JP2000171739A - Optical scanner, scanning image formation optical system and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make high density and excellent write-in possible by realizing a stable light spot whose spot size is small by excellently correcting wave front aberration. SOLUTION: This is a scanning image formation optical system condensing a deflecting luminous flux deflected by an optical deflecting means 20 having a deflecting reflection surface 20A on a surface to be scanned 26 as a light spot, and incorporates one or more lenses 22 and 24, and at least one of lens surfaces is made as a sub-noncircular arc surface, and a shape within a subscanning cross section is also made non-circular arc in the sub-noncircular arc surface, and the noncircular arc shape is a surface changing in accordance with the position of the subscanning cross section in a main scanning direction, and the shape of a sub-noncircular arc surface is set so as to correct the wave front aberration at each scanning position on the surface to be scanned.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an optical scanning device, a scanning image forming optical system, and an image forming apparatus.

[0002]

2. Description of the Related Art In recent years, writing density has been increased for an optical scanning device known in connection with a recording unit of a facsimile or a digital copying machine or a laser printer, and an optical spot to be condensed on a surface to be scanned. There is a strong demand for smaller diameter and stability. In order to obtain a good recorded image with a constant image resolution, it is important that the spot diameter of the light spot does not vary with the scanning position, that is, that the light spot is stable on the scanning line. In order to realize such "stability of the light spot", it is necessary to satisfactorily correct the curvature of field in the optical system, and various proposals have been made to realize the satisfactorily correction of the curvature of field. In order to perform good image writing at an extremely high writing density, such as 600 dpi and 1200 dpi, which are being put into practical use recently, a light spot having a correspondingly small spot diameter is required.
In order to realize a light spot having a small spot diameter with good stability and good stability, it is not enough to perform only geometrical optical correction such as curvature of field and optical magnification, as in the past. It is important to set constant regardless of the image height of the light spot. That is, as the spot diameter becomes smaller,
Since a "large luminous flux diameter" is required for a luminous flux incident on an imaging system for imaging a light spot, paraxial correction by geometrical optics is insufficient.

[0003]

SUMMARY OF THE INVENTION It is an object of the present invention to satisfactorily correct wavefront aberration, realize a stable light spot with a small spot diameter, and enable high-density and good writing.

[0004]

SUMMARY OF THE INVENTION A scanning image forming optical system according to the present invention comprises a scanning image forming optical system for converging a deflected light beam deflected by a light deflecting means having a deflecting and reflecting surface as a light spot on a surface to be scanned. System "having the following characteristics (claim 1). That is, the scanning imaging optical system includes one or more lenses, and at least one of the lens surfaces is a “sub-non-arc surface”.
It is. That is, the scanning image forming optical system can be constituted by “one lens” as the simplest constitution. Of course, it can be constituted by two or more lenses, or can be constituted by a combination of one or more lenses and one or more reflection imaging systems (concave mirrors and the like). Here, "the main scanning direction and the sub-scanning direction" in this specification will be additionally described. Both of these main-sub scanning directions are originally "directions to be defined on the surface to be scanned", but in this specification, the main-sub scanning direction and the main-sub scanning direction are used on the optical path from the light source to the surface to be scanned. The corresponding directions are also referred to as a main scanning direction and a sub-scanning direction, respectively. Therefore, the main scanning direction and the sub-scanning direction may not always be parallel to the main scanning direction and the sub-scanning direction on the surface to be scanned. The “sub-non-arc surface” is a surface in which the shape in the sub-scan section is a non-arc shape, and the non-arc shape changes according to the position of the sub-scan section in the main scanning direction. The “sub-scanning cross section” refers to a virtual plane cross section orthogonal to the main scanning direction near the lens surface. In addition, a virtual plane cross-section near the lens surface, which coincides with a plane swept by the ideal main beam of the deflected light beam, is referred to as a “main scanning cross-section”. The shape of the sub-non-circular surface in the scanning image forming optical system is determined by each scanning position (light spot focusing position) on the surface to be scanned.
Is determined so as to correct the wavefront aberration at. Thereby, the best wavefront aberration can be set for each scanning position on the surface to be scanned. The shape of the sub-non-arc surface may be a non-arc shape even in the main scanning section. By doing so, it is possible to satisfactorily correct the wavefront aberration over the entire pupil plane (the cross section of the deflected light beam incident on an arbitrary position on the sub-non-arc surface).

[0005] In the scanning imaging optical system according to claim 1 or 2, the wavefront aberration correction is performed by setting the wavelength to be used to λ and setting the amount of wavefront aberration on the pupil to 0.1 in RMS (root mean square).
It is desirable that it is not more than 1λ, more preferably not more than 0.07λ (Marechal's diffraction limit). At each scanning position on the surface to be scanned, the wavefront aberration is reduced by RMS on the pupil:
If it is 0.1λ or less, a small-diameter light spot having a good shape can be stably realized. When the spot diameter of the light spot on the surface to be scanned is defined as 1 / e ² intensity in the line spread function of the light intensity distribution in the light spot, the spot diameter of the small diameter light spot is determined by the main-sub scanning. Both directions are within the effective writing range.
The imaging function of the scanning imaging optical system can be set to be equal to or less than μm. The above "line spread function"
Is based on the center coordinates of the light spot formed on the surface to be scanned, and the light intensity distribution of the light spot is represented by f (Y, Z), where Y and Z are the coordinates in the main scanning direction and the sub-scanning direction. The line spread function in the Z direction: LSZ is
LSY (Z) = ∫f (Y, Z) dY (integration is performed for the entire width of the light spot in the Y direction), and a line spread function in the Y direction: LSY is LSY (Y) = ∫f
(Y, Z) dZ (integration is performed for the entire width of the light spot in the Z direction). These line spread functions: LSZ (Z) and LSY (Y) are usually approximately Gaussian-distributed, and the spot diameters in the Y and Z directions are determined by these line spread functions: LZZ (Z) and LSY.
(Y) is the Y, Z of the area where the maximum value is 1 / e ² or more.
It is given in the direction width. What is stated in claim 4 is that the spot diameter in the Y and Z directions defined in this way is 50 μm or less within the effective writing range regardless of the image height of the light spot. The spot diameter defined as above by the line spread function is
The light spot can be scanned at a constant speed by the slit, the light passing through the slit can be received by the photodetector, and the amount of light received can be easily measured by integration. A device for performing such a measurement is also commercially available. Only the correction of the geometric optical field curvature is 5
Although it is not easy to form a good light spot having a spot diameter of 0 μm or less, as in the present invention, by using one or more sub-non-circular surfaces in a scanning imaging optical system,
A good light spot having a spot diameter of 50 μm or less can be reliably formed.

In the scanning image forming optical system according to claim 1, the lateral magnification on the optical axis in the sub-scanning direction: β ₀ , the condition: (1) 0.2 <| β ₀ | <1.5 is preferably satisfied (claim 5). When the value exceeds the upper limit of 1.5 of the condition (1), the lateral magnification of the scanning imaging optical system increases. Therefore, when the spot diameter is to be reduced, the exit pupil diameter in the sub-scanning direction becomes too large. It is difficult to "correct the aberration over the entire pupil." Further, the NA of the coupling lens for taking in the light flux from the light source must be improved. In addition, image plane position fluctuations due to environmental fluctuations and mounting errors of the scanning image forming optical system are likely to increase, and it is difficult to reduce the spot diameter. If the lower limit of 0.2 is exceeded, the magnification is too low, the aperture diameter of the aperture becomes small, the light transmission efficiency decreases, and high-speed writing becomes difficult. Claims 1-5
In the scanning imaging optical system according to any one of (1) and (2) 0, in the sub-scanning direction, the lateral magnification on the optical axis: β ₀ , the lateral magnification at an arbitrary image height: h: β _h .93 <| β _h / β ₀ | <1.07 (claim 6). When condensing a light spot, the beam waist diameter of the light beam varies substantially in proportion to the change in the lateral magnification of the scanning imaging optical system. It is important to keep the lateral magnification constant every time, and specifically, it is preferable to satisfy the condition (2). Any one of claims 1 to 6
In the scanning image forming optical system described in (1), the “non-arc amount” of the non-arc shape in the sub-scan section of the sub-non-arc surface can be changed asymmetrically in the main scanning direction (claim 7).
The “non-arc amount” is a deviation amount from the arc (paraxial radius of curvature). When using a "rotating polygon mirror" as the light deflecting means,
The center of rotation is displaced from the optical axis of the scanning imaging optical system, so that the reflection point on the deflecting / reflecting surface changes according to the deflection, and the starting point of the deflection of the deflecting light beam changes. "Optical sag" occurs. When sag exists, the + image height side and the − image height side of the optical axis of the scanning image forming optical system,
The light path is different. Therefore, the amount of generated wavefront aberration varies asymmetrically in accordance with the image height of the light spot, but the amount of non-arc of the sub-non-arc surface of the scanning imaging optical system according to claim 7 is changed in the main scanning direction. By making them asymmetric, it is possible to correct asymmetric wavefront aberration due to the sag and set the best wavefront aberration for each image height.

In the scanning imaging optical system according to any one of the first to seventh aspects, the paraxial curvature in the sub-scanning section changes asymmetrically in the main scanning direction, and the paraxial curvature changes by 2 in the main scanning direction. At least one lens surface having the above extreme value can be provided (claim 8). The optical sag causes deterioration of field curvature in the sub-scanning direction (hereinafter referred to as “sub-scanning field curvature”). By using at least one surface in which the paraxial curvature in the cross section changes in the main scanning direction and the change in curvature is asymmetric in the main scanning direction and has two or more extreme values, the sub-scanning field curvature is particularly improved. And the lateral magnification in the sub-scanning direction can be kept substantially constant over the effective writing area, and a light spot with a stable spot diameter can be realized. The “extreme value” is the paraxial curvature in the sub-scanning section with respect to the lens height: h, expressed by a function: C (h) with respect to the lens height: h, and its first derivative: dC (h) / dh = 0, and a point at which the sign of dC (h) / dh changes before and after (takes a maximum value or a minimum value). Generally, if the lateral magnification is to be kept constant, “higher-order curved field curvature” tends to occur. In particular, in an imaging optical system having a small number of lenses, sagittal field curvature expressed in the form of “aH ² + bH ⁴ ” is likely to occur, where H is the image height and a and b are the coefficients. As described above, by using a surface having a plurality of extreme values for the change in the main scanning direction of the paraxial radius of curvature in the sub-scanning cross section, the lens surface is used for the high-order curved field curvature. The power is changed in a higher order to perform the correction, and the sub-scanning field curvature can be effectively corrected.

