JP2018151502A - Optical scanner and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical scanner achieving reduction in size and curvature of an image plane and further reduction in curvature of a scanning line.SOLUTION: The optical scanner of the present invention includes a deflector for deflecting first and second luminous fluxes exiting from first and second light sources by a first deflection surface to scan first and second scanning target surfaces in a main scanning direction, and first and second imaging optical elements for guiding the first and second luminous fluxes deflected by the deflector to the first and second scanning target surfaces. The first and second luminous fluxes are incident to the first deflection surface at different angles from each other in a main scanning cross section and in a sub-scanning cross section; the difference between the maximum and minimum of height in the sub-scanning direction of the incident position of the first luminous flux on the first deflection surface is greater than the difference in the second luminous flux; and the difference between the maximum and minimum of an average of inclinations in the sub-scanning cross section of an incident surface and an exiting surface of the first imaging optical element, at each position in the main scanning direction, is greater than the difference in the second imaging optical element.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an optical scanning device, and is particularly suitable for an image forming apparatus such as a laser beam printer (LBP), a digital copying machine, or a multifunction printer (MFP).

In recent years, in order to achieve miniaturization of an optical scanning device, a plurality of light beams are incident on a deflector at different angles in the main scanning section and the sub-scanning section, and a plurality of scanned surfaces are formed by the plurality of light beams. A configuration for scanning is proposed.
Japanese Patent Application Laid-Open No. H10-228561 discloses designing the shape of the imaging optical element so as to reduce the curvature of field in such an optical scanning device.

JP 2013-33129 A

However, in Patent Document 1, no consideration is given to the scanning line curvature that occurs when a plurality of light beams are incident on the deflector at different angles.
SUMMARY OF THE INVENTION An object of the present invention is to provide an optical scanning device that can reduce the curvature of the scanning line while reducing the size and reducing the curvature of field.

  The optical scanning device according to the present invention deflects the first and second light beams emitted from the first and second light sources by the first deflecting surface so that the first and second scanned surfaces are in the main scanning direction. A deflector for scanning, and first and second imaging optical elements for guiding the first and second light beams deflected by the deflector to the first and second scanned surfaces, The second light flux is incident on the first deflection surface at different angles in the main scanning section and the sub-scanning section, and the incident position of the first light flux on the first deflection surface is the same. The difference between the maximum value and the minimum value of the height in the sub-scanning direction is larger than the difference between the maximum value and the minimum value of the height of the incident position of the second light beam on the first deflection surface in the sub-scanning direction. The maximum of the average values of the inclinations in the sub-scan section of the entrance surface and exit surface of the first imaging optical element at each position in the main scanning direction is large. The difference between the value and the minimum value is based on the difference between the maximum value and the minimum value of the average values of the inclinations in the sub-scan section of the incident surface and the exit surface of the second imaging optical element at each position in the main scanning direction. Is also large.

  According to the present invention, it is possible to provide an optical scanning device capable of reducing the scanning line curve while achieving downsizing and field curvature reduction.

FIG. 3 is a main scanning sectional view and a sub-scanning sectional view of the optical scanning device according to the first embodiment. In the optical scanning device which concerns on 1st embodiment, the figure which showed a mode that the light beam was deflected by the deflector, and the definition of the rotation angle of a deflector. The figure which showed the change of the height of the deflection | deviation point with respect to the rotation angle of the deflector in the optical scanning device which concerns on 1st embodiment. The optical scanning device according to the first embodiment relates to the sub-scanning tilt amount of the incident surface and the exit surface of the second fθ lens, the average value of the sub-scanning tilt amount, and the position of the average value of the sub-scanning tilt amount in the main scanning direction. The figure which showed the main scanning direction position dependence of the first-order differentiation. The figure which showed typically the shape in the subscanning cross section of the 2nd f (theta) lens in each main scanning direction position in the optical scanning device which concerns on 1st embodiment. The figure which showed the image height dependence of the subscanning direction height of the condensing position of the light beam on each to-be-scanned surface which the optical scanning device which concerns on 1st embodiment scans. The main scanning sectional view and sub-scanning sectional view of the optical scanning device concerning a second embodiment. FIG. 9 is a main scanning sectional view and a sub-scanning sectional view of an optical scanning device according to a third embodiment. 1 is a cross-sectional view of main parts of a color image forming apparatus equipped with an optical scanning device according to the present invention.

  Hereinafter, the optical scanning device according to the present embodiment will be described with reference to the drawings. It should be noted that the drawings shown below may be drawn at a scale different from the actual scale so that the present embodiment can be easily understood.

  In the following description, the main scanning direction (Y direction) corresponds to the direction perpendicular to the rotation axis of the deflector and the optical axis (X direction) of the optical system, and the sub-scanning direction (Z direction) is the deflector. Corresponds to the direction parallel to the rotation axis. The main scanning section corresponds to a section perpendicular to the sub scanning direction, and the sub scanning section corresponds to a section perpendicular to the main scanning direction.

[First embodiment]
FIG. 1A shows a main scanning sectional view of the optical scanning device 10 according to the first embodiment. FIG. 1B shows a sub-scan sectional view of the incident optical systems 111a and 111b included in the optical scanning device 10 according to the first embodiment. FIG. 1C shows a sub-scanning sectional view of the imaging optical systems 112a and 112b included in the optical scanning device 10 according to the first embodiment.

  The optical scanning device 10 according to the present embodiment includes a light source 101a (first light source) and 101b (second light source), sub-scanning apertures 102a and 102b, collimator lenses 103a and 103b, cylindrical lenses 104a and 104b, a main scanning aperture. 105a and 105b. The optical scanning device 10 includes a deflector 106, a first fθ lens 107, a second fθ lens 108a (first imaging optical element) and 108b (second imaging optical element), a dustproof glass 109a, and 109b, reflecting members 115, 116, 117 and 118 are provided.

As the light sources 101a and 101b, for example, a semiconductor laser having a plurality of light emitting points is used.
The sub-scan stops 102a and 102b limit the beam diameters in the sub-scanning direction of the light beams LA (first light beam) and LB (second light beam) emitted from the light sources 101a and 101b, respectively.
The collimator lenses 103a and 103b convert the light beams LA and LB emitted from the light sources 101a and 101b into parallel light beams, respectively. Here, the parallel light beam includes not only a strict parallel light beam but also a substantially parallel light beam such as a weak divergent light beam or a weakly convergent light beam.
Each of the cylindrical lenses 104a and 104b has a finite power (refractive power) in the sub-scan section, and condenses the light beams LA and LB that have passed through the collimator lenses 103a and 103b in the sub-scan direction.
The main scanning stops 105a and 105b limit the light beam diameters in the main scanning direction of the light beams LA and LB that have passed through the cylindrical lenses 104a and 104b, respectively.

