JP2001318334A - Optical scanner reducing shading - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical scanner which can easily reduce shading at low cost. SOLUTION: This optical scanner while deflecting the luminous flux emitted by a laser light source 1 or laser array by an optical deflector images the luminous flux on an image plane through a scanning lens 5 and makes an optical scan in the horizontal scanning direction Y' of the image plane; and the scanning lens 5 has uniform coloring transparency, and absorption characteristics and/or transmission characteristics at least in the horizontal scanning direction Y' and reduces the shading according to the shape of the scanning lens 5.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an optical scanning device with reduced shading.

[0002]

2. Description of the Related Art A scanning device is widely known for an image forming apparatus such as a copying machine, and its general configuration is, for example, as shown in FIG. While being deflected by the optical deflector, an image is formed on the scanned surface 9a (image surface) of the photoconductor 9 via the scanning lens 11, and scanning is performed in the main scanning direction. During the scanning of one line, the position of transmission through each optical element such as the scanning lens 11 also changes continuously in the main scanning direction. Therefore, the relative illuminance (light amount) of the light flux formed on the photoconductor 9
Is determined by the characteristics of the optical elements on the optical path from the optical deflector to the surface to be scanned 9a. It is well known that such a change in relative illuminance is generally referred to as shading.

In a general scanning optical system, optical elements for determining shading characteristics include an optical deflector, a scanning lens, a folding mirror, and dust-proof glass. The angle of incidence of the light beam incident on these optical elements increases from the vicinity of the optical axis perpendicular to the surface 9a to be scanned toward the periphery, so that the scanning lines on the surface 9a to be scanned can be formed with uniform illuminance. It becomes difficult, and shading occurs in which the illuminance decreases from the center position in the main scanning direction toward the periphery.

Conventionally, several methods have been proposed for reducing unevenness in the amount of light on the surface 9a to be scanned.
Japanese Patent No. 224002 discloses an illuminance correction film provided on one surface of a scanning optical system, an illuminance correction film using a difference in incident angle, and the like. According to the publication, illuminance non-uniformity is corrected by depositing an illuminance correction film on a specific surface of a scanning lens such that light intensifies toward a peripheral portion.

[0005] Further, the applicant of the present application discloses Japanese Patent Application Laid-open No. Hei 5-3030.
As disclosed in Japanese Patent No. 49, among the optical element surfaces on the optical path from the light deflecting means to the surface to be scanned, an antireflection coating is provided only on a refraction surface whose incident angle changes most greatly with the deflection of a light beam; An optical scanning device that reduces shading by, for example, gradually changing the thickness of an anti-reflection film from the center to the periphery is provided.

[0006]

However, in the above-mentioned conventional method, it is necessary to apply a surface treatment or the like for anti-reflection (increased transmission) to the optical component. Since optical components are large and have many strip shapes, the number of optical components cannot be increased. Therefore, the process time is not short, and there is a problem in production cost.
Further, if the concept of the gradient film is introduced, the process becomes more complicated.

[0007] On the other hand, the laser wavelength used in the optical scanning device is mostly in the infrared to red range, and in this wavelength range, the internal absorption Ab of most optical materials is 0.01 or less. This is the result of improvements that have been made to improve the internal absorption rate in the past, and such improvements have also resulted in high costs.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described circumstances, and has as its object to provide an optical scanning device which is low-cost and easy to realize and has reduced shading.

[0009]

In order to achieve the above object, an optical scanning apparatus according to the present invention which has reduced shading is provided.
A scanning device that forms an image on an image plane via a scanning lens while deflecting a light beam emitted from a laser light source or a laser array by an optical deflector and performs optical scanning in a main scanning direction of the image plane; At least one of the lenses constituting the lens has at least uniform coloring transparency, absorption characteristics and / or transmission characteristics in the main scanning direction, and has desired shading characteristics based on the shape of the scanning lens. And

It is desirable that the lens having the largest refractive power in the main scanning direction has the desired shading characteristics.

