical system 6 by which the luminous fluxes deflected by the same deflecting face are imaged on different photoreceptors 7a and 7b. The imaging optical system has a first optical system in which a sheet of reflecting member 8c is disposed in the optical path of a luminous flux guided to the photoreceptor separated from the deflecting means further than the other photoreceptor. The reflecting member is disposed in an optical path between the photoreceptor 7A and an imaging optical element 6b closest to the photoreceptor in the optical path among imaging optical elements composing the first optical system. If the effective scanning width of the photoreceptor in a main scanning direction is W (mm), the focal length of the imaging optical system in the main scanning direction is f (mm), an optical length from the deflecting point of the deflecting means to the photoreceptor is L (mm), and a distance between the centers of the two photoreceptors adjacent to each other in the sub-scanning cross-section is Dp (mm), the image forming apparatus satisfies following respective conditional experssions: (1/3)W≤f≤W, (1/3)f≤Dp≤(2/3)f, and (1/3)f≤L-1.5Dp≤(4/5)f. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image forming apparatus, and is suitable for an image forming apparatus such as a laser beam printer having an electrophotographic process, a digital copying machine, or a multifunction printer (multifunction printer).

  In a conventional laser beam printer (LBP) optical scanning device, a light beam modulated and emitted from a light source means according to an image signal is periodically deflected by an optical deflector composed of, for example, a rotating polygon mirror. Yes.

  Then, the deflected light beam is focused in a spot shape on a photosensitive recording medium (photosensitive drum) surface by an imaging optical system (imaging lens system) having an fθ characteristic described later, and the surface is optically scanned to form an image. We are recording.

  Various color image forming apparatuses equipped with such an optical scanning device have been proposed (see Patent Document 1).

  FIG. 16 is a schematic view of a main part of a conventional color image forming apparatus.

  In the figure, a light beam emitted from a light source means (not shown) passes through a cylindrical lens (not shown), a polygon mirror 53 rotated by a motor 52, and a resin fθ lens 54. The light beam that has passed through the fθ lens 54 forms an image on the surface to be scanned (photosensitive drum surface) 14 through the first flat mirror 55, the toroidal lens 56, the second flat mirror 57, the third flat mirror 58, and the dustproof glass 59. .

In a color image forming apparatus equipped with such an optical scanning device, in order to record image information with high accuracy,
The field curvature is well corrected over the entire surface to be scanned;
The spot diameter on the scanned surface is uniform at each image height,
Having a tilt correction function for correcting the position of the scanning line so as not to occur even when the deflection surface of the deflecting means tilts;
Distortion is corrected well,
is required. Various types of optical scanning devices satisfying such optical characteristics or correction optical systems (imaging optical elements) have been proposed.

  On the other hand, in an image forming apparatus such as a laser beam printer or a digital copying machine, there is a demand for downsizing and simplification of the entire apparatus. Accordingly, similar demands have been made for optical scanning devices.

In Patent Document 1, six optical lenses (54, 56) and twelve plane mirrors (55, 57, 58) are used after the polygon mirror 53 as an optical scanning device mounted on a color image forming apparatus. .
JP 2004-264396 A

  If the number of optical elements such as imaging lenses and plane mirrors arranged in the optical path is large as in Patent Document 1, the size of the optical scanning device is increased, and further, the size of the image forming apparatus using the optical scanning device is increased. End up.

  Conventionally, in an image forming apparatus such as a laser beam printer or a digital copying machine, the entire apparatus has been made compact. Therefore, it has been necessary to guide a plurality of light beams emitted from the light source means to the surface to be scanned in a single space in which a plurality of plane mirrors are arranged in consideration of the optical path. Therefore, the optical scanning device tends to be large.

  In order to make the image forming apparatus compact, it is necessary to shorten the focal length of the imaging lens system, that is, to shorten the distance from the deflection point of the optical deflector to the surface to be scanned.

  However, generally, when the focal length of the imaging lens system is shortened, the distance from the lens surface of the imaging lens closest to the scanned surface to the scanned surface (lens (Back) becomes shorter. Then, when a plane mirror is arranged in the optical path between the imaging lens surface closest to the scanned surface and the scanned surface, there arises a problem that the degree of freedom is reduced.

  Further, due to the demand for further downsizing of the entire apparatus, the number of reflecting surfaces of the rotating polygon mirror is reduced, and a plurality of light beams emitted from the light source means are obliquely directed to a surface orthogonal to the rotation axis of the rotating polygon mirror. When the light enters the scanning line, the scanning line on the surface to be scanned is curved. Furthermore, it has been difficult to obtain a good image, such as rotation of the imaging spot.

  An object of the present invention is to provide an image forming apparatus capable of obtaining a compact and high-quality image.

The image forming apparatus of the invention of claim 1
A plurality of light source means, an incident optical system for guiding a plurality of light beams emitted from the plurality of light source means to the same deflection surface of the deflection means at different angles in the sub-scan section, and the same deflection surface of the deflection means An image forming optical system that forms an image on a plurality of different photoconductors, the image forming apparatus comprising:
The imaging optical system has a first optical system in which one reflecting member is arranged in the optical path of a light beam guided to the photoreceptor most distant from the deflecting unit,
The reflecting member is provided in the optical path between the imaging optical element closest to the photosensitive member in the optical path and the photosensitive member among the imaging optical elements constituting the first optical system,
The effective scanning width of the photoconductor in the main scanning direction is W (mm), the focal length of the imaging optical system in the main scanning direction is f (mm), and the optical path length from the deflection point of the deflecting means to the photoconductor is L (mm), where Dp (mm) is the distance between the centers of two adjacent photoconductors in the sub-scan section.
(1/3) W ≦ f ≦ W
(1/3) f ≦ Dp ≦ (2/3) f
(1/3) f ≦ L−1.5Dp ≦ (4/5) f
It is characterized by satisfying the following conditions.

The invention of claim 2 is the invention of claim 1,
The plurality of light beams deflected by the deflecting means pass through the same imaging optical element closest to the photosensitive member in the optical path among the imaging optical elements constituting the imaging optical system.

The invention of claim 3 is the invention of claim 1 or 2, wherein
Among the imaging optical elements constituting the imaging optical system, the imaging optical element closest to the photosensitive member in the optical path has a plurality of light beams deflected by the deflecting means having different regions in the sub-scanning section. The imaging optical element that passes through and is closest to the photosensitive member includes at least one optical surface having a shape defined by a different function for each of the different regions in the sub-scan section. It is said.