In this way, the light beams LA and LB emitted from the light sources 101a and 101b are condensed only in the sub-scanning direction in the vicinity of the deflection surface 106a (first deflection surface) of the deflector 106, and are long lines in the main scanning direction. It is formed as an image.
The sub-scanning aperture 102a, the collimator lens 103a, the cylindrical lens 104a, and the main scanning aperture 105a constitute the first incident optical system 111a of the optical scanning device 10 according to the present embodiment.
The sub-scanning aperture 102b, the collimator lens 103b, the cylindrical lens 104b, and the main scanning aperture 105b constitute a second incident optical system 111b of the optical scanning device 10 according to the present embodiment.

In the main scanning section, an angle formed by the optical axis of the incident optical system 111a with respect to the optical axis of the imaging optical system 112a, and an angle formed by the optical axis of the incident optical system 111b with respect to the optical axis of the imaging optical system 112b. Are 86 degrees and 80 degrees, respectively.
That is, the light beams LA and LB emitted from the light sources 101a and 101b are incident on the deflector 106 at different angles in the main scanning section.
In the sub-scan section, the angles formed by the optical axes of the incident optical systems 111a and 111b with respect to the main scan section are 2.2 degrees and -2.2 degrees.
That is, the light beams LA and LB emitted from the light sources 101a and 101b are incident on the deflector 106 at different angles in the sub-scan section.

  Here, the first incident optical system 111 a and the second incident optical system 111 b may be collectively referred to as the incident optical system 111.

The deflector 106 is rotated in the direction of arrow A in the figure by a driving means such as a motor (not shown) to deflect the light beams LA and LB toward the scanned surfaces 110a and 110b, respectively. For example, the deflector 106 includes a polygon mirror.
The first fθ lens 107 and the second fθ lenses 108 a and 108 b are anamorphic imaging lenses having different powers in the main scanning section and the sub-scanning section, and the light beams LA and LB deflected by the deflector 106. Is condensed (guided) on the scanned surfaces 110a and 110b.
In addition, the incident surfaces and the exit surfaces of the second fθ lenses 108a and 108b become sub-scanning tilt changing surfaces in which the inclination (tilt) in the sub-scanning section changes according to the position in the main scanning direction, as will be described later. ing.

The reflecting members 115, 116, 117, and 118 are means for reflecting the light flux, and vapor deposition mirrors are used.
The dust-proof glasses 109a and 109b are provided to prevent dust and the like from entering the inside of the optical scanning device 10, and are configured by parallel plates or the like.

The first fθ lens 107 and the second fθ lens 108a constitute the first imaging optical system 112a of the optical scanning device 10 according to the present embodiment.
Further, the first fθ lens 107 and the second fθ lens 108b constitute a second imaging optical system 112b of the optical scanning device 10 according to the present embodiment.
The first imaging optical system 112a and the second imaging optical system 112b may be collectively referred to as an imaging optical system 112.

The light beam LA emitted from the light source 101a passes through the sub-scanning stop 102a and is converted into a parallel light beam by the collimator lens 103a. The converted light beam LA is condensed in the sub-scanning direction by the cylindrical lens 104a, passes through the main scanning stop 105a, and enters the deflection surface 106a of the deflector 106 from the lower side in the sub-scanning direction.
The light beam LB emitted from the light source 101b passes through the sub-scanning aperture 102b and is converted into a parallel light beam by the collimator lens 103b. The converted light beam LB is condensed in the sub-scanning direction by the cylindrical lens 104b, passes through the main scanning stop 105b, and enters the deflection surface 106a of the deflector 106 from the upper side in the sub-scanning direction.

Then, the light beam LA emitted from the light source 101a and incident on the deflecting surface 106a of the deflector 106 is deflected by the deflector 106, and then passes through the first fθ lens 107 and the second fθ lens 108a to be a reflecting member. By being reflected by 115, the light is condensed on the scanned surface 110a (first scanned surface), and the scanned surface 110a is scanned at a constant speed.
Further, the light beam LB emitted from the light source 101b and incident on the deflecting surface 106a of the deflector 106 is deflected by the deflector 106, and then passes through the first fθ lens 107 and the second fθ lens 108b to be a reflecting member. The light is reflected by 116, 117, and 118 so as to be condensed on the scanned surface 110b (second scanned surface), and the scanned surface 110b is scanned at a constant speed.

  Since the deflector 106 rotates in the direction A in the figure, the deflected and scanned light beams LA and LB scan the scanned surfaces 110a and 110b in the direction B in the figure, respectively.

In this embodiment, photosensitive drums are used as the scanned surfaces 110a and 110b.
Also, the creation of the exposure distribution in the sub-scanning direction on the photosensitive drums 110a and 110b is achieved by rotating the photosensitive drums 110a and 110b in the sub-scanning direction for each main scanning exposure.

  Next, various characteristics of the incident optical systems 111a and 111b and the imaging optical systems 112a and 112b of the optical scanning device 10 according to the present embodiment are shown in Tables 1 to 3 below.

In Tables 1 to 3, the optical axis direction, the axis orthogonal to the optical axis in the main scanning section, and the optical axis in the sub-scanning section when the intersection of each lens surface and the optical axis is the origin. The orthogonal axes are the X axis, Y axis, and Z axis, respectively. In Tables 1 and 3, “E-x” means “× 10 ^−x ”.

ここで、Ｒは曲率半径、ｋは離心率である。 In the present embodiment, the collimator lenses 103a and 103b are spherical lenses, and their shapes are represented by the following formula (1).

Here, R is a radius of curvature and k is an eccentricity.

ここで、Ｒは曲率半径、ｋは離心率、Ｂ_i（ｉ＝４、６、８、…、１６）は非球面係数である。なお、ｙに関してプラス側とマイナス側で係数Ｂ_iが異なる場合は、表２及び表３にあるように、プラス側の係数には添字ｕを付し（すなわち、Ｂ_iu）、マイナス側の係数には添字ｌを付している（すなわち、Ｂ_il）。 Further, the aspherical shape (bus shape) in the main scanning section of the lens surfaces of the first fθ lens 107 and the second fθ lenses 108a and 108b is expressed by the following equation (2).