Further, the above-mentioned colored transparency is ND (neutral
density).

In general, the lens having the desired shading characteristics has a configuration in which the internal absorption ratio Ab at a thickness of 5 mm in the laser wavelength range satisfies the condition of 0.015 <Ab <0.15. It is.

The shading characteristic of the scanning lens may be a characteristic imparted by a lens material, or may be a characteristic imparted by adding a coloring agent to the lens material.

It is preferable that the scanning lens having the desired shading characteristics is formed by molding a resin material. In this case, the resin material is formed of an acrylic resin, and the colorant is formed of a dye. be able to.

Further, the scanning lens having the desired shading characteristics may be made of colored glass.

[0016]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows the configuration of a first embodiment of the optical scanning device to which the present invention is applied. In this embodiment, the number of scanning lenses is one. The light beam emitted from the laser light source 1 is coupled by a coupling lens system 2 and is linearly elongated in a main scanning direction Y ′ in the vicinity of a reflection surface 4a of an optical polarizer composed of a polygon mirror 4 by a cylindrical lens system 3. It is imaged. The laser reflected by the reflecting surface 4a is deflected at a constant angular velocity by the rotation of the polygon mirror 4, and the scanning lens 5, the dust-proof glass 6, and the two return mirrors 7, 8
, The light is condensed in the form of a light spot near the scanned surface 9a, and scans the scanned surface 9a at a substantially constant speed.

The specifications and arrangement of each optical component that generates shading after the optical deflector are as follows. The reference wavelength of the laser light source 1 is 650 nm, and the angle between the light beam emitted from the light source and the reference line X '(the optical axis direction orthogonal to the surface 9a to be scanned) is 60 degrees. The optical deflector is a six-sided polygon mirror 4, the distance from the center of rotation to the reflection surface 4a is 18 mm, and the rotation angle of the polygon mirror 4 when the light beam goes to the reference line X 'is 30 degrees.

The scanning lens 5 is formed from an acrylic material having excellent optical characteristics. As will be described later, the scanning lens 5 according to the present embodiment is required to have a uniform and desired internal absorption characteristic for a transmitted light beam. This kind of internal absorption property Ab may be given at the time of selecting or manufacturing the material of the target lens, focusing on the so-called colored transparency, transmission property or absorption property of the lens material itself.

A commonly used laser is monochromatic light, and its absorption characteristics and transmission characteristics near the corresponding wavelength are important. Further, regarding the colored transparency, there are two types of transparent members, that is, colorless transparent and colored (colored) transparent. Among the colored transparent materials, if they have ND (neutral density) characteristics, they can be changed to lasers having different wavelengths. This is advantageous in that it can be used in common. The characteristic of this ND (uniform in the wavelength range) is colored and transparent colored in gray, and the term "colored transparency" as used herein is used in a broad sense including gray and other achromatic colors other than colorless. . That is, the characteristics (brightness, hue) and the like of the colored color are not limited. However, an opaque member having light diffusion inside which causes cloudiness is not preferable.

In general, an optical material which is colorless and has a high transmittance is considered to be a good material, but a desired shading reduction effect may be deviated only by the absorption and transmission characteristics of a resin material. For this reason, the coloring agent is added to the resin material positively to give the desired color transparency, and the ratio of the addition of the coloring agent to the resin material (Wt%) is adjusted to correct the shading with high accuracy. It is also possible. When a dye is used as a coloring agent, turbidity is small, and when combined with an acrylic resin, problems such as color migration are small. In addition, as a dye, an anthranoquine type, an indigoid type, an azo type structure or the like is desirable.

