JP2003156704A - Optical scanner and image forming device using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an optical scanner capable of excellently compensating wave aberration and excellently correcting the curvature of field and the variance of a spot diameter, and an image forming device using the optical scanner. SOLUTION: This optical scanner is equipped with a light source means 1, a deflection means 5 reflecting and deflecting luminous flux emitted from the light source means, and a scanning optical system 6 guiding the luminous flux from the deflection means to a surface to be scanned 7 so as to scan the surface to be scanned. In the scanner, the scanning optical system has two or more optical elements 6a and 6b, which have one or more aspherical surfaces having positive refractive power on a main scanning cross section. The radii of curvature of at least two surfaces of two optical elements have one extreme value in a main scanning direction on a subscanning cross section.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical scanning device and an image forming apparatus using the same, and more particularly to an asymmetry of curvature of field due to the presence of a sag (a surface coming in and out due to rotation of an optical deflector). It is suitable for an image forming apparatus such as a laser beam printer, a digital copying machine, a multifunction printer (multifunctional printer), or the like, which has a thin lens thickness in which variations in the beam diameter are suppressed and wavefront aberrations are favorably corrected.

[0002]

2. Description of the Related Art Conventionally, in an optical scanning device used in a laser beam printer, a digital copying machine or the like, a light beam (light beam) emitted from a light source in accordance with an image signal is cycled by an optical deflector such as a rotating polygon mirror. A scanning lens having a fθ characteristic is used to form a spot while scanning the surface of the photosensitive drum, which is the surface to be scanned, at a substantially constant speed. As a result, image information is recorded on the surface of the photosensitive drum as a recording medium.

FIG. 13 is a schematic view of a main part of an optical system of a conventional optical scanning device.

In the figure, the divergent light beam emitted from the light source means 91 is made into a substantially parallel light beam or a convergent light beam by a condenser lens (collimator lens) 92, and the light beam is limited by a diaphragm 93 to have a refracting power in the sub-scanning direction. It is incident on the cylindrical lens 94 that it has. Since the substantially parallel light flux incident on the cylindrical lens 94 is imaged only in the sub-scanning direction, it is substantially imaged on the deflection surface 95a of the optical deflector 95 as a long line image in the main scanning direction. The light beam deflected by the deflecting surface 95a of the optical deflector 95 scans the photosensitive drum surface 97, which is the surface to be scanned, through the scanning optical system 96 having the fθ characteristic to record an image.

In this type of optical scanning device, in order to record a high-definition image (ar 1) the field curvature is well corrected over the entire surface to be scanned, (ar 2) the surface to be scanned is The spot diameter and the spot shape of (3) are good, and (Ar 3) has a tilt correction function that corrects so as not to cause positional deviation of the scanning line even if the deflection surface of the optical deflector tilts. 4) It is necessary that the distortion is corrected well.

Further, with the recent miniaturization of the image forming apparatus,
The optical scanning device must be downsized, and the scanning lens is required to have a compact lens shape.

If the scanning lens is made compact, it becomes difficult to correct aberrations. In particular, since the sag of the optical deflector (the entrance and exit of the deflecting surface due to the rotation of the optical deflector) becomes large, the asymmetry of the aberration caused by the sag is corrected. Must be done. Conventionally, various optical scanning devices have been proposed which correct the asymmetry of the aberration caused by the sag of the optical deflector and satisfy desired optical characteristics.

For example, in order to correct only the asymmetry of the field curvature in the sub-scanning direction due to the sag of the optical deflector, the radius of curvature in the sub-scanning direction is changed asymmetrically along the main scanning direction with respect to the optical axis. An optical scanning device having (hereinafter referred to as “sub-scanning radius of curvature asymmetrical surface”) is disclosed in, for example, Japanese Patent Publication No. 7-5952.
Japanese Patent Laid-Open No. 1-113950 and Japanese Laid-Open Patent Publication No. 7-113950.
Various proposals have been made in Japanese Patent No. 22635. An optical scanning device that corrects not only the curvature of field but also the variation of the beam diameter due to the image height is proposed in, for example, Japanese Patent Laid-Open No. 2000-081567.

[0009]

In recent years, compact optical scanning devices have been required, and these compact optical scanning devices satisfactorily correct field curvature, distortion, and beam diameter fluctuation due to image height. However, it is particularly important to correct the fluctuation of the beam diameter due to the image height in a multi-beam scanning device having a plurality of light sources.

However, JP-B-7-69521, JP-A-7-113950 and JP-A-8-1
Japanese Patent No. 22635 has only one sagittal line changing surface (the surface in which the radius of curvature in the sub-scanning direction changes along the main scanning direction) and does not consider the change in the beam diameter due to the image height at all. , Is not suitable for an optical scanning device using a multi-beam light source as a light source. Further, since the scanning lens having a negative refracting power, which is not suitable for downsizing the optical scanning device, is included, it is difficult to downsize the entire device and the lens having a positive refracting power becomes thick. There is also.

In Japanese Unexamined Patent Publication No. 2000-081567, it is difficult to correct the wavefront aberration because the sagittal change surface has two or more extreme values in the change, and the spot shape is likely to deteriorate. Further, since a thick lens is used, there is a problem in that it is difficult to obtain surface accuracy in manufacturing the lens.

The present invention provides a compact and high-quality optical scanning device capable of satisfactorily correcting wavefront aberration and satisfactorily correcting field curvature and spot diameter variation, and an image forming apparatus using the same. To aim.

[0013]

According to another aspect of the present invention, there is provided an optical scanning device including a light source means, a deflecting means for reflecting and deflecting a light beam emitted from the light source means, and a light beam from the deflecting means on a surface to be scanned. In an optical scanning device including a scanning optical system that guides light to a surface and scans the surface to be scanned, the scanning optical system has two or more optical elements, and the two optical elements are included in the main scanning section. The element has at least one aspherical surface having a positive refractive power, and in the sub-scan section, at least two surfaces of the two optical elements have a radius of curvature of one along the main scanning direction. It is characterized by having extreme values.