The invention of claim 4 is the invention of claim 1, 2 or 3,
When the imaging magnification in the sub-scanning section of the imaging optical system when the light beam on the deflection surface forms an image on the photoconductor in the sub-scanning section is βs,
| Βs | ≧ 1.5
It is characterized by satisfying the following conditions.

The invention of claim 5 is the invention of any one of claims 1 to 4,
At least one of the imaging optical elements constituting the imaging optical system has a maximum effective diameter in the main scanning direction of Ymax (mm).
Ymax ≦ (4/5) f
It is characterized by satisfying the following conditions.

The invention of claim 6 is the invention of any one of claims 1 to 5,
A plurality of reflecting members are arranged in the optical path for guiding the light beam to the photosensitive member closest to the deflecting unit, and the reflecting point of the reflecting member closest to the deflecting unit side in the optical path among the plurality of reflecting members. The distance in the direction perpendicular to the rotation axis of the deflection means in the sub-scan section from the reflection point of the reflection member closest to the photoreceptor side to the reflection member closest to the deflection means side in the optical path is L1 (mm). When the angle between the principal ray of the incident light beam and the principal ray of the reflected light beam is θ (°),
(L1 + 0.5Dp-L / (1+ | βs |)) tan θ ≧ 10 (mm)
It is characterized by satisfying the following conditions.

The invention of claim 7 is the invention of any one of claims 1 to 6,
When the distance from the reflection point of the reflecting member closest to the photoconductor side in the optical path to the photoconductor among the reflecting members that guide the light beam to the photoconductor closest to the deflecting unit is L2 (mm),
L2 ≧ 40 (mm)
It is characterized by satisfying the following conditions.

The invention of claim 8 is the invention of any one of claims 1 to 7,
Each of the plurality of light source means has a plurality of light emitting portions.

  According to the present invention, an image forming apparatus capable of obtaining a compact and high-quality image can be achieved.

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

  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. 3 is a cross-sectional view (sub-scanning cross-sectional view) of the main part in the sub-scanning direction including the plane mirror according to the first embodiment of the present invention.

  In the following description, the main scanning direction is a direction perpendicular to the rotation axis of the rotating polygon mirror and the optical axis of the imaging optical system (the direction in which the light beam is reflected and deflected (deflected and scanned) by the rotating polygon mirror). The sub-scanning direction is a direction parallel to the rotation axis of the rotary polygon mirror. The main scanning section is a plane including the main scanning direction and the optical axis of the imaging optical system. The sub-scanning section is a section perpendicular to the main scanning section.

  In the figure, reference numerals 1a and 1b denote light source means each made of a semiconductor laser.

  Reference numerals 2a and 2b denote aperture stops, respectively, which shape divergent light beams emitted from the light source means 1a and 1b into specific optimum beam shapes.

  Reference numerals 3a and 3b denote condensing lenses (collimator lenses) that convert divergent light beams that have passed through the aperture stops 2a and 2b into parallel light beams (or convergent light beams).

  Reference numerals 4a and 4b denote lens systems (cylindrical lenses) each having a finite refractive power (power) only in the sub-scanning direction (within the sub-scanning section).

  Each element of the light source means 1a, the aperture stop 2a, the condensing lens 3a, and the cylindrical lens 4a constitutes one element of the incident optical system LA. Each element of the light source means 1b, the aperture stop 2b, the condenser lens 3b, and the cylindrical lens 4b constitutes one element of the incident optical system LB.

  The condensing lens 3a (3b) and the cylindrical lens 4a (4b) may be constituted by one optical element.

  An optical deflector 5 as a deflecting means is composed of, for example, φ20 (diameter 20 mm), a four-sided polygon mirror (rotating polygon mirror), and is driven in the direction of arrow A in the figure by a motor driving means (not shown). It is rotating at a constant speed (equal angular speed).

  Reference numeral 6 denotes an imaging optical system (imaging lens system) having a condensing function and an fθ characteristic, and first and second imaging lenses (scanning lenses) having different powers in the main scanning direction and the sub-scanning direction. (Also referred to as an fθ lens.) 6a and 6b.

  The fθ characteristic means that a light beam incident at an angle of view (scanning angle) θ is imaged on the surface to be scanned at a position of Y = f × θ, where Y is the height from the optical axis and f is a constant. It has a relationship. That is, the scanning width (scanning speed) scanned per unit angle of view is the same over the entire scanning surface. The constant f is called an fθ coefficient. When the incident light beam to the lens is a parallel light beam, the constant f has the same value as the paraxial focal length f.

  The first and second imaging lenses 6a and 6b are made of a plastic material, and form a light beam based on image information reflected and deflected by the optical deflector 5 on the scanned surfaces (photosensitive drum surfaces) 7a and 7b. Yes. The imaging optical system 6 performs surface tilt compensation of the deflecting surface by making a conjugate relationship between the deflecting surface 5a of the optical deflector 5 and the scanned surfaces 7a and 7b in the sub-scan section.

  In the present embodiment, the first imaging lens 6a has a positive power in the main scanning section, and the second imaging lens 6b has a positive power in the sub-scanning section.

  8a, 8b, and 8c are plane mirrors as reflecting members, respectively, and fold the light beams that have passed through the first and second imaging lenses 6a and 6b toward the corresponding photoreceptors 7A and 7B. The plane mirrors 8a, 8b, and 8c may have power in the main scanning section or the sub-scanning section.

  In the present embodiment, two divergent light beams modulated and emitted from the light sources 1a and 1b according to the image information are regulated by the corresponding aperture stops 2a and 2b, converted into parallel light beams by the collimator lenses 3a and 3b, The light enters the cylindrical lenses 4a and 4b. Out of the light beams incident on the cylindrical lenses 4a and 4b, they are emitted as they are in the main scanning section. In the sub-scan section, the light beams converge to form a line image (a line image elongated in the main scanning direction) on the same deflection surface 5a of the optical deflector 5 at different angles. The two light beams reflected and deflected by the deflecting surface 5a of the optical deflector 5 are scanned by the imaging optical system 6 through the corresponding plane mirrors 8a, 8b, 8c, and the scanned surfaces 7a of the different photoreceptors 7A, 7B, The image is spot-formed on 7b.

