JP2002258152A - Optical scanning lens, optical scanner and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an optical scanning lens where variation in beam waist position due to waviness of a lens surfaces can be suppressed, an optical scanner with no thickening of the beam and an image forming device where a good image without any deterioration is acquired by setting a maintenance item of curvature distribution. SOLUTION: In the device, when the maximum value of the variation amount of the curvature distribution of a curved surface is ΔC in a range where a luminous flux of the lens is passed, the following formula is satisfied. ΔC<=2×w<2> / (n-1)×λ×S'<2> } wherein, w: radius of a beam spot on a surface to be scanned n: curvature index of refraction of the lens λ: light source wave length S': the distance from the backside main point of a scanning image formation of an optical system to the image surface.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical scanning lens, an optical scanning device, and an image forming apparatus used for a laser printer, a laser facsimile, a digital copier, and the like. High optical performance can be obtained.

[0002]

2. Description of the Related Art Laser printers, laser facsimile machines, digital copiers, and the like are strictly required to have low cost, compact size, and high performance. Compactness and high performance are progressing. It is effective to reduce the number of lenses by making the optical scanning lens aspherical in order to make the optical scanning optical system low cost, compact, and high performance. To make the lens aspherical, the introduction of plastic lenses Is effective.

[0003] Generally, a plastic lens is integrally molded using a molding die, but the molding surface partially undulates. When an image is formed by optical scanning using a undulating plastic lens, the beam waist position fluctuates on the surface to be scanned, and a black streak in the sub-scanning direction may occur at a portion corresponding to the undulation. In particular, in an optical scanning device or an image forming device in which higher resolution and higher density gradation have been advanced, black streaks caused by the waviness on the lens surface are more conspicuous.

FIGS. 5 and 6 show how the beam waist position fluctuates due to the undulation of the lens surface.
The undulation amplitude is on the order of several nm to several μm, and the beam waist position variation is on the order of 0.1 mm to 1 mm. In FIG. 5, undulations and beam waist position variations are exaggerated. 5, a diffused light beam emitted from a laser light source 10 is converged by a coupling lens 12, passed through an aperture 14 to be shaped in cross section, and furthermore, is subjected to a cylindrical lens 16 in a sub-scanning direction (in FIG. 5, perpendicular to the plane of FIG. 5). The light is focused only in the y-direction, and a long line image is formed in the main scanning direction (x-direction in FIG. 5) in the vicinity of the deflecting reflection surface of the optical deflector 20. In addition, between the cylindrical lens 16 and the optical deflector 20, a mirror 18 that bends the light beam from the cylindrical lens 16 and guides it to the optical deflector 20.
Is arranged.

The light beam incident on the deflecting / reflecting surface of the optical deflector 20 is deflected at a constant angular velocity by the deflecting / reflecting surface when the optical deflector 20 is driven to rotate. This deflected light beam passes through the optical scanning lens 30 to form the scanned surface 40.
The light is focused as a light spot on the upper surface and the
It is scanned at a constant velocity in the x direction. Scanned surface 4
The scanning range on 0 is indicated by W.

As described above, the undulation on the optical scanning lens surface affects the beam profile, that is, the beam intensity distribution, and has a problem that it appears as a black streak in an output image. In FIG. 5, the undulation of the surface of the lens 30 is exaggerated by reference numeral 31, and the fluctuation of the beam waist position on the scanned surface 40 due to the undulation 31 is exaggerated by reference numeral 41. The presence of the undulation 31 on the surface of the lens 30 is the same as the occurrence of unevenness on the surface of the lens 30. Therefore, the beam waist position on the scanned surface 40 is indicated by reference numeral 41 in a portion corresponding to the unevenness. It will fluctuate like a line. When the beam waist position changes, as shown in FIG. 6, the center position of the light spot fluctuates around the scanned surface 40, and the scanned surface 4
At 0, the beam becomes thicker.

[0007]

In order to suppress the beam waist position fluctuation as described above and the beam thickening on the surface to be scanned 40 caused by the fluctuation, it is necessary to suppress the PV of the lens surface waviness. However, to achieve this, it is necessary to process the lens mold while controlling it in the order of nanometers, and high-precision control is also required during molding and measurement, and there is a limit to meeting the required accuracy. .