Even if attention is paid to colored transparency, transmission characteristics or absorption characteristics as described above, in the present invention, since the characteristics and shape of the lens material itself are utilized, the gradient film and the characteristics of the characteristics can be reduced as in the prior art. There is no need to make a difference depending on the location, and there is no cost and the implementation is easy. In addition, when using resin as a material, it is possible to achieve desired absorption characteristics and transmission characteristics simply by selecting a resin material or selecting a combination of coloring agents according to the resin material, and to manufacture using an established molding method. Can be. Therefore, it is advantageous not only for controlling the shading characteristics but also for mass production and can be implemented at low cost.

In the general optical arrangement of the above-described optical scanning device, shading on the surface 9a to be scanned moves from a center position (near the reference line X ') in the main scanning direction Y' to a peripheral position in both the left and right directions. Occurs in the form of reduced illumination. Therefore, shading is reduced by using the shape of the scanning lens 5 in which the thickness at the center is large and the thickness is reduced toward the periphery. The scanning lens 5 has a shape effective for reducing the shading of the present apparatus, and a technique for controlling the lens material characteristics is generally established in the manufacturing process. The shading characteristic of the scanning lens 5, that is, the degree of reduction in the amount of transmitted light is distributed by the difference in thickness.

That is, the optical path length of the transmitting portion differs depending on the angle of incidence of the laser beam on the scanning lens 5 having power in the main scanning direction Y '(for example, the rotation angle of the polygon mirror 4). Different light amount absorptions are given in the scanning direction Y '. In the present invention, such shading characteristics are used, and shading on the image plane caused by other optical components and the like is relatively uniformed in the main scanning direction Y '. As will be described later, the shading characteristic of the scanning lens 5 having a uniform transmission characteristic in the wavelength range of the laser light source 1 is defined by the shape in the main scanning direction Y ′ described below.

The scanning lens 5 of this embodiment has a non-arcuate shape in the main scanning direction Y 'on both surfaces. The coordinates in the optical axis (reference line X') direction are X, the coordinates in the main scanning direction Y 'are Y, and the near side is Y. The radius of curvature of the shaft is R, the conic constant is K, and the higher order coefficients are M ₄ , M ₆ , M ₈ , M
_{When the number is 10} , the shape of the scanning lens 5 in the main scanning direction Y 'is represented by the following relational expression (1). ^{X = Y 2 / [R +} R√ {1- (1 + K) Y 2 / R 2} + M 4 · Y 4 + M 6 · Y 6 + M 8 · Y 8 + M 10 · Y 10 (1)

Table 1 shows the specifications of the scanning lens 5.

[Table 1]

Further, for each optical component of the first embodiment,
The main specifications are as follows. Center thickness of scanning lens 5; 21 mm Lens material of scanning lens 5; Acrylic resin, Nd = 1.4
91547.8: νd = 57.8: N650 = 1.48917 Scanning lens 5; no coating Dustproof glass 6; no coating, internal absorption ratio Ab =
0.01 / 5 mm folding mirror 7; four-layer film (alternate layer of MgF ₂ and TiO ₂ ) folding mirror 8; four-layer film (alternate layer of MgF ₂ and TiO ₂ ) Polygon mirror 4; single-layer SiO film and nd Optimized to reduce angle characteristics around λ / 2

Next, in the optical scanning device having the above configuration,
An example is given of how the shading characteristic of the scanning lens 5 is given by the transmission characteristic of the lens material, and how it affects shading on the surface 9a to be scanned.

When the rotation angle of the polygon mirror 4 is taken as a variable as the scanning angle and the internal absorption ratio Ab is taken as a comparison parameter, the relative transmission including the surface reflection of the scanning light beam of the scanning lens 5 is shown in Table 2 below. Table 3 shows the shading characteristics on the image plane. In this example, the internal absorption ratio Ab equivalent to 5 mm was set to Ab = 0.045 in the example intended to reduce shading, and Ab = 0.005, which is a representative value of the same acrylic resin as a comparative example.

[0029]

[Table 2]

[0030]

[Table 3]

FIG. 2 is a diagram plotting the relative transmittance in Table 2, and FIG. 3 is a diagram plotting the shading characteristics in Table 3 with the horizontal axis of the polygon rotation angle. As is apparent from FIG. 2, in the embodiment in which the internal absorption Ab is set to a moderately high value (Ab = 0.045), the scanning lens 5 transmits light that is inconsistent with the normal transmittance at Ab = 0.005. The characteristics were shown. That is, coupled with the shape whose thickness changes gradually from the reference line X ′ (polygon rotation angle of 30 deg) to the peripheral angle, the selection of a moderately high characteristic of Ab = 0.045 allows transmission near the center. The transmittance is low, and the transmittance increases toward the periphery.

As shown in FIG. 3, in the optical system as a whole, the shading which was about 10% in the comparative example in which Ab = 0.005 was inevitably changed in the example in which Ab = 0.045. It can be seen that the improvement was favorably improved to about 3.4% only by selecting.

The selection of the internal absorption ratio Ab will be described. In the material of the scanning lens 5 and the wavelength range of the laser according to the present embodiment, it is desirable that the numerical value range is 0.015 <Ab <0.15 with respect to the lens thickness of 5 mm.

For example, the center thickness and the peripheral thickness are each 20 mm.
When the shading is about 5 mm, the above-mentioned upper limit has a shading reduction effect of about 6%, and when the shading is relatively small such as when the dustproof glass 9 is not used, there is a sufficient reduction effect. If the upper limit is exceeded, the effect is relatively small. In the same case, the lower limit has a reduction effect of about 40%, and it is possible to cope with an extremely large shading such as eliminating the anti-reflection coat of the dustproof glass 9. That is, if the lower limit is exceeded, the loss of light quantity increases, which is not desirable.
In addition, the vicinity of the above upper and lower limits is accompanied by lack of effects, side effects, and the like in both cases, so that the following numerical ranges are more preferable.
0.03 <Ab <0.12

Incidentally, the laser light source used in the optical scanning device is often infrared to red, and the internal absorption Ab of most optical materials is less than 0.01 in this wavelength range. This is the result of repeated improvements in the improvement of the internal absorption ratio Ab. However, in the application of the present invention, the number of cases where a material having a large internal absorption ratio Ab can be selected increases, leading to a reduction in cost. When attention is paid to colored transparency in selection of such a material, it is effective to configure one of the scanning lenses with colored glass. For example, blue plate glass may be used. In addition, it is also possible to select from commercially available glass for color filters, and in this case, the lens can be easily processed by polishing or molding.

FIG. 4 shows the configuration of a second embodiment of the optical scanning device to which the present invention is applied. In the second embodiment, the scanning lens system 5 includes two lenses including a first scanning lens 5a and a second scanning lens 5b. Further, a soundproof glass 10 is provided near the polygon mirror 4. The soundproof glass 10 is used when the weight of the noise required for the system is high when the polygon motor has a high-speed rotation specification. Light passes into and out of the soundproof glass 10 twice when the light enters and exits the polygon mirror 4, but does not affect shading at the time of incidence. Therefore, only the effect at the time of emission needs to be considered.

Since the first scanning lens 5a receives almost all the power in the main scanning direction Y ', the concept of the internal absorption (giving the shading characteristic) is applied to the first scanning lens 5a. In the case where the scanning lens 5 is composed of a plurality of lenses as in this example, the refractive power in the main scanning direction Y ′ (=
By selecting a lens having the largest reciprocal of the focal length) and the largest difference between the center thickness and the peripheral thickness, shading can be effectively reduced.

Each of the scanning lenses 5a and 5b is formed of a polyolefin resin. Each shape in the main scanning direction Y 'is
It can be calculated using the above-described relational expression (1). Tables 4 and 5 below list the specifications of the scanning lenses 5a and 5b.