  For example, the light beam from the light source means 1a incident obliquely from above is deflected obliquely downward with respect to the deflecting surface 5a of the optical deflector 5, and the light beam from the light source means 1b incident obliquely downward is directed obliquely upward. Reflected.

  Then, by rotating the optical deflector 5 in the arrow A direction, optical scanning is performed on the scanned surfaces 7a and 7b in the arrow B direction (main scanning direction) at a constant speed. As a result, image recording is performed on the photoconductors 7A and 7B, which are recording media.

  The surface shapes of the refractive surfaces of the first and second imaging lenses 6a and 6b in the present embodiment are expressed by the following shape expression.

  When the intersection with the optical axis is the origin, the optical axis direction is the X axis, the axis orthogonal to the optical axis in the main scanning plane is the Y axis, and the axis orthogonal to the optical axis in the sub scanning plane is the Z axis, The bus direction corresponding to the scanning direction is

(Where R is the radius of curvature of the generatrix on the optical axis, and K, B ₄ , B ₆ , B ₈ , and B ₁₀ are aspheric coefficients)
In this embodiment, the bus line connecting the vertices of the child lines is shifted in the sub-scanning direction by a function defined below. However, the origin of Z is the optical reference axis CO.

  The sub-scanning direction (the direction including the optical axis and orthogonal to the main scanning direction) and the sub-line direction are

Where r ′ = r ₀ (1 + D ₂ Y ² + D ₄ Y ⁴ + D ₆ Y ⁶ + D ₈ Y ⁸ + D ₁₀ Y ¹⁰ )
(Where r ₀ is the radius of curvature on the optical axis on the optical axis, and D ₂ , D ₄ , D ₆ , D ₈ and D ₁₀ are coefficients)
Note that the radius of curvature r ′ outside the optical axis is defined in a plane perpendicular to the main scanning plane, including the normal of the bus at each position. The polynomial in the shape expression is expressed by a function up to the 10th order, but the order may be higher or lower. If the surface shape expression itself is an expression having the same degree of freedom of surface expression, the effect of the present invention can be obtained without any problem.

  Tables 1 and 2 show the optical arrangement of the optical element of Numerical Example 1 and the surface shape of the imaging optical element (imaging lens) in this example.

  Here, the aspheric coefficients Ku to B10u and D2u to D10u are coefficients that specify the shape in one direction (one of the main scanning directions) across the optical axis of the lens surface. The aspheric coefficients Kl to B10l and D2l to D10l are coefficients that specify the shape in the other direction (the other of the main scanning directions) across the optical axis of the lens surface.

  In this embodiment, the light beams emitted from the light source means 1a and 1b are incident on the deflection surface 5a of the optical deflector 5 at an angle with respect to the optical axis in the main scanning section. Surface entry / exit (sag) occurs asymmetrically between the scan start side and the scan end side.

  The second imaging lens 6b has a curvature in the sub-scanning direction in order to satisfactorily correct the variation in the field curvature and spot diameter in the main scanning direction with respect to the optical axis due to this asymmetric sag. It has a surface whose radius changes asymmetrically along the main scanning direction with respect to the optical axis.

  As shown in Table 2, the aspherical coefficients Ku to B10u and Kl to B10l in the main scanning section of the second surface (outgoing surface) of the first imaging lens 6a are different, and the shape in the main scanning section is different. It can be seen that within the effective diameter of the lens surface, it changes asymmetrically about the optical axis from the on-axis to the off-axis.

  On the fourth surface (outgoing surface) of the second imaging lens 6b, the aspheric coefficients D2u to D10u and D2l to D10l in the sub-scanning section are different, and the curvature in the sub-scanning surface is effective for the lens surface. It can be seen that within the diameter, it changes asymmetrically about the optical axis from the axis to the axis.

  In the present embodiment, the entrance surface 6a1 and the exit surface 6a2 of the first imaging lens 6a are formed in an aspheric shape (non-arc shape) expressed by a function up to the 10th order in the main scanning section (main scanning direction). The inside of the sub-scanning cross section is formed in a planar shape (non-arc shape). The shape in the sub-scanning section is not limited to a flat surface, and may be a spherical surface or an aspherical surface, for example.

  The incident surface 6b1 of the second imaging lens 6b is formed in an arc shape, and the exit surface 6b2 is formed in an aspheric shape (non-arc shape) expressed by a function up to the 10th order in the main scanning section (main scanning direction). Yes. Further, since the power in the sub-scanning direction decreases from on-axis to off-axis in the main scanning direction, the field curvature in the sub-scanning direction is corrected well.

  Next, means and effects for achieving the object of the present embodiment will be described.

  In this embodiment, the two light beams emitted from the two light source means 1a and 1b and deflected by the optical deflector 5 are passed through the same first and second imaging lenses 6a and 6b to be scanned. Images are formed on 7a and 7b. As a result, in this embodiment, the number of imaging lenses is reduced, and the apparatus can be simplified and miniaturized.

  Then, the two light beams pass through the first and second imaging lenses 6a and 6b, and then are optically separated by the plane mirrors 8a, 8b and 8c, and are guided onto the two scanned surfaces 7a and 7b.

  In this embodiment, the light beam is separated by the plane mirrors 8a, 8b and 8c after the light beam passes through all the first and second imaging lenses 6a and 6b. Therefore, conventionally, the light beam reflected by the plane mirror is incident again on the imaging lens and is caused by an arrangement error of the plane mirror that has occurred when an image is formed on the surface to be scanned (the light beam deviates from a specific beam passage position). Therefore, the occurrence of bending or bending of the scanning line can be suppressed.

  At this time, the plane mirror that guides the light beam to the scanned surface 7a of the photoconductor 7A farthest from the optical deflector 5 is constituted by a single plane mirror 8c. In addition, the plane mirror for guiding the light beam to the scanned surface 7b of the photoconductor 7B located on the optical deflector 5 side with respect to the most separated photoconductor 7A is composed of two plane mirrors 8a and 8b.

  In this embodiment, the optical system in which the plane mirror 8c is disposed in the optical path between the second imaging lens 6b and the photoreceptor 7A is referred to as a first optical system. The optical system in which the plane mirrors 8a and 8b are disposed in the optical path between the second imaging lens 6b and the photoconductor 7B is referred to as a second optical system. These first and second optical systems are included in the imaging optical system 6.