In the scanning image forming optical system according to the present invention, at least one of the extreme values in the change of the paraxial curvature in the sub-scanning cross section is such that the position in the main scanning direction: he is: Or, for the effective lens height: hmax from the lens optical axis on the image height side, the condition: (3) | (he) / (hmax) |> 0.5 can be satisfied (claim 9). . The above “aH ² +
bH ⁴ , the image height at the “maximum bulging position” of the sagittal curvature of field: Hn is H when the effective writing height is Hm.
n = (1 / √2) Hm = 0.71Hm (Fumio Kondo, “Lens Design Techniques (Optical Industrial Technology Association)”, pp. 146-148). In order to correct the bulging in the vicinity of 0.71 times the effective writing height Hm, it is effective to have an extreme value of the curvature in the sub-scan section near the lens surface position corresponding to the position. . In consideration of correcting even a higher-order field curvature exceeding the fourth order,
It is preferable that he and hmax satisfy the condition (3). Here, hmax is the effective lens height on the + image height side when he ≧ 0, and the effective lens height on the -image height side when he <0.
Here, the + side of the image height is the side where the light beam from the light source enters the deflecting / reflecting surface. 10. The scanning image forming optical system according to claim 8, wherein the paraxial curvature in the sub-scanning section changes asymmetrically in the main scanning direction, and the change in the paraxial curvature has an extreme value of 2 or more. , Can be referred to as a “sub non-arc surface” (claim 10). Of course, the lens surface may be a surface other than the sub-non-arc surface. The scanning imaging optical system according to any one of claims 1 to 10, wherein the effective writing width is W and the width of the sub-scanning field curvature within the effective writing width is Fs. (4) Fs /W<0.005 can be satisfied (claim 11). It is preferable that the condition (4) be satisfied in order to obtain a stable small-diameter light spot by suppressing the fluctuation of the sub-scanning field curvature. In the scanning imaging optical system according to any one of claims 1 to 11 described above, the shape of the sub-non-circular surface in the main scanning section may be determined so as to correct the constant velocity characteristic of the light spot. (Claim 12). Of course, the shape of the other surface in the main scanning section is also optimized according to the above purpose.

The scanning image forming optical system according to any one of the first to twelfth aspects has a function of making the vicinity of the deflecting reflection surface and the position of the surface to be scanned geometrically conjugate with respect to the sub-scanning direction. Anamorphic optical system "(claim 13). As described above, by making the scanning image forming optical system anamorphic, it is possible to correct surface tilt in the light deflecting unit. The scanning image forming optical system according to the present invention can be constituted by one or more lenses as described above, and therefore can be constituted by two lenses. The scanning image forming optical system according to claim 13 can also be constituted by two lenses (claim 14). When the scanning image forming optical system is composed of two lenses, the degree of freedom with respect to the “number and arrangement” of the sub-non-circular surface is high, and the degree of freedom in the shape of the other surface is high, so that desired optical characteristics can be easily realized. . In the scanning image forming optical system according to the fourteenth aspect, in the two lenses forming the scanning image forming optical system, the sub-non-circular surface is defined as “the lens surface on the scanned surface side and the lens surface on the scanned surface side”. (Claim 15), or may be adopted for the “lens surface of the lens on the scanning surface side on the light deflection unit side” (Claim 16). The scanning image forming optical system according to claim 15 can have a function of "condensing a deflected light beam, which is a weakly focused light beam in the main scanning direction, on a surface to be scanned" (claim 17). Can have a function of condensing a deflected light beam, which is a parallel light beam in the main scanning direction, on a surface to be scanned (claim 18).

According to a nineteenth aspect of the present invention, a light beam from a light source is deflected by a light deflector having a deflecting / reflecting surface, and the deflected light beam is condensed as a light spot on a surface to be scanned by a scanning image forming optical system. An optical scanning device that performs optical scanning by
The scanning imaging optical system is characterized in that the scanning imaging optical system according to any one of claims 1 to 12 is used. The optical scanning device according to the twelfth aspect of the present invention is to provide an optical scanning apparatus comprising: An optical scanning device that performs optical scanning by condensing light as a light spot on a surface to be scanned by an image optical system,
A scanning image forming optical system according to any one of claims 13 to 18 is used as the scanning image forming optical system.
In the optical scanning device according to the twentieth aspect, the deflecting light beam deflected by the light deflecting means is referred to as a “convergent light beam weak in the main scanning direction”, and the scanning image forming optical system according to the seventeenth aspect is provided. Can be used (claim 21).
Alternatively, the deflecting light beam deflected by the light deflecting means is referred to as a "parallel light beam in the main scanning direction", and the scanning image forming optical system may be the scanning image forming optical system according to claim 18 (claim 22). . As the “light deflecting unit”, a rotating polygon mirror, a rotating dihedral mirror or a rotating single mirror can be suitably used. Since the scanning image forming optical system according to any one of the first to twelfth aspects includes "the one having no surface tilt correcting function", the optical scanning apparatus according to the nineteenth aspect provides the scanning image forming optical system with the surface tilt correcting function. If there is no function, a rotating polygon mirror or rotating two-sided mirror with good surface accuracy may be used, or a "rotating single-sided mirror" without surface tilt may be used. In this case, a light beam from a light source (generally a semiconductor laser is used) is taken in by a coupling lens, and the parallel light beam or a weakly convergent or weakly divergent light beam is incident on the deflecting and reflecting surface of the light deflecting means. It should be done. Of course, the coupled light beam is "beam shaped" by passing through the aperture of the aperture. In the optical scanning device according to the twentieth aspect, the scanning image forming optical system has a “surface tilt correction function”,
The luminous flux from the light source side is near the deflecting reflection surface of the light deflecting means,
An image is formed as a long line image in the main scanning direction. To achieve this, the light beam from the light source is captured by a coupling lens, and the captured light beam (coupled light beam) is converted into a cylindrical lens or a “concave mirror having a concave cylinder surface”.
In this case, a linear image may be formed in the vicinity of the deflecting reflection surface. The optical scanning device according to claim 21 or 22, wherein a light beam from a semiconductor laser as a light source is taken in by a coupling lens and beam-shaped by an aperture, and then near a deflecting reflection surface by a line image forming optical system. In the case where the image is formed as a long line image in the main scanning direction, the aperture shape of the beam shaping aperture should be a shape that blocks “the four corners in the main-sub scanning direction” of the coupled light flux. (Claim 23).

An optical scanning device according to a twenty-fourth aspect includes: a light source;
It has a first lens system, light deflecting means, and a second lens system. A "light source" emits a light beam. "First lens system"
Receives a light beam from a light source and converts the light beam form.
The “light deflecting unit” is a unit having a deflecting / reflecting surface and deflecting a light beam from the first lens system. "Second lens system"
Focuses the deflected light beam deflected by the light deflecting means on the surface to be scanned as a light spot whose image height changes according to the deflection angle. At least one of the lens surfaces included in the second lens system has a non-circular shape in a plurality of sub-scan sections, and the non-arc shapes in at least two sub-scan sections are different from each other. The effective writing width: W, and the width of the sub-scanning field curvature within the effective writing width: Fs satisfies the condition: (4) Fs / W <0.005.

In the optical scanning apparatus according to the twenty-fourth aspect, the second lens system has at least two independent lenses, and the four lens surfaces of the two lenses are non-circular in the main scanning section. It can have a shape (claim 25). Further, in the optical scanning device according to the twenty-fourth aspect, the second lens system has at least two independent lenses, and at least three of the four lens surfaces of the two lenses are main scanning. It may have a non-circular shape in the cross section (claim 26).
25. The optical scanning device according to claim 24, wherein the second lens system has at least two independent lenses, and at least one of the four lens surfaces of the two lenses is in the sub-scanning cross section. Has a non-arc shape, and the non-arc shape is a curve in which the center line of curvature connecting the paraxial radius of curvature in the main scanning direction is different from the shape of the lens surface in the main scanning cross section. It can be used (claim 27).
In the optical scanning device according to claim 24, the second lens system may include three or more lenses.
8). As in the optical scanning device according to claims 25 and 26, the second lens system includes a lens surface having a non-circular shape in the main scanning section. 29. Increasing the number of lenses constituting the second lens system as in the optical scanning device according to claim 28, by including a lens surface having a "curvature center line" This is effective in favorably correcting the curvature.