FIG. 7 shows the relationship between the swell spatial frequency f and the allowable amplitude. As shown in FIG. 7, the required accuracy for processing a lens shape having a length of about several hundred mm and a height of about several tens mm is as high as several nanometers under the strictest condition (1). Accordingly, the accuracy required for measurement is further increased, and ultra-high accuracy of sub-nanometer is required. Further, since the accuracy depends on the frequency of the undulation, the accuracy must be managed for each frequency. FIG. 7 shows an example in which four points (1) to (4) are managed. However, there is a limit in the conventional technology to satisfy such a demand for ultra-high accuracy.

On the other hand, in addition to such a problem on the required accuracy, there is still room for study on the evaluation method. As a method of evaluating the undulation of the lens surface, conventionally, x, y, z
This is expressed in three-dimensional coordinates and evaluated, but it has been difficult to perform an evaluation that meets the demand for ultra-high accuracy. The present invention has been made in order to solve the above-described problems of the related art, and by setting a completely new management item called a curvature distribution, it is possible to suppress a beam waist position variation due to undulation of a lens surface. It is an object of the present invention to provide an optical scanning lens, an optical scanning device having no beam enlargement, and an image forming apparatus capable of obtaining a good image without deterioration.

[0010]

According to the first aspect of the present invention,
An optical scanning lens used in a scanning imaging optical system for condensing a light beam deflected by an optical deflector in the vicinity of a surface to be scanned, and having a maximum curvature distribution variation amount of a curved surface in a region through which the light beam of the lens passes. When the value is ΔC, ΔC ≦ 2 × w ² / {(n−1) × λ × S ′ ² } where w: beam spot radius on the surface to be scanned n: refractive index of lens λ: light source wavelength S ': The distance from the rear principal point of the scanning imaging optical system to the image plane.

According to a second aspect of the present invention, there is provided an optical scanning lens used in a scanning image forming optical system for condensing a light beam deflected by an optical deflector near a surface to be scanned, wherein an area through which the light beam of the lens passes. Where, when the maximum value of the curvature distribution variation amount in the main scanning direction of the curved surface is ΔC, ΔC ≦ 2 × w ² / {(n−1) × λ × F ² } where, w: Beam spot radius n: refractive index of lens λ: light source wavelength F: focal length of the entire scanning imaging optical system in the main scanning direction.

According to a third aspect of the present invention, there is provided an optical scanning lens for use in a scanning image forming optical system for converging a light beam deflected by an optical deflector near a surface to be scanned, wherein an area through which the light beam of the lens passes. Is the maximum value of the curvature distribution variation of the curved surface
When C is set, 0.2 / K ≦ ΔC × (n−1) × λ × (S ′ / w) ² ≦
2 where K: number of optical elements from the optical deflector to the image surface w: beam spot radius on the surface to be scanned n: refractive index of lens λ: light source wavelength S ′: rear main of the scanning image forming optical system It is characterized by the distance from the point to the image plane.

According to a fourth aspect of the present invention, there is provided an optical scanning lens used in a scanning image forming optical system for converging a light beam deflected by an optical deflector near a surface to be scanned, wherein an area through which the light beam of the lens passes. In the equation, the average curvature of the curved surface in the main scanning direction is q
(X), the approximation curve of order 10 or less of q (x) is expressed as q0 (x)
Where q_PV × (n−1) × λ × (F / wd) ² ≦ 1 where wd: beam spot diameter on the surface to be scanned in the main scanning direction n: refractive index of lens λ: light source wavelength F: Focal length of the entire scanning imaging optical system in the main scanning direction q_PV = max {q (x) -q0 (x)}-min
{Q (x) -q0 (x)}.

According to a fifth aspect of the present invention, there is provided an optical scanning lens used in a scanning image forming optical system for condensing a light beam deflected by an optical deflector near a surface to be scanned, wherein an area through which the light beam of the lens passes. Within, the average curvature of the curved surface is q (x), q
When an approximation curve of order 10 or lower of (x) is q0 (x), 0.1 / K ≦ q_PV × (n−1) × λ × (S ′ / w
d) ² ≦ 1 where wd: beam spot diameter on the surface to be scanned n: refractive index of lens λ: light source wavelength S ′: distance from the rear principal point of the scanning imaging optical system to the image surface q_PV = max ｛ q (x) -q0 (x)｝-min
{Q (x) -q0 (x)}.