  The location of the plane mirror is often limited by the optical path length. Conventionally, when the focal length of the imaging optical system is long, the light beam is guided to the scanned surface 7a of the photoconductor 7A farthest from the optical deflector 5. Required two or three flat mirrors.

In this embodiment, when the effective scanning width in the main scanning direction of the photoreceptors 7A and 7B is W (mm) and the focal length of the imaging optical system 6 in the main scanning direction is f (mm),
(1/3) W ≦ f ≦ W (1)
The focal length in the main scanning direction of the imaging optical system 6 is set so as to satisfy the following condition. As a result, only one plane mirror can be configured to guide the light beam to the scanned surface 7a of the photoconductor 7A farthest from the optical deflector 5.

  Conditional expression (1) defines the focal length of the imaging optical system 6 in the main scanning direction. When the lower limit of conditional expression (1) is exceeded and the focal length f of the imaging optical system is shortened, the distance (lens back) from the lens surface of the imaging lens closest to the scanning surface to the scanning surface is generally short. Become. Therefore, when a plane mirror is arranged in the optical path between the lens surface of the imaging lens closest to the scanned surface and the scanned surface, the degree of freedom is reduced. In addition, it becomes difficult to mount the image forming apparatus on an image forming apparatus having a large distance between the centers of the photosensitive members. If the upper limit of conditional expression (1) is exceeded and the focal length of the imaging optical system is increased, the main body height of the image forming apparatus is increased.

In this embodiment, the effective scanning width W (mm) in the main scanning direction of the photoconductors 7A and 7B and the focal length f (mm) in the main scanning direction of the imaging optical system 6 are respectively W = 220 mm.
f = 140mm
It is said. This satisfies the conditional expression (1).

As described above, in this embodiment, a single plane mirror that guides the light beam to the scanned surface 7a is configured by performing an appropriate power arrangement so that the focal length f in the main scanning direction of the imaging optical system 6 is shortened. Nevertheless, the main body height of the image forming apparatus can be reduced. The main body height here is a distance h from the deflection point 5b of the optical deflector 5 shown in FIG. 3 to the scanned surfaces 7a and 7b. In this embodiment, h = 74 mm.
It is said.

In this embodiment, the optical path length from the deflection point 5b of the optical deflector 5 to the photoconductors 7A and 7B is L (mm), and the distance between the centers of two adjacent photoconductors 7A and 7B in the sub-scan section is Dp. (Mm)
(1/3) f ≦ Dp ≦ (2/3) f (2)
(1/3) f ≦ L−1.5Dp ≦ (4/5) f (3)
Each element is set to satisfy the following condition.

  Conditional expression (2) defines the distance Dp between the centers of two adjacent photoreceptors. If the conditional expression (2) is not satisfied, it is difficult to reduce the size of the entire apparatus.

  Conditional expression (3) relates to the main body height of the image forming apparatus and the focal length of the imaging optical system. If the upper limit of conditional expression (3) is exceeded, the main body width of the image forming apparatus can be shortened, but the main body height becomes high, which is not good. If the lower limit value of conditional expression (3) is exceeded, the main body height of the image forming apparatus can be lowered, but the main body width becomes wide, which is not good.

In this embodiment, the distance Dp (mm) between the centers of two adjacent photoconductors and the optical path length L (mm) from the deflection point 5b of the optical deflector 5 to the photoconductors 7A and 7B are represented by Dp = 60 mm.
L = 161mm
Is set. This satisfies the conditional expressions (2) and (3).

  Here, FIG. 4 is a graph for determining the conditions when only one plane mirror is used to guide the light beam to the scanned surface 7a of the photosensitive member furthest away from the optical deflector 5.

  In FIG. 4, it is assumed that the printing width corresponding to the A4 size paper is scanned, and the effective scanning width W on the surface to be scanned is set to W = 220 mm. Therefore, the focal length f in the main scanning direction of the imaging optical system 6 is set. Is set to f = 100 to 200 mm. When the focal length f takes the above value, the distance L along the optical axis from the deflection point 5b of the optical deflector to the surface to be scanned is generally about 115 to 230 mm, which is about 1.15 times the focal length f. .

  From FIG. 4, it is assumed that only one plane mirror is used to guide the light beam to the scanned surface 7a of the photosensitive member 7A farthest from the optical deflector 5. Under this condition, the condition of the distance Dp between the centers of the photosensitive members is added. Then, it can be seen that the distance h from the deflection point 5b to the scanned surfaces 7a and 7b is in a range surrounded by straight lines of f = 100 mm and f = 200 mm.

  Further, after passing through the first and second imaging lenses 6a and 6b, the light beam is guided to the scanned surface 7b of the photoreceptor 7B close to the optical deflector 5, and the light is reflected from the reflection point 8b1 of the plane mirror 8b. A condition is set such that the distance L2 to the scanned surface 7b of the body 7B is 40 mm or more. Then, the distance h from the deflection point 5b of the optical deflector to the scanned surfaces 7a and 7b is in a range surrounded by a dotted line, a one-dot chain line, a two-dot chain line, and a thick line in the figure.

  Each of the enclosed ranges is βs = −3.0, where βs is the imaging magnification in the sub-scan section of the imaging optical system 6 when the light beam on the deflection surface forms an image on the photoconductors 7A and 7B. This is the existence range when βs = −2.0, βs = −1.7, and βs = −1.4. As shown in FIG. 4, it can be seen that the range that can be taken increases as the absolute value of the imaging magnification βs in the sub-scan section increases.

In this embodiment, the second imaging lens 6b closest to the scanned surface 7b is brought closer to the optical deflector 5 side, and the imaging magnification βs is set to βs = −1.9.
Thus, the degree of freedom of arrangement of the plane mirror is increased, and the image forming apparatus with a wide range of distance Dp between the centers of the photoconductors 7A and 7B and the distance h from the deflection point 5b to the scanned surfaces 7a and 7b can be obtained. Is provided.

In this embodiment, the imaging magnification βs in the sub-scan section of the imaging optical system 7 is
| Βs | ≧ 1.5 (4)
Is set to satisfy the following conditions.

  More preferably, the conditional expression (4) is set as follows.

3.0 ≧ | βs | ≧ 1.5 (4a)
As described above, in this embodiment, by satisfying the conditional expression (1), it is possible to reduce the height of the main body of the image forming apparatus even though the single plane mirror is configured. Further, by satisfying the conditional expressions (2), (3), and (4), the selection range of the distance Dp between the centers of the photosensitive members and the distance h from the deflection point to the scanned surface is expanded, and a compact image forming apparatus Can be provided.