In the optical scanning device according to the twenty-fourth aspect, the second lens system can of course be constituted by "one lens only" (claim 29), as described in the embodiment described later. The second lens system includes two or more lenses ”(claim 30). By configuring the second lens system with one or two lenses, cost reduction and compactness of the optical scanning device can be promoted. In the optical scanning device according to the twenty-fourth aspect, the writing density can be set in a range of approximately 600 to 1200 dpi (the number of dots per inch).
1) It can also be set in the range of approximately 1200 to 2400 dpi (claim 32), and may be set to approximately 2400 dpi or more (claim 33). Of course, this invention
Write density lower than 600 dpi, for example, approximately 300 to
It can be effectively applied to a case where writing is performed at a writing density of 600 dpi. An optical scanning device for performing multi-beam scanning using not only the case of “single beam scanning” in which the light source emits a single light beam but also the case of “light emitting two or more light beams” as the light source. The optical scanning device described above can also be configured (claim 34). 25. The optical scanning device according to claim 24, wherein the second lens system comprises: a sub-non-circular surface whose surface shape is determined so that the beam waist position of the deflected light beam coincides with the geometrical optical imaging position of the deflected light beam. Lens having at least one lens ”. Further, the second lens system may be an "anamorphic optical system having a function of making the vicinity of the deflecting reflection surface and the position of the surface to be scanned in the sub-scanning direction have a geometrical conjugate relationship in the sub-scanning direction". (Claim 36). 25. The optical scanning device according to claim 24, wherein the second lens system is configured such that, in the sub-scanning direction, a lateral magnification on the optical axis: β ₀ and a lateral magnification at an arbitrary image height: h: β _h are: 2) It is preferable to satisfy the following condition: 0.93 <| β _h / β ₀ | <1.07 (claim 37).
The optical scanning device according to claim 24, wherein at least one of the lens surfaces included in the second lens system is a sub-non-arc surface,
The shape of this sub-non-circular surface can be determined such that "the beam waist position matches the position of the surface to be scanned" with respect to the entire image height of the light spot within the effective writing width (claim 38).

An optical scanning device according to claim 39, comprising: a light source;
It has a first lens system, light deflecting means, and a second lens system. A "light source" emits a light beam. "First lens system"
Receives a light beam from a light source and converts the light beam form.
The “light deflecting unit” is a unit having a deflecting / reflecting surface and deflecting a light beam from the first lens system. "Second lens system"
Focuses a deflected light beam deflected by a light deflecting means on a surface to be scanned as a light spot whose image height changes according to a deflection angle, and at least one of the lens surfaces is a sub-non-circular surface. The shape of the sub-non-arc surface can be determined so as to correct the wavefront aberration at each scanning position on the surface to be scanned. The optical scanning device according to claim 39, wherein “a light beam cross section on a pupil plane is divided into n parts, and the divided parts are divided into 1, 2, 3,... I,. The wavefront aberration amount at these divided portions: i (i = 1, 2, 3,..., N) is Xi, and the average value of the wavefront aberration amount: Xi is ΣXi / n.
When the X, √ defined by ^{{Σ (Xi-X) 2} / n}, RMS wavefront aberration on the pupil plane, as the used wavelength λ, √ {Σ (Xi- X) 2 / n} ≤ 0.1λ "(waveform aberration can be corrected).

The sum relating to the sum symbol: Σ is 1 to n per i. The number of divisions: n may be "a size that can uniquely determine the wavefront aberration amount: Xi in each divided part", and can be arbitrarily selected within a range satisfying this condition. , About 100 or more is desirable.

In the optical scanning device according to the thirty-ninth aspect, if the “non-arc amount”, which is the shift amount of the non-arc shape in the sub-scan section in the sub-scan section from the arc, is different from the total image height. (Claim 42), so that the amount of non-arc in the vicinity of the optical axis and the peripheral portion in the main scanning direction is different from each other (Claim 43). In addition, the first lens system can be configured to “correct wavefront aberration”. The configurations of claims 42 to 44 are effective in satisfying the conditions for the RMS. The writing density of the optical scanning device according to claim 39 may be set in a range of approximately 600 to 1200 dpi (claim 45), or approximately 1200 to 2400d.
pi (claim 46) and approximately 240
It may be set to 0 dpi or more (claim 47). Of course,
Write density lower than 600 dpi, e.g.
The writing density can be set in the range of 600 dpi. Further, the number of light beams emitted from the light source can be not only one light beam (single beam scanning) but also two light beams or more (multi-beam scanning). The second lens system may be “an anamorphic optical system having a function of making the vicinity of the deflecting reflection surface and the position of the scanned surface in the sub-scanning direction have a geometrical conjugate relationship in the sub-scanning direction”. (Claim 49) Regarding the sub-scanning direction, the lateral magnification on the optical axis: β ₀ and the lateral magnification at an arbitrary image height: h: β _h satisfies the following condition: (2) 0.93 <| β _h / β ₀ | <1.07 is preferably satisfied (claim 50).
When the spot diameter of the light spot on the surface to be scanned is defined as 1 / e ² intensity in the line spread function of the light intensity distribution at the light spot, the spot diameter is
In the sub-scanning direction, it can be configured to be 50 μm or less within the effective writing range. The lateral magnification of the second lens on the optical axis in the sub-scanning direction: β ₀ , preferably satisfies the condition: (1) 0.2 <| β ₀ | <1.5 (claim 52). Claim 39
In the optical scanning device described above, the “non-arc amount”, which is the amount of deviation of the sub-non-arc surface from the arc in the sub-arc shape in the sub-scan section, can be changed asymmetrically in the main scanning direction. Item 53) With this configuration, it is possible to correct the influence of sag when a rotating polygon mirror is used as the light deflecting unit. Of course, when a device that does not generate sag, such as a rotating single-sided mirror, is used as the light deflecting unit, the amount of non-arc may be set to “change symmetrically in the main scanning direction”. ). In the optical scanning device according to the thirty-ninth aspect, the shape of at least one sub-non-circular surface in the second lens system can be determined so as to “correct wavefront aberration with respect to the entire image height”. .

The image forming apparatus of the present invention is an "image forming apparatus for forming a latent image on a latent image carrier by optical scanning and developing the formed latent image to obtain a desired image". As an optical scanning device for optically scanning a body, the optical scanning device according to any one of claims 19 to 55 is used (claim 56). In this case, a photoconductive photoconductor is used as the latent image carrier, the formed latent image is visualized as a toner image, and the toner image is printed on a sheet-shaped recording medium (transfer paper or a plastic sheet for an overhead projector). The image forming apparatus can be configured so as to obtain a desired image by fixing. In the image forming apparatus according to claim 56, for example, a silver halide photographic film can be used as the image carrier. In this case, the latent image formed by the optical scanning by the optical scanning device can be visualized by a normal silver halide photographic process. Such an image forming apparatus can be implemented as, for example, an “optical plate making apparatus”.
The image forming apparatus according to claim 57 can be specifically implemented as a laser printer, a laser plotter, a digital copying machine, a facsimile machine, or the like.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1A, a light source 10 is a semiconductor laser and emits a divergent light beam. Light source 1
The light beam radiated from 0 is taken in by the coupling lens 12 to become a “light beam having a weak converging property”, is beam-shaped by passing through the aperture of the aperture 14, and is converged while being a “linear image forming optical system”. The light enters the lens 16 and is condensed in the sub-scanning direction (the direction perpendicular to the drawing) by the cylindrical lens 16, the optical path is bent by the mirror 18, and the deflecting / reflecting surface 20 </ b> A of the rotary polygon mirror 20 as “light deflecting means” Incident on. Deflective reflection surface 20
The light beam reflected by A becomes a deflected light beam that is deflected at a constant angular velocity as the rotary polygon mirror 20 rotates at a constant speed, and transmits through the lenses 22 and 24. The lenses 22 and 24 form a “scanning optical system” and converge the deflected light beam as a light spot on the surface 26 to be scanned. The light spot optically scans the effective writing width: W on the scanned surface 26 at a constant speed. The scanned surface 26 is substantially a “photoconductive photoconductor or a photosensitive surface of a silver halide film”.
It is. FIG. 1B shows the deflection reflecting surface 2 of the rotary polygon mirror 20.
Of the deflected light beam in the optical path from 0A to the surface to be scanned 26,
The state of image formation in the sub-scanning direction (vertical direction in the figure) is shown. In this embodiment, as shown in FIG. 1B, of the lenses 22 and 24 constituting the scanning image forming optical system, the “sub-non-circular surface” is adopted as the lens surface on the scanning surface side of the lens 24. Thus, the wavefront aberration is corrected.

In FIG. 2A, which is drawn similarly to FIG. 1A, a divergent light beam emitted from a light source 10 which is a semiconductor laser is converted into a "parallel light beam" by a coupling lens 11. The beam is shaped by passing through the opening of the aperture 13, enters the cylindrical lens 15, and is condensed by the cylindrical lens 15 in the sub-scanning direction.
The optical path is bent by the mirror 18 and enters the deflecting / reflecting surface 19 </ b> A of the rotary polygon mirror 19. The luminous flux reflected by the deflecting / reflecting surface 19A becomes a deflecting luminous flux deflected at a constant angular velocity with the rotation of the rotary polygon mirror 19 at a constant speed, and passes through the lenses 21 and 23 constituting the “scanning optical system”. . Lens 2
Numerals 1 and 23 converge the deflected light beam as a light spot on the surface to be scanned 26, and the converged light spot optically scans the surface to be scanned 26 at a constant speed. FIG. 2 (b) shown following FIG. 1 (b)
As shown in FIG. 7, in this embodiment, of the lenses 21 and 23 constituting the scanning image forming optical system, the “sub-non-circular surface” is adopted as the lens surface of the lens 23 on the rotating polygon mirror side, and the wavefront aberration is adopted. Has been corrected. Reference numeral 25 denotes soundproof glass (provided in a window of a casing surrounding the rotary polygon mirror to prevent the rotation noise of the rotary polygon mirror 19). here,
The lens 2 according to the embodiment shown in FIG.
The surface 4 on the side of the surface to be scanned will be described as an example. 3 shows a state in which the lens 24 is viewed from the sub-scanning direction, and the vertical direction is the main scanning direction. As shown, three sub-scanning sections SC1, SC2, and SC3 are considered, and the cross-sectional shape of the sub-non-circular surface in these sub-scanning sections is shown in the right diagram of FIG. The cross-sectional shapes NA1, NA2, and NA3 are non-arc shapes in the sub-scanning cross-sections SC1, SC2, and SC3.
The “dashed circles” drawn in contact with these cross-sectional shapes NA1, NA2, and NA3 indicate circles with paraxial curvature radii of the respective non-circular shapes. On the sub-non-arc surface, “the non-arc shape in the sub-scan section changes according to the sub-scan section position in the main scanning direction”
are doing. Also, the center of the circle defined by the paraxial curvature radius, that is, the curvature center line CL in which the “paraxial curvature center” is connected in the main scanning direction
Is a curve different from the shape of the lens surface (the right lens surface in the left diagram of FIG. 3) in the main scanning section. The shapes of these sub-non-arc-shaped surfaces are set so as to favorably correct the wavefront aberration on the surface 26 to be scanned.