According to a sixth aspect of the present invention, a light beam from a light source is deflected at an equal angular velocity by an optical deflector having a deflecting and reflecting surface, and the deflected light beam is condensed as a light spot on a surface to be scanned by an optical scanning lens. An optical scanning device that optically scans the surface to be scanned with the light spot at a constant speed is equipped with the optical scanning lens according to any one of claims 1 to 5.

According to a seventh aspect of the present invention, there is provided an image forming apparatus having the optical scanning device according to the sixth aspect, wherein the surface to be scanned is made of a photosensitive member, and the surface to be scanned is optically scanned by the optical scanning device. Thereby, an electrostatic latent image is formed on the surface to be scanned.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of an optical scanning lens, an optical scanning device, and an image forming apparatus according to the present invention will be described with reference to the drawings. As can be seen from the above explanation, the reason why the slight amplitude of the undulation generated in the area where the light beam passes through the optical scanning lens causes the fluctuation of the beam waist position near the surface to be scanned is due to the influence of the undulation described above. This causes the curvature of the lens curved surface to fluctuate, and as a result, the focal length of the lens locally fluctuates.

In the convex scanning lens model shown in FIG. 5, the curvature of the portion where the waviness acts as a concave lens becomes loose and the focal length becomes long. Conversely, in a portion where the undulation acts as a convex lens, the curvature of that portion becomes tight and the focal length becomes short. In the conventional method,
Because we were trying to indirectly manage surface coordinates,
The lens surface was required to be finished with ultra-high precision.

However, since the curvature distribution on the lens surface directly affects the optical performance, it should be possible to suppress the beam waist position fluctuation by managing the curvature distribution from the viewpoint of the curvature distribution. It is easy to manage both in terms of measurement. In other words, it has been found that by suppressing the fluctuation amount of the curvature distribution in the area where the light beam of the optical scanning lens passes within an allowable range, it is possible to suppress the beam diameter from being increased due to the fluctuation of the beam spot position and further the deterioration of the output image. Was.

Generally, when z = z (x, y) is a continuous curved surface, the curvature Cx (x, x) at the point (x, y) in the x direction is obtained.
y) and the radius of curvature Rx (x, y) are represented by the following equations. Similarly, the curvature Cy (x, y) in the y direction and the radius of curvature R
y (x, y) is represented by the following formula. Hereinafter, the shape z (x) and the curvature C will be described for the sake of simplicity.
(X) However, it is obvious that the above holds true in the y direction.

In the following description, the curvature distribution ΔC
(X) means the difference from the ideal curvature state when the actual curvature C (x) of the test object is in the ideal curvature state. Therefore, if the actual test object is finished in an ideal state, ΔC (x) = 0 regardless of the shape of the spherical or aspherical surface. If ΔC (x) <> 0, it means that the test object has undulated.

Now, as shown in FIGS. 1 and 2, the optical element between the optical deflector and the image plane, that is, the focal length of the optical scanning lens 30 is f, and the optical element in the area through which the light beam of the optical scanning lens 30 passes. The surface undulation is considered as a curvature distribution ΔC (x), and ΔC
Let the maximum value of (x) be ΔC. Lens 3 by swell
Assuming that a plano-convex lens is added to 0, the focal length fa of the lens 30 due to the undulation is 1 / fa = (n-1) (1 / Δr) = (n-1) ΔC. Where n is the refractive index of the optical element

The focal length fluctuation Δ of the lens 30 due to the undulation
f approximately holds the relationship of Δf ≒ f ² / fa = f ² (n−1) ΔC (1). The beam radius w (z) at a position z away from the beam waist radius w0 is represented by the following equation. ^{W 2 (z) = w0 2} {1+ (λz / πw0 2) 2} However, lambda: if put the light source wavelength w (z) = (1 + α) w0, z = (√ (α 2 + 2α) × π) w0 since tolerance ² / lambda beam diameter variation can be regarded as 20% or less, and ^{α = 0.2 z ≦ 2w0 2 /} λ (2).