  In this embodiment, the maximum effective diameter of the first imaging lens 6a is set to 95 mm by bringing the second imaging lens 6b closest to the scanned surface 7b closer to the optical deflector 5 side. As a result, the number of lenses to be taken at the time of injection molding can be increased, and as a result, the cost can be reduced. The term “maximum effective diameter” as used herein refers to the lens passing position in the main scanning direction of the principal ray of the light beam when scanning outside the outermost axis in the effective scanning area.

In this embodiment, the maximum effective diameter Ymax (mm) in the main scanning direction of at least one of the imaging lenses constituting the imaging optical system 6 is
Ymax ≦ (4/5) f (5)
Is set to satisfy the following conditions.

In the present embodiment, among the plane mirrors that guide the light beam to the scanned surface 7b of the photoconductor 7B closest to the optical deflector 5, the most scanned surface from the reflection point 8a1 of the planar mirror 8a closest to the optical deflector 5 side. The distance in the direction perpendicular to the rotation axis of the optical deflector 5 to the reflection point 8b1 of the plane mirror 8b on the 7b side is L1 (mm). Furthermore, when the angle between the principal ray of the incident light beam and the principal ray of the reflected light beam on the flat mirror 8a closest to the optical deflector 5 is θ (°),
(L1 + 0.5Dp-L / (1+ | βs |)) tan θ ≧ 10 (mm) (6)
Each element is set to satisfy the following condition.

In this embodiment, the distance L1 (mm) from the reflection point 8a1 of the plane mirror 8a to the reflection point 8b1 of the plane mirror 8b and the angle θ (°) formed between the incident light beam and the reflected light beam on the plane mirror 8a are respectively L1 = 43.5mm,
θ = 46.1 °
Is set. This satisfies the conditional expression (6).

  Thus, in this embodiment, the arrangement is optimized so that the light beam reflected by the plane mirror 8a does not interfere with the second imaging lens 6b closest to the scanned surface 7b.

At this time, among the plane mirrors that guide the light beam from the optical deflector 5 to the scanned surface 7b of the photoconductor 7B closest to the optical deflector 5, the distance from the reflection point 8b1 of the planar mirror 8b closest to the scanned surface 7b to the scanned surface 7b. Is L2 (mm),
L2 ≧ 40 (mm) (7)
Satisfy the following conditions.

In this embodiment, the distance L2 (mm) from the reflection point 8b1 of the plane mirror 8b to the scanned surface 7b is L2 = 40 mm,
Is set. This satisfies the conditional expression (7).

  Thus, in this embodiment, the flat mirror 8b is prevented from being contaminated by toner scattering.

  The distance L2 from the reflection point 8b1 of the flat mirror 8b to the surface to be scanned 7b is not limited to this, and varies depending on, for example, the size of the image forming apparatus and the required optical performance.

  In the present embodiment, as shown in FIG. 5, the exit surface 6b2 of the second imaging lens 6b is decentered in the sub-scanning direction, so that even when an oblique incidence optical system is used, the scanning line is curved and the spot is rotated. Corrected well. The same effect can be obtained by decentering the incident surface 6b1 of the second imaging lens 6b in the sub-scanning direction. In FIG. 5, reference numerals 10a and 10b denote light beams emitted from the first and second light source means 1a and 1b, respectively.

  In this embodiment, the coefficient A0 of the generating function of the incident surface 6b1 of the second imaging lens 6b is set to ± 1.1, and the incident surface 6b1 of the second imaging lens 6b is decentered by ± 1.1 mm in the sub-scanning direction. I am letting. The two light beams deflected by the optical deflector 5 pass through different regions of the second imaging lens 6b in the sub-scan section. The second imaging lens 6b has at least one optical surface having a shape defined by a different function in the sub-scan section with respect to the different regions.

  Here, “different functions” means that the definition equations are the same, but the values of the coefficients are different, or the absolute values of the coefficients are the same but the signs are different. Also, the definition formula itself may be different.

  FIG. 6 is a diagram showing the geometrical aberration, the uniformity of the sub-scanning magnification of the imaging optical element (imaging lens) according to the image height, and the amount of curvature of the scanning line in this embodiment.

  It can be seen from FIG. 6 that each aberration is corrected to a level where there is no practical problem. It can also be seen that the change in the sub-scan magnification due to the image height is suppressed to 2% or less. Note that the change in the sub-scanning magnification depending on the image height may be 10% or less. More desirably, it may be 5% or less. The curvature of the scanning line is also corrected well.

  FIG. 7 is an explanatory diagram showing the spot shape on the surface to be scanned in this embodiment. As shown in the figure, the rotation of the spot on the surface to be scanned generated when the light beam emitted from the light source means is obliquely incident on the deflecting surface 5a of the optical deflector 5 in the sub-scan section is well corrected. I understand that.

  In the present embodiment, the material of the first and second imaging lenses 6a and 6b is formed of a plastic material. However, the material is not limited to this, and may be a glass material, for example.

  Further, in this embodiment, the second imaging lens 6b is composed of one sheet to form two beams on the respective scanned surfaces 7a and 7b. However, the present invention is not limited to this. For example, one sheet is formed for each beam. The second imaging lens 6b, that is, the second imaging lens 6b may be composed of two pieces.

  In this embodiment, the imaging optical system 6 is composed of the first and second imaging lenses 6a and 6b. However, the present invention is not limited to this. For example, the imaging optical system 6 is composed of a single imaging lens or three or more lenses. May be. Further, even if the imaging optical system 6 is configured using an optical element such as an fθ mirror or a diffractive optical element, the same effect as in the first embodiment can be obtained.

  In the present embodiment, it is assumed that the print width corresponding to the A4 size is scanned, and the optical system of the image forming apparatus is optimized by setting the effective scanning width W on the surface to be scanned to 220 mm. Larger or smaller sizes can also be handled.

  In the present embodiment, the light source means 1a and 1b may each be constituted by a monolithic multi-beam light source having a plurality of light emitting portions (light emitting points) on the same chip. By using a multi-beam light source, high-speed optical scanning is possible without increasing the rotational speed of the optical deflector 5.