That is, the optical scanning device shown in FIG. 1 (FIG. 2) according to the embodiment converts the light beam from the light source 10 into a deflecting / reflecting surface 20A.
The light is deflected by the light deflecting means 20 (19) having (19A), and the deflected light beam is scanned by the scanning / imaging optical systems 22, 24 (21, 21).
3) is an optical scanning device that performs optical scanning by condensing light as a light spot on the surface 26 to be scanned.
2, 24 (21, 23) include one or more lenses, at least one of the lens surfaces is a sub-non-arc surface, and the shape thereof favorably corrects the wavefront aberration at each scanning position on the scanned surface 26. (Claims 1, 1
9). Further, the optical scanning device shown in FIG.
The light beam from 0 is formed as a long line image in the main scanning direction,
The light is deflected by a light deflecting means 20 (19) having a deflecting / reflecting surface 20A (19A) in the vicinity of the image forming position of the line image, and the deflected light beam is scanned by a scanning image forming optical system 22, 24 (21, 23). An optical scanning device that performs optical scanning by converging light as a light spot thereon (Claim 20), wherein the scanning imaging optical systems 22, 24 (21, 23) includes a deflecting / reflecting surface 20A (19).
A) The vicinity and the position of the surface to be scanned 26 are defined in the sub-scanning direction.
This is an anamorphic optical system having a function of establishing a geometric conjugate relationship (claim 13), and is constituted by two lenses (claim 14).

Further, in the embodiment shown in FIG. 1, the deflecting light beam deflected by the light deflecting means 20 is a converging light beam weak in the main scanning direction, and the scanning image forming optical systems 22 and 24 are " (A function of condensing the deflected light beam, which is a weakly focused light beam, on the surface to be scanned) (Claim 17), and the lens surface on the surface to be scanned of the lens 24 on the surface to be scanned is a sub-non-circular surface ( Claim 15). Therefore, the embodiment shown in FIG. 1 is also an embodiment of the optical scanning device according to claim 19. FIG.
In the embodiment shown in (1), the deflecting light beam deflected by the light deflecting means 19 is a parallel light beam in the main scanning direction, and the scanning image forming optical systems 21 and 23 output “a polarized light beam that is a parallel light beam in the main scanning direction”. Having a function of condensing light on the surface to be scanned ”.
8) The lens surface on the light deflecting means side of the lens 23 on the scanning surface side is a sub-non-circular surface (claim 16). Therefore, FIG.
The embodiment shown in FIG. 21 is also an embodiment of the optical scanning device according to claim 22.

[0022]

EXAMPLES Three specific examples will be described below. The shape of the lens surface is specified by the following equation. “Coaxial aspherical surface” This is represented by a depth difference from the optical axis (H = 0) with respect to the lens height: H.

That is, paraxial radius of curvature: R, circle constant: K,
Higher order coefficients: A ₄ , A ₆ ,. . . By using the following (A)
It is expressed by an equation. ^{X = (H 2 / R)} / [1 + √ {1- (1 + K) (H / R) 2}] + A 4 H 4 + A 6 H 6 + A 8 H 8 +. . . . (A) “Non-arc shape in main scanning section” Paraxial radius of curvature in the main scanning section: Rm, distance from the optical axis in the main scanning direction: Y, conical constant: Km, higher-order coefficients are A ₁ ,
A ₂ , A ₃ , A ₄ , A ₅ , A ₆ ,. . . Is expressed by the following polynomial (B), where X is the depth in the optical axis direction. ^{X = (Y 2 / Rm)} / [1 + √ {1- (1 + Km) (Y / Rm) 2}] + A 1 Y + A 2 Y 2 + A 3 Y 3 + A 4 Y 4 + A ₅ Y ⁵ +. . . . (B) In equation (B), odd-order A ₁ , A ₃ , A ₅ ,. . . Is non-zero, the shape becomes asymmetric in the main scanning direction. "The curvature in the sub-scanning section" When the curvature changes in the main scanning direction (coordinates with the optical axis position as the origin: indicated by Y) in the sub-scanning section, the following equations (C) and (D) are used. Represent. Equation (C) is for the case where the curvature is represented by Cs (Y), and (D) is for the case where the curvature radius is represented by Rs (Y). Rs (0) represents the radius of curvature on the optical axis in the sub-scan section.

[0024] Cs (Y) = {1 / Rs (0)} + B 1 Y + B 2 Y 2 + B 3 Y 3 + B 4 Y 4 + B 5 Y 5 +. . . . (C) Rs (Y) = Rs (0) + B 1 Y + B 2 Y 2 + B 3 Y 3 + B 4 Y 4 + B 5 Y 5 +. . . . (D) In the equations (c) and (D), the odd-order coefficient of Y: B ₁ ,
B ₃ , B ₅ ,. . Is a non-zero number,
The curvature (or radius of curvature) in the sub-scan section becomes asymmetric in the main scanning direction. "Sub-non-arc surface" is expressed by equation (E) using the position in the main scanning direction of the sub-scanning section: Y and the coordinate: Z in the sub-scanning direction. ^{X = (Y 2 / Rm)} / [1 + √ {1- (1 + Km) (Y / Rm) 2}] + A 1 Y + A 2 Y 2 + A 3 Y 3 + A 4 Y 4 + A ₅ Y ⁵ +. . . . ^{+ (Z 2 × Cs) /} [1 + √ {1- (1 + Ks) (Z × Cs) 2} + (F 0 + F 1 Y + F 2 Y 2 + F 3 Y 3 + F 4 Y 4 _{+ ....) Z + (G 0} + G 1 Y + G 2 Y 2 + G 3 Y 3 + G 4 Y 4 + ....) Z 2 + (H 0 + H 1 Y + H 2 Y ^{_{2 + H 3 Y 3 + H}} 4 Y 4 + ....) Z 3 + (I 0 + I 1 Y + I 2 Y 2 + I 3 Y 3 + I 4 Y 4 + ....) Z 4 _{+ (J 0 + J 1 Y} + J 2 Y 2 + J 3 Y 3 + J 4 Y 4 + ....) Z 5 + (K 0 + K 1 Y + K 2 Y 2 + K 3 Y 3 + ^{_{K 4 Y 4 + ....) Z}} 6 + (L 0 + L 1 Y + L 2 Y 2 + L 3 Y 3 + L 4 Y 4 + ....) Z 7 + (M 0 + M 1 ^{_{Y + M 2 Y 2 + M}} 3 Y 3 + M 4 Y 4 + ....) Z 8 + (N 0 + N 1 Y + N 2 Y 2 + N 3 Y 3 + O 4 Y 4 + .. _{^{..) Z 9 + (O 0}} + O 1 Y + O 2 Y 2 + O 3 Y 3 + O 4 Y 4 + ....) Z 10 +. . . . (E) Here, Cs is Cs (Y) defined by the above equation (C). Ks is defined by the following equation (F). Ks = Ks (0) + C 1 Y + C 2 Y 2 + C 3 Y 3 + C 4 Y 4 + C 5 Y 5 +. . . (F) The odd-numbered power coefficient of B in the formula (C) of Cs (Y), B ₁ ,
B ₃ , B ₅ ,. . . Takes a non-zero number,
The change in the radius of curvature in the sub-scan section becomes asymmetric in the main scanning direction. Similarly, F ₁ , F ₃ , F ₅ ,. . . , G ₁ , G ₃ ,
G ₅ ,. . . Substituting a numerical value other than zero into a value such as a non-arc in the sub-scan section becomes asymmetric in the main-scan direction. That is,
The sub-non-arc surface is, as described above, “a surface in the sub-scan section is a non-arc shape, and the non-arc shape in the sub-scan section changes according to the position of the sub-scan section in the main scanning direction”. In the expression (E), the first and second rows on the right side are “functions in the main scanning direction: Y only” and “the shape in the main scanning section”.
Represents In addition, in the third row and below on the right side, when the Y coordinate of the sub-scan section is determined, the coefficient of each next term of Z is uniquely determined,
The “non-arc shape in the sub-scan section” at the coordinate: Y is determined. The coaxial aspheric surface, the non-arc shape in the main scanning section, the curvature in the sub-scanning section, and the analytical expression of the sub-non-arc surface are not limited to those described above, and various things are possible. The surface shape in the present invention is not limited to the above expression.

Example 1 Example 1 given first is a specific example of the embodiment shown in FIG. The light beam from the semiconductor laser that is the light source 10 is coupled by the coupling lens 12 to become a “light beam having a weak converging property”. Assuming that this weakly converging light beam is not affected by the refraction of the optical element on the optical path, a position where light is naturally condensed due to the converging property of the light beam is referred to as a “natural light converging point”. In the first embodiment, the position of the natural focal point is such that when the deflecting light beam approaches the image height of the light spot on the scanning surface: 0, the position of the natural focusing point is 70 from the deflecting reflection surface toward the scanning surface.
It is at the position of 0 mm. Accordingly, the deflected light beam is weakly convergent in the main scanning direction and divergent in the sub-scanning direction, and the scanning imaging optical systems 22 and 24 scan the vicinity of the deflecting reflection surface 20A and the position of the scanning surface 26 in the sub-scanning direction. An anamorphic optical system having a geometrical conjugate relationship with respect to the direction, and has a function of condensing a deflected light beam, which is a weak convergent light beam in the main scanning direction, on the surface to be scanned. The rotating polygon mirror 20 as the light deflecting means has a deflection reflecting surface number: 6 and an inscribed circle radius: 18 mm
The incident angle shown in FIG. 1 is θ = 60 degrees, and the interval between the rotation axis 20X and the optical axis AX of the scanning image forming optical system is h = 7.8.
0 mm. Here, as for the optical axis AX shown in FIG. 1, in the first embodiment, a “tilt angle” is given to the lens surfaces of the two lenses 22 and 24 constituting the scanning image forming optical system. I have. The optical axis AX is a criterion that can be considered when the tilt angle is set to 0, and the tilt given to this criterion determines the actual surface directions of the lenses 22 and 24. The coaxial aspheric surface, the non-arc shape in the main scanning section, the sub-non-arc surface, and the like are shapes specified when the tilt angle is 0. The angle of view of the scanning image forming optical system is −40.14 degrees to +40 degrees. The lens 22 has a “coaxial aspherical surface” on both sides. The lens 24 has a “non-arc surface” on the surface to be scanned, a “non-arc shape” in the main scanning section and a “arc shape” in the sub-scanning section on the rotating polygon mirror side. The data after the deflecting reflection surface (the radius of curvature is the paraxial radius of curvature in the case of a non-circular arc shape) is as follows.