Since the main scanning direction is substantially parallel to the direction of deflection by the optical deflector, it can be considered that focal length variation / beam waist position variation. That is, it may be considered that z = Δf. Assuming that w is the beam spot radius on the surface to be scanned, more specifically, the diameter when 1 / e ² of the maximum intensity is the threshold level, the beam waist position is near the surface to be scanned due to the design concept. Therefore, it can be considered that w = w0. Assuming that the focal length in the main scanning direction is F (= f), from (1) and (2), ΔC ≦ 2 × w ² / {(n−1) × λ × F ² } (3) where w: scanned Beam spot radius on the surface n: Refractive index of lens λ: Light source wavelength F: Focal length of the entire scanning imaging optical system in the main scanning direction. If ΔC satisfies this condition, a good output image can be obtained by the optical scanning device and the image forming apparatus using the optical scanning lens.

In an optical system that is not parallel to the sub-scanning direction or the direction of deflection by the optical deflector, the deflecting reflection surface of the optical deflector and the image plane have a substantially conjugate relationship, so that it is necessary to consider the imaging magnification. There is. As shown in FIG. 1, it may be considered that z = ΔS ′ (imaging position variation). Paraxial imaging formula (1 / S '= 1 /
S + 1 / f) is as follows. ΔC ≦ 2 × w ² / {(n−1) × λ × S ′ ² } where S ′ is the distance from the rear principal point of the scanning imaging optical system to the image plane. If ΔC satisfies this condition, a good output image can be obtained by the optical scanning device and the image forming apparatus using the optical scanning lens.

For practical use, the following range is desirable. 0.2 / K ≦ ΔC × (n−1) × λ × (S ′ / w) ² ≦
If the lower limit of 0.2 / K is less than 0.2 / K, it can be regarded as an error in optical performance. In addition, not only errors due to measurement cannot be ignored, but also the time required for molding and the cooling time become longer, which may be a factor of cost increase. Here, K is the number of optical element surfaces. It is obvious that the more the optical element surface, the thicker the beam when the interaction occurs.
Therefore, the quality per surface must be high. For example, K = 2 for one lens and K for two lenses
= 4.

In particular, since the main scanning direction is substantially parallel to the one rear surface of the optical deflector, 0.2 / K ≦ ΔC × (n−1) × λ × (f / w) ² ≦ 2, If ΔC satisfies this condition, a good output image and a practically desirable lens can be provided by the optical scanning device and the image forming apparatus using the optical scanning lens.

Next, several embodiments will be described. Example 1 λ = 650 nm, two lenses (K = 4), beam diameter:
27 μm (w = 13.5 μm), f = 225.3 mm,
In the case of an optical system of n = 1.52398, ΔC in the main scanning direction
ΔC ≦ 2.1084E-05 is a necessary condition for suppressing the fluctuation of the beam spot position, and ΔC ≧ 5.2709E-07 is a sufficient condition.

Example 2 λ = 780 nm, two lenses (K = 4), beam diameter:
65 μm (w = 32.5 μm), f = 185.4 mm,
In the case of an optical system of n = 1.52398, ΔC in the main scanning direction
ΔC ≦ 1.8535E-04 is a necessary condition for suppressing beam spot position fluctuation, and ΔC ≦ 4.6338E-06 is a sufficient condition.

Example 3 λ = 780 nm, one lens (K = 2), beam diameter:
90 μm (w = 45 μm), S ′ = 121.9, n =
In the case of the optical system of 1.52398, ΔC ≦ 6.6687E-04 is a necessary condition for suppressing the fluctuation of the beam spot position, and ΔC ≧ 3.3343E-05 is a sufficient condition.

Note that if there is a spatially high-frequency surface roughness, the curvature greatly changes and ΔC increases, but this does not significantly affect the focal length variation. Therefore 0.05m
It is preferable to perform smoothing or averaging processing in the range of m or more to remove abnormal values.