The light beam incident on the first imaging lens 6a is not limited to a parallel light beam, and may be a convergent light beam, for example.
[Color image forming apparatus]
The light source means, the imaging optical system, and the photosensitive member are arranged symmetrically on both sides about the rotation axis of the optical deflector. Then, by deflecting the light beam on both sides of the surface including the rotation axis of the optical deflector, it is possible to provide an image forming apparatus that can be mounted on a four-color full-color image forming apparatus as shown in FIG.

  The image forming apparatus that can be mounted on the full-color image forming apparatus of this embodiment uses only four imaging lenses and six plane mirrors after the optical deflector. The image forming apparatus and the full-color image forming apparatus It is possible to make it compact.

  In FIG. 8, the same elements as those shown in FIG. 3 are given the same reference numerals.

  As described above, in this embodiment, as described above, the number of imaging lenses and plane mirrors can be reduced, a lens back can be secured, and the degree of freedom in arranging the plane mirrors can be increased. Further, it is possible to satisfactorily correct curvature of field, distortion, variation in beam diameter due to image height, scan line curvature, and spot rotation. Thus, in this embodiment, an image forming apparatus capable of obtaining a compact and high quality image can be provided.

  9 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. FIG. 10 is a sectional view (sub scanning sectional view) of the main part in the sub scanning direction according to the second embodiment of the present invention. FIG. 11 is a sectional view (sub-scanning sectional view) of the principal part in the sub-scanning direction including the plane mirror according to the second embodiment of the present invention. 9 to 11, the same elements as those shown in FIGS. 1 to 3 are denoted by the same reference numerals.

  This embodiment differs from the first embodiment in that the first and second imaging lenses 16a and 16b are formed in different shapes, and the imaging magnification in the sub-scan section of the imaging optical system 16 is different. This increases the degree of freedom in arranging the plane mirror. 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, reference numeral 16 denotes an imaging optical system (imaging lens system) having a condensing function and fθ characteristics, and first and second imaging lenses (also referred to as scanning lenses or fθ lenses) 16a, It consists of 16b.

  In the present embodiment, the entrance and exit surfaces of the first and second imaging lenses 16a and 16b are formed in an aspherical shape in which the main scanning cross section is expressed by a function up to the 10th order, and the sub scanning cross section is within the sub scanning cross section. Is formed in a planar shape.

  Reference numerals 18a, 18b, and 18c denote flat mirrors as reflecting members, which are made of flat mirrors and fold the light beams that have passed through the first and second imaging lenses 16a and 16b toward the corresponding photoreceptors 7A and 7B. . The plane mirrors 18a, 18b, and 18c may have refractive power in the main scanning section or the sub-scanning section.

  Tables 3 and 4 show the optical arrangement of the optical element of Numerical Example 2 and the surface shape of the imaging optical element in this embodiment.

  In the present embodiment, the entrance surface 16a1 and the exit surface 16a2 of the first imaging lens 16a are formed in an aspherical shape in which the main scanning section is expressed by a function up to the 10th order, and the sub-scanning section is flat. It is.

  The incident surface 16b1 and the exit surface 16b2 of the second imaging lens 16b are formed in an aspherical shape in which the main scanning section is expressed by a function up to the 10th order, and the subscanning section is a function up to the 10th order. It is expressed and formed in an arc shape whose curvature changes corresponding to the main scanning direction. The power in the sub-scanning direction is reduced from on-axis to off-axis in the main scanning direction, so that the field curvature in the sub-scanning direction is corrected well.

  It should be noted that by decentering the exit surface 16b2 of the second imaging lens 16b in the sub-scanning direction, the curvature of the scanning line and the rotation of the imaging spot on the surface to be scanned, which occurs when using the oblique incidence optical system. Corrected well.

  In the present embodiment as well, the same first and second imaging lenses 16a are emitted from the two light source means 1a and 1b and deflected by the optical deflector 5 as in the first embodiment. , 16b are imaged on the scanned surfaces 7a, 7b. As a result, in this embodiment, the number of imaging lenses is reduced, and the apparatus can be simplified and miniaturized.

  Then, after the two light beams pass through the first and second imaging lenses 16a and 16b, the optical paths are separated by the plane mirrors 18a, 18b and 18c, and the respective light beams are guided onto the two scanned surfaces 7a and 7b. ing.

  In this embodiment, the light beam is separated by the plane mirrors 18a, 18b, and 18c after the light beam passes through all the first and second imaging lenses 16a and 16b. Therefore, conventionally, the light beam reflected by the plane mirror is incident again on the imaging lens and is caused by an arrangement error of the plane mirror that has occurred when an image is formed on the surface to be scanned (the light beam deviates from a specific beam passage position). Therefore, the occurrence of bending or bending of the scanning line can be suppressed.

  At this time, the plane mirror for guiding the light beam to the scanned surface 7a of the photoconductor 7A farthest from the optical deflector 5 is constituted by one plane mirror 18c. In addition, a plane mirror that guides a light beam to the scanned surface 7b of the photoconductor 7B that is closer to the optical deflector 5 than the most separated photoconductor 7A is composed of two plane mirrors 18a and 18b.

In this embodiment, as in the first embodiment, the effective scanning width W (mm) in the main scanning direction and the focus in the main scanning direction of the imaging optical system 16 on the photoconductors 7A and 7B so as to satisfy the conditional expression (1). The distance f (mm) is W = 220mm respectively.
f = 140mm
Is set. As a result, the height h of the main body of the image forming apparatus can be reduced despite the single plane mirror that guides the light beam to the scanned surface 7a. In this embodiment, the main body height h (mm) of the image forming apparatus is h = 90.3 mm.
It is said.

In this embodiment, as in the first embodiment, the optical path length L (mm) from the deflection point 5b of the optical deflector 5 to the photoconductors 7A and 7B, the sub-expression is satisfied so as to satisfy the conditional expressions (2) and (3). The distance Dp (mm) between the centers of two adjacent photoconductors 7A and 7B in the scanning section is represented by Dp = 60 mm.
L = 161mm
Is set. Thus, a compact image forming apparatus is provided.

  Further, in this embodiment, the refractive power in the sub-scanning section of the second imaging lens 16b is weakened so that the second imaging lens 16b is brought closer to the optical deflector 5 side to increase the imaging magnification in the sub-scanning direction. It is set. As a result, in this embodiment, an image forming apparatus in which the degree of freedom of arrangement of the plane mirror is further increased as compared with the first embodiment.

