JP3472205B2 - Optical scanning optical device and image forming apparatus using the same - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical scanning optical device and an image forming apparatus using the optical scanning optical device, and more particularly, to a deflecting surface of an optical deflector for deflecting a light beam emitted from a light source means in the main scanning direction. It is suitable for an image forming apparatus, such as a laser beam printer or a digital copying machine, which uses an overfilled scanning optical system for making the light incident in a state wider than the width.

[0002]

2. Description of the Related Art In an overfilled scanning optical system in which a light beam (light beam) emitted from a light source composed of a semiconductor laser is made incident on a deflection surface of an optical deflector in a state wider than the width of the deflection surface in the main scanning direction. , Surface to be scanned (photosensitive drum surface)
The area of the beam width of the light beam focused on the upper part is used by cutting off a part of the light beam incident on the optical deflector at the deflection surface of the optical deflector.

Further, in the overfill scanning optical system, as compared with the underfill type optical system, the field curvature is generated due to the spherical aberration of the incident optical system, which tends to cause side lobes in the beam profile. This S
There is a problem in that the image written on the surface to be scanned is adversely affected by the deterioration of the / N ratio, such as a reduction in resolution and a thick thin line. Further, the side lobe becomes larger as the beam diameter becomes smaller, so that there has been a particularly serious problem when the beam spot diameter on the surface to be scanned is made small in order to cope with high image quality.

An optical scanning optical device using an overfilled scanning optical system that solves the above-mentioned problems is disclosed in, for example, Japanese Patent Laid-Open No. Hei 9-1999
It is proposed in Japanese Patent Publication No. 304720. The publication has a light source, a first optical system that converts a divergent light beam from at least the main scanning direction into a substantially parallel light beam, and a plurality of deflection surfaces (reflection surfaces) parallel to a rotation axis, and A rotating polygon mirror that rotates at an approximately constant angular velocity about a rotation axis and deflects and reflects an incident light beam along a predetermined main scanning direction by the deflecting surface, and a light beam deflected and reflected by the rotating polygon mirror on a surface to be scanned. A second optical system for converging a light beam deflected and reflected so as to scan the upper part along the main scanning direction at a substantially constant speed on the surface to be scanned, and to direct the light beam from the light source to the rotary polygon mirror. The first optical system, which is of an overfilled type that is made to enter so as to straddle a plurality of deflecting surfaces and in which all the light flux from the light source is incident, is deflected and reflected by one deflecting surface of the rotary polygon mirror. Front surface for correcting aberration in the second optical system to which the light flux of the other part is incident It is configured to form.

In the overfilled scanning optical system, the beam width region of the light beam imaged on the surface to be scanned is used by cutting out a part of the light beam incident on the optical deflector. The beam profile at the image forming position may collapse. In addition, the alignment of the light flux may shift due to variations in the precision and arrangement of the optical components, and the beam profile on the scanned surface may collapse.

Therefore, in the prior art, for example, Japanese Patent Laid-Open No. 11-01
As disclosed in Japanese Patent No. 4923, an ND filter provided with gradation is arranged between a light source and an optical deflector as a light amount adjusting means for adjusting the exposure amount to a surface to be scanned,
The ND filter can be moved in the gradation direction,
In addition, the above-mentioned problems are solved by making it rotatable in a plane including the ND filter surface.

[0007]

However, the above-mentioned conventional example has the following problems.

Since the first optical system and the second optical system have a pair of designs, it is difficult to apply them to apparatuses of other specifications. Further, since the devices have different scanning speeds, it is necessary to redesign the second optical system when the first optical system is redesigned.

The ND filter provided with gradation is expensive and has a large cost disadvantage.

Due to the loss of light quantity due to the ND filter, a high-output light source is required, which is a great cost disadvantage.

According to the present invention, in an optical scanning optical device using an overfilled scanning optical system, the curvature of field is satisfactorily corrected and the surface to be scanned on the surface to be scanned is properly set by appropriately setting each element constituting the device. The uniformity of the light intensity distribution can be achieved with a simple configuration, and at the same time it can support various specifications.
An object of the present invention is to provide an optical scanning optical device capable of realizing a versatile optical system and an image forming apparatus using the optical scanning optical device.