Considering the abnormal value of the curvature due to the roughness of the lens surface as described above, it is more realistic to focus on the average curvature. When calculating the average curvature q (x), the curvature C
General method of calculating from the result of (x) However, when the measurement method is considered, the following method for directly obtaining q (x) from the first derivative z ′ (x) of the curved surface is more effective. Δq (x) = q (x) −q0 (x) q_PV = max (Δq (x)) − min (Δq
(X)). However, a polynomial approximation curve q0 (x) of order 10 or less of q0 (x): q (x) is for subtracting a design shape such as an aspherical surface. In the case of a spherical surface, the curvature is fixed by design, so that the processing of the approximate curve is unnecessary. Δq (x): average curvature fluctuation amount max (Δq (x)): maximum value of Δq (x) min (Δq (x)): minimum value of Δq (x) The value of the width b for calculating the average is optical It is desirable that the diameter be equal to or less than the beam luminous flux diameter on the element surface. This gives q
_PV is equivalent to the amount of curvature variation as a light beam. Therefore, in equation (3), ΔC = q_PV / 2, w
= Wd / 2, q_PV × (n−1) × λ × (S ′ / wd) ² ≦ 1, where wd is a lens having a beam spot diameter on the surface to be scanned and having a good output image. It can be said that the condition and the evaluation method.

Similarly, since the main scanning direction is substantially parallel light from the optical deflector, it can be regarded that focal length 焦点 beam waist position fluctuation. PV × (n−1) × λ × (f / wd) ² ≦ 1 In practical use, the following range is preferable. 0.1 / K ≦ q_PV × (n−1) × λ × (S ′ / w
d) ² ≦ 1 FIG. 2 shows the relationship between the curved surface shape z (x), the curvature c (x) and the average curvature q (x), ΔC and q_PV.

FIG. 4 shows a principle diagram of the curvature distribution measuring method.
The laser light emitted from the laser light source 51 passes through the optical unit 52 and passes through the optical scanning lens 30 as the test object.
And the reflected light is detected by the light receiving element 53. As the light receiving element 53, a position sensor, a CCD, a split photodiode, or the like is used. The center position xi of the beam is calculated by analyzing the beam intensity generated on the light receiving element 53 and obtaining the center of gravity.

For simplicity, the shape of the surface of the test object on the (x, z) plane is z (x), and the inclination angle distribution is θ (x). Assuming that the distance between the beam irradiation position of the test object and the detection surface on the light receiving element 53 is L1 and the distance between the incident beam and the reflected beam passing through the detection surface on the light receiving element 53 is xi, tan (2θ (x) ) = Xi / L1 (11) 2θ (x) = arctan (xi / L1) (12) θ (x) = 0.5 ^* arctan (xi / L1) (13), and the inclination angle θ (x) is measured. can do. From the inclination angle θ (x), a first derivative z ′ (x) of z (x) can be calculated by the following equation. z ′ (x) = tan (θ (x)) (14)

The optical scanning lens 30 is moved in the x-direction in order to measure the curvature distribution of the surface of the optical scanning lens 30 to be inspected. With this movement, the reflection angle of the surface of the lens 30 changes, and the light receiving position of the light receiving element 53 changes.
The light receiving element 53 is moved by following the movement of the position of the reflected light beam.
In a predetermined direction of the light receiving element 53 so that the reflected light from the lens 30 can be received. Thereby, the inclination angle distribution of the lens 30 surface in the x direction can be measured.

When L1 changes with the movement of the surface of the test object, correction may be performed using a design value known in advance, or the test object surface may be relatively moved in the z-axis direction so that L1 is constant. May be moved. Similarly, by scanning in the y direction, it is possible to measure the inclination angle distribution of the curved surface in the xy plane. The light receiving element is also scanned in the xy directions, and the position (xi, yi) of the reflected light is measured, so that the tilt angle distribution θx independent of the two axes in the surface of the test object is obtained.
(X, y) and θy (x, y) can be measured.
The curvature of the test object surface is 2 like the AC (anamorphic) surface.
It is particularly effective when the axes differ. If the angle of inclination of the lens surface is close to 0 degrees, the light source 51 and the light receiving element 53 overlap. Therefore, the optical path may be separated by a half mirror or the like.

FIG. 3 schematically shows an embodiment of an optical scanning device to which the optical scanning lens according to the present invention can be applied. Since the appearance is the same as that of the conventional optical scanning device described with reference to FIG. 5, the same components are denoted by the same reference numerals. In FIG. 3, a divergent light beam emitted from a semiconductor laser 10 that is a “light source” is converted into a light beam form (such as a “parallel light beam”) suitable for the subsequent optical system by a coupling lens 12, The beam is “beam-shaped” through the aperture, and is reflected by the mirror 18 while being focused by the cylinder lens 16 in the sub-scanning direction.
An image is formed as a long line image in the main scanning direction near the deflecting reflection surface of the rotary polygon mirror 20, which is an "optical deflector".