According to a second aspect of the present invention, in the first aspect of the present invention, the scanning optical system has one or more surfaces in the sub-scanning section in which the change in the radius of curvature is asymmetric with respect to the optical axis in the main scanning direction. It is characterized by having.

According to a third aspect of the invention, in the first aspect of the invention, the radius of curvature of the optical surface of the optical element closest to the optical deflector in the main scanning direction is the scanning optical system in the sub-scanning section. It is characterized by being asymmetrical.

According to a fourth aspect of the present invention, in the first aspect, at least one optical element of the scanning optical system is shifted or / and tilted with respect to the optical axis.

According to a fifth aspect of the present invention, in the first aspect of the invention, the radius of curvature of the scanning optical system is asymmetric with respect to the optical axis in the main scanning direction in the sub-scan section, and the main scanning is performed from the optical axis. It is characterized in that it has a surface that changes so that the absolute value of the radius of curvature becomes smaller as it separates in the direction.

The invention of claim 6 is characterized in that, in the invention of any one of claims 1 to 5, the light source means is a multi-beam light source having a plurality of light sources.

According to a seventh aspect of the invention, in the invention according to any one of the first to sixth aspects, each optical element constituting the scanning optical system has a thickness of 10 mm or less.

According to an eighth aspect of the present invention, in the first aspect of the invention, the first optical system for converting the state of the light beam emitted from the light source means to another state, and the light beam converted by the first optical system are provided. A second optical system for forming a long line image in the main scanning direction on the deflection surface of the deflection means.

An optical scanning device according to a ninth aspect of the present invention comprises a light source means, a deflecting means for reflecting and deflecting a light beam emitted from the light source means, and a light beam from the deflecting means for guiding the light beam onto a surface to be scanned,
In an optical scanning device having a scanning optical system for scanning the surface to be scanned, the scanning optical system has an optical element, and the optical element has an aspherical shape having a positive refractive power in a main scanning section. One or more surfaces are provided, and the curvature radius of at least one of the optical elements has one extreme value along the main scanning direction in the sub-scan section.

According to a tenth aspect of the present invention, in the invention of the ninth aspect, the scanning optical system has one or more surfaces in which a change in radius of curvature is asymmetric in the main scanning direction with respect to the optical axis in the sub-scan section. It is characterized by having.

According to an eleventh aspect of the present invention, in the ninth aspect, the scanning optical system has a curvature radius of an optical surface of the optical element closest to the optical deflector in the main scanning direction with respect to the optical axis in the sub-scanning section. It is characterized by being asymmetrical.

According to a twelfth aspect of the present invention, in the ninth aspect, the optical element of the scanning optical system is shifted or / and tilted with respect to the optical axis.

According to a thirteenth aspect of the present invention, in the ninth aspect of the invention, the radius of curvature of the scanning optical system is asymmetric with respect to the optical axis in the main scanning direction in the sub-scanning section, and the main scanning is performed from the optical axis. It is characterized in that it has a surface that changes so that the absolute value of the radius of curvature becomes smaller as it separates in the direction.

According to a fourteenth aspect of the invention, in the invention according to any one of the ninth to thirteenth aspects, the light source means is a multi-beam light source having a plurality of light sources.

According to a fifteenth aspect of the invention, in the invention according to any one of the ninth to fourteenth aspects, the optical element of the scanning optical system has a thickness of 10 mm or less.

According to a sixteenth aspect of the present invention, in the invention of the ninth aspect, the first optical system for converting the state of the light beam emitted from the light source means to another state and the light beam converted by the first optical system are provided. A second optical system for forming a long line image in the main scanning direction on the deflection surface of the deflection means.

An optical scanning device according to a seventeenth aspect of the invention is directed to a light source means, a deflecting means for reflecting and deflecting a light beam emitted from the light source means, and a light beam from the deflecting means for guiding the light beam onto a surface to be scanned. In an optical scanning device having a scanning optical system for scanning a surface to be scanned, the scanning optical system has one or more optical elements, and in a sub-scan section, at least two surfaces have a radius of curvature in the main scanning direction. It is characterized by having one extreme value along.

According to an eighteenth aspect of the invention, in the seventeenth aspect of the invention, the scanning optical system has one or more surfaces in the sub-scanning section in which the change of the radius of curvature is asymmetric with respect to the optical axis in the main scanning direction. It is characterized by having.

In a nineteenth aspect based on the seventeenth aspect, the scanning optical system has a curvature radius of an optical surface of an optical element closest to the optical deflector in the main scanning direction with respect to the optical axis in the sub-scanning section. It is characterized by being asymmetrical.

According to a twentieth aspect of the invention according to the seventeenth aspect, at least one optical element of the scanning optical system is
It is characterized in that it is shifted and / or tilted with respect to the optical axis.

According to a twenty-first aspect of the invention, in the seventeenth aspect of the invention, the radius of curvature of the scanning optical system is asymmetric with respect to the optical axis in the main scanning direction in the sub-scan section, and the main scanning is performed from the optical axis. It is characterized in that it has a surface that changes so that the absolute value of the radius of curvature becomes smaller as it separates in the direction.

The invention of claim 22 is characterized in that, in the invention of any one of claims 17 to 22, the light source means is a multi-beam light source having a plurality of light sources.

A twenty-third aspect of the present invention is characterized in that, in any one of the seventeenth to twenty-second aspects of the present invention, each optical element forming the scanning optical system has a thickness of 10 mm or less.