Here, R is a radius of curvature, k is an eccentricity, and B _i (i = 4, 6, 8,..., 16) is an aspheric coefficient. When the coefficient B _i is different between the positive side and the negative side with respect to y, as shown in Tables 2 and 3, the positive side coefficient is attached with the subscript u (that is, B _iu ), and the negative side coefficient is added. Is suffixed with l (ie, B _il ).

ここで、Ｍ_jk（ｊ＝０、２、４、６、８、及びｋ＝１）は非球面係数である。なお、ｙに関してプラス側とマイナス側で係数Ｍ_jkが異なる場合は、表２及び表３にあるように、プラス側の係数には添字ｕを付し（すなわち、Ｍ_jku）、マイナス側の係数には添字ｌを付している（すなわち、Ｍ_jkl）。 Further, the aspherical shape (sub-wire shape) in the sub-scan section of the lens surfaces of the first fθ lens 107 and the second fθ lenses 108a and 108b is expressed by the following equation (3).

Here, M _jk (j = 0, 2, 4, 6, 8, and k = 1) is an aspheric coefficient. When the coefficient M _jk is different between the plus side and the minus side with respect to y, as shown in Tables 2 and 3, the plus side coefficient is attached with the subscript u (that is, M _jku ), and the minus side coefficient. Is appended with a subscript l (ie, M _jkl ).

ここで、ｒは光軸上における副走査断面内の曲率半径、Ｅ_j（ｊ＝２、４、６、８、１０）は副走査断面内の曲率半径の変化係数である。なお、ｙに関してプラス側とマイナス側で係数Ｅ_jが異なる場合は、表２及び表３にあるように、プラス側の係数には添字ｕを付し（すなわち、Ｅ_ju）、マイナス側の係数には添字ｌを付している（すなわち、Ｅ_jl）。 Further, the radius of curvature r ′ in the sub-scan section changes continuously according to the y coordinate of the lens surface as in the following formula (4).

Here, r is a radius of curvature in the sub-scan section on the optical axis, and E _j (j = 2, 4, 6, 8, 10) is a change coefficient of the radius of curvature in the sub-scan section. When the coefficient E _j is different between the plus side and the minus side with respect to y, as shown in Tables 2 and 3, the plus side coefficient is attached with the subscript u (that is, E _ju ), and the minus side coefficient. Is appended with a subscript l (ie, E _jl ).

The first-order term of Z relating to the sub-line shape S in Expression (3) is a term that contributes to the tilt amount (sub-line tilt amount) of the lens surface in the sub-scan section. Therefore, by making the aspheric coefficient M _j1u on the plus side in the y-axis direction and the aspheric coefficient M _j1l on the minus side different from each other, the _sub- line tilt amount can be changed asymmetrically in the main scanning direction. it can.

  Next, the sub-scanning tilt changing surfaces of the second fθ lenses 108a and 108b in the optical scanning device 10 according to the present embodiment will be described in detail.

In the following description, the coordinate system shown in the figure is used to explain the effect of the sub-scanning tilt changing surfaces of the second fθ lenses 108a and 108b. Specifically, the main scanning direction (Y direction) corresponds to the direction perpendicular to the rotation axis of the deflector and the optical axis (X direction) of the incident optical system, and the sub scanning direction (Z direction) corresponds to the direction of the deflector. Corresponds to the direction parallel to the rotation axis. The main scanning section corresponds to a section including the main scanning direction and the optical axis of the incident optical system, and the sub-scanning section corresponds to a section perpendicular to the main scanning direction.
The rotation direction is defined as a counterclockwise direction as a positive direction, and the angle is counterclockwise as a positive direction.

FIGS. 2A and 2B are diagrams respectively showing the state in which the light beams LA and LB are deflected by the deflector 106 in the main scanning section and the sub-scanning section in the optical scanning device 10 according to the present embodiment. It is.
Here, C and D in the figure are the optical axes of the incident optical systems 111a and 111b, respectively.
FIG. 2C shows the definition of the rotation angle θ of the deflector 106.

As shown in FIG. 2A, since the deflector 106 is rotating, the deflecting surface 106a of the deflector 106 takes, for example, positions 106a1 and 106a2.
Further, as shown in FIG. 1A, since the deflector 106 rotates in the A direction, the deflecting surface 106a of the deflector 106 moves from the position 106a2 to 106a1.

The light beams LA and LB are deflected at the deflection point E to become the light beams LA1 and LB1 when the deflection surface 106a is at the position 106a1, respectively.
Further, the light beams LA and LB are deflected at the deflection point F and the deflection point G to become the light beams LA2 and LB2, respectively, when the deflection surface 106a is at the position 106a2.

As shown in FIG. 2B, the light beam LA is incident on the deflection surface 106a from the lower side in the sub-scanning direction, while the light beam LB is incident on the deflection surface 106a from the upper side in the sub-scanning direction. Incident.
Therefore, regarding the positions 106a1 and 106a2 of the deflection surface 106a, the difference EF in the height (Z coordinate) in the sub-scanning direction between the deflection point (incidence position) E and the deflection point F of the light beam LA and the deflection point of the light beam LB. The height difference EG in the sub-scanning direction between E and the deflection point G is different from each other.
Therefore, at each position taken by the deflection surface 106a, the sub-scan with respect to the main-scan section of the deflection point depends on the difference in the incident angle in the main-scan section and the sub-scan section incident on the respective deflection surfaces 106a of the light beams LA and LB. The height in the direction (hereinafter referred to as the sub-scanning direction height) is different.

FIG. 3 shows changes in the sub-scanning direction heights (Z coordinates) of the deflection points of the light beam LA and the light beam LB with respect to the rotation angle θ of the deflector 106 in the optical scanning device 10 according to the present embodiment.
Here, the rotation angle θ of the deflector 106 is defined as an angle formed by the optical axis of the imaging optical system and the normal line of the deflection surface 106a in the main scanning section.
As for the height of the deflection point in the sub-scanning direction, the position of the main scanning section including the optical axis of the imaging optical system is set to zero.

As shown in FIG. 3, in the optical scanning device 10 according to the present embodiment, the difference between the maximum value and the minimum value of the height in the sub-scanning direction of the deflection point in the light beam LA is smaller than that in the light beam LB (hereinafter referred to as “light beam LA”). This is called PV (Peak to Valley), which is the height of the deflection point in the sub-scanning direction.
Specifically, the PV of the deflection point of the light beam LA in the sub-scanning direction is 0.087 mm, and the PV of the deflection point of the light beam LB in the sub-scanning direction is 0.070 mm.
Here, the difference between the maximum value and the minimum value is the maximum value−minimum value, and may take an absolute value in some cases. The same applies to the subsequent PVs.