Surface number Rm Rs (0) x α n Deflection reflective surface 0 ∞ ∞ 26.38 Lens 22 1 -100.91 -100.91 18.00 0.10 1.52441 2 -76.40 -76.40 13.06 -0.17 Lens 24 3 4657.6 100.03 15.00 -0.46 1.52441 4 -159.24 -30.04 143.0 -0.46 "x" is the surface interval on the optical axis (when the tilt angle is set to 0), "α" is the tilt angle (unit: degree, positive is counterclockwise), and "n" is It shows the refractive index of the lens material (with respect to the working wavelength: 780 nm in all of Examples 1 to 3). Surface number 1,
Numeral 2 is a coaxial aspherical surface, which is specified by giving each constant of the formula (A). The non-circular shape of the surface number 3 in the main scanning section is specified by giving each constant of the above equation (B). Although the shape in the sub-scanning cross section is a circular arc, the radius of curvature changes in the main scanning direction, and is specified by giving each constant of the above formula (C) or (D). Since surface number 4 is a sub-non-arc surface,
By giving each constant of the equation (B), the shape in the main scanning section is determined, and the change in the curvature in the sub-scanning section in the main scanning direction is determined by giving each constant of the equation (C). Is specified by giving each constant of the equations (E) and (F). Table 1 shows coefficients of the main scanning direction and the sub-scanning direction of each surface.

[0027]

[Table 1]

Table 2 shows the coefficients in the sub-scanning direction of the surface number 4 (the sub-non-circular surface on the scanning surface side of the lens 24).

[0029]

[Table 2]

FIG. 4 shows the field curvature (solid line in the left-hand direction in the sub-scanning direction, broken line in the main-scanning direction) and constant velocity characteristics (solid line in the right-hand side, linearity, broken line is the fθ characteristic) relating to the first embodiment. Both the curvature of field and the constant speed characteristic are corrected very well. FIG. 5 shows “depth curve of spot diameter (fluctuation of spot diameter with respect to defocus of light spot)” at the image height of light spot: 0, ± 50 mm, ± 100 mm in Example 1. (a) relates to the main scanning direction and (b) relates to the sub-scanning direction. The first embodiment intends that the spot diameter defined by the 1 / e ² intensity of the line spread function is about 50 μm, and 50 μm or less on the image plane. As shown in the figure, it has a good depth in both the main and sub-scanning directions, and has high tolerance for positional accuracy of the surface to be scanned.

Example 2 Example 2 given below is a specific example of the embodiment shown in FIG. The light beam from the semiconductor laser, which is the light source 10, is coupled by the coupling lens 11 to become a “parallel light beam”. Therefore, the position of the natural light converging point is at a position ∞ from the deflecting reflection surface toward the surface to be scanned. Accordingly, the deflected light beam is a parallel light beam in the main scanning direction and is divergent in the sub-scanning direction. Is an anamorphic optical system having a function of establishing a geometrical conjugate relationship, and has a function of converging a deflected light beam, which is a parallel light beam in the main scanning direction, onto a surface to be scanned. The rotating polygon mirror 19 as the light deflecting means has a number of deflecting / reflecting surfaces: 5 and a radius of an inscribed circle: 13 mm. The incident angle: θ = 60 degrees shown in FIG. Optical axis A
Interval from X: h = 7.53 mm. In the second embodiment, the two lenses 21 and 2 constituting the scanning image forming optical system
3, the shift amount (parallel movement in the main scanning direction, with the upper side being positive in FIG. 1) is given to the lens surface of the lens 23 on the side of the rotating polygon mirror. The optical axis AX is a criterion that can be considered when the shift amount is set to 0, and the shift amount given to this criterion determines the actual position of the lens surface. In this case, the coaxial aspheric surface, the non-circular shape in the main scanning section, the sub-non-circular surface, and the like are shapes specified in a state where the shift amount is 0. The angle of view of the scanning image forming optical system is from -39.97 degrees to +39.97 degrees. The lens 21 is “coaxial aspheric” on both sides. The lens 23 has a “sub-non-circular surface” on the rotating polygon mirror side and a “arc shape” on the scanned surface side in both the main scanning section and the sub-scanning section (the radius of curvature in the sub-scanning section changes in the main scanning direction. ) ". The data after the deflecting reflection surface (the radius of curvature is the paraxial radius of curvature in the case of a non-circular arc shape) is as follows.

Surface number Rm Rs (0) xy αn Deflection reflective surface 0 ∞ ∞ 25.44 Soundproof glass 1 ∞ ∞ 2.01 8 1.51433 2 ∞ ∞ 25.42 8 Lens 21 3 -312.60 -312.60 31.40 1.52716 4 -82.95 -82.95 78.00 Lens 23 5 -500.0 -42.67 3.50 -0.41 1.52716 6 -1000.0 -23.32 141.50 "x" is the surface spacing on the optical axis (when the shift is 0)
“Y” is the shift amount, and “α” represents the tilt angle (unit: degrees) of the soundproof glass. The surface numbers 3 and 4 are both coaxial aspherical surfaces, and are specified by giving the respective constants of the formula (A). The radius of curvature of the circular arc shape in the sub-scanning section of surface number 6 changes in the main scanning direction, and is specified by giving each constant of the above formula (C) or (D). Since the surface number 5 is a sub-non-arc surface, the constant in the main scanning section is determined by giving each constant by the equation (B), and the change in the curvature in the main scanning direction in the sub-scanning section is expressed by (C).
The constants in the sub-scanning section and the change in the main scanning direction in the sub-scanning section are specified by giving the constants in the formulas, and the constants in the formulas (E) and (F) are specified. Table 3 shows coefficients in the main scanning direction and the sub-scanning direction of each surface.

[0033]

[Table 3]

Table 4 shows coefficients in the sub-scanning direction of the surface number 5 (the sub-non-circular surface on the rotating polygon mirror side of the lens 23).

[0035]

[Table 4]

FIG. 6 shows the curvature of field and the constant velocity characteristic according to the second embodiment in a manner similar to FIG. Both the curvature of field and the constant speed characteristic are corrected very well. FIG. 7 shows the image height of the light spot in Example 1: 0, ± 100 mm, ±
3 shows a “spot diameter depth curve” at 150 mm.
(a) relates to the main scanning direction and (b) relates to the sub-scanning direction. The spot diameter intended in the second embodiment is a spot diameter of 1 / e ² intensity of the line spread function, which is about 30 μm. As shown in the figure, it has a good depth in both the main and sub scanning directions, and has high tolerance for positional accuracy of the surface to be scanned.

FIG. 8 shows the “wavefront aberration” in the second embodiment.
Is shown. (a) shows the wavefront aberration at an image height of +150 mm, (b) shows the wavefront aberration at an image height of +100 mm,
(c) shows the wave height at the image height of 0 mm, and (d) and (e) show the wavefront aberration at the image height of -100 mm and -150 mm, respectively. At this time, an aperture 13 for beam shaping having a “rectangular opening” is used. As shown in FIG. 8, in the second embodiment,
The wavefront aberration is almost completely corrected when the image height of the light spot is 0, but the four corners are slightly undercorrected when the image height is +150 mm. The deterioration of the wavefront aberration at the four corners on the pupil as shown in FIG. 7A affects the shape-spot diameter of the light spot. In the second embodiment, as described above, a “rectangular shape (a rectangular shape having a long side in the main scanning direction and a short side in the sub-scanning direction)” is used as the opening shape of the aperture 13 for beam shaping. In order to remove the influence of the deterioration of the wavefront aberration at the four corners on the pupil on the light spot as shown in FIG. 7A, the aperture shape of the aperture 13 is set as the “main-sub” of the coupled light flux. It is effective to use a shape that cuts off "the four corners in the scanning direction", for example, a shape in which the four corners of the rectangle are rounded or an ellipse. Example 2
5 shows the wavefront aberration on the pupil when the image height of the light spot is 0, ± 100 mm, and ± 150 mm when “a shape obtained by rounding the four corners of a rectangle” is used as the aperture shape of the aperture 13. That is, FIG. 9A shows that the image height is 150 m.
m, wavefront aberration at image height: 100 mm, (c) wavefront aberration at image height: 0, (d) wavefront aberration at image height: -100 mm, (e) image height:-
The wavefront aberration at 150 mm is shown. The RMS wavefront aberration on the pupil plane is greatly improved as compared with the wavefront aberration shown in FIG. FIG. 12 shows the “spot diameter depth curve” at the image height of the light spot in this case: 0, ± 100 mm, ± 150 mm. (A) is the main scanning direction, (b)
Is related to the sub-scanning direction. Compared to the case of FIG. 7 (using an aperture having a rectangular opening)
In particular, the depth margin in the sub-scanning direction can be increased.
FIG. 10 shows the change in the main scanning direction of the “paraxial curvature of the sub-scanning section” of the sub-non-arc surface (the surface on the side of the rotating polygon mirror of the lens on the side to be scanned, surface number 5) in the second embodiment. ing.
As shown in the figure, the paraxial curvature in the sub-scan section changes in the main scanning direction, and the change in curvature is asymmetric in the main scanning direction and has two or more extreme values.