The light beam reflected by the deflecting / reflecting surface is incident on an optical scanning lens 30 constituting a "scanning optical system" while being deflected at a constant angular velocity by the rotation of the rotary polygon mirror 20 at a constant speed. The light is condensed in the vicinity of the surface to be scanned (substantially, the “photosensitive surface of the photoconductive photoreceptor”) 40 by the operation of 30, and forms a light spot on the surface to be scanned 40. The scanned surface 40 is scanned in the main scanning direction by the light spot.
The scanned surface 40 is a drum, a belt, or any other suitable shape. The photosensitive surface is moved in the sub-scanning direction (a direction perpendicular to the plane of FIG. 3) while the scanning surface 40 is in the main scanning direction. By repeating the optical scanning, writing is performed on the sightseeing surface, and an electrostatic latent image is formed. The main scanning by the light spot is performed at a constant speed by the action of the constant speed characteristic of the scanning image forming optical system including the optical scanning lens 30.

In the embodiment shown in FIG. 3, the optical scanning lens 30 itself constitutes a scanning image forming optical system. When the scanning image forming optical system includes a plurality of optical elements, that is, a plurality of lenses or a combination of a lens and a concave mirror, one or a plurality of optical scanning lenses can be included therein. . The optical scanning lens 30 is formed by molding a plastic material or a glass material. Instead of the optical scanning lens 30, a reflecting mirror having the same optical function may be used.

If the optical scanning device using the optical scanning lens according to the above embodiment is applied to an image forming apparatus such as a copying machine, a facsimile, a printer, etc., it is possible to obtain a high quality image with suppressed image deterioration. That is, the surface to be scanned by the optical scanning device is used as the surface of the photoreceptor, and the uniformly charged surface of the photoreceptor is scanned with the light spot as described above, so that the surface of the photoreceptor that is to be scanned is electrostatically charged Form a latent image. The electrostatic latent image is subjected to a known electrophotographic process such as development, transfer, fixing, and cleaning of the surface of the photoconductor. By going through the above transfer step and fixing step,
An image can be formed on transfer paper. Since the principle of such an image forming apparatus is well known, it is not shown.

[0042]

According to the first and third aspects of the present invention,
Since it is possible to manufacture a lens in which the waviness generated by the processing step or the forming step of the optical scanning lens is kept within an allowable range, an optical system satisfying the optical performance can be configured.

According to the second aspect of the present invention, it is possible to manufacture a lens in which the surface waviness caused by the processing step or the molding step of the optical scanning lens is suppressed within an allowable range, so that the optical system satisfying the optical performance. Can be configured. The invention according to claim 2 can cope with both incident and non-parallel incident light,
In the case of parallel, focal length fluctuation = beam spot position fluctuation, and the main scanning direction of the scanning optical system is substantially parallel light, which is more effective.

According to the fourth and fifth aspects of the present invention, by using the average curvature as an evaluation item in consideration of the measuring method, it is possible to manufacture a lens in which the fluctuation of the beam waist position caused by the undulation of the surface is suppressed. Therefore, an optical system satisfying the optical performance can be configured.

According to the invention of claim 6, claims 1 to
By configuring an optical scanning device using any one of the optical scanning lenses described in No. 5, a highly reliable optical scanning device can be configured without deteriorating an output image due to an increase in beam diameter. be able to.

According to the seventh aspect of the present invention, since the image forming apparatus is configured by using the optical scanning device which is less likely to cause deterioration of the output image due to the increase in the beam diameter, high image quality with reduced image deterioration is achieved. Image can be obtained.

[Brief description of the drawings]

FIG. 1 is a side view showing an optical scanning device according to an embodiment of the present invention from a direction corresponding to sub-scanning.

FIG. 2 shows an optical scanning lens used in the optical scanning device.
6 is a graph showing a relationship between a curved surface shape, a curvature, an average curvature, a maximum value of a variation amount of a curvature distribution of the curved surface, and an amplitude of undulation of the curved surface.

FIG. 3 is a side view showing an embodiment of the optical scanning device according to the present invention, as viewed from a main scanning corresponding direction.

FIG. 4 is a conceptual diagram showing an example of an apparatus for measuring a curvature distribution fluctuation amount of a curved surface of an optical scanning lens according to the present invention.