[Table 4]

[0039]

[Table 5]

Further, for each optical component of the second embodiment,
The main specifications are as follows. 18 mm Central thickness of the first scanning lens 5a; 4.5 mm Central thickness of the second scanning lens 5b; Material of each scanning lens; Both are polyolefin resin materials; Nd = 1.53046: νd = 55.5: N650 = 1.52787 Polygon mirror 41: SiO single layer film, nd = λ / 2 First scanning lens 5a; No coating Second scanning lens 5b; No coating, internal absorption fixed at 0.01 / 5 mm Dustproof glass 6; Double layer film (Al ₂ O ₃ , MgF ₂ ) Folded mirror 7; Four-layer film (Alternate layer of MgF ₂ and TiO ₂ ) Folded mirror 8; Four-layer film (Alternate layer of MgF ₂ and TiO ₂ ) Soundproof glass 10; Two-layer film (SiO, MgF ₂ )

In evaluating the shading of the optical scanning device having the above-described configuration, the internal scanning rate Ab selected by the first scanning lens 5a is used as a comparison parameter, and the first scanning lens of the embodiment intended to reduce shading. Ab = 0.048 / 5 mm for 5a, and Ab = 0.010 / 5 mm for the first scanning lens 5a of the comparative example, which is a typical value of the same polyolefin resin. Table 6 below shows the relative transmittance of the first scanning lens 5a, and Table 7 shows shading characteristics on the image plane.

[0042]

[Table 6]

[0043]

[Table 7]

FIG. 5 is a diagram plotting the relative transmittance of Table 6, and FIG. 6 is a diagram plotting the shading characteristics of Table 7 with the polygon rotation angle as the horizontal axis. As is clear from FIGS. 5 and 6, the internal absorptivity was set to a moderately high value (Ab = 0.04).
8), the general numerical value Ab = 0.
The change of the relative transmittance is larger than that of the comparative example of No. 010, and the transmittance particularly at the central portion (around the polygon rotation angle of 30 deg) decreases. Along with this, the shading of the whole system is inevitably observed as shown in FIG. 6, but in the comparative example with Ab = 0.010, it is about 5.6%, but the material with Ab = 0.047 is selected. In this example, the shading is made uniform to about 1.6%, and it can be seen that the shading is improved very well.

In the embodiment described above, an optical system in which the relative illuminance decreases from the center to the periphery in the main scanning direction Y 'is described as an example. If the illuminance increases toward the periphery, contrary to the general distribution of the shading characteristics, a scanning lens having a negative refractive power (absolute value) in the main scanning direction Y 'is selected. By applying the present invention as in the embodiment, the shading can be reduced.

In each of the embodiments described above, the case where one laser light source (LD) is used has been described.
Is synthesized in a crossing method, it is also applicable to the case of a laser array. In this case, when combining a plurality of LDs using polarized light using a prism, a 1 / 2λ plate may be used in combination.

[0047]

As is apparent from the above description, in the optical scanning device according to the present invention, at least one of the lenses constituting the scanning lens has at least the uniform colored transparency, absorption characteristics and absorption characteristics in the main scanning direction. And / or having a transmission characteristic and a desired shading characteristic based on the shape of the scanning lens, it is possible to easily reduce the relative illuminance unevenness on the image plane.

According to the configuration in which the lens having the largest refractive power in the main scanning direction has the desired shading characteristics, shading generally occurs so that the amount of light decreases from the center in the main scanning direction to the periphery. In this case, the shading can be effectively reduced by giving the above-described shading characteristic to a scanning lens having a large refractive power in the main scanning direction and a positive power.

Further, the above-mentioned colored transparency is ND (neutral
According to the configuration having the density) characteristic, there is a degree of freedom in changing the laser wavelength in reducing shading.

In the lens having the desired shading characteristics, according to the configuration in which the internal absorptance Ab at a thickness of 5 mm in the laser wavelength range satisfies the condition of 0.015 <Ab <0.15, the general laser wavelength In the optical scanning device using the method, shading can be effectively reduced.

According to the configuration in which the shading characteristic of the scanning lens is a characteristic given by the lens material, shading can be reduced only by selecting the material of the scanning lens, and an increase in cost can be avoided.