According to a twenty-fourth aspect of the invention, in the seventeenth aspect of the invention, there is provided a first optical system for converting the state of the light beam emitted from the light source means to another state, and a light beam converted by the first optical system. A second optical system for forming a long line image in the main scanning direction on the deflection surface of the deflection means.

An image forming apparatus according to a twenty-fifth aspect of the present invention is an optical scanning device according to any one of the first to twenty-fourth aspects, a photoconductor disposed on the surface to be scanned, and the optical scanning device for scanning. Developing device that develops the electrostatic latent image formed on the photoconductor as a toner image by the generated light flux, a transfer device that transfers the developed toner image to a transfer material, and the transferred toner image is transferred. It is characterized by having a fixing device for fixing the material.

An image forming apparatus according to a twenty-sixth aspect of the present invention is the optical scanning apparatus according to any one of the first to twenty-fourth aspects, and the optical scanning apparatus, wherein code data input from an external device is converted into an image signal. It is characterized by having a printer controller for inputting to.

[0039]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS [Embodiment 1] FIG. 1 is a sectional view (main scanning sectional view) of a main portion in a main scanning direction of Embodiment 1 of the present invention, and FIG. 2 is a sub scanning direction of Embodiment 1 of the present invention. 3 is a cross-sectional view (sub-scanning cross-sectional view) of a main part of FIG.

In this specification, the surface formed by the optical axis of the scanning optical system and the light beam deflected by the optical deflector is the main scanning section, and the surface including the optical axis of the scanning optical system and orthogonal to the main scanning section. Is defined as a sub-scan section.

In FIGS. 1 and 2, 1 is a light source means,
For example, it is made of a semiconductor laser. Reference numeral 2 denotes a condenser lens (collimator lens) as a first optical system, which converts the divergent light flux emitted from the light source means 1 into a substantially parallel light flux or a convergent light flux. An aperture stop 3 limits the passing light flux to shape the beam shape. Reference numeral 4 denotes a cylindrical lens as a second optical system, which has a predetermined power only in the sub-scanning direction, and deflects the light beam that has passed through the aperture stop 3 in the sub-scanning section of the optical deflector 5 which will be described later. The image is formed on the (reflecting surface) 5a as a substantially linear image. still,
Each element such as the condenser lens 2, the aperture stop 3, and the cylindrical lens 4 constitutes one element of the incident optical means.

Reference numeral 5 denotes an optical deflector as a deflecting means, which is composed of, for example, a polygon mirror (rotating polygonal mirror) having a four-sided structure, and is driven at a constant speed in the direction of arrow A by a driving means (not shown) such as a motor. Is spinning at.

Reference numeral 6 denotes a scanning optical system (fθ lens system) as a third optical system having a condensing function and fθ characteristics. The scanning optical system 6 is made of a plastic material in order from the optical deflector 5 side.
2 fθ lenses 6a and 6b, the light beam based on the image information reflected and deflected by the optical deflector 5 is imaged in a spot shape on the photosensitive drum surface 7 as the surface to be scanned, and the sub-scanning cross section is formed. A tilt correction function is provided by forming a conjugate relationship between the deflection surface 5a of the optical deflector 5 and the photosensitive drum surface 7 inside.

In the main scanning section, both the first and second fθ lenses 6a and 6b in the present embodiment have at least one aspherical surface (toric surface) having a positive refracting power, and sub-scanning. In the cross section, the radius of curvature of at least two surfaces of the first and second fθ lenses 6a and 6b changes with one extreme value along the main scanning direction. The thickness of the first and second fθ lenses 6a and 6b is 10 mm or less.

Reference numeral 7 is a photosensitive drum surface as a surface to be scanned.

In this embodiment, the divergent light beam emitted from the semiconductor laser 1 is converted into a substantially parallel light beam or a convergent light beam by the condenser lens 2, and the light beam (light amount) is limited by the aperture stop 3 and is incident on the cylindrical lens 4. ing. Of the substantially parallel light flux that has entered the cylindrical lens 4, it exits as it is in the main scanning cross section. Further, in the sub-scanning cross section, they converge and form a substantially linear image on the deflecting surface 5a of the optical deflector 5 (a linear image longitudinal in the main scanning direction). Then, the light beam reflected and deflected by the deflecting surface 5a of the optical deflector 5 is imaged in a spot shape on the photosensitive drum surface 7 via the first and second fθ lenses 6a and 6b, and the optical deflector 5 is indicated by an arrow. By rotating in the A direction, the photosensitive drum surface 7 is optically scanned in the arrow B direction (main scanning direction) at a constant speed. As a result, the photosensitive drum surface 7 as a recording medium
The image is recorded on the top.

The shapes of the first and second fθ lenses 6a and 6b constituting the scanning optical system 6 in the present embodiment are expressed by the following function.

For example, with the intersection of the first and second fθ lenses and the optical axis as the origin, as shown in FIG. 1, the surface in the main scanning section on the scanning start side 7a and the scanning end side 7b with respect to the optical axis. As for the shape, when the optical axis is the X axis, the direction orthogonal to the optical axis in the main scanning cross section is the Y axis, and the direction orthogonal to the optical axis in the sub scanning cross section is the Z axis, the surface shape on the scanning start side 7a is

[0049]

[Equation 1]

It is represented by

However, R is the radius of curvature, K, B ₄ , B ₆ ,
B ₈ and B ₁₀ are aspherical coefficients. The coefficient suffix s represents the scanning start side, and the suffix e represents the scanning end side.

In the sub-scanning section, at least two of the first and second fθ lenses 6a and 6b on the scanning start side and the scanning end side with respect to the optical axis have a curvature radius in the sub-scanning direction which is effective for the lens. Change continuously within the department,
The shapes of the second fθ lenses 6a and 6b in the main scanning cross section are formed symmetrically with respect to the optical axis.