FIG. 5 is a plan view showing an example of the above-described conventional optical scanning device, and the concept of undulation of an optical scanning lens used in the optical scanning device and fluctuation of a beam waist position on a surface to be scanned.

FIG. 6 is a graph showing a beam thickening state in the conventional optical scanning device.

FIG. 7 is a graph showing the relationship between the spatial frequency of the undulation of the curved surface of the optical scanning lens and the allowable amplitude.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Laser light source 20 Optical deflector 30 Optical scanning lens 40 Scanning surface

Claims (7)

[The claims] An optical scanning lens used in a scanning imaging optical system for converging a light beam deflected by an optical deflector near a surface to be scanned, wherein a curvature of a curved surface is within an area through which the light beam of the lens passes. When the maximum value of the distribution variation amount is ΔC, ΔC ≦ 2 × w ² / {(n−1) × λ × S ′ ² } where w: beam spot radius on the surface to be scanned n: refractive index of lens λ: light source wavelength S ′: distance from the rear principal point of the scanning image forming optical system to the image plane, an optical scanning lens. 2. An optical scanning lens used in a scanning image forming optical system for converging a light beam deflected by an optical deflector near a surface to be scanned, wherein a main surface of a curved surface is located within a region through which the light beam of the lens passes. When the maximum value of the variation amount of the curvature distribution in the scanning direction is ΔC, ΔC ≦ 2 × w ² / {(n−1) × λ × F ² } where w: beam spot radius on the surface to be scanned n: lens Λ: light source wavelength F: focal length of the entire scanning imaging optical system in the main scanning direction. 3. An optical scanning lens used in a scanning imaging optical system for converging a light beam deflected by an optical deflector near a surface to be scanned, wherein a curvature of a curved surface is within a region through which the light beam of the lens passes. When the maximum value of the amount of distribution variation is ΔC, 0.2 / K ≦ ΔC × (n−1) × λ × (S ′ / w) ² ≦
2 where K is the number of optical elements from the optical deflector to the image plane w is the beam spot radius on the surface to be scanned n is the refractive index of the lens λ is the light source wavelength S 'is the rear main of the scanning imaging optical system An optical scanning lens characterized by a distance from a point to an image plane. 4. An optical scanning lens used in a scanning image forming optical system for condensing a light beam deflected by an optical deflector near a surface to be scanned, wherein a main surface of a curved surface is located within a region where the light beam of the lens passes. The average curvature in the scanning direction is 10 of q (x) and q (x).
Assuming that the following approximate curve is q0 (x), q_PV × (n−1) × λ × (F / wd) ² ≦ 1, where wd: beam spot diameter on the surface to be scanned in the main scanning direction n: Refractive index of lens λ: light source wavelength F: focal length of the entire scanning imaging optical system in the main scanning direction q_PV = maxｍq (x) -q0 (x)｝-min
An optical scanning lens characterized by {q (x) -q0 (x)}. 5. An optical scanning lens used in a scanning imaging optical system for condensing a light beam deflected by an optical deflector near a surface to be scanned, wherein an average of curved surfaces is within a region through which the light beam of the lens passes. When the curvature is q (x), and an approximate curve of order 10 or less of q (x) is q0 (x), 0.1 / K ≦ q_PV × (n−1) × λ × (S ′ / w)
d) ² ≦ 1 where wd: beam spot diameter on the surface to be scanned n: refractive index of lens λ: light source wavelength S ′: distance from the rear principal point of the scanning imaging optical system to the image surface q_PV = max ｛ q (x) -q0 (x)｝-min
An optical scanning lens characterized by {q (x) -q0 (x)}. 6. A light beam from a light source is deflected at an equal angular velocity by an optical deflector having a deflecting / reflecting surface, and the deflected light beam is condensed as a light spot on a surface to be scanned by an optical scanning lens. An optical scanning device for optically scanning a surface to be scanned at a constant speed, wherein the optical scanning device according to claim 1 is mounted thereon. 7. An image forming apparatus having the optical scanning device according to claim 6, wherein the surface to be scanned is made of a photosensitive member, and the surface to be scanned is optically scanned by the optical scanning device.
An image forming apparatus wherein an electrostatic latent image is formed on a surface to be scanned.