According to the configuration in which the shading characteristic of the scanning lens is a characteristic imparted by adding a coloring agent to the lens material, the shading characteristic can be easily controlled only by adding the coloring agent to the lens material. Since the processing method has been established, shading can be reduced with high accuracy and at low cost.

According to the configuration in which the scanning lens having the desired shading characteristics is formed by molding a resin material, shading can be reduced at low cost because it can be manufactured by an established molding method and mass-produced.

The resin material is made of an acrylic resin, and the colorant is made of a dye. The dye material has excellent optical characteristics, and the use of the dye reduces turbidity and is excellent in transparency. According to the combination, the occurrence of color migration is small.

Further, according to the configuration in which the scanning lens having the desired shading characteristics is made of colored glass, it can be selected from commercially available glass for color filters, and can be easily processed into a lens by polishing or molding.

[Brief description of the drawings]

FIG. 1 is a plan view showing the configuration of a first embodiment of an optical scanning device according to the present invention.

FIG. 2 is a diagram showing a relative transmittance of a scanning lens in the first embodiment.

FIG. 3 is a diagram illustrating shading characteristics of the optical scanning device according to the first embodiment.

FIG. 4 is a plan view showing a configuration of a second embodiment.

FIG. 5 is a diagram showing a relative transmittance of the second embodiment.

FIG. 6 is a diagram illustrating shading characteristics of a second embodiment.

FIG. 7 is a perspective view illustrating a typical configuration of an optical scanning device.

[Explanation of symbols]

 Reference Signs List 1 laser light source 4 polygon mirror (optical deflector) 5, 5a, 5b scanning lens Y 'main scanning direction 9a scanned surface (image surface)

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI theme coat ゛ (reference) H04N 1/036 B41J 3/00 D 1/113 H04N 1/04 104A F-term (reference) 2C362 BA84 BA86 2H045 AA01 BA02 BA23 CA68 CB35 2H087 KA19 LA22 NA00 PA01 PA02 PB01 PB02 QA02 QA03 QA07 QA12 QA14 QA22 QA34 QA37 QA41 RA04 RA05 RA12 RA13 RA43 5C051 AA02 CA07 DB02 DB22 DB24 DB30 DC04 DC07 DE18 FA03 BA08A08

Claims (9)

[Claims] A scanning device that forms an image on an image plane via a scanning lens while deflecting a light beam emitted from a laser light source or a laser array by an optical deflector, and optically scans the image plane in a main scanning direction. , At least one of the lenses constituting the scanning lens has at least uniform coloring transparency, absorption characteristics and / or transmission characteristics in the main scanning direction,
An optical scanning device having reduced shading, wherein the optical scanning device has desired shading characteristics based on the shape of the scanning lens. 2. The optical scanning apparatus according to claim 1, wherein the lens having the largest refractive power in the main scanning direction has the desired shading characteristics. 3. The colored transparency is ND (neutral den
The optical scanning device according to claim 1, wherein the optical scanning device has reduced shading. 4. The lens having the desired shading characteristic, wherein the internal absorption ratio Ab at a thickness of 5 mm in the laser wavelength range satisfies the condition of 0.015 <Ab <0.15. 4. The optical scanning device according to any one of items 1 to 3, wherein shading is reduced. 5. The optical scanning device according to claim 1, wherein the shading characteristic of the scanning lens is a characteristic given by a lens material. 6. The light with reduced shading according to claim 1, wherein the shading characteristic of the scanning lens is a characteristic imparted by adding a coloring agent to the lens material. Scanning device. 7. The optical scanning device according to claim 1, wherein the scanning lens having the desired shading characteristics is formed by molding a resin material. 8. The resin material is made of an acrylic resin,
The optical scanning device according to any one of claims 1 to 7, wherein the colorant comprises a dye. 9. The optical scanning device according to claim 1, wherein the scanning lens having the desired shading characteristics is made of colored glass.