FIG. 4A shows the position dependency in the main scanning direction of the sub-scanning tilt amount φ1 of the incident surface and the sub-scanning tilt amount φ2 of the exit surface of the second fθ lens 108a in the optical scanning device 10 according to the present embodiment. ing.
FIG. 4B shows the position dependency in the main scanning direction of the sub-scanning tilt amount φ1 of the incident surface and the sub-scanning tilt amount φ2 of the exit surface of the second fθ lens 108b in the optical scanning device 10 according to this embodiment. ing.
FIG. 4C shows the main scanning direction position dependency of the average value (φ1 + φ2) / 2 of the sub-scanning tilt amounts of the incident surfaces and the exit surfaces of the second fθ lenses 108a and 108b.
FIG. 4D shows the first-order differential d ((φ1 + φ2) / 2) / dY with respect to the position in the main scanning direction of the average value of the sub-scanning tilt amounts of the incident surfaces and the exit surfaces of the second fθ lenses 108a and 108b. The position dependency in the main scanning direction is shown.

5A, 5B, and 5C, the position in the main scanning direction (hereinafter referred to as the main scanning direction position) Y in the optical scanning apparatus 10 according to the present embodiment is 105 mm, 0 mm, and −150 mm, respectively. The shapes in the sub-scanning cross section (sub-scanning tilt plane) of the second fθ lenses 108a and 108b are schematically shown.
In FIGS. 5A, 5B, and 5C, the left side is the entrance surface and the right side is the exit surface.
In FIGS. 5A, 5B, and 5C, reference numerals 401 to 406 denote average shapes (average values of the sub-scanning tilt amounts) of the incident surfaces and the exit surfaces of the second fθ lenses 108a and 108b. ing.
In FIGS. 5A, 5B, and 5C, reference numerals 407 to 418 indicate directions corresponding to the tilts of the incident surfaces and the exit surfaces of the second fθ lenses 108a and 108b.

  Here, the tilt (inclination in the sub-scan section) of the entrance surface and the exit surface, that is, the sub-scan tilt amount is determined by the optical axis of the imaging optical system of the sub-line of the entrance surface and the exit surface of the second fθ lens. It is defined by the angle formed by the normal line at the intersection with the main scanning section including the main scanning section.

As shown in FIGS. 4A and 4B, in the optical scanning device 10 according to the present embodiment, the incident surface and the exit surface of the second fθ lenses 108a and 108b are at positions in the main scanning direction. It is a sub-scanning tilt changing surface in which the tilt changes accordingly.
In addition, the absolute values of the tilts of the entrance and exit surfaces of the second fθ lenses 108a and 108b increase from the optical axis toward the off-axis in the main scanning direction.

Here, as shown in FIGS. 4A and 4B, the difference between the maximum value and the minimum value of the sub-scanning tilt amount φ1 on the incident surface of the second fθ lens 108a (hereinafter referred to as the sub-scanning tilt amount φ1). The scan tilt amount is referred to as PV.) Is 398.7 minutes, and the PV of the sub-scan tilt amount φ1 of the incident surface of the second fθ lens 108b is 380.4 minutes.
Further, as shown in FIGS. 4A and 4B, the PV of the sub-scanning tilt amount φ2 of the exit surface of the second fθ lens 108a is 497.8 minutes, and the second fθ lens 108b. The PV of the sub-scanning tilt amount φ2 on the exit surface is 477.9 minutes.
Further, as shown in FIG. 4C, the difference between the maximum value and the minimum value of the average value (φ1 + φ2) / 2 of the sub-scanning tilt amounts of the entrance surface and the exit surface of the second fθ lens 108a. (Hereinafter, this is called PV of the sub-scanning tilt amount average value) is 448.3 minutes, and the PV of the sub-scanning tilt amount average value of the second fθ lens 108b is 429.1 minutes.

  As described above, in the optical scanning device 10 according to the present embodiment, the second fθ lens 108a disposed on the optical path of the light beam LA having a large incident angle to the deflector 106 in the main scanning section with respect to the light beam LB. The second fθ lenses 108a and 108b are adjusted so that the PV of the sub-scanning tilt amount average value is larger than the PV of the sub-scanning tilt amount average value of the second fθ lens 108b arranged on the optical path of the light beam LB. Designing.

FIG. 6 shows the image height dependence of the height in the sub-scanning direction of the condensed positions of the light beams LA and LB on the scanned surfaces 110a and 110b scanned by the optical scanning device 10 according to the present embodiment.
In FIG. 6, as a comparative example, the second imaging optical system 112b also shows a case where the second fθ lens 108a is arranged instead of the second fθ lens 108b. In this comparative example, the second fθ lens 108a is inverted in the sub-scanning direction.

As shown in FIG. 6, when the optical scanning device 10 according to the present embodiment is used, the maximum value and the minimum value of the height in the sub-scanning direction of the condensing position of the light beam LA on the surface to be scanned 110a. The difference (hereinafter referred to as the PV of the condensing position height in the sub-scanning direction) and the PV of the condensing position of the light beam LB on the scanned surface 110b in the sub-scanning direction height are 0.005 mm and 0, respectively. The variation is sufficiently suppressed to 0.004 mm, and as a result, a substantially uniform scanning line can be drawn.
On the other hand, in the comparative example, PV of the height of the condensing position in the sub-scanning direction is 0.050 mm, and it can be seen that the scanning line is inclined.

As described above, in the optical scanning device 10 according to the present embodiment, the absolute value of the angle (acute angle) formed by the optical axis of the incident optical system 111a with respect to the optical axis of the imaging optical system 112a is within the main scanning section. The optical axis of the incident optical system 111b is larger than the absolute value of the angle (acute angle) formed with respect to the optical axis of the imaging optical system 112b. Accordingly, the PV of the deflection point height of the light beam LA is larger than that of the light beam LB, and the PV of the sub-scanning tilt amount average value of the second fθ lens 108a is corresponding to the PV. The second fθ lenses 108a and 108b are designed so as to be larger than the PV of the average sub-scanning tilt amount of the second fθ lens 108b.
Thereby, a substantially uniform scanning line can be drawn by sufficiently suppressing variations in the height in the sub-scanning direction of the converging positions of the light beams LA and LB on the scanned surfaces 110a and 110b. it can.