As shown in FIG. 2, the shape in the sub-scanning cross section is on the scanning start side and the scanning end side with respect to the optical axis, the optical axis is the X axis, and the direction orthogonal to the optical axis in the main scanning cross section is the Y axis. When the direction orthogonal to the optical axis in the sub-scan section is the Z axis, it can be expressed by the following continuous function.

The surface shape of the scanning start side 7a is

[0055]

[Equation 2]

The surface shape of the scanning end side 7b is

[0057]

[Equation 3]

It is represented by

However, r is the radius of curvature in the sub-scanning direction, D ₂ ,
D ₄ , D ₆ , D ₈ and D ₁₀ are coefficients.

The suffix s of the coefficient represents the scanning start side, and e represents the scanning end side.

The radius of curvature in the sub-scanning direction is the radius of curvature in the cross section orthogonal to the shape (bus line) in the main scanning direction.

In this embodiment, the focus correction in the sub-scanning direction
(Field curvature correction) and in order to correct the uniformity of the magnification in the sub-scanning direction in the scanning optical system (variation due to the image height of the spot diameter), both lens surfaces R1 and R2 of the first fθ lens 6a and The curvature radii of both lens surfaces R3 and R4 of the second fθ lens 6b in the sub-scanning direction are continuously changed within the lens effective portion, and the radius of curvature of the exit surface R2 of the first fθ lens 6a is defined by one of the above functions. It has an extreme value and is changed asymmetrically with respect to the optical axis.

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

The first and second fθ lenses 6 of this embodiment
Both a and 6b are made of plastic lenses,
The shape in the main scanning cross section is formed symmetrically with respect to the optical axis on the scanning start side and the scanning end side so as to be advantageous in molding.

Further, the radius of curvature in the sub-scanning direction is at least 2
The surface changes continuously in the effective part of the lens,
This corrects field curvature, wavefront aberration, and spot diameter variation.

In the present embodiment, the light beam emitted from the light source means is incident on the deflecting surface 5a of the optical deflector 5 at an angle α (≠ 0) with respect to the optical axis in the main scanning cross section. The surface entering / exiting (sag) due to the rotation of the container 5 occurs asymmetrically on the scanning start side and the scanning end side. Due to this asymmetrical sag, the scanning optical system 6 has a curvature in the sub-scanning direction in order to satisfactorily correct changes in field curvature, wavefront aberration, and spot diameter variation that are asymmetrical in the main scanning direction with respect to the optical axis. It has at least one surface whose radius changes asymmetrically with respect to the optical axis along the main scanning direction (hereinafter referred to as “sub-scanning curvature radius asymmetric surface”).

In this embodiment, the curvature radius of the asymmetric surface in the sub-scanning radius of curvature is changed with one extreme value to improve the asymmetry of the wavefront aberration and the variation of the spot diameter due to all sags. Correcting.

Further, by forming a sub-scanning radius of curvature asymmetry on the first fθ lens 6a closest to the optical deflector 5,
The asymmetry due to the sag of wavefront aberration is well corrected.

Further, by making the axis of symmetry of the second fθ lens 6b in the main scanning direction asymmetrical with respect to the perpendicular bisector of the surface to be scanned 8, the asymmetry of field curvature can be corrected well. There is.

The axis of symmetry in the main scanning direction is the optical axis of the fθ lens.

In this embodiment, the optical axis of the scanning optical system 6 is aligned with the vertical bisector of the surface 7 to be scanned in the main scanning direction.

On the other hand, unless the radius of curvature in the sub-scanning direction is changed by at least two surfaces, both the field curvature and the spot diameter fluctuation cannot be corrected simultaneously, which is not good. If the sub-scanning radius of curvature asymmetry has two or more extreme values in its change, the wavefront aberration cannot be corrected well, and the spot shape on the surface of the photosensitive drum deteriorates, which is not preferable.

In the present embodiment, the second scanning lens 6b is shifted or / and tilted with respect to the optical axis as described above. However, the present invention is not limited to this, and the first scanning lens 6a or the first and second scanning lenses 6a. The scanning lenses 6a and 6b may be shifted and / or tilted with respect to the optical axis.

Table 1 shows the optical parameters of this embodiment. Further, FIG. 3 shows the optical characteristics of this embodiment, and FIG. 4 shows the change of the radius of curvature in the sub-scanning direction of this embodiment.

[0075]

[Table 1]

In this embodiment, the first fθ lens 6a
Is a positive meniscus shape with a convex surface facing the surface to be scanned in the main scanning section, and as described above, the first and second
Of the fθ lenses 6a and 6b, the radius of curvature of at least one surface in the sub-scanning direction is continuous in the effective portion of the lens,
In addition, by changing asymmetrically in the main scanning direction with respect to the optical axis, and further by configuring the axis of symmetry of the second fθ lens 6b in the main scanning direction to be asymmetric with respect to the perpendicular bisector of the scanned surface 8, The field curvature asymmetry and the spot diameter variation are simultaneously corrected.

In this embodiment, the asymmetric surface in the sub-scanning radius of curvature is composed of one surface, and the sagittal line changing surface (the surface in which the radius of curvature in the sub-scanning direction changes along the main scanning direction) is off-axis. I am changing without having.

Further, in order to simultaneously correct the asymmetry of the curvature of field and the fluctuation of the spot diameter, the second side closest to the surface to be scanned is used.
The axis of symmetry of the fθ lens 6b in the main scanning direction is asymmetric with respect to the perpendicular bisector of the surface 8 to be scanned. That is, this is an asymmetrical surface in the sub-scanning radius of curvature (a surface in which the radius of curvature in the sub-scanning direction is changed asymmetrically along the main scanning direction with respect to the optical axis).
The effect similar to that of the above is obtained, and the asymmetry can be corrected without using the sub-scanning curvature radius asymmetric surface, which is advantageous in lens molding.

Although the scanning optical system 6 is composed of two lenses in the present embodiment, the present invention is not limited to this, and it may be composed of, for example, a single lens or three or more lenses, and an fθ mirror or a diffractive optical element. Even if an optical element such as the above is used, the same effect can be obtained.

Further, in the present embodiment, the condenser lens 2, the cylindrical lens 4 and the like may be omitted, and the light flux emitted from the light source means 1 may be directly guided to the deflection surface via the aperture stop 3.

As described above, in the present embodiment, as described above, the thin lens which is advantageous in manufacturing the lens is used, and the sagittal line changing surface is changed without having an off-axis extreme value, and the second fθ lens 6b is formed. By arranging the axis of symmetry in the main scanning direction asymmetrical with respect to the perpendicular bisector of the surface to be scanned 8, it is possible to simultaneously correct the asymmetry of the curvature of field and the fluctuation of the spot diameter. It is possible to obtain a high-performance optical scanning device that is advantageous in manufacturing.

[Second Embodiment] Next, a second embodiment of the present invention will be described.

Table 2 shows the optical parameters of this embodiment. Further, FIG. 5 shows the optical characteristics of this embodiment, and FIG. 6 shows the change of the radius of curvature in the sub-scanning direction of this embodiment.

[0084]

[Table 2]

The present embodiment is different from the first embodiment described above in that the first and second fθ lenses are formed with different lens shapes (curvature radii in the sub-scanning direction). Other configurations and optical functions are substantially the same as those of the first embodiment, and the same effect is obtained.

That is, both the first and second fθ lenses of the present embodiment are made of plastic lenses, and the shape in the main scanning cross section has an optical axis (scanned surface 8
Is formed symmetrically on the scanning start side and the scanning end side.

The radius of curvature in the sub-scanning direction is at least 2
The surface changes continuously in the effective part of the lens,
This corrects field curvature, wavefront aberration, and spot diameter variation.

Further, in order to satisfactorily correct the field curvature, the wavefront aberration, and the variation of the spot diameter which are asymmetrical with respect to the optical axis in the main scanning direction due to the asymmetric sag, the scanning optical system is arranged in the sub-scanning direction. There is at least one surface (sub-scanning curvature radius asymmetric surface) whose radius of curvature changes asymmetrically with respect to the optical axis along the main scanning direction. The change in that surface is to correct wavefront aberration satisfactorily. It is changing with one extreme value.

Further, by forming the sub-scanning radius of curvature asymmetry on the first fθ lens closest to the optical deflector, the asymmetry due to the sag of the wavefront aberration is satisfactorily corrected, and the sub-scanning radius of curvature asymmetry is used as the optical surface. The radius of curvature is changed so that the absolute value of the radius of curvature becomes smaller with distance from the axis in the main scanning direction, and the axis of symmetry of the second fθ lens in the main scanning direction is made symmetrical with respect to the perpendicular bisector of the surface to be scanned. With this configuration, the asymmetry of curvature of field is corrected well without shifting or / and tilting the lens.

In this embodiment, the field curvature, wavefront aberration, and spot diameter variation are corrected more favorably than in the first embodiment, and the axis of symmetry of the second fθ lens in the main scanning direction is the surface to be scanned. Since it is configured symmetrically with respect to the vertical bisector 8, it is possible to reduce performance deterioration due to mounting error.

As described above, in the present embodiment, as described above, the sagittal line changing surface is changed without having an extreme value off the axis, and the second
By configuring the axis of symmetry of the fθ lens in the main scanning direction to be symmetrical with respect to the perpendicular bisector of the surface to be scanned, it is possible to obtain a high-performance optical scanning device in which the performance is less deteriorated due to a mounting error.

[Third Embodiment] FIG. 7 shows a third embodiment of the present invention.
FIG. 4 is a main-portion cross-sectional view (main-scan sectional view) in the main-scan direction. In the figure, the same elements as those shown in FIG. 1 are designated by the same reference numerals.

The present embodiment differs from the second embodiment in that the light source means 11 is composed of a multi-beam light source having a plurality of light emitting portions (light sources), and the diaphragm 4 is composed of a cylindrical lens 4 and an optical deflector 5. It is a point arranged in the optical path between. Other configurations and optical functions are the same as those of the second embodiment.
Is almost the same as the above, and thereby the same effect is obtained.

That is, in the figure, reference numeral 11 designates a multi-beam light source (monolithic multi-laser) having a plurality of light emitting portions on the same chip. An aperture stop 13 is provided in the optical path between the cylindrical lens 4 and the optical deflector 5 in order to reduce the relative dot deviation of the multi-beam light source in the main scanning direction.

The first and second fθ lenses 6 of this embodiment
Both a and 6b are made of plastic lenses,
The shape in the main scanning cross section is formed symmetrically with respect to the optical axis (vertical bisector of the surface to be scanned 8) on the scanning start side 7a and the end side 7b so as to be advantageous in molding.

The radius of curvature in the sub-scanning direction is at least 2
The surface changes continuously in the effective part of the lens,
This corrects field curvature, wavefront aberration, and spot diameter variation.

Further, in order to satisfactorily correct the field curvature, the wavefront aberration, and the variation of the spot diameter which are asymmetrical with respect to the optical axis in the main scanning direction due to the asymmetric sag, the scanning optical system is arranged in the sub scanning direction. There is at least one surface (sub-scanning curvature radius asymmetric surface) whose radius of curvature changes asymmetrically with respect to the optical axis along the main scanning direction. The change in that surface is to correct wavefront aberration satisfactorily. It is changing with one extreme value.

Further, by forming the sub-scanning radius of curvature asymmetrical surface on the first fθ lens 6a closest to the optical deflector, the asymmetry due to the sag of the wavefront aberration is satisfactorily corrected, and the sub-scanning radius of curvature asymmetrical surface is formed. The radius of curvature is changed so that the absolute value of the radius of curvature becomes smaller as the distance from the optical axis in the main scanning direction increases, and the axis of symmetry of the second fθ lens 6b in the main scanning direction is set with respect to the perpendicular bisector of the scanned surface 8. With the symmetric structure, the asymmetry of the curvature of field is corrected well without shifting or / and tilting the lens.

When the light source means is composed of a multi-beam light source, for example, in the case of an image forming apparatus having a resolution of 600 dpi, the distance between the beams in the sub-scanning direction is about 42.3 μm on the surface to be scanned. Have to be adjusted. Further, it is desirable that the inter-beam distance in the sub-scanning direction is uniform at each image height on the surface to be scanned.

The variation in the beam spacing in the sub-scanning direction at each image height (pitch spacing error) is approximately proportional to the lateral magnification in the sub-scanning direction at each image height (variation in spot diameter due to image height), and the pitch spacing error is 2 If it is more than%, the uniformity of the sub-scanning magnification of the scanning optical system 6 must be corrected so that the pitch interval error is less than 2% because it is visually conspicuous.

FIG. 8 shows a graph of the pitch interval error of this embodiment.

It can be seen from the figure that the pitch interval error is well corrected to less than 2%. In the present embodiment, since the multi-beam light source is used as the light source means, the system is suitable for increasing the speed of the image forming apparatus, and it is possible to provide a compact, high-speed, and high-definition multi-beam optical scanning device. it can.

As described above, in the present embodiment, as described above, the sagittal line changing surface is changed without having an extremal value off-axis, and the second line is changed.
By configuring the axis of symmetry of the fθ lens 6b in the main scanning direction to be symmetrical with respect to the perpendicular bisector of the surface to be scanned 8, a high-performance multi-beam optical scanning device in which performance deterioration due to mounting error is small can be obtained. be able to.

[Fourth Embodiment] Next, a fourth embodiment of the present invention will be described.

Table 3 shows the optical parameters of this embodiment. Further, FIG. 9 shows the optical characteristics of this embodiment, and FIG. 10 shows the change of the radius of curvature in the sub-scanning direction.

[0106]

[Table 3]

The present embodiment is different from the above-described third embodiment in that the first and second fθ lenses are formed with different lens shapes (curvature radii in the sub-scanning direction). Other configurations and optical functions are substantially the same as those of the first embodiment, and the same effect is obtained.

That is, both the first and second fθ lenses of this embodiment are made of plastic lenses, and the shape in the main scanning cross section has an optical axis (scanned surface 8
Is formed symmetrically on the scanning start side and the scanning end side.

The radius of curvature in the sub-scanning direction is at least 2
The surface changes continuously in the effective part of the lens,
This corrects field curvature, wavefront aberration, and spot diameter variation.

In order to satisfactorily correct the field curvature, wavefront aberration, and variation in spot diameter that are asymmetrical with respect to the optical axis in the main scanning direction due to the asymmetric sag, the scanning optical system is arranged in the sub-scanning direction. It has at least one surface whose curvature radius changes asymmetrically along the main scanning direction with respect to the optical axis (sub-scanning curvature radius asymmetric surface), and the change of that surface is to correct wavefront aberration satisfactorily. Has one extreme value and is changing.

Further, by forming the sub-scanning radius of curvature asymmetrical surface on the first fθ lens closest to the optical deflector, the asymmetry due to the sag of the wavefront aberration is satisfactorily corrected, and the sub-scanning radius of curvature asymmetrical surface is converted into the optical axis. The radius of curvature is changed so that the absolute value of the radius of curvature becomes smaller with distance from the axis in the main scanning direction, and the axis of symmetry of the second fθ lens in the main scanning direction is made symmetrical with respect to the perpendicular bisector of the surface to be scanned. With this configuration, the asymmetry of curvature of field is corrected well without shifting or / and tilting the lens.

In the present embodiment, the field curvature, the wavefront aberration, and the fluctuation of the spot diameter are corrected more favorably than in the third embodiment, and the axis of symmetry of the second fθ lens in the main scanning direction is the surface to be scanned. Since it is configured symmetrically with respect to the vertical bisector, it has a feature that deterioration of performance due to mounting error can be reduced. Also, the uniformity of the lateral magnification in the sub-scanning direction is
Since the correction is further excellently performed, the pitch interval error of the multi-beam is further reduced as shown in the graph of FIG. FIG. 11 is a graph showing the pitch interval error of this embodiment.

From the figure, it can be seen that the pitch interval error is well corrected to less than 2%. In this embodiment, since a multi-beam light source is used as the light source means, the system is suitable for increasing the speed of the image forming apparatus, and it is possible to provide a compact, high-speed, and high-definition optical scanning device.

As described above, in the present embodiment, as described above, the sagittal line changing surface is changed without having an off-axis value, and the second
By configuring the symmetry axis of the fθ lens in the main scanning direction symmetrically with respect to the perpendicular bisector of the surface to be scanned, there is little deterioration in performance due to mounting errors, and there is little multi-beam pitch error and high performance. A multi-beam optical scanning device can be obtained.

In each of the above embodiments, the scanning optical system is composed of one or more optical elements, and the optical element has one aspherical surface having a positive refractive power in the main scanning cross section. The same effect can be obtained even if the radius of curvature of at least one surface of the optical element has one extreme value along the main scanning direction in the sub-scanning cross section.

In addition, the scanning optical system is composed of one or more optical elements, and the radii of curvature of at least two surfaces in the sub-scanning section have one extreme value along the main scanning direction. Also has the same effect.

[Image Forming Apparatus] FIG. 12 is a main part in a sub-scan section showing an embodiment of an image forming apparatus (electrophotographic printer) using the optical scanning apparatus of the first, second, third or fourth embodiment. FIG. In FIG. 12, reference numeral 10
Reference numeral 4 represents an image forming apparatus. Code data Dc is input to the image forming apparatus 104 from an external device 117 such as a personal computer. This code data Dc is
The image is converted into image data (dot data) Di by the printer controller 111 in the apparatus. This image data Di is input to the optical scanning unit 100 having the configuration shown in each of the first, second, third, and fourth embodiments. A light beam (light flux) 103 modulated according to the image data Di is emitted from the light scanning unit (light scanning device) 100, and the light beam 103 causes the photosensitive drum 101.
The photosensitive surface of is scanned in the main scanning direction.

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

As described above, the light beam 103 is
The light beam 103 is modulated based on the image data Di, and an electrostatic latent image is formed on the surface of the photosensitive drum 101 by irradiating the light beam 103. This electrostatic latent image is more sensitive to the photosensitive drum 101 than the irradiation position of the light beam 103.
The toner is developed as a toner image by the developing device 107 arranged so as to come into contact with the photosensitive drum 101 on the downstream side in the rotational cross section.

The toner image developed by the developing device 107 is transferred onto the paper 112, which is the material to be transferred, by the transfer roller (transfer device) 108 arranged below the photosensitive drum 101 so as to face the photosensitive drum 101. To be done. Paper 1
12 is the front of the photosensitive drum 101 (right side in FIG. 12)
Although the paper is stored in the paper cassette 109, the paper can be manually fed. A paper feed roller 110 is arranged at the end of the paper cassette 109,
The paper 112 inside is sent to the transport path.

The sheet 112 on which the unfixed toner image has been transferred as described above is further rearward of the photosensitive drum 101 (see FIG. 1).
2 is conveyed to the fixing device on the left side). The fixing device includes a fixing roller 113 having a fixing heater (not shown) inside.
And a pressure roller 114 arranged so as to be in pressure contact with the fixing roller 113, and the sheet 112 sent from the transfer portion is fixed to the fixing roller 113 and the pressure roller 1.
The unfixed toner image on the sheet 112 is fixed by heating while applying pressure at the pressure contact portion 14 of the sheet. Further, a paper discharge roller 116 is disposed behind the fixing roller 113, and discharges the fixed paper 112 to the outside of the image forming apparatus.

Although not shown in FIG. 12, the print controller 111 performs not only the data conversion described above, but also the motor 115, each unit in the image forming apparatus, the polygon motor in the optical scanning unit 100, and the like. Control.

[0123]

According to the present invention, as described above, a scanning optical system is constructed by using an optical element having a small thickness, and the radius of curvature of at least one surface in the sub-scanning direction is changed along the main scanning direction.
Further, by changing the sagittal line changing surface with one extreme value, it is possible to excellently correct the wavefront aberration, and it is possible to excellently correct the field curvature and the spot diameter variation, and an optical scanning device thereof. It is possible to achieve an image forming apparatus using.

Further, in a multi-beam optical scanning device using a multi-beam light source as a light source means, there is little variation in the pitch interval in the sub-scanning direction due to image height, and a high-quality and high-speed multi-beam optical scanning device and image formation using the same. A device can be achieved.

[Brief description of drawings]

FIG. 1 is a main-scan sectional view of a first embodiment of the present invention.

FIG. 2 is a sub-scan sectional view of the first embodiment of the present invention.

FIG. 3 is a diagram showing optical characteristics according to the first embodiment of the present invention.

FIG. 4 is a diagram showing changes in a sub-scanning radius of curvature according to the first embodiment of the present invention.

FIG. 5 is a diagram showing optical characteristics of Embodiment 2 of the present invention.

FIG. 6 is a diagram showing changes in a sub-scanning radius of curvature according to the second embodiment of the present invention.

FIG. 7 is a main-scan sectional view of a third embodiment of the present invention.

FIG. 8 is a diagram showing a sub-scanning pitch interval error according to the third embodiment of the present invention.

FIG. 9 is a diagram showing optical characteristics of Embodiment 4 of the present invention.

FIG. 10 is a diagram showing changes in the sub-scanning radius of curvature according to the fourth embodiment of the present invention.

FIG. 11 is a diagram showing a sub-scanning pitch interval error according to the fourth embodiment of the present invention.

FIG. 12 is a sub-scanning sectional view showing a configuration example of an image forming apparatus (electrophotographic printer) using the scanning optical system of the present invention.

FIG. 13 is a main-scan sectional view of a conventional optical scanning device.

[Explanation of symbols]

1 Light source means (semiconductor laser) 2 First optical system (collimator-lens) 3,13 Aperture stop 4 Second optical system (Cylindrical lens) 5 Deflection means (optical deflector) 5a Deflection surface 6 Third optical system (scanning optical system) 6a First fθ lens 6b Second fθ lens 7 Scanned surface (photosensitive drum surface) 11 Multi-beam light source 100 Optical scanning device 101 photosensitive drum 102 charging roller 103 light beam 104 image forming apparatus 107 developing device 108 transfer roller 109 paper cassette 110 paper feed roller 111 Printer controller 112 Transfer material (paper) 113 fixing roller 114 pressure roller 115 motor 116 paper ejection roller 117 External device

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Claims (26)