[0012]

According to a first aspect of the present invention, there is provided an optical scanning optical device including a light source means for converting a light beam emitted from the light source means into a substantially parallel light beam in a main scanning section.
And an optical system which includes the first optical system and makes the deflecting surface of the optical deflector incident on the deflecting surface in a state wider than the width of the deflecting surface in the main scanning direction. In a light scanning optical device having a third optical system for forming an image of the reflected light flux on the surface to be scanned, the absolute maximum spherical aberration generated within the effective diameter of the first optical system is SA, The first,
When the focal lengths in the main scanning section of the optical systems 2 and 3 are f1, f2 and f3 respectively,

[0013]

[Equation 2]

However, it is characterized in that it has means for satisfying the condition that the numerical value of SA is expressed in mm and correcting the deviation of the light quantity distribution of the first optical system.

According to a second aspect of the present invention, in the first aspect of the invention, the first optical system moves in a main scanning section in a direction perpendicular to the optical axis of the first optical system and in the main scanning direction. It is characterized by being possible.

According to a third aspect of the invention, in the first or second aspect of the invention, the first optical system has an achromatic lens.

A fourth aspect of the present invention is characterized in that, in the first or second aspect of the present invention, the first optical system has a single lens having at least one aspherical surface.

According to a fifth aspect of the invention, in the first aspect of the invention, the light beam emitted from the light source means is obliquely incident on the deflection surface of the optical deflector within the sub-scan section.

According to a sixth aspect of the invention, in the first aspect of the invention, the light flux emitted from the light source means is obliquely incident on the deflection surface of the optical deflector in the main scanning section.

According to a seventh aspect of the present invention, in the first aspect of the invention, the light beam emitted from the light source means is obliquely incident on the deflecting surface of the optical deflector within the main scanning section, and the optical deflector is provided. It is characterized in that the center of the light beam incident on is set to be displaced by a predetermined amount with respect to the optical axis of the first optical system.

The invention of claim 8 is characterized in that, in the invention of claim 1, the light beam entering the optical deflector enters the deflecting surface from substantially the center of the deflection angle of the optical deflector.

According to a ninth aspect of the present invention, in the first aspect of the invention, at least a part of the optical elements forming the third optical system also forms the second optical system.

The invention of claim 10 is characterized in that, in the invention of claim 1, the following conditional expression | SA | <0.02 (mm) is satisfied. The invention of claim 11 is characterized in that, in the invention of claim 1, the center of the light beam incident on the optical deflector is set to be displaced by a predetermined amount with respect to the optical axis of the first optical system. An image forming apparatus according to a twelfth aspect of the invention is characterized in that an image is formed by using the optical scanning optical device according to any one of the first to eleventh aspects.

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS [Embodiment 1] FIG. 1 is a top view of essential parts when an optical scanning optical device according to a first embodiment of the present invention is applied to an image forming apparatus such as a laser beam printer or a digital copying machine. , Shows the state where each element is projected in the main scanning section. FIG. 2 is a side view of the main part of FIG. 1, showing a state in which each element is projected in the sub-scan section.

In this specification, a coordinate system as shown in FIG. 1 is taken with the optical axis of the incident optical system as the z axis. An x, y, z coordinate system with the x-axis being the main scanning direction when the optical path is developed is taken. The main scanning section is defined as an xz section and the sub scanning section is defined as a yz section.

In FIG. 1 and FIG. 2, 1 is a light source means,
For example, it consists of a semiconductor laser. Reference numeral 2 denotes a collimator lens part, which is an achromatic lens having a combination of two first negative lenses (concave lenses) 2a having negative refracting power and positive lenses (convex lenses) 2b having positive refracting power. It has a lens and converts the light beam emitted from the semiconductor laser 1 into a substantially parallel light beam in the main scanning cross section.

Each element of the semiconductor laser 1 and the collimator lens section 2 constitutes one element of the first optical system 11. The first optical system 11 in the present embodiment is configured to be movable in the main scanning section in a direction perpendicular to the optical axis 11a of the first optical system 11 and in the main scanning direction. .