  Further, in the optical scanning device 10 according to the present embodiment, in order to reduce the difference between the scanning line curve on the scanned surface 110a and the scanning line curve on the scanned surface 110b, the light source side of the second fθ lens 108a. The power in the sub-scanning section of the second fθ lens 108b is made smaller than the power in the sub-scanning section on the light source side.

Further, as shown in FIG. 4D, in the optical scanning device 10 according to the present embodiment, the main scanning of the average value of the sub-scanning tilt amounts of the incident surface and the exit surface of the second fθ lens 108a is performed. The difference between the maximum value and the minimum value of the first-order derivative d ((φ1 + φ2) / 2) / dY related to the direction position (hereinafter referred to as the first-order derivative PV of the sub-scanning tilt amount average value) and the second. The PV of the first derivative of the average value of the sub-scanning tilt amount of the fθ lens 108a is 27.6 minutes / mm and 27.7 minutes / mm, respectively, and both are 100 minutes / mm or less.
Thus, in the optical scanning device 10 according to the present embodiment, the second fθ lenses 108a and 108b are moved in the main scanning direction by setting the PV of the first derivative of the average value of the sub-scanning tilt amount to 100 minutes / mm or less. It is possible to reduce the deterioration of the scanning line when it is displaced (laterally shifted).
Further, as in the optical scanning device 10 according to this embodiment, setting the PV of the first derivative of the average value of the sub-scanning tilt amount to 50 minutes / mm or less can further reduce the deterioration of the scanning line. This is a more preferable configuration.

Further, in the optical scanning device 10 according to the present embodiment, the absolute value of the tilt of the incident surface of the second fθ lens 108a and the absolute value of the tilt of the exit surface on and near the optical axis of the imaging optical system 112a. The difference between the absolute value of the tilt of the entrance surface of the second fθ lens 108b and the absolute value of the tilt of the exit surface on and near the optical axis of the imaging optical system 112b is 10 minutes or less, respectively. Yes.
Thereby, it is possible to reduce the deterioration of the scanning line, the difference between the scanned surfaces of the scanning line, that is, the color misregistration and the like.

In the optical scanning device 10 according to the present embodiment, the absolute value of the average value of the tilt of the entrance surface and the exit surface of the second fθ lens 108a on and near the optical axis of the imaging optical system 112a, And the absolute value of the average value of the tilt of the entrance surface and the exit surface of the second fθ lens 108b on and near the optical axis of the imaging optical system 112b is 5 minutes or less, respectively.
Thereby, it is possible to reduce the deterioration of the scanning line, the difference between the scanned surfaces of the scanning line, that is, the color misregistration and the like.

Table 4 shows various characteristics of the optical scanning device 10 according to the present embodiment.

[Second Embodiment]
FIG. 7A shows a main scanning sectional view of the optical scanning device 20 according to the second embodiment. FIG. 7B shows a sub-scanning sectional view of the incident optical systems 111a, 111b, 111c, and 111d provided in the optical scanning device 20 according to the second embodiment. FIG. 7C is a sub-scan sectional view of the imaging optical systems 112a, 112b, 112c, and 112d provided in the optical scanning device 20 according to the second embodiment.
Unlike the optical scanning device 10 according to the first embodiment, the optical scanning device 20 according to the second embodiment employs a both-side scanning optical system.

The optical scanning device 20 according to the present embodiment includes a light source 101a (first light source), 101b (second light source), 101c (third light source) and 101d (fourth light source), and sub-scanning apertures 102a and 102b. , 102c and 102d. The optical scanning device 20 according to the present embodiment includes collimator lenses 103a, 103b, 103c and 103d, cylindrical lenses 104a, 104b, 104c and 104d, and a main scanning stop 105. The optical scanning device 20 includes a deflector 106, first fθ lenses 107a and 107b, a second fθ lens 108a (first imaging optical element), 108b (second imaging optical element), and 108c ( A third imaging optical element) and 108d (fourth imaging optical element). Further, the optical scanning device 20 includes dustproof glasses 109a, 109b, 109c and 109d, and reflecting members 115a, 116a, 117a, 118a, 115b, 116b, 117b and 118b.
Note that in the optical scanning device 20 according to the second embodiment, each member is the same as that of the optical scanning device 10 according to the first embodiment, and therefore, the same reference numerals are given and description thereof is omitted. .

A light beam LA (first light beam) emitted from the light source 101a passes through the sub-scanning aperture 102a and is converted into a parallel light beam by the collimator lens 103a. Then, the converted light beam LA is condensed in the sub-scanning direction by the cylindrical lens 104a, passes through the main scanning stop 105, and enters the deflection surface 106a (first deflection surface) of the deflector 106 from the lower side in the sub-scanning direction. Incident.
A light beam LB (second light beam) emitted from the light source 101b passes through the sub-scanning diaphragm 102b and is converted into a parallel light beam by the collimator lens 103b. The converted light beam LB is condensed in the sub-scanning direction by the cylindrical lens 104b, passes through the main scanning stop 105, and enters the deflection surface 106a of the deflector 106 from the upper side in the sub-scanning direction.
A light beam LC (third light beam) emitted from the light source 101c passes through the sub-scanning aperture 102c and is converted into a parallel light beam by the collimator lens 103c. The converted light beam LC is condensed in the sub-scanning direction by the cylindrical lens 104c, passes through the main scanning stop 105, and enters the deflection surface 106b (second deflection surface) of the deflector 106 from the upper side in the sub-scanning direction. To do.
A light beam LD (fourth light beam) emitted from the light source 101d passes through the sub-scanning diaphragm 102d and is converted into a parallel light beam by the collimator lens 103d. The converted light beam LD is condensed in the sub-scanning direction by the cylindrical lens 104d, passes through the main scanning stop 105, and enters the deflection surface 106b of the deflector 106 from the lower side in the sub-scanning direction.
In this way, the light beams LA and LB emitted from the light sources 101a and 101b are condensed only in the sub-scanning direction in the vicinity of the deflecting surface 106a of the deflector 106, and formed as a long line image in the main scanning direction. Further, the light beams LC and LD emitted from the light sources 101c and 101d are condensed only in the sub-scanning direction in the vicinity of the deflection surface 106b of the deflector 106, and are formed as a long line image in the main scanning direction.

The sub-scanning aperture 102a, the collimator lens 103a, the cylindrical lens 104a, and the main scanning aperture 105 constitute the first incident optical system 111a of the optical scanning device 20 according to the present embodiment.
The sub-scanning aperture 102b, the collimator lens 103b, the cylindrical lens 104b, and the main scanning aperture 105 constitute the second incident optical system 111b of the optical scanning device 20 according to the present embodiment.
Further, the sub-scanning diaphragm 102c, the collimator lens 103c, the cylindrical lens 104c, and the main scanning diaphragm 105 constitute a third incident optical system 111c of the optical scanning device 20 according to the present embodiment.
The sub-scanning aperture 102d, the collimator lens 103d, the cylindrical lens 104d, and the main scanning aperture 105 constitute a fourth incident optical system 111d of the optical scanning device 20 according to the present embodiment.
The first incident optical system 111a, the second incident optical system 111b, the third incident optical system 111c, and the fourth incident optical system 111d may be collectively referred to as the incident optical system 111.

Then, the light beam LA emitted from the light source 101a and incident on the deflecting surface 106a of the deflector 106 is deflected by the deflector 106, passes through the first fθ lens 107a and the second fθ lens 108a, and is reflected by the reflecting member. By being reflected by 115a, it is condensed on the surface to be scanned 110a (first surface to be scanned), and the surface to be scanned 110a is scanned at a constant speed.
The light beam LB emitted from the light source 101b and incident on the deflecting surface 106a of the deflector 106 is deflected by the deflector 106, and then passes through the first fθ lens 107a and the second fθ lens 108b, thereby reflecting the reflecting member. The light is reflected by 116a, 117a, and 118a to be condensed on the surface to be scanned 110b (second surface to be scanned), and the surface to be scanned 110b is scanned at a constant speed.
The light beam LC emitted from the light source 101c and incident on the deflecting surface 106b of the deflector 106 is deflected by the deflector 106, and then passes through the first fθ lens 107b and the second fθ lens 108c, and is reflected by the reflecting member. The light is reflected by 116b, 117b, and 118b to be condensed on the scanned surface 110c (third scanned surface), and the scanned surface 110c is scanned at a constant speed.
The light beam LD emitted from the light source 101d and incident on the deflecting surface 106b of the deflector 106 is deflected by the deflector 106, and then passes through the first fθ lens 107b and the second fθ lens 108d, thereby reflecting the reflecting member. By being reflected by 115b, it is condensed on the surface to be scanned 110d (fourth surface to be scanned), and the surface to be scanned 110d is scanned at a constant speed.

The first fθ lens 107a and the second fθ lens 108a constitute the first imaging optical system 112a of the optical scanning device 20 according to the present embodiment.
Further, the first fθ lens 107a and the second fθ lens 108b constitute a second imaging optical system 112b of the optical scanning device 20 according to the present embodiment.
Further, the first fθ lens 107b and the second fθ lens 108c constitute a third imaging optical system 112c of the optical scanning device 20 according to the present embodiment.
Further, the first fθ lens 107b and the second fθ lens 108d constitute a fourth imaging optical system 112d of the optical scanning device 20 according to the present embodiment.
The first imaging optical system 112a, the second imaging optical system 112b, the third imaging optical system 112c, and the fourth imaging optical system 112d may be collectively referred to as the imaging optical system 112. .

In the optical scanning device 20 according to the present embodiment, the first incident optical system 111a, the first imaging optical system 112a, the third incident optical system 111c, and the third imaging optical system 112c are deflectors. A rotationally symmetrical relationship about 180 degrees around the Y axis with the center of 106 as the origin.
Further, the second incident optical system 111b, the second imaging optical system 112b, the fourth incident optical system 111d, and the fourth imaging optical system 112d are around the Y axis with the center of the deflector 106 as the origin. Of 180 degrees rotational symmetry.
With this configuration, in the optical scanning device 20 according to the present embodiment, the same members as those of the optical scanning device 10 according to the first embodiment can be used for each member.
Specifically, the second fθ lens 108a and the second fθ lens 108c can have the same shape, and the second fθ lens 108b and the second fθ lens 108d can have the same shape.

Similar to the optical scanning device 10 according to the first embodiment, also in the optical scanning device 20 according to the present embodiment, the difference in incident angles on the deflecting surfaces 106a and 106b of the deflector 106 between the light beams LA to LD. Accordingly, the sub-scanning tilt amounts of the incident surfaces and the exit surfaces of the second fθ lenses 108a to 108d are adjusted.
Thereby, the variation in the height in the sub-scanning direction of the condensing positions of the light beams LA to LD on the scanned surfaces 110a to 110d can be sufficiently suppressed, and as a result, a substantially uniform scanning line can be drawn.

[Third embodiment]
FIG. 8A shows a main scanning sectional view of the optical scanning device 30 according to the third embodiment. FIG. 8B shows a sub-scanning sectional view of the incident optical systems 111a and 111b included in the optical scanning device 30 according to the third embodiment. FIG. 8C shows a sub-scan sectional view of the imaging optical systems 112a and 712b included in the optical scanning device 30 according to the third embodiment.
The optical scanning device 30 according to the third embodiment has the same configuration as that of the optical scanning device 10 according to the first embodiment, except that the second fθ lens 708b is provided instead of the second fθ lens 108b. Therefore, the same members are denoted by the same reference numerals, and description thereof is omitted.

  The optical scanning device 30 according to the present embodiment includes light sources 101a and 101b, sub-scanning apertures 102a and 102b, collimator lenses 103a and 103b, cylindrical lenses 104a and 104b, and main scanning apertures 105a and 105b. In addition, the optical scanning device 30 includes a deflector 106, a first fθ lens 107, and second fθ lenses 108a and 708b. Furthermore, the optical scanning device 30 includes dust-proof glasses 109a and 109b and reflecting members 115, 116, 117, and 118.

The light beam LA emitted from the light source 101a passes through the sub-scanning stop 102a and is converted into a parallel light beam by the collimator lens 103a. The converted light beam LA is condensed in the sub-scanning direction by the cylindrical lens 104a, passes through the main scanning stop 105a, and enters the deflection surface 106a of the deflector 106 from the lower side in the sub-scanning direction.
The light beam LB emitted from the light source 101b passes through the sub-scanning aperture 102b and is converted into a parallel light beam by the collimator lens 103b. The converted light beam LB is condensed in the sub-scanning direction by the cylindrical lens 104b, passes through the main scanning stop 105b, and enters the deflection surface 106a of the deflector 106 from the upper side in the sub-scanning direction.
In this way, the light beams LA and LB emitted from the light sources 101a and 101b are condensed only in the sub-scanning direction in the vicinity of the deflecting surface 106a of the deflector 106, and formed as a long line image in the main scanning direction.
In the optical scanning device 30 according to the third embodiment, unlike the optical scanning device 10 according to the first embodiment, each of the optical axes of the incident optical systems 111a and 111b is relative to the main scanning cross section in the sub-scanning cross section. The angles formed are 2.2 degrees and -3.0 degrees.
That is, the absolute values of the angles are different in the sub-scanning section, and are incident on the deflecting surface 106a of the deflector 106 asymmetrically with respect to the main scanning section.

The sub-scanning aperture 102a, the collimator lens 103a, the cylindrical lens 104a, and the main scanning aperture 105a constitute a first incident optical system 111a of the optical scanning device 30 according to the present embodiment.
The sub-scanning aperture 102b, the collimator lens 103b, the cylindrical lens 104b, and the main scanning aperture 105b constitute a second incident optical system 111b of the optical scanning device 30 according to the present embodiment.
The first incident optical system 111a and the second incident optical system 111b may be collectively referred to as the incident optical system 111.

Then, the light beam LA emitted from the light source 101a and incident on the deflecting surface 106a of the deflector 106 is deflected by the deflector 106, and then passes through the first fθ lens 107 and the second fθ lens 108a to be a reflecting member. By being reflected by 115, the light is condensed on the surface to be scanned 110a, and the surface to be scanned 110a is scanned at a constant speed.
The light beam LB emitted from the light source 101b and incident on the deflecting surface 106a of the deflector 106 is deflected by the deflector 106, and then passes through the first fθ lens 107 and the second fθ lens 708b, thereby reflecting the member. The light is reflected by 116, 117, and 118 to be condensed on the surface to be scanned 110b, and the surface to be scanned 110b is scanned at a constant speed.

The first fθ lens 107a and the second fθ lens 108a constitute the first imaging optical system 112a of the optical scanning device 30 according to the present embodiment.
Further, the first fθ lens 107a and the second fθ lens 708b constitute a second imaging optical system 712b of the optical scanning device 30 according to the present embodiment.
The first imaging optical system 112a and the second imaging optical system 712b may be collectively referred to as an imaging optical system 712.

  Next, various characteristics of the incident optical systems 111a and 111b and the imaging optical system 712b of the optical scanning device 30 according to the present embodiment are shown in Tables 5 and 6 below.

Table 7 shows various characteristics of the optical scanning device 30 according to the present embodiment.

As shown in Table 7, in the optical scanning device 30 according to the present embodiment, the angle (acute angle) formed by the optical axis of the incident optical system 111a with respect to the optical axis of the imaging optical system 112a in the main scanning section. ) Is larger than the absolute value of the angle (acute angle) formed by the optical axis of the incident optical system 111b with respect to the optical axis of the imaging optical system 712b. In the sub-scan section, the absolute value of the angle formed by the optical axis of the incident optical system 111a with respect to the main scan section is greater than the absolute value of the angle formed by the optical axis of the incident optical system 111b with respect to the main scan section. small. Accordingly, unlike the optical scanning device 10 according to the first embodiment, the light beam LB has a larger PV at the deflection point height than the light beam LA.
Correspondingly, the second sub-scanning tilt amount average value PV of the second fθ lens 708b is larger than the sub-scanning tilt amount average value PV of the second fθ lens 108a. The fθ lenses 108a and 708b are designed.
As a result, the sub-scanning direction height PV of the condensing positions of the light beams LA and LB on the scanned surfaces 110a and 110b is both 0.005 mm, and the variation is sufficiently suppressed. Simple scanning lines can be drawn.

The optical scanning device according to the first to third embodiments has been described above, but the present invention is not limited to this, and various modifications can be made.
For example, in the optical scanning device according to the first to third embodiments, two light beams are incident on one deflection surface. However, the present invention is not limited to this. Three or more light beams are incident on one deflection surface. It doesn't matter. Even in this case, the same effect as in the first to third embodiments can be obtained as long as the PV of the deflection point height and the PV of the sub-scanning tilt amount average value satisfy the above relationship.

[Image forming apparatus]
FIG. 9 is a cross-sectional view of main parts of a color image forming apparatus 90 on which the optical scanning device according to the first or third embodiment is mounted.

The image forming apparatus 90 is a tandem type color image forming apparatus in which two optical scanning devices according to the first or third embodiment are arranged in parallel and image information is recorded on each photosensitive drum surface as an image carrier. It is.
The image forming apparatus 90 includes optical scanning devices 11 and 12 according to the first or third embodiment, photosensitive drums 23, 24, 25, and 26 as image carriers, and developing units 15, 16, 17, and 18. . The image forming apparatus 90 includes a conveyance belt 91, a printer controller 93, and a fixing device 94.

  The image forming apparatus 90 receives R (red), G (green), and B (blue) color signals (code data) output from an external device 92 such as a personal computer. The input color signal is converted into C (cyan), M (magenta), Y (yellow), and K (black) image data (dot data) by a printer controller 93 in the image forming apparatus 90. The converted image data is input to the optical scanning devices 11 and 12, respectively. Then, light beams 59, 60, 61, 62 modulated according to the respective image data are emitted from the optical scanning devices 11, 12, respectively, and the photosensitive drums 23, 24, 25, 26 are exposed by these light beams. The surface is exposed.

  A charging roller (not shown) for uniformly charging the surfaces of the photosensitive drums 23, 24, 25, and 26 is provided so as to contact the surfaces. Then, light beams 59, 60, 61, and 62 are applied to the surfaces of the photosensitive drums 23, 24, 25, and 26 charged by the charging roller by the optical scanning devices 11 and 12, respectively.

  As described above, the light beams 59, 60, 61, and 62 are modulated based on the image data of each color, and the photosensitive drums 23, 24, and 25 are irradiated by irradiating the light beams 59, 60, 61, and 62. , 26 is formed with electrostatic latent images. The formed electrostatic latent image is developed as a toner image by the developing devices 15, 16, 17, and 18 arranged so as to contact the photosensitive drums 23, 24, 25, and 26.

  The toner images developed by the developing devices 15 to 18 are transported on the transport belt 91 by a transfer roller (transfer device) (not shown) disposed so as to face the photosensitive drums 23 to 26 (not shown). Multiple transfer is performed on the (transfer material) to form one full-color image.

  As described above, the sheet on which the unfixed toner image is transferred is further conveyed to the fixing device 94 behind the photosensitive drums 23, 24, 25, and 26 (left side in FIG. 9). The fixing device 94 includes a fixing roller having a fixing heater (not shown) inside and a pressure roller disposed so as to be in pressure contact with the fixing roller. The sheet conveyed from the transfer unit is heated while being pressed at the pressing portion between the fixing roller and the pressure roller, whereby the unfixed toner image on the sheet is fixed. Further, a paper discharge roller (not shown) is disposed behind the fixing roller, and the paper discharge roller discharges the fixed paper to the outside of the image forming apparatus 90.

The color image forming apparatus 90 has two optical scanning devices 11 and 12 arranged, each corresponding to each color of C, M, Y, and K, and in parallel on the photosensitive surface of the photosensitive drums 23, 24, 25, and 26, respectively. An image signal (image information) is recorded on the printer, and a color image is printed at high speed.
As the external device 92, 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 90 constitute a color digital copying machine.

In the color image forming apparatus 90, two optical scanning devices according to the first or third embodiment are used, but instead, one optical scanning device according to the second embodiment may be used. .
Further, the recording density of the image forming apparatus according to the present embodiment is not particularly limited. However, considering that the higher the recording density is, the higher the image quality is required, the effects of the first to third embodiments are more exhibited in an image forming apparatus of 1200 dpi or more.

10 Optical scanning devices 101a, 101b Light sources (first light source, second light source)
106 Deflector 106a Deflection surface (first deflection surface)
108a, 108b Second fθ lens (first imaging optical element, second imaging optical element)
110a, 110b Scanned surface (first scanned surface, second scanned surface)
LA, LB luminous flux (first luminous flux, second luminous flux)

Claims (11)

A deflector that deflects the first and second light beams emitted from the first and second light sources by the first deflection surface and scans the first and second scanned surfaces in the main scanning direction;
First and second imaging optical elements for guiding the first and second light beams deflected by the deflector to the first and second scanned surfaces;
The first and second light beams are incident on the first deflection surface at different angles in the main scanning section and the sub-scanning section, respectively.
The difference between the maximum value and the minimum value of the height of the incident position of the first light beam on the first deflection surface in the sub-scanning direction is the difference between the first light beam on the first deflection surface. Greater than the difference between the maximum and minimum height of the incident position in the sub-scanning direction,
The difference between the maximum value and the minimum value of the average value in the sub-scan section of the entrance surface and the exit surface of the first imaging optical element at each position in the main scanning direction is different at each position in the main scanning direction. An optical scanning device characterized in that the difference between the maximum value and the minimum value of the average value of the inclination in the sub-scan section of the incident surface and the exit surface of the second imaging optical element is larger. Comprising first and second incident optical systems for causing the first and second light beams emitted from the first and second light sources to enter the first deflecting surface of the deflector;
In the main scanning section, the absolute value of the angle formed by the optical axis of the first incident optical system and the optical axis of the first imaging optical element is the optical axis of the second incident optical system. The optical scanning device according to claim 1, wherein the optical scanning device is larger than an absolute value of an angle formed by the optical axis of the imaging optical element. Comprising first and second incident optical systems for causing the first and second light beams emitted from the first and second light sources to enter the first deflecting surface of the deflector;
In the sub-scan section, the absolute value of the angle formed by the optical axis of the first incident optical system and the main scan section is greater than the absolute value of the angle formed by the optical axis of the second incident optical system and the main scan section. The optical scanning device according to claim 1, wherein the optical scanning device is large.   The absolute value of the inclination in the sub-scan section of the incident surface and the exit surface of the first and second imaging optical elements increases in the main scanning direction from the optical axis to the off-axis direction. The optical scanning device according to any one of claims 1 to 3.   First-order differentiation of the average value of the inclination in the sub-scanning section of the incident surface of the first imaging optical element and the inclination in the sub-scanning section of the exit surface at each position in the main scanning direction with respect to the position in the main scanning direction And the average of the inclination of the incident surface of the second imaging optical element in the sub-scanning section and the inclination of the exit surface in the sub-scanning section at each position in the main scanning direction 5. The optical scanning according to claim 1, wherein a difference between the maximum value and the minimum value of the first-order derivative with respect to the position in the main scanning direction is 100 minutes / mm or less. apparatus.   The difference between the absolute value of the inclination of the incident surface in the sub-scanning section on the optical axis of the first imaging optical element and the absolute value of the inclination of the exit surface in the sub-scanning section, the second imaging optical element The difference between the absolute value of the inclination in the sub-scan section of the incident surface on the optical axis and the absolute value of the inclination in the sub-scan section of the exit surface is 10 minutes or less, respectively. The optical scanning device according to claim 5.   An absolute value of an average value of an inclination in the sub-scanning section of the incident surface and an inclination in the sub-scanning section of the exit surface on the optical axis of the first imaging optical element, and the second imaging optical element 7. The absolute value of the average value of the inclination of the incident surface in the sub-scan section and the inclination of the exit surface in the sub-scan section on the optical axis is 5 minutes or less, respectively. An optical scanning device according to claim 1. A third and a fourth imaging optical element for guiding the third and fourth light beams deflected by the deflector to the third and fourth scanned surfaces;
The deflector deflects the third and fourth light beams emitted from the third and fourth light sources by a second deflecting surface and scans the third and fourth scanned surfaces in the main scanning direction. ,
The third and fourth light beams are incident on the second deflection surface at different angles in the main scanning section and the sub-scanning section, respectively.
The difference between the maximum value and the minimum value of the height of the incident position of the third light beam on the second deflection surface in the sub-scanning direction is the difference between the maximum value and the minimum value of the fourth light beam on the second deflection surface. Greater than the difference between the maximum and minimum height of the incident position in the sub-scanning direction,
The difference between the maximum value and the minimum value of the average value in the sub-scan section of the entrance surface and the exit surface of the third imaging optical element at each position in the main scanning direction is different at each position in the main scanning direction. 8. The method according to claim 1, wherein a difference between a maximum value and a minimum value of an average value of inclinations in the sub-scan section of the entrance surface and the exit surface of the fourth imaging optical element is larger. The optical scanning device according to one item.   The optical scanning according to claim 8, wherein the first and third imaging optical elements have the same shape, and the second and fourth imaging optical elements have the same shape. apparatus.   The optical scanning device according to claim 1, a developing device that develops an electrostatic latent image formed on the surface to be scanned by the optical scanning device as a toner image, and the developed toner An image forming apparatus comprising: a transfer device that transfers an image to a transfer material; and a fixing device that fixes the transferred toner image to the transfer material.   An optical scanning device according to claim 1, and a printer controller that converts code data output from an external device into an image signal and inputs the image signal to the optical scanning device. Image forming apparatus.

Images