Example 3 Example 3 given at the end is also a specific example of the embodiment shown in FIG. The light beam from the semiconductor laser, which is the light source 10, is coupled by the coupling lens 11 to become a “parallel light beam”. Accordingly, the deflected light beam is a parallel light beam in the main scanning direction and is divergent in the sub-scanning direction, and the scanning imaging optical systems 21 and 23 move the vicinity of the deflecting reflection surface 19A and the position of the scanned surface 26 in the sub-scanning direction. Is an anamorphic optical system having a function of making a geometrical conjugate relationship, and deflects a deflecting light beam, which is a parallel light beam in the main scanning direction, to the surface 2 to be scanned.
6 has a function of collecting light. The rotating polygon mirror 19 as a light deflecting means has a deflection reflecting surface number: 5 and an inscribed circle radius: 13 mm
1, the incident angle shown in FIG. 1: θ = 60 degrees, and the distance between the rotation axis and the scanning image forming optical system optical axis AX: h = 5.22 mm
It is. In the third embodiment, no tilt angle-shift amount is given to the two lenses 21 and 23 forming the scanning image forming optical system. The angle of view of the scanning imaging optical system is -42 degrees or more.
+42 degrees. The lens 21 has a “concentric spherical surface” on the rotating polygon mirror side, a non-arc shape in the main scanning section and a circular arc in the sub-scanning section on the scanning surface side, and the radius of curvature changes in the main scanning direction. The lens 23 has a “sub-non-arc surface” on the rotating polygon mirror side and a toroidal surface on the scanned surface side. The data after the deflecting reflection surface (the radius of curvature is the paraxial radius of curvature in the case of a non-circular arc shape) is as follows. Surface number Rm Rs (0) xy α n Deflection reflective surface 0 ∞ ∞ 25.44 1.588 Soundproof glass 1 ∞ ∞ 2.01 8 1.51433 2 ∞ ∞ 25.42 8 Lens 21 3 -312.60 -312.60 31.40 1.52716 4 -82.95 104.02 78.00 Lens 23 5- 500.0 -63.50 3.50 1.52716 6 -1000.0 -23.38 143.38 The shift “y” means that the optical system after the deflecting reflection surface is “shifted by 1.588 as a whole”.
“Α” represents the tilt angle (unit: degrees) of the soundproof glass.
The surface number 3 is a coaxial aspherical surface, and is specified by giving each constant of the formula (A). The non-circular shape in the main scanning section of the surface number 4 is expressed by equation (B), and the change in the radius of curvature in the sub-scanning section in the main scanning direction is expressed by equation (C), and each constant is specified. Since the surface number 5 is a sub-non-arc surface, the constant in the main scanning section is determined by giving each constant of the equation (B), and the change in the curvature in the main scanning direction in the sub-scanning section is determined by the equation (C). A constant is given to determine the non-arc shape in the sub-scanning cross section and its change in the main scanning direction.
It specifies by giving each constant of the formula and the formula (F). Table 5 shows coefficients in the main scanning direction and the sub-scanning direction of each surface.

[0039]

[Table 5]

Tables 6 and 7 show the coefficients in the sub-scanning direction of surface number 5 (the sub-non-arc surface on the rotating polygon mirror side of the lens 23).

[0041]

[Table 6]

[0042]

[Table 7]

In Tables 5 to 7, the "signed numerical value" at the end of the numerical value of the data, for example, "+02" or "-01" in "-0.10052 + 02" or "0.10465-01" is " 10 ² "," 10 ^-2 "
Is over the previous number.

FIG. 11 shows the curvature of field and the constant velocity characteristic according to the third embodiment in a manner similar to FIG. Both the curvature of field and the constant speed characteristic are corrected very well. The “non-arc amount” of the non-arc shape in the sub-scanning cross section of the fifth surface (the lens surface on the optical deflector side of the lens to be scanned) which is the sub-non-arc surface in the third embodiment, that is, the deviation amount from the arc ( (Unit: mm) is shown in Table 8.

[0045]

[Table 8]

The amount of non-arc changes asymmetrically with respect to the lens optical axis in accordance with the position of the sub-scan section in the main scanning direction. By setting the amount of non-circular arc in this way, it is possible to form a good small-diameter light spot by correcting the wavefront aberration on the pupil and removing the influence of optical sag at all image heights.

With respect to the first to third embodiments described above, claim 4
The values of the parameters of the condition (1) in (1) and the condition (4) in claim 11 are as follows. Condition (1) Example 1: | β ₀ | = 2.51 Example 2: | β ₀ | = 0.78 Example 3: | β ₀ | = 0.73. In the second and third embodiments, the condition (1) is satisfied, but the first embodiment is not satisfied. Therefore, the first embodiment has a smaller spot diameter than the second and third embodiments. Has a big limit. Condition (4) Example 1: Fs / W = 0.131 / 216 = 0.0006 Example 2: Fs / W = 0.031 / 300 = 0.0001 Example 3: Fs / W = 0.137 / 320 = 0.0004 Conditions for Examples 1 to 3 By satisfying (4) and suppressing the fluctuation of the sub-scanning field curvature, a stable small-diameter light spot is obtained. In addition, all of Examples 1 to 3 satisfy the condition (2). That is, in each embodiment, the front-rear principal point position is set to a desired position by using two or more surfaces in which the paraxial curvature in the sub-scanning cross section changes according to the main scanning direction, and the image height is set. Each magnification is kept constant, and a stable beam spot is obtained. In the first and second embodiments, the principal point position is arbitrarily set by bending the incident side surface and the exit side surface of the lens on the scanning surface side, and the lateral magnification is kept constant. In the third embodiment, the principal point position is set arbitrarily and the lateral magnification is fixed by bending the exit side surface of the lens on the rotating polygon mirror side and the incident side surface on the scanned surface side. In the second embodiment,
As shown in FIG. 10, the paraxial curvature in the sub-scanning cross section of the lens on the rotating polygon mirror side (incident side) of the lens on the scanning surface side of the scanning image forming optical system changes asymmetrically in the main scanning direction. And has three extreme positions: a, b, and c. When the parameters of the condition (3) are calculated for these a, b, and c, the results are as follows. a point: | (he) / (hmax) | = | (-65) / (-90) | = 0.72 b point: | (he) / (hmax) | = | (0) / (44.8) | = 0 c point: | (he) / (hmax) | = | (+62) / (+ 90) | = 0.69 Among the three extreme values, the extreme value that effectively corrects the curvature of field is the condition ( The points a and c satisfy the condition 3). The optical scanning devices according to the first to third embodiments include a light source 10 that emits a light beam, and a first light beam that receives the light beam from the light source and converts the light beam form.
A lens system 12, 16 (11, 15) and a deflecting / reflecting surface 20;
A (19A), the light deflecting means 20 (19) for deflecting the light beam from the first lens system, and the deflecting light beam deflected by the light deflecting means on the surface to be scanned according to the deflection angle. Second lens systems 22 and 24 (21 and 23) for condensing as a light spot having a variable image height, and at least one of the lens surfaces included in the second lens system (the side surface of the scanning surface of the lens 24, The rotating polygon mirror side surface of the lens 23) has a non-arc shape in a plurality of sub-scan sections, and the non-arc shapes in at least two sub-scan sections are different from each other. W, the width of the sub-scanning field curvature within the effective writing width: Fs satisfies the condition: (4) Fs / W <0.005 (claim 24). The second lens system includes at least two independent lenses 22 and 24 (21 and 22).
(3) (Claim 30), and the four lens surfaces of these two lenses have a non-arc shape within the main scanning section (Claim 25). Also, in the depth curve diagrams of FIG. 7 and the like, it is clear from the fact that the change of the light spot system with respect to the focus is extremely small, and as shown in FIG. The sub-non-circular surface of the second lens system has a surface shape determined so that the beam waist position of the deflected light beam coincides with the geometrical optical image forming position (the field curvature position) of the deflected light beam ( Claim 3
5). The second lens systems 22, 24 (21, 23) have a function of making the vicinity of the deflecting / reflecting surface 20A (19A) and the position of the scanned surface 26 geometrically conjugate in the sub-scanning direction in the sub-scanning direction. In the sub-scanning direction, a lateral magnification on the optical axis: β ₀ and a lateral magnification at an arbitrary image height: h: β _h are satisfied in the following conditions: (2) 0 .93 <| β _h / β ₀ | <1.07 (claim 37).

Further, in the first to third embodiments, the light source 10 for emitting a light beam and the first lens systems 12, 16 (11, 15) for receiving the light beam from the light source and converting the light beam form are used.
A light deflecting means 20 (19) having a deflecting / reflecting surface 20A (19A) and deflecting a light beam from the first lens system;
A second lens system 22, 24 (21, 23) for converging as a light spot whose image height changes according to the deflection angle, and at least one of the lens surfaces included in the second lens system (The side of the surface to be scanned of the lens 24 and the side of the rotating polygon mirror of the lens 23) are sub-non-arc-shaped surfaces. The shape of the sub-non-arc surface is determined so as to “correct wavefront aberration at each scanning position on the surface to be scanned”.
0), and as is clear from FIG wavefront aberrations such as FIG. 7, RMS wavefront aberration, as the used wavelength λ, √ {Σ (Xi- X) so as to be ² /N}≦0.1Ramuda In addition, the wavefront aberration is corrected.
1). The "non-arc amount" of the sub-non-arc surface differs with respect to the entire image height (claim 41), and the non-arc amounts near the optical axis and the peripheral portion in the main scanning direction are different from each other (claim 42). And the second
The lens systems 22 and 24 (21 and 23) are anamorphic optical systems having a function of making the vicinity of the deflecting reflection surface and the position of the surface to be scanned geometrically conjugate in the sub-scanning direction in the sub-scanning direction. (Claim 49) Regarding the sub-scanning direction, the lateral magnification on the optical axis: β ₀ and the lateral magnification at an arbitrary image height: h: β _h satisfies the following condition: (2) 0.93 <| β _h / β ₀ | <1.07 is satisfied (claim 50). Further, in all of Examples 1 to 3,
The spot diameter defined by 1 / e ² intensity in the line spread function is 50 μm or less in the effective writing range in both the main and sub scanning directions. In the second and third embodiments, the second lenses 21 and 23 move in the sub-scanning direction.
The lateral magnification on the optical axis: β ₀ satisfies the condition: (1) 0.2 <| β ₀ | <1.5 (claim 52). Further, in all of Examples 1 to 3,
The non-arc amount of the sub-non-arc surface "changes asymmetrically in the main scanning direction"
Therefore, the shape of the sub-non-circular arc surface is determined so as to correct the wavefront aberration with respect to the entire image height (claim 55). The scanning image forming optical system according to the present invention includes a special surface shape as described above, and therefore, its manufacturing is suitably performed by molding using a plastic material.