The imaging magnification βs in the sub-scanning direction on the optical axis of the imaging optical system 16 in this embodiment is
βs = −2.3
Thus, it is possible to ensure a long lens back even if the optical path length is short. Therefore, the degree of freedom of arrangement of the plane mirror is increased, and an image forming apparatus having a wider range of distance Dp between the centers of the photoconductors 7A and 7B and the distance h from the deflection point to the surface to be scanned can be provided. it can.

  Also in this embodiment, the maximum effective diameter of the first imaging lens 16a is set to 83 mm by further bringing the second imaging lens 16b closest to the scanned surface 7b closer to the optical deflector 5 side. This facilitates lens production.

Further, in this embodiment, the distance L1 in the direction perpendicular to the rotation axis of the optical deflector 5 from the reflection point 18a1 of the flat mirror 18a closest to the optical deflector 5 to the reflection point 18b1 of the flat mirror 18b closest to the scanned surface 7b. (Mm) and the angle formed between the principal ray of the incident light beam to the plane mirror 18a and the principal ray of the reflected light beam is θ (°), L1 = 39.5 mm,
θ = 32.1 °
Is set. Thus, in this embodiment, the arrangement is optimized so that the light beam reflected by the plane mirror 18a does not interfere with the second imaging lens 16b closest to the scanning surface.

  FIG. 12 is a diagram showing the geometrical aberration, the uniformity of the sub-scanning magnification of the imaging optical element (imaging lens) according to the image height, and the amount of curve of the scanning line in this embodiment.

  From FIG. 12, it can be seen that each aberration is corrected to a level where there is no practical problem. It can also be seen that the change in the sub-scan magnification due to the image height is suppressed to 2% or less. Note that the change in the sub-scanning magnification depending on the image height may be 10% or less. More desirably, it may be 5% or less. The curvature of the scanning line is also corrected well.

FIG. 13 is an explanatory view showing the spot shape on the surface to be scanned in this embodiment. As shown in the figure, the rotation of the spot on the surface to be scanned generated when the light beam emitted from the light source means is obliquely incident on the deflecting surface 5a of the optical deflector 5 in the sub-scan section is well corrected. I understand that.
[Color image forming apparatus]
Also in the present embodiment, as shown in FIG. 8 of the above-described first embodiment, the light source means, the imaging optical system, and the photosensitive member are arranged symmetrically on both sides with the rotation axis of the optical deflector as the center. An image forming apparatus that can be mounted on a four-color full-color image forming apparatus can be provided by deflecting a light beam on both sides of the surface including the rotation axis of the optical deflector.

  As described above, in this embodiment, by setting each element as described above, the optical path length remains short as compared with the first embodiment, and a longer lens back is secured, so that the plane mirror can be arranged freely. You can raise the degree. Furthermore, it is possible to provide an image forming apparatus having a simple configuration in which the distance Dp between the centers of two adjacent photosensitive members and the distance h from the deflection point to the surface to be scanned can be further widened.

  FIG. 14 is a sectional view (sub-scanning sectional view) of the main part in the sub-scanning direction according to the third embodiment of the present invention. In the figure, the same elements as those shown in FIG.

  This embodiment is different from the above-described second embodiment in that the distance Dp between the centers of two adjacent photoconductors 7A and 7B and the arrangement of the plane mirror are changed, and a thinner image forming apparatus is provided. . Other configurations and optical actions are the same as those in the second embodiment, and the same effects are obtained.

  That is, in the figure, reference numerals 28a, 28b, and 28c denote plane mirrors as reflecting members, which are constituted by plane mirrors and correspond to the photoreceptors 7A and 7B corresponding to the light beams that have passed through the first and second imaging lenses 16a and 16b. Folded to the side. The flat mirrors 28a, 28b, and 28c may have refractive power in the main scanning section or the sub-scanning section.

  In general, a space between two adjacent photosensitive members is a space where a developing device is disposed, and this developing device is required to have various shapes and sizes depending on the image forming apparatus.

In this embodiment, the optical path length L (mm) from the deflection point 5b of the optical deflector 5 to the photosensitive members 7A and 7B, sub-scanning, so as to satisfy the conditional expressions (2) and (3) as in the second embodiment. The distance Dp (mm) between the centers of two adjacent photoconductors 7A and 7B in the cross section is expressed as Dp = 70 mm.
L = 161mm
Is set. Thus, a compact image forming apparatus is provided.

Further, in this embodiment, the optical deflector from the reflection point 28a1 of the flat mirror 28a closest to the optical deflector 5 to the reflection point 28b1 of the flat mirror 28b closest to the scanned surface 7b so as to satisfy the conditional expression (6) described above. 5, the angle L1 (mm) in the direction perpendicular to the rotation axis, and the angle formed between the principal ray of the incident light beam and the principal ray of the reflected light beam on the plane mirror 28a, respectively, L1 = 42.2 mm,
θ = 36.8 °
Is set. Thus, in this embodiment, the arrangement is optimized so that the light beam reflected by the plane mirror 28a does not interfere with the second imaging lens 26b closest to the scanned surface 7b.

In this embodiment, the image forming apparatus can be mounted on an image forming apparatus in which the distance between the centers of two adjacent photoconductors 7A and 7B is 10 mm longer than that in the second embodiment. As a result, it can be mounted on a full-color image forming apparatus having a large capacity of the developing device. Furthermore, the height h of the main body is further reduced to 75 mm by increasing the distance between the centers of the photoconductors.
[Color image forming device]
FIG. 15 is a schematic view of a main part of a color image forming apparatus according to an embodiment of the present invention.

  The present embodiment is a tandem type color image forming apparatus that scans four beams by an image forming apparatus and records image information on a photoconductor as an image carrier in parallel. In FIG. 15, 100 is a color image forming apparatus, 11 is an image forming apparatus having any one of the configurations shown in the first to third embodiments, 21, 22, 23, and 24 are photosensitive drums as image carriers, Reference numerals 32, 33, and 34 denote developing units, and 51 denotes a conveyance belt.