[Claims] 1. A light source unit, a deflecting unit for reflecting and deflecting a light beam emitted from the light source unit, and a scanning optical system for guiding the light beam from the deflecting unit onto a surface to be scanned and scanning the surface to be scanned. In the optical scanning device including a system, the scanning optical system has two or more optical elements, and the two optical elements have an aspherical surface having a positive refractive power within a main scanning section. Having more than one surface, within the sub-scan section,
An optical scanning device characterized in that at least two surfaces of the two optical elements have one radius of curvature in the main scanning direction. 2. The scanning optical system has at least one surface in which a change in radius of curvature is asymmetric in the main scanning direction with respect to the optical axis in the sub-scanning cross section.
The optical scanning device described. 3. The scanning optical system is characterized in that, in a sub-scan section, the radius of curvature of the optical surface of the optical element closest to the optical deflector is asymmetric with respect to the optical axis in the main scanning direction. 1. The optical scanning device according to 1. 4. The optical scanning device according to claim 1, wherein at least one optical element of the scanning optical system is shifted and / or tilted with respect to an optical axis. 5. The scanning optical system has a curvature radius asymmetric in the main scanning direction with respect to the optical axis in a sub-scan section, and the absolute value of the curvature radius increases as the distance from the optical axis in the main scanning direction increases. The optical scanning device according to claim 1, wherein the optical scanning device has a surface that changes so as to become smaller. 6. The light source means is a multi-beam light source having a plurality of light sources.
The optical scanning device according to claim 1. 7. The optical scanning device according to claim 1, wherein each optical element forming the scanning optical system has a thickness of 10 mm or less. 8. A first optical system for converting a state of a light beam emitted from a light source means to another state, and a light beam converted by the first optical system on a deflecting surface of the deflecting means. The optical scanning device according to claim 1, further comprising a second optical system that forms a long line image in the scanning direction. 9. A light source means, a deflecting means for reflecting and deflecting a light beam emitted from the light source means, and a scanning optical for guiding the light beam from the deflecting means onto a surface to be scanned and scanning the surface to be scanned. In the optical scanning device having a system, the scanning optical system has an optical element, and in the main scanning section, the optical element has at least one aspherical surface having a positive refractive power, and the sub scanning In the cross section, the radius of curvature of at least one surface of the optical element is 1 along the main scanning direction.
An optical scanning device having two extreme values. 10. The scanning optical system according to claim 9, wherein in the sub-scanning cross section, a change in radius of curvature has one or more surfaces that are asymmetric with respect to the optical axis in the main scanning direction.
The optical scanning device described. 11. The scanning optical system is characterized in that, in the sub-scanning cross section, the radius of curvature of the optical surface of the optical element closest to the optical deflector is asymmetric with respect to the optical axis in the main scanning direction. 9. The optical scanning device according to 9. 12. The optical scanning device according to claim 9, wherein the optical element of the scanning optical system is shifted and / or tilted with respect to the optical axis. 13. In the scanning optical system, the radius of curvature is asymmetric in the main scanning direction with respect to the optical axis in the sub-scanning section, and the absolute value of the radius of curvature increases as the distance from the optical axis in the main scanning direction increases. The optical scanning device according to claim 9, wherein the optical scanning device has a surface that changes so as to become smaller. 14. The optical scanning device according to claim 9, wherein the light source unit is a multi-beam light source having a plurality of light sources. 15. The optical element of the scanning optical system has a thickness of 10 mm or less.
The optical scanning device according to claim 1. 16. A first optical system for converting a state of a light beam emitted from a light source means into another state, and a light beam converted by the first optical system on a deflecting surface of the deflecting means. The optical scanning device according to claim 9, further comprising a second optical system that forms a long line image in the scanning direction. 17. A light source unit, a deflecting unit for reflecting and deflecting a light beam emitted from the light source unit, and a scanning optical system for guiding the light beam from the deflecting unit onto a surface to be scanned and scanning the surface to be scanned. In the optical scanning device including a system, the scanning optical system has one or more optical elements, and in the sub-scanning cross section, at least two surfaces have a radius of curvature having one extreme value along the main scanning direction. An optical scanning device. 18. The scanning optical system according to claim 1, wherein in the sub-scanning section, a change in radius of curvature has one or more surfaces that are asymmetric with respect to the optical axis in the main scanning direction.
7. The optical scanning device according to 7. 19. The scanning optical system is characterized in that, in the sub-scanning cross section, the radius of curvature of the optical surface of the optical element closest to the optical deflector is asymmetric in the main scanning direction with respect to the optical axis. 17. The optical scanning device according to 17. 20. The optical scanning device according to claim 17, wherein at least one optical element of the scanning optical system is shifted and / or tilted with respect to the optical axis. 21. In the scanning optical system, the radius of curvature is asymmetric in the main scanning direction with respect to the optical axis in the sub-scanning section, and the absolute value of the radius of curvature increases as the distance from the optical axis in the main scanning direction increases. The optical scanning device according to claim 17, wherein the optical scanning device has a surface that changes so as to become smaller. 22. The optical scanning device according to claim 17, wherein the light source unit is a multi-beam light source having a plurality of light sources. 23. The optical scanning device according to claim 17, wherein each optical element constituting the scanning optical system has a wall thickness of 10 mm or less. 24. A first optical system for converting a state of a light beam emitted from a light source means into another state, and a light beam converted by the first optical system on a deflecting surface of the deflecting means. The optical scanning device according to claim 17, further comprising a second optical system that forms a long line image in the scanning direction. 25. An optical scanning device according to any one of claims 1 to 24, and a photoconductor disposed on the surface to be scanned.
A developing device that develops an electrostatic latent image formed on the photoconductor as a toner image by a light beam scanned by the optical scanning device, a transfer device that transfers the developed toner image to a transfer material, and An image forming apparatus comprising: a fixing device that fixes the toner image to the transfer material. 26. An optical scanning device according to any one of claims 1 to 24, and a printer controller for converting code data input from an external device into an image signal and inputting the image signal into the optical scanning device. An image forming apparatus characterized by the above.