In the scanning image forming optical system, the one in which the surface shape in the sub-scan section is set to a non-arc shape is disclosed in JP-A-9-18.
Japanese Patent Application Laid-Open No. 5006 and Japanese Patent Application Laid-Open No. 9-49967, etc., are known. Since the incident light flux on the lens surface increases, there are problems such as the need to improve the surface accuracy of all surfaces of the optical system and to increase the NA of the coupling lens.
It is difficult to reduce the diameter of the light spot. In addition, since the amount of non-arc is constant in the main scanning direction and the wavefront aberration cannot be satisfactorily corrected at all image heights in the main scanning direction, it is difficult to obtain a small diameter light spot.

Finally, an embodiment of the image forming apparatus of the present invention will be described with reference to FIG. This image forming apparatus is a laser printer. The laser printer 100 has a “photoconductive photosensitive member formed in a cylindrical shape” as the image carrier 110. Around the image carrier 110, a charging roller 120 as a charging unit, a developing device 130, a transfer roller 140, and a cleaning device 150 are provided. "Corona charger" can be used as the charging means. Optical scanning device 1 using laser beam LB
70 is provided to perform “exposure by optical writing” between the charging roller 120 and the developing device 130.
The optical scanning device is as described above with reference to the first to third embodiments. In FIG. 13, reference numeral 160 denotes a fixing device,
Reference numeral 180 denotes a cassette, reference numeral 190 denotes a pair of registration rollers, reference numeral 200 denotes a feed roller, reference numeral 210 denotes a conveyance path, reference numeral 220 denotes a pair of discharge rollers, reference numeral 230 denotes a tray, and reference numeral P denotes a transfer sheet as a recording medium. I have. When forming an image, the image carrier 110, which is a photoconductive photoconductor, is rotated clockwise at a constant speed, the surface thereof is uniformly charged by the charging roller 120, and the optical writing of the laser beam by the optical scanning device 170 is performed. To form an electrostatic latent image. The formed electrostatic latent image is a so-called “negative latent image”, and the image portion is exposed. This electrostatic latent image is reversely developed by the developing device 130 to form a toner image on the image carrier 110. The cassette 180 containing the transfer paper P is detachable from the main body of the image forming apparatus 100. When the cassette 180 is mounted as shown in FIG. Then, the leading end of the fed transfer paper P is held by the registration roller pair 190. The registration roller pair 190 sends the transfer paper P to the transfer unit at the same timing as the toner image on the image carrier 110 moves to the transfer position. The transferred transfer paper P is
The toner image is superimposed on the toner image at the transfer portion, and the toner image is electrostatically transferred by the action of the transfer roller 140. The transfer paper P on which the toner image has been transferred is sent to the fixing device 160, where the toner image is fixed.
It is discharged on 30. The surface of the image carrier 110 after the transfer of the toner image is cleaned by the cleaning device 150 to remove residual toner, paper dust, and the like.
By using the optical scanning device 170 as in the first to third embodiments, extremely good image formation can be performed. That is, the image forming apparatus shown in FIG. 13 forms a latent image on the latent image carrier 110 by optical scanning, and develops the formed latent image to obtain a desired image. The optical scanning device according to any one of claims 19 to 55 is used as the optical scanning device for performing the optical scanning (claim 56), wherein the latent image carrier 110 is a photoconductive photoconductor. The formed latent image is visualized as a toner image, and the toner image is formed into a sheet-shaped recording medium P.
(Claim 57).

[0051]

As described above, according to the scanning image forming optical system of the present invention, since the wavefront aberration is effectively corrected by using the sub-non-circular surface, a light spot having a small diameter of about 50 μm or less can be obtained. It can be obtained stably. Further, the optical scanning device of the present invention can realize good writing with a high writing density by using a stable light spot having a small diameter by using the above scanning image forming optical system. Good image formation can be achieved by using the optical scanning device.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining one embodiment of the invention of an optical scanning device.

FIG. 2 is a diagram for explaining another embodiment of the invention of the optical scanning device.

FIG. 3 is a view for explaining a sub-non-arc surface.

FIG. 4 is a diagram illustrating field curvature and constant velocity characteristics according to the first embodiment.

FIG. 5 is a diagram showing a depth curve of a spot diameter according to the first embodiment.

FIG. 6 is a diagram illustrating field curvature and constant velocity characteristics according to a second embodiment.

FIG. 7 is a diagram showing a depth curve of a spot diameter according to the second embodiment.

FIG. 8 shows image heights of light spots in Example 2: 0 and ± 1.
It is a figure which shows the wavefront aberration in the position of 00mm and +/- 150mm.

FIG. 9 shows an image height of a light spot when an aperture in which four corners are cut by 40% is used in Example 2.
It is a figure which shows the wavefront aberration in the position of 0, ± 100mm, and ± 150mm.

FIG. 10 is a diagram illustrating a change in the main scanning direction of the paraxial curvature in the sub-scanning section of the sub-non-arc surface in the second embodiment.

FIG. 11 is a diagram illustrating field curvature and constant velocity characteristics according to a third embodiment.

FIG. 12 is a diagram illustrating wavefront aberrations at positions of image heights of light spots: 0, ± 100 mm, and ± 150 mm when an aperture having an opening shape with rounded four corners is used in Example 2. .

FIG. 13 is a diagram showing an embodiment of the invention of the image forming apparatus.

[Explanation of symbols]

 Reference Signs List 20 light deflecting means 20A deflecting / reflecting surface 22, 24 lens constituting scanning image forming optical system 26 surface to be scanned

Claims (57)