Reference numeral 21 denotes a second negative lens (concave lens) having a negative refracting power, which makes the substantially parallel light flux from the collimator lens portion 2 a weakly divergent light flux. Reference numeral 3 denotes an incident system cylindrical lens made of a glass material, which has a positive refracting power only in the sub-scanning direction, and a light beam passing through the second negative lens 21 is described later in the main scanning section. The image is formed on the deflecting surface (reflecting surface) 8a of 8 as a substantially linear image. Four
Is an aperture stop, which regulates the passing light flux to shape the beam shape. Reference numeral 5 denotes a folding mirror, which folds the light beam that has passed through the aperture stop 4 toward the optical deflector 8 side.

Each element of the semiconductor laser 1, collimator lens section 2, second negative lens 21, cylindrical lens 3, aperture stop 4, and folding mirror 5 constitutes one element of the second optical system 12. ing. Further, the collimator lens unit 2 and the first cylindrical lens 7 and the second cylindrical lens 6 which will be described later constitute a collimator system.

Reference numeral 8 denotes a polygon mirror (rotary polygonal mirror) as an optical deflector, which is rotated at a constant speed in the direction of arrow A in the figure by driving means (not shown) such as a motor. The polygon mirror 8 is composed of 12 surfaces having an inscribed circle radius of 14 mm.

Reference numeral 13 denotes a third optical system having an fθ characteristic, and an fθ lens system 14 having a first cylindrical lens 7 and a second cylindrical lens 6 having a positive power only in the main scanning direction, and a main And a third cylindrical lens (long cylindrical lens) 9 having power in the sub-scanning direction. The third optical system 13 forms an image of the deflected light flux from the optical deflector 8 on the surface to be scanned 10 and substantially conjugates between the deflecting surface 8a of the optical deflector 8 and the surface to be scanned 10 within the sub-scan section. By making the relationship, the tilt of the deflecting surface 8a is corrected. The fθ lens system 14
Also constitutes a part of the second optical system 12.

Reference numeral 10 is a photosensitive drum surface as a surface to be scanned.

In this embodiment, the light beam which is optically modulated and emitted from the semiconductor laser 1 is converted into a substantially parallel light beam by the collimator lens portion 2, converted into a weakly divergent light beam by the negative lens 21, and is incident on the cylindrical lens 4. . Here, of the weakly divergent light fluxes that have entered the cylindrical lens 4 of the incident system, the light fluxes are converged in the sub-scanning cross section, restricted by the aperture stop 3, and passed through the folding mirror 5 to the second cylindrical lens 6 and the first cylindrical lens. The light passes through the lens 7 and enters the deflecting surface 8a of the optical deflector 8, and is formed as a substantially linear image (a longitudinal linear image in the main scanning direction) near the deflecting surface 8a. At this time, the light beam incident on the deflection surface 8a falls on a plane (rotation plane of the optical deflector) perpendicular to the rotation axis of the optical deflector 8 and the optical axis 14a of the fθ lens system 14 in the sub-scan section. It is incident at an angle of 0.8 degrees (oblique incidence optical system). That is, the second optical system 1
The light flux from 2 is incident on the deflecting surface 8a in the sub-scanning section from an oblique direction.

In the other main scanning cross section, the light beam is converted into a substantially parallel light beam by passing through the second cylindrical lens 6 and the first cylindrical lens 7 in the same state (weakly divergent light beam state), The light is incident on the deflection surface 8a from approximately the center of the deflection angle of the optical deflector 8 (front incidence). The beam width of the substantially parallel beam at this time is set to be sufficiently wider than the facet width of the deflection surface 8a of the optical deflector 8 in the main scanning direction (overfilled scanning optical system).

The light beam deflected and reflected by the deflecting surface 8a of the optical deflector 8 is guided to the photosensitive drum surface 10 through the first cylindrical lens 7, the second cylindrical lens 6 and the third cylindrical lens 9. When the light is deflected, the light deflector 8 is rotated in the direction of arrow A to optically scan the surface of the photosensitive drum 10 in the direction of arrow B (main scanning direction). As a result, the photosensitive drum surface 10 as a recording medium
The image is recorded on the top.

FIG. 3 is a schematic view of a main part of the first optical system 11 shown in FIG. In the figure, the same elements as those shown in FIG. 1 are designated by the same reference numerals.

The collimator lens unit 2 in the figure is composed of an achromatic lens which is a combination of the first negative lens 2a and the positive lens 2b as described above, and its focal length f1 is f1 = 35. It is 2 (mm).

FIG. 4 is an explanatory view showing the light intensity distribution in the main scanning direction of the semiconductor laser 1 of this embodiment. The angle at which the light intensity is halved is called the half-value angle. In this embodiment, half-value angle =
A 22 ° semiconductor laser 1 is used.

FIG. 5 is an explanatory view showing a case where the light intensity distribution of the semiconductor laser 1 is biased in manufacturing. This deviation occurs about 3 ° in manufacturing.

FIG. 6 is an explanatory view showing the light intensity distribution of the light flux emitted from the collimator lens unit 2 in the main scanning direction. In the figure, the horizontal axis represents the distance from the optical axis of the collimator lens unit 2, and the vertical axis represents the light intensity. In the overfilled scanning optical system, a region of the beam width of the light beam imaged on the image surface (photosensitive drum surface) 10 is used by cutting out a part of the light beam incident on the optical deflector. On-axis (y = 0) as shown in the figure,
Off-axis (y = ± 148.5) collimator lens unit 2
A part of the light flux from the light reaches the image plane. Therefore, the deviation of the light intensity distribution as shown in FIG. 7 causes the deviation of the light amount distribution on the image plane. In FIG. 7, the horizontal axis represents image height and the vertical axis represents light intensity. In the figure, there are shown a case where the light intensity distribution of the semiconductor laser 1 is not biased (0 °) and a case of ± 3 °.

In the present embodiment, in order to correct the above deviation, the entire first optical system 11 is slid in the main scanning direction in the main scanning direction by the shift adjusting mechanism in the direction perpendicular to the optical axis. As a result, the image surface (photosensitive drum surface) 1
It is configured so that the light amount distribution on 0 is substantially uniform. The adjustment amount of the first optical system 11 at this time is f1 = 35.2 (mm) from the focal length f1 of the collimator lens unit 2 to f1.
Since xtan3 ° = 1.84 (mm), approximately 2
(mm).

As shown in FIG. 6, by design, the light flux from the collimator lens portion 2 uses ± 2.2 (mm) from the optical axis, and the adjustment amount needs to be 2 (mm). Therefore, the luminous flux width of the luminous flux from the collimator lens unit 2 is set to 10 (mm).

In this embodiment, the maximum spherical aberration of the absolute value generated within the effective diameter of the first optical system 11 is SA, and the focus is within the main scanning section of the first, second, third optical systems 11, 12, and 13. When the distances are f1, f2 and f3 respectively,

[0044]

[Equation 3]

However, the numerical value of SA is expressed in mm. Each element is set to satisfy the following condition.

The amount of movement of the image plane in the main scanning direction on the image plane 10 caused by the maximum spherical aberration SA of the first optical system 11 depends on the magnification relationship.

[0047]

[Equation 4]

It is When the first optical system 11 is shifted by the shift adjusting mechanism, the image plane moves by the amount shown in the equation (2). When using the product, if the amount of movement of the image plane is within 1 (mm), it does not affect the image. Therefore, in this embodiment, each element is set so as to satisfy the conditional expression (1).

FIG. 8 is an aberration diagram showing spherical aberration of the collimator lens unit 2 of this embodiment. As shown in the figure, the maximum spherical aberration SA is | SA | <0.02 (mm).

The focal length f2 of the second optical system 12 in this embodiment is f2 = 111.1 (mm), and the focal length f3 of the third optical system 13 is f3 = 345.7 (mm). .

Therefore,

[0052]

[Equation 5]

Which satisfies the conditional expression (1).

FIG. 9 is a view showing the field curvature in the main scanning direction of this embodiment. The case where the maximum spherical aberration SA of the first optical system is zero, and the case where the collimator lens unit 2 of this embodiment is used
Shows the case of using. As shown in the figure, even if the first optical system 11 is parallel-shifted by 2 (mm) in order to correct the deviation of the light amount distribution, the image plane hardly moves.

Next, as a comparative example, a case where the first optical system which does not satisfy the conditional expression (1) is used will be described.

FIG. 10 is an aberration diagram showing spherical aberration of a single-lens collimator lens. As shown in the figure, the maximum value of the maximum spherical aberration | SA | is about 0.4 (mm).

Therefore,

[0058]

[Equation 6]

It becomes

FIG. 11 shows the field curvature in the main scanning direction in that case. As shown in the figure, the field curvature is larger in the first optical system than in the case where the maximum spherical aberration SA is zero. Further, it can be seen that when the first optical system is parallel-shifted by 2 (mm) in order to correct the deviation of the light amount distribution, the image plane is largely tilted. In this embodiment, the first optical system is moved by means (not shown).

Numerical examples of the present embodiment will be shown below.

However, in the numerical examples, N1: the refractive index of the material at the operating wavelength of the first cylindrical lens 7, N2: the refractive index of the material at the operating wavelength of the second cylindrical lens 6, N11: the first negative lens 2a Refractive index of the material at the used wavelength N12: Refractive index of the material at the used wavelength of the positive lens 2b N13: Refractive index of the material at the used wavelength of the second negative lens 21 N14: Material at the used wavelength of the incident cylindrical lens 3 Refractive index D0: distance from the deflection surface of the optical deflector 8 to the first cylindrical lens 7 D1: lens thickness of the first cylindrical lens 7 D2: from the first cylindrical lens 7 to the second cylindrical lens 6 Distance D3: Lens thickness of the second cylindrical lens 6 D4: From the second cylindrical lens 6 to the third cylindrical lens 9 Distance D5: Lens thickness of the third cylindrical lens 9 D6: Distance from the third cylindrical lens 9 to the scanned surface 10 D10: Light emitting portion of the semiconductor laser 1 to the first negative lens 2
Distance to a D11: Lens thickness of the first negative lens 2a D12: Distance from the first negative lens 2a to the positive lens 2b D13: Lens thickness of the positive lens 2b D14: Positive lens 2b to the second negative lens 21 Distance D15: Lens thickness of second negative lens 21 D16: Distance from second negative lens 21 to incident system cylindrical lens 3 D17: Lens thickness of incident system cylindrical lens 3 D18: Incident system cylindrical lens 3 to the return mirror 5 D19: distance from the return mirror 5 to the second cylindrical lens 6 R1: radius of curvature of the first cylindrical lens 7 on the optical deflector 8 side in the main scanning direction R2: first cylindrical Curvature radius R3 of the lens 7 in the main scanning direction on the surface 10 to be scanned: Curvature radius R4 of the second cylindrical lens 6 in the main scanning direction on the side of the optical deflector 8: Second cylinder Curvature radius R5 of the lens 6 on the scanned surface 10 side in the main scanning direction: Curvature radius of the third cylindrical lens 9 on the optical deflector 8 side in the main scanning direction R6: Scanned surface 10 side of the third cylindrical lens 9 Radius of curvature r3 in the main scanning direction: radius of curvature rd3 of the third cylindrical lens 9 on the optical deflector 8 side in the sub-scanning direction: aspherical coefficient of the third cylindrical lens 9 on the optical deflector 8 side in the sub-scanning direction r4: radius of curvature in the sub-scanning direction of the surface to be scanned 10 side of the third cylindrical lens rd4: aspheric surface in the sub-scanning direction of the surface to be scanned 10 of the third cylindrical lens 9 coefficient second cylindrical lens 6 surface With respect to the distance y from the axis in the longitudinal direction above, r ′ in the sub-scanning direction at y is r3 ′ = r3 · (1 + rd3 · y ² ) r4 ′ = r4 · (1 + rd4 · y ² ) R11 : Radius of curvature R12 of the first negative lens 2a on the semiconductor laser 1 side: first negative lens 2 a radius of curvature on the side opposite to the semiconductor laser 1 R13: radius of curvature of the positive lens 2b on the side of the semiconductor laser 1 R14: radius of curvature of the positive lens 2b on the side opposite to the semiconductor laser 1 R15: semiconductor laser of the second negative lens 21 Radius of curvature R1 on the first side: Curvature radius of second negative lens 21 opposite to semiconductor laser 1 R17: Radius of curvature of incident side cylindrical lens 3 on the side of semiconductor laser 1 in the sub-scanning direction.

Numerical examples are all expressed in units of mm.

Numerical Example Working wavelength = 655 nm N1 = 1.7761 D0 = 25 R1 = -356.0 N2 = 1.6966 D1 = 4 R2 = ∞ N11 = 1.7982 D2 = 41.5 R3 = ∞ N12 = 1.7252 D3 = 15 R4 = -152.6 N13 = 1.5139 D4 = 214 R5 = -1000 N14 = 1.5139 D5 = 4 R6 = -1000 D6 = 168 D10 = 31.61 r3 = 114.1 D11 = 2.0 rd3 = 6.634 × 10 ^-6 D12 = 0.5 r4 = -109.8 D13 = 3.0 rd4 = 7.914 × 10 ^-6 D14 = 10.1 D15 = 5.0 R11 = 350.74 D16 = 18.0 R12 = 28.01 D17 = 6.0 R13 = 32.76 D18 = 163.3 R14 = 22.94 D19 = 84.5 R15 = -56.19 R16 = ∞ R17 = 48.14 Embodiment 2 FIG. 12 is a sectional view (main scanning sectional view) of a main part in a main scanning direction according to the second embodiment of the present invention. In the figure, the same elements as those shown in FIG. 1 are designated by the same reference numerals.

The present embodiment is different from the first embodiment in that the collimator lens portion 22 is composed of a single aspherical lens 22a having at least one aspherical surface, and the second optical system 32. It is configured by an over-field scanning optical system in which the light flux from is incident on the deflecting surface 8a of the optical deflector 8 in an oblique direction in the main scanning cross section. Other configurations and optical functions are the same as those of the first embodiment.
Is almost the same as the above, and thereby the same effect is obtained.

Each element of the semiconductor laser 1 and the collimator lens section 22 constitutes one element of the first optical system 31. Each element of the semiconductor laser 1, the collimator lens section 22, the incident cylindrical lens 3, and the aperture stop 4 constitutes one element of the second optical system 32.

FIG. 13 is an aberration diagram showing spherical aberration of the collimator lens portion 22 of this embodiment. As shown in the figure, the maximum spherical aberration SA is | SA | = 0.015 (mm).

In this embodiment, the focal lengths f1 and f2 of the first and second optical systems 31 and 32 in the main scanning section are both f1 = f2 = 70.4 (mm), and the third optical system 1
The focal length f3 of 3 is f3 = 345.7 (mm).

Therefore,

[0070]

[Equation 7]

This satisfies the conditional expression (1), and the same effect as that of the first embodiment is obtained.

In this embodiment, the collimator lens portion 22 is composed of a single aspherical lens 22a, but it may be a two-lens system including a negative lens and a positive lens, as in the first embodiment.

[Third Embodiment] FIG. 14 is a schematic view of a main portion of a first optical system according to a third embodiment of the present invention. In the figure, the same elements as those shown in FIG. 3 are designated by the same reference numerals.

The present embodiment differs from the second embodiment described above in that the center M of the light beam incident on the optical deflector in the first optical system 51 is set to a predetermined amount with respect to the optical axis L of the first optical system 51. The difference is that the difference is set by Δ, and the collimator lens unit 42 is composed of an achromatic lens in which two lenses, a negative lens 42a and a positive lens 42b, are combined as in the first embodiment. Other configurations and optical actions are substantially the same as those of the second embodiment, and the same effect is obtained.

That is, in the present embodiment, as shown in the figure, the center M of the light beam incident on the optical deflector (not shown) in the first optical system 51 is set with respect to the optical axis L of the first optical system 51. It is set by shifting by a predetermined amount Δ. A shift adjusting mechanism may be provided to adjust the light amount distribution around the predetermined amount Δ.

In an overfilled scanning optical system in which a light beam is obliquely incident on the deflecting surface of the optical deflector within the main scanning cross section, there is a problem that the emission FNO (F number) to the image plane is asymmetrical. is there.

Here, the focal length of the third optical system 13 in the main scanning direction is fm3, the angle between the optical axis L of the first optical system 51 and the optical axis La of the third optical system 13 is β, and the light is If the deflector width of the deflector is Fa and the image height is hgt,

[0078]

[Equation 8]

It can be represented by

In this embodiment, fm3 = 345 (mm) Fa = 7.77 (mm) β = 60 ° Is.

FIG. 15 shows the change of the output FNO depending on the image height hgt. As shown in the figure, the peak value is standardized at 100%.

If the light quantity distribution of the light beam entering the optical deflector from the first optical system 51 is symmetrical with respect to the axis as shown in FIG. 6, the light quantity distribution will be asymmetric. In order to correct this asymmetry, in the present embodiment, as shown in FIG. 14, the center M of the light beam incident on the optical deflector (not shown) is shifted by a predetermined amount Δ with respect to the optical axis L of the first optical system 51. With this setting, the light amount distribution of the light beam incident on the light deflector is made asymmetric.

FIG. 16 shows the light quantity distribution of the light beam incident on the optical deflector.

In this embodiment, Δ = 4.5 (mm) Half-value angle FFP = 22 ° of the semiconductor laser 1 The focal length f1 of the first optical system 51 and the focal length f2 of the second optical system are both f1 = f2. = 70.4 (mm) The image height hgt and the change y in the center of the light flux reaching the image plane in the first optical system 51 in this embodiment are as shown in Table 1 below.

[0085]

[Table 1]

The light quantity G (y,
Δ) can be expressed by the following equation.

[0087]

[Equation 9]

FIG. 16 shows the light quantity distribution obtained from the above equation (3).
Shown in. In the figure, the peak value is standardized to be 100%.

FIG. 17 shows the change of the output FNO of FIG. 15 depending on the image height from the light amount distribution of the incident light beam to the optical deflector of FIG. 16 to the light amount distribution on the image plane. In this embodiment, the value of the predetermined amount Δ is set so that the light amount distribution is symmetrical with respect to the axis as shown in FIG.

Also in this embodiment, each element is set so as to satisfy the conditional expression (1) as in the case of the above-described second embodiment, and thereby the same effect as that of the second embodiment is obtained.

Further, in the present embodiment, the collimator lens portion 42 is composed of an achromatic lens, but it may be composed of a single aspherical lens as in the second embodiment.

[0092]

According to the present invention, in the optical scanning optical device using the overfilled scanning optical system as described above, the field curvature is satisfactorily corrected by properly setting the respective elements constituting the device. At the same time, an optical scanning optical device and an image forming apparatus using the optical scanning optical device which can realize the uniformity of the light amount distribution on the surface to be scanned with a simple configuration, can simultaneously meet various specifications, and can realize a versatile optical system. Can be achieved.

[Brief description of drawings]

FIG. 1 is a top view of essential parts of a first embodiment of the present invention.

FIG. 2 is a side view of a main part of the first embodiment of the present invention.

FIG. 3 is a schematic view of a main part of a first optical system according to the first embodiment of the present invention.

FIG. 4 is an explanatory diagram showing a light intensity distribution in the main scanning direction of the semiconductor laser according to the first embodiment of the present invention.

FIG. 5 is an explanatory diagram showing a case where the light intensity distribution of the semiconductor laser according to the first embodiment of the present invention is biased.

FIG. 6 is an explanatory diagram showing a light intensity distribution in the main scanning direction of a light beam emitted from the collimator lens unit according to the first embodiment of the present invention.

FIG. 7 is an explanatory diagram showing a light amount distribution according to the first embodiment of the present invention.

FIG. 8 is an aberration diagram showing spherical aberration of the collimator lens unit 2 according to the first embodiment of the present invention.

FIG. 9 is a diagram showing field curvature in the main scanning direction according to the first embodiment of the present invention.

FIG. 10 is an aberration diagram showing conventional spherical aberration.

FIG. 11 is a diagram showing conventional field curvature in the main scanning direction.

FIG. 12 is a main-scan sectional view of a second embodiment of the present invention.

FIG. 13 is an aberration diagram showing spherical aberration of the first optical system according to the second embodiment of the present invention.

FIG. 14 is a schematic view of a main part of a first optical system according to a third embodiment of the present invention.

FIG. 15 is an explanatory diagram showing a change of the output FNO according to the image height according to the third embodiment of the present invention.

FIG. 16 is an explanatory diagram showing a light amount distribution of a light beam incident on the optical deflector according to the third embodiment of the present invention.

FIG. 17 is an explanatory diagram showing a light amount distribution on an image plane according to the third embodiment of the present invention.

[Explanation of symbols]

1 Light source means (semiconductor laser) 2,22,42 Collimator lens part 2a, 42a First negative lens 2b, 42b Positive lens 3 Cylindrical lens 4 aperture 5 folding mirror 6 Second cylindrical lens 7 First cylindrical lens 8 Optical deflector 9 Third cylindrical lens 10 Scanned surface 11, 31, 51 First optical system 12,32 Second optical system 13 Third optical system 14 fθ lens system 21 Second negative lens 22 Aspherical lens

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-11-149055 (JP, A) JP-A-10-206778 (JP, A) JP-A-2-181712 (JP, A) JP-A-5- 257080 (JP, A) JP-A-10-213773 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) G02B 26/10

Claims (12)

(57) [Claims] 1. A first optical system including a light source means for converting a light beam emitted from the light source means into a substantially parallel light beam in a main scanning section; and a deflection of an optical deflector including the first optical system. A second optical system for making the light incident on the surface wider than the width of the deflecting surface in the main scanning direction, and a third optical system for forming an image of the light beam deflected and reflected by the optical deflector on the surface to be scanned. In the optical scanning optical device having ,, the maximum spherical aberration of the absolute value generated within the effective diameter of the first optical system is SA, and the focal length of the first, second, and third optical systems in the main scanning cross section is When f1, f2, and f3 are set in order, respectively, However, means for satisfying the condition that the numerical value of SA is expressed in mm and correcting the deviation of the light amount distribution of the first optical system is provided.
An optical scanning optical device having. 2. The first optical system is movable in a main scanning section in a direction perpendicular to the optical axis of the first optical system and in the main scanning direction. The optical scanning optical device described. 3. The optical scanning optical device according to claim 1, wherein the first optical system has an achromatic lens. 4. The optical scanning optical device according to claim 1, wherein the first optical system has a single lens having at least one aspherical surface. 5. The optical scanning optical device according to claim 1, wherein the light beam emitted from the light source means is incident on the deflection surface of the optical deflector in an oblique direction in the sub-scan section. 6. The optical scanning optical device according to claim 1, wherein the light beam emitted from the light source means is incident on a deflection surface of the optical deflector in an oblique direction within a main scanning section. 7. A light beam emitted from the light source means is incident on a deflection surface of the optical deflector in an oblique direction in a main scanning cross section, and the center of the light beam incident on the optical deflector is the first beam. The optical scanning optical device according to claim 1, wherein the optical scanning optical device is set to be displaced by a predetermined amount with respect to the optical axis of the optical system. 8. The optical scanning optical device according to claim 1, wherein the light beam incident on the optical deflector is incident on the deflection surface from substantially the center of the deflection angle of the optical deflector. 9. The optical scanning optical device according to claim 1, wherein at least a part of the optical elements forming the third optical system also forms the second optical system. 10. The following conditional expression | SA | <0.02 (mm) 2. The optical scanning optical system according to claim 1, wherein
apparatus. 11. The center of the light beam incident on the optical deflector
It is set by shifting a predetermined amount with respect to the optical axis of the first optical system.
The optical scanning optical device according to claim 1, wherein
Place 12. An image forming apparatus characterized by forming an image using the optical scanning optical apparatus according to any one of claims 1 to 11.