  In FIG. 15, the color image forming apparatus 60 receives R (red), G (green), and B (blue) color signals from an external device 52 of 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 11. The image forming apparatus 11 emits light beams (multi-beam lasers) 41, 42, 43, and 44 that are modulated according to each image data, and 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 scans four beams by the image forming apparatus 11, and each corresponds to each color of C (cyan), M (magenta), Y (yellow), and B (black). In parallel, image signals (image information) are recorded on the surfaces of the photosensitive drums 21, 22, 23, and 24, and color images are printed at high speed.

  In the color image forming apparatus in this embodiment, as described above, the image forming apparatus 11 forms the latent images of the respective colors on the corresponding photosensitive drums 21, 22, 23, and 24 using the light beams based on the respective image data. is doing. Thereafter, a single full color image is formed by multiple transfer onto a recording material.

  As the external device 52, for example, a color image reading device including a CCD sensor may be used. In this case, the color image reading apparatus and the color image forming apparatus 100 constitute a color digital copying machine.

FIG. 3 is a main scanning sectional view of the image forming apparatus according to the first exemplary embodiment of the present invention. FIG. 3 is a sub-scan sectional view of the image forming apparatus according to the first exemplary embodiment of the present invention. FIG. 3 is a sub-scan sectional view of the image forming apparatus according to the first exemplary embodiment of the present invention. Diagram for determining conditions when a single plane mirror is used FIG. 3 is an enlarged view of the imaging lens of Embodiment 1 of the present invention The figure which shows the geometric aberration of Example 1 of this invention, the uniformity of a subscanning magnification, and the amount of scanning line curvature. The figure which shows the spot shape of Example 1 of this invention. FIG. 2 is a diagram when the image forming apparatus according to the first exemplary embodiment of the present invention is mounted on a color image forming apparatus. FIG. 5 is a main scanning sectional view of an image forming apparatus according to a second embodiment of the invention. FIG. 6 is a sub-scan sectional view of the image forming apparatus according to the second embodiment of the present invention. FIG. 6 is a sub-scan sectional view of the image forming apparatus according to the second embodiment of the present invention. The figure which shows the geometric aberration of Example 2 of this invention, the uniformity of a subscanning magnification, and the amount of scanning line curvature. The figure which shows the spot shape of Example 2 of this invention. FIG. 6 is a sub-scan sectional view of the image forming apparatus according to the third embodiment of the present invention. 1 is a schematic view of a main part of a color image forming apparatus according to an embodiment of the present invention. Sub-scan sectional view of a conventional color image forming apparatus

Explanation of symbols

1a, 1b Light source means 2a, 2b Aperture stop 3a, 3b Condensing lens (collimator lens)
4a, 4b Cylindrical lens 5 Deflection means (polygon mirror)
6a, 6b, 16a, 16b Imaging lens 7a, 7b Scanned surface (photosensitive drum surface)
8a, 8b, 8c, 18a, 18b, 18c, 28a, 28b, 28c Planar mirror LA, LB Incident optical system 6, 16 Imaging optical system 100 Color image forming apparatus 11 Image forming apparatus 21, 22, 23, 24 Image carrier Body (photosensitive drum)
31, 32, 33, 34 Developer 41, 42, 43, 44 Light beam 51 Conveying belt 52 External device 53 Printer controller

Claims (8)

A plurality of light source means, an incident optical system for guiding a plurality of light beams emitted from the plurality of light source means to the same deflection surface of the deflection means at different angles in the sub-scan section, and the same deflection surface of the deflection means An image forming optical system that forms an image on a plurality of different photoconductors, the image forming apparatus comprising:
The imaging optical system has a first optical system in which one reflecting member is arranged in the optical path of a light beam guided to the photoreceptor most distant from the deflecting unit,
The reflecting member is provided in the optical path between the imaging optical element closest to the photosensitive member in the optical path and the photosensitive member among the imaging optical elements constituting the first optical system,
The effective scanning width of the photoconductor in the main scanning direction is W (mm), the focal length of the imaging optical system in the main scanning direction is f (mm), and the optical path length from the deflection point of the deflecting means to the photoconductor is L (mm), where Dp (mm) is the distance between the centers of two adjacent photoconductors in the sub-scan section.
(1/3) W ≦ f ≦ W
(1/3) f ≦ Dp ≦ (2/3) f
(1/3) f ≦ L−1.5Dp ≦ (4/5) f
An image forming apparatus satisfying the following conditions:   The plurality of light beams deflected by the deflecting unit pass through the same imaging optical element closest to the photosensitive member in the optical path among the imaging optical elements constituting the imaging optical system. Item 2. The image forming apparatus according to Item 1.   Among the imaging optical elements constituting the imaging optical system, the imaging optical element closest to the photosensitive member in the optical path has a plurality of light beams deflected by the deflecting means having different regions in the sub-scanning section. The imaging optical element that passes through and is closest to the photosensitive member includes at least one optical surface having a shape defined by a different function for each of the different regions in the sub-scan section. The image forming apparatus according to claim 1 or 2. When the imaging magnification in the sub-scanning section of the imaging optical system when the light beam on the deflection surface forms an image on the photoconductor in the sub-scanning section is βs,
| Βs | ≧ 1.5
The image forming apparatus according to claim 1, wherein the following condition is satisfied. At least one of the imaging optical elements constituting the imaging optical system has a maximum effective diameter in the main scanning direction of Ymax (mm).
Ymax ≦ (4/5) f
The image forming apparatus according to claim 1, wherein the following condition is satisfied. A plurality of reflecting members are arranged in the optical path for guiding the light beam to the photosensitive member closest to the deflecting unit, and the reflecting point of the reflecting member closest to the deflecting unit side in the optical path among the plurality of reflecting members. The distance in the direction perpendicular to the rotation axis of the deflection means in the sub-scan section from the reflection point of the reflection member closest to the photoreceptor side to the reflection member closest to the deflection means side in the optical path is L1 (mm). When the angle between the principal ray of the incident light beam and the principal ray of the reflected light beam is θ (°),
(L1 + 0.5Dp-L / (1+ | βs |)) tan θ ≧ 10 (mm)
The image forming apparatus according to claim 1, wherein the following condition is satisfied. When the distance from the reflection point of the reflecting member closest to the photoconductor side in the optical path to the photoconductor among the reflecting members that guide the light beam to the photoconductor closest to the deflecting unit is L2 (mm),
L2 ≧ 40 (mm)
The image forming apparatus according to claim 1, wherein the following condition is satisfied. The image forming apparatus according to claim 1, wherein each of the plurality of light source units includes a plurality of light emitting units.

Images