[Claims] 1. A scanning image forming optical system for converging a deflected light beam deflected by an optical deflecting means having a deflecting reflection surface as a light spot on a surface to be scanned, comprising: at least one lens; One of the surfaces is a sub-non-arc surface, and the sub-non-arc surface has a non-arc shape in the sub-scan section.
The non-arc shape is a surface that changes in accordance with the position of the sub-scan section in the main scanning direction, and the shape of the sub-non-arc surface is determined so as to correct wavefront aberration at each scanning position on the surface to be scanned. A scanning image forming optical system. 2. The scanning imaging optical system according to claim 1, wherein the shape of the sub-non-arc surface in the main scanning section is a non-arc shape. 3. The scanning image forming optical system according to claim 1, wherein the wavefront aberration correction on the sub-non-arc surface is performed by RMS:
A scanning image forming optical system having a wavelength of 0.1λ or less (λ is a working wavelength) or less. 4. A scanning image forming optical system according to claim 1, wherein the spot diameter of the light spot on the surface to be scanned is 1/1 in a line spread function of the light intensity distribution of the light spot.
A scanning imaging optical system having an imaging function of defining the spot diameter as 50 μm or less in the effective writing range in both the main scanning direction and the sub-scanning direction as defined by e ² intensity. 5. The scanning image forming optical system according to claim 1, wherein the lateral magnification on the optical axis in the sub-scanning direction: β ₀ satisfies the following condition: (1) 0.2 <| β A scanning imaging optical system characterized by satisfying ₀ | <1.5. 6. A scanning image forming optical system according to claim 1, wherein a lateral magnification on the optical axis in the sub-scanning direction: β ₀ , an arbitrary image height:
A scanning imaging optical system characterized in that a lateral magnification at _h : β _h satisfies the following condition: (2) 0.93 <| β _h / β ₀ | <1.07. 7. The scanning image forming optical system according to claim 1, wherein a non-arc amount is a shift amount of the sub-non-arc surface from the arc in the non-arc shape in the sub-scan section. However, the scanning image forming optical system changes asymmetrically in the main scanning direction. 8. A scanning imaging optical system according to claim 1, wherein the paraxial curvature in the sub-scanning section changes asymmetrically in the main scanning direction, and the paraxial curvature is smaller than the paraxial curvature. A scanning image forming optical system comprising at least one lens surface having an extreme value having a change of 2 or more. 9. The scanning image forming optical system according to claim 8, wherein at least one of the extreme values in the change of the paraxial curvature in the sub-scanning section has a position in the main scanning direction: he at the + image height side. Or-the effective lens height from the lens optical axis on the image height side: hmax
(3) | (he) / (hmax) |> 0.5. 10. The scanning imaging optical system according to claim 8, wherein the paraxial curvature in the sub-scanning section changes asymmetrically in the main scanning direction, and the change in the paraxial curvature is 2 or more. A scanning imaging optical system, wherein a lens surface having an extreme value is a sub-non-arc surface. 11. The scanning image forming optical system according to claim 1, wherein the effective writing width is W and the width of the sub-scanning field curvature within the effective writing width is Fs. (4) A scanning imaging optical system, wherein Fs / W <0.005 is satisfied. 12. A scanning image forming optical system according to claim 1, wherein the shape of the sub-non-arc surface in the main scanning section is determined so as to correct the constant velocity characteristic of the light spot. A scanning image forming optical system. 13. A scanning image forming optical system according to claim 1, wherein a function of making the vicinity of the deflecting reflection surface and the position of the surface to be scanned geometrically conjugate with respect to the sub-scanning direction. A scanning imaging optical system, characterized in that the optical system is an anamorphic optical system. 14. A scanning image forming optical system according to claim 13, wherein said optical system comprises two lenses. 15. The scanning image forming optical system according to claim 14, wherein the lens surface on the scanned surface side of the lens on the scanned surface side is a sub-non-circular surface. 16. A scanning image forming optical system according to claim 14, wherein the lens surface on the light deflection means side of the lens on the surface to be scanned is a sub-non-circular surface. 17. A scanning image forming optical system according to claim 15, wherein said scanning image forming optical system has a function of converging a deflected light beam which is a weakly focused light beam in the main scanning direction on a surface to be scanned. system. 18. A scanning image forming optical system according to claim 16, wherein said scanning image forming optical system has a function of converging a deflected light beam which is a parallel light beam in a main scanning direction on a surface to be scanned. . 19. An optical scanning device for deflecting a light beam from a light source by an optical deflecting means having a deflecting / reflecting surface, and condensing the deflected light beam as a light spot on a surface to be scanned by a scanning image forming optical system to perform optical scanning. An optical scanning device, wherein the scanning image forming optical system according to any one of claims 1 to 12 is used as the scanning image forming optical system. 20. A light beam from a light source is formed as a long line image in the main scanning direction, is deflected by a light deflecting means having a deflecting reflection surface near the line image, and the deflected light beam is received by a scanning image forming optical system. An optical scanning device that performs optical scanning by condensing light as a light spot on a scanning surface, wherein the scanning imaging optical system according to any one of claims 13 to 18 is used as a scanning imaging optical system. Optical scanning device characterized by the following. 21. An optical scanning device according to claim 20, wherein the deflecting light beam deflected by the light deflecting means is a converging light beam weak in the main scanning direction, and is used as a scanning image forming optical system.
An optical scanning device using the scanning image forming optical system according to claim 7. 22. An optical scanning device according to claim 20, wherein the deflecting light beam deflected by the light deflecting means is a parallel light beam in the main scanning direction, and is used as a scanning image forming optical system. An optical scanning device using an optical system. 23. The optical scanning device according to claim 21, wherein a light beam from a semiconductor laser as a light source is taken in by a coupling lens, and is brought into the vicinity of a deflecting reflection surface by a line image forming optical system in a main scanning direction. An aperture for shaping the beam between the light source and the deflecting / reflecting surface, and the aperture of the aperture is provided in the main-sub-scanning direction of the coupled light beam in the main-sub scanning direction. An optical scanning device having a shape that blocks a corner portion. 24. A light source that emits a light beam, a first lens system that receives the light beam from the light source and converts the light beam form, and a deflection / reflection surface, and deflects the light beam from the first lens system. A light deflecting means, and a second lens system for condensing the deflected light beam deflected by the light deflecting means on a surface to be scanned as a light spot whose image height changes according to the deflection angle; At least one of the lens surfaces included in the two-lens system has a non-arc shape in a plurality of sub-scan cross sections, and the non-arc shapes in at least two sub-scan cross sections are different from each other. An optical scanning device characterized in that a writing width: W and a width of the sub-scanning field curvature within the effective writing width: Fs satisfy the following condition: (4) Fs / W <0.005. 25. The optical scanning device according to claim 24, wherein the second lens system has at least two independent lenses, and the four lens surfaces of the two lenses are located within the main scanning section. An optical scanning device having a non-arc shape. 26. The optical scanning device according to claim 24, wherein the second lens system has at least two independent lenses, and at least three of the four lens surfaces of the two lenses are at least three. An optical scanning device having a non-circular shape in a main scanning section. 27. The optical scanning device according to claim 24, wherein the second lens system has at least two independent lenses, and at least one of the four lens surfaces of the two lenses is at least one. Has a non-circular shape in the sub-scan section, and
The optical scanning device according to claim 1, wherein the non-circular shape has a curved center line in which the paraxial radius of curvature is continued in the main scanning direction and a curve different from the shape of the lens surface in the main scanning cross section. 28. The optical scanning device according to claim 24, wherein the second lens system includes three or more lenses. 29. The optical scanning device according to claim 24, wherein the second lens system comprises only one lens. 30. The optical scanning device according to claim 24, wherein the second lens system includes two or more lenses. 31. The optical scanning device according to claim 24, wherein the writing density is set in a range of approximately 600 to 1200 dpi. 32. The optical scanning device according to claim 24, wherein the writing density is set in a range of approximately 1200 to 2400 dpi. 33. The optical scanning device according to claim 24, wherein the writing density is set to approximately 2400 dpi or more. 34. The optical scanning device according to claim 24, wherein the light source emits two or more light beams. 35. The optical scanning device according to claim 24, wherein the second lens system is located at a geometric optical imaging position of the deflected light beam.
An optical scanning device, comprising: at least one lens having a sub-non-arc surface whose surface shape is determined so as to match the beam waist position of the deflected light beam. 36. The optical scanning device according to claim 24, wherein the second lens system sets the vicinity of the deflecting reflection surface and the position of the surface to be scanned in the sub-scanning direction in a geometrical conjugate relationship with respect to the sub-scanning direction. An optical scanning device comprising an anamorphic optical system having a function. 37. An optical scanning apparatus according to claim 24, wherein the second lens system, the sub-scanning direction, the lateral magnification of the optical axis: the beta _0, any image height lateral magnification in h: and beta _h Satisfies the following condition: (2) 0.93 <| β _h / β ₀ | <1.07. 38. The optical scanning device according to claim 24, wherein at least one of the lens surfaces included in the second lens system is a sub-non-arc surface, and the shape of the sub-non-arc surface is within the effective writing width. An optical scanning device wherein a beam waist position is determined so as to match a position of a surface to be scanned with respect to an entire image height of a light spot. 39. A light source that emits a light beam, a first lens system that receives the light beam from the light source and converts the light beam form, and a deflection / reflection surface, and deflects the light beam from the first lens system. A light deflecting means, and a second lens system for condensing the deflected light beam deflected by the light deflecting means on a surface to be scanned as a light spot whose image height changes according to the deflection angle; An optical scanning device, wherein at least one of the lens surfaces included in the two-lens system is a sub-non-arc surface. 40. The optical scanning device according to claim 39, wherein the shape of the sub-non-arc surface is determined so as to correct the wavefront aberration at each scanning position on the surface to be scanned. apparatus. 41. The optical scanning device according to claim 39, wherein the light beam cross section on the pupil plane is divided into n parts, and the divided parts are divided into 1, 2, 3,. . , I,. . , N,
These divided parts: i (i = 1, 2, 3, ..., n)
Where Xi is the wavefront aberration amount and Xi / n is the average value of the wavefront aberration amount: Xi, and RMS of the wavefront aberration on the pupil plane defined by {(Xi−X) ² / n} Wherein the wavefront aberration is corrected such that {(Xi−X) ² /n}≦0.1λ, where λ is the wavelength used. 42. The optical scanning device according to claim 39, wherein the amount of non-arc, which is the amount of deviation from the arc, of the non-arc in the sub-scan section of the sub-non-arc surface is different from the total image height. An optical scanning device, comprising: 43. The optical scanning device according to claim 42, wherein the amount of non-arc in the vicinity of the optical axis and the peripheral portion in the main scanning direction are different from each other. 44. The optical scanning device according to claim 42, wherein the first lens system is corrected for wavefront aberration. 45. The optical scanning device according to claim 39, wherein the writing density is set in a range of approximately 600 to 1200 dpi. 46. The optical scanning device according to claim 39, wherein the writing density is set in a range of approximately 1200 to 2400 dpi. 47. The optical scanning device according to claim 39, wherein the writing density is set to approximately 2400 dpi or more. 48. The optical scanning device according to claim 39, wherein the light source emits two or more light beams. 49. The optical scanning device according to claim 39, wherein the second lens system sets the vicinity of the deflecting reflection surface and the position of the surface to be scanned in the sub-scanning direction to have a geometrical conjugate relationship in the sub-scanning direction. An optical scanning device comprising an anamorphic optical system having a function. 11. 50. A light scanning device according to claim 39, the second lens system, the sub-scanning direction, the lateral magnification of the optical axis: the beta _0, any image height lateral magnification in h: and beta _h Satisfies the following condition: (2) 0.93 <| β _h / β ₀ | <1.07. 51. The optical scanning device according to claim 39, wherein the spot diameter of the light spot on the surface to be scanned is 1 / the value of the line spread function of the light intensity distribution at the light spot.
An optical scanning device characterized in that the spot diameter is 50 μm or less in the effective writing range in both the main and sub-scanning directions as defined by e ² intensity. 52. The optical scanning device according to claim 39, wherein the lateral magnification β _{0 of} the second lens on the optical axis in the sub-scanning direction is:
Conditions: (1) 0.2 <| β 0 | < optical scanning device that features that satisfies 1.5. 53. The optical scanning device according to claim 39, wherein the non-arc amount, which is a shift amount of the non-arc shape in the sub-scan section in the sub-scan section, from the arc changes asymmetrically in the main scanning direction. A scanning image forming optical system. 54. The optical scanning device according to claim 39, wherein the amount of non-arc, which is the amount of deviation of the non-arc shape in the sub-scan section from the arc in the sub-scan section, changes symmetrically in the main scanning direction. A scanning image forming optical system. 55. The optical scanning device according to claim 39, wherein the shape of at least one sub-non-arc surface is determined so as to correct wavefront aberration with respect to the entire image height. Scanning device. 56. An image forming apparatus for forming a latent image on a latent image carrier by optical scanning and developing the formed latent image to obtain a desired image, wherein the optical scanning device performs optical scanning of the latent image carrier. Claim 1
An image forming apparatus using the optical scanning device according to any one of 9 to 55. 57. The image forming apparatus according to claim 56, wherein the latent image carrier is a photoconductive photoconductor, the formed latent image is visualized as a toner image, and the toner image is a sheet-shaped recording medium. An image forming apparatus, wherein: