JP2004145352A - Optical scanner and image forming apparatus using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical scanner in which the quantity of light quantity variation due to internal absorption of a plastic lens is suppressed practically sufficiently small, as an optical scanner using a short-wavelength light source of ≤500 nm. <P>SOLUTION: The optical scanner has a deflection optical system which deflects the light beam from a light source and a scanning imaging lens system which images the light beam from the deflection optical system on a scanned surface, wherein the wavelength of the light source is ≤500 nm and the scanning imaging lens system has at least one plastic lens, and the inequality of Lmax-Lmin<10 mm is satisfied, where Lmax is the maximum value of the total light beam passage distance which corresponds to an angle of deflection from the optical axis of the plastic lens and the Lmin is the minimum value. <P>COPYRIGHT: (C)2004,JPO

Description

The present invention relates to an optical scanning device used for an image forming apparatus such as a laser printer, a digital copying machine, and a multifunction printer.

Generally, this type of optical scanning device deflects a light beam from a laser light source by a polygon mirror and forms an image as a light spot on a surface to be scanned by an imaging lens system.

半導体 Semiconductor lasers and the like are frequently used as laser light sources, and divergent light emitted from the laser light source is converted into a substantially parallel light beam by a collimator lens, and the outer shape of the light beam is limited by an aperture. The light beam whose outer shape is limited is deflected by a polygon mirror that rotates at a constant angular velocity and enters the imaging lens system. The imaging lens system has an fθ characteristic of scanning a light beam deflected at a constant angular velocity on a surface to be scanned arranged at a predetermined interval at an equal distance velocity, and forms a minute light spot over the entire scanning area. It is necessary that the curvature of field be well corrected.

Also, since the polygon mirror has a processing error on the mirror surface, a vibration of the rotation axis, and the like, many imaging lens systems are tilted to correct a deviation of a scanning position in a direction perpendicular to the main scanning direction, that is, in the sub-scanning direction. A correction function is provided. For this reason, the imaging lens system is an anamorphic lens system having different imaging characteristics in the main scanning direction and the sub-scanning direction.

Conventionally, an imaging lens system is processed by a glass material so as to have a toric surface and a cylindrical surface, and an antireflection film is applied to this type of glass lens by vapor deposition or the like. On the other hand, processing of glass lenses is difficult and expensive, and in recent years, plastic lenses that are low in cost and that can correct aberrations with a free shape are frequently used.

Further, since a semiconductor laser conventionally used as a light source is an infrared laser (780 nm) or a visible laser (675 nm), a polygon mirror, a folding mirror, and the like have a high reflectance and a small wavelength dependency and small angle dependency. Copper mirrors have been used.

FIG. 8 shows the reflectivity characteristics of the copper film itself, and FIG. 9 shows the reflectivity characteristics of a conventionally used copper mirror. In this conventional mirror, a copper film is formed on an aluminum base material, and alumina (Al2O3) and SiO2 are further deposited thereon. It can be seen that excellent reflection characteristics are exhibited in the wavelength bands of the infrared laser and the visible laser.

Furthermore, the development of an optical scanning device capable of obtaining a minute spot shape using a light source of a short wavelength has recently been promoted due to a demand for higher resolution.

(Issue 1)
However, as is clear from FIGS. 8 and 9, the reflectance of the copper mirror decreases as the wavelength becomes shorter, and the wavelength dependence and the angle dependence of the reflectance also deteriorate. When a copper mirror is used with a short-wavelength laser as in the prior art, it is necessary to increase the power of the laser or use a collimator lens having a bright F-number in order to secure a predetermined light amount. Therefore, a burden is placed on the laser itself, and there are factors for cost increase such as increasing the number of collimator lenses in order to satisfactorily correct aberrations.

半導体 In addition, a semiconductor laser, which is a light source, has a temperature characteristic of an oscillation wavelength, so that a wavelength change in an operating environment is inevitable. Therefore, it is required that optical characteristics such as transmittance and reflectance of optical components used in the scanning optical system have little change near the oscillation wavelength of the laser. Copper mirrors show good properties in infrared lasers and visible lasers, but at wavelengths of 600 nm and below, the wavelength dependence of the reflectance causes uneven light quantity due to environmental fluctuations, that is, uneven image density. .

Further, due to the angle dependence of the reflectance, the image density was not uniform between the scanning center and the scanning end, and was far from high-quality images.

Therefore, the present invention provides an optical scanning device using a short wavelength light source of 500 nm or less,
It is an object of the present invention to provide an optical scanning device using a reflection mirror having a high absolute reflectance and having a small wavelength dependency and a small angle dependency.

(Issue 2)
However, the optical material used as a plastic lens generally decreases in transmittance due to internal absorption in the material as the wavelength becomes shorter, so that an optical scanning device using a short wavelength light source has a high cost. Glass lenses have been used.

FIG. 15 is a graph showing the transmittance of a general optical resin. In the vicinity of the oscillation wavelength of the infrared laser (780 nm) and visible laser (675 nm) conventionally used as a light source, the change in transmittance due to internal absorption is almost negligible, but a short wavelength light source near 400 nm was used. In this case, the decrease in transmittance due to internal absorption cannot be ignored. Further, since the light passage distance in the plastic lens changes at each image height, image deterioration due to uneven light amount distribution at the scanning image plane position has become a problem rather than a decrease in absolute light amount.

半導体 In addition, a semiconductor laser, which is a light source, has a temperature characteristic of an oscillation wavelength, so that a wavelength change in an operating environment is inevitable. Therefore, it is required that optical characteristics such as transmittance and reflectance of optical components used in the scanning optical system have little change near the oscillation wavelength of the laser. When a plastic lens is used in a short wavelength region near 400 nm, as shown in FIG. 15, there is a problem of image density unevenness due to light quantity fluctuation on the surface to be scanned due to wavelength dependence of transmittance.

Accordingly, it is an object of the present invention to provide an optical scanning device in which unevenness in light amount distribution is suppressed and image density is uniform.

In order to achieve the object, the present invention provides an optical scanning device that deflects a light beam from a light source and forms an image on a surface to be scanned.
A deflection optical system that deflects the light beam from the light source, and a scanning imaging lens system that forms an image of the light beam from the deflection optical system on the surface to be scanned.
The wavelength of the light source is 500 nm or less,
The scanning image forming lens system has at least one plastic lens, and when the maximum value of the total ray passing distance according to the deflection angle of the plastic lens from the optical axis is Lmax, and the minimum value is Lmin,
Lmax-Lmin <10mm
Take a configuration that satisfies

According to the present invention, by using a lens that satisfies Lmax−Lmin <10.0 (mm), the amount of fluctuation in the amount of light due to the internal absorption of the plastic lens can be sufficiently reduced in practical use.

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a cross-sectional view of a main part of an optical scanning device that best illustrates the features of the present invention. After the divergent light from the semiconductor laser 1 as the light source is converted into a substantially parallel light beam by the collimator lens 2, the aperture 3 limits the light beam diameter so that a desired spot diameter is obtained. The semiconductor laser used in this embodiment is a gallium nitride based semiconductor laser, and its oscillation wavelength is 408 nm. Reference numeral 5 denotes a rotating polygon mirror (polygon mirror) that scans the light beam from the light source toward the surface to be scanned, and scans the reflected light from the polygon mirror 5 with minute light over the entire scanning area by scanning imaging lenses 6 and 7. Form into spots. Further, the scanning imaging lenses 6 and 7 are required to have fθ characteristics for converting a constant angular velocity light beam deflected by the polygon mirror 5 into a constant distance velocity light beam.

The scanning imaging lenses 6 and 7 used in the present embodiment may be made of glass or plastic, but in the case of a plastic lens, Lmax described in the fourth and fifth embodiments is used. −Lmin <3 · log ₁₀ 0.93 / S, S = log ₁₀ (1−3.55 × 10 ⁸ / λ ⁴ ), λ: It is preferable to use a lens that satisfies the wavelength (nm) of the light beam.

Or a lens that satisfies Lmax−Lmin <10.0 (mm) is preferably used.

In addition, at least one of a reflection mirror, a filter, and an optical thin film deposited on an optical member, which is a correction member for correcting unevenness in the light amount distribution of the sixth embodiment, may be used in the present embodiment.

{Circle around (2)} Further, an optical member having the reverse characteristic to the transmittance spectral characteristic of the optical resin of the seventh embodiment (for example, the reflectance b of the folding mirror) may be used. As an optical member having characteristics opposite to the transmittance spectral characteristics of the optical resin, a filter or an optical thin film deposited on an optical member may be used in addition to the folding mirror.

Further, the parallel light beam is once focused on the polygon mirror 5 in the sub-scanning direction by the cylindrical lens 4 and the polygon mirror 5 and the surface 8 to be scanned are brought into an optically conjugate relationship in the sub-scanning cross section. 5 can be corrected.

Here, the relationship between the complex refractive index and the reflectance of the metal film reflecting mirror will be described. When the complex refractive index N of the metal film is defined as follows,
N (λ) = n (λ) −ik (λ) where n, k> 0
n (λ): real part of complex refractive index i = √−1
k (λ): imaginary part of complex refractive index (extinction coefficient)
λ: wavelength reflectance R is
^{R = {(n0-n)} 2 + k 2} / {(n0 + n) 2 + k 2}
Can be expressed as Here, n0 is the refractive index of the incident medium, and normally, n0 = 1.0.

Expanding the equation further,
^{R = 1-4n / (k 2 +} n 2 + 2n + 1)
When the lower limit of the reflectance of the metal reflecting mirror used in the optical scanning device is 0.8,
^{1-4n / (k 2 + n 2} + 2n + 1)> 0.8
^{k 2> -n 2 + 18n-} 1
k> √ (−n ² + 18n−1)
It is led. Here, the right side is set to A, and the complex refractive index and A of a typical metal film are summarized in Table 1.

From Table 1, it can be seen that for copper (Cu), k> A on the longer wavelength side than 600 nm and the reflectance exceeds 80%, but k <A on the shorter wavelength side below 600 nm, and the reflectance does not exceed 80%. . Further, for aluminum (Al) and silver (Ag), k> A at 400 to 800 nm, so that a sufficient light amount can be secured even when a light source of 500 nm or less is used.

Table 2 summarizes the reflectance R of each metal film. This is the reflectance R when the light beam having the wavelength λ is perpendicularly incident on the incident surface.

FIG. 2 divides the reflectance R of the aluminum (Al) film into S-polarized light, which is a component wave oscillating perpendicular to the incident surface, and P-polarized light, which is a component wave oscillating parallel to the incident surface. The display was shaken at 20 °, 40 °, and 60 °.

Here, a general process of forming an anodic oxide film on the surface of the aluminum base material will be described.

The polygon mirror used in the present embodiment is made of aluminum as a base material, and a dozen or so of such polygon blanks are used as an anode in an electrolytic solution (such as boric acid) satisfying certain conditions. When electrolysis is performed at a voltage of 30 to 40 V for 5 to 10 seconds, an oxide film is formed on the surface. This alumite film is excellent in adhesion and uniformity and can be controlled by the electrolytic conditions and time, so that the film thickness can be easily controlled. In the present embodiment, the electrolysis conditions are set so that the angle characteristics are minimized near 408 nm. Further, in order to form a dielectric film as a protective layer on the anodic oxide film, the film may be formed by known deposition or dipping.

In the present embodiment, not only aluminum was used for the first layer of the metal film of the polygon mirror 5, but also aluminum was used for its base material. By doing so, it is possible to omit the step of forming the metal reflection film on the base material, so that cost reduction can be achieved.

Although it is possible to satisfy the above-mentioned reflectance with a silver film, it is desirable to use aluminum because silver is expensive and environmental degradation is severe.

However, in the present invention, the base material is not limited to a metal such as aluminum. An insulator may be used as long as it satisfies various characteristics required for the polygon mirror.

FIG. 3 shows an alumina (A) having a function of reducing the angle dependency in an aluminum film.
12 shows the reflection characteristics of a polygon mirror formed by evaporating (12O3) and further forming a protective film (dielectric film) thereon. With such a film configuration, the angle dependency of the polygon mirror in P-polarized light and S-polarized light is reduced, and the durability is improved.

FIG. 4 is a cross-sectional view of a main part of an optical scanning device according to a second embodiment of the present invention in the sub-scanning direction. Although not shown here, the incident optical system from the semiconductor laser to the polygon mirror is the same as in the first embodiment. When an optical scanning device is used as the image forming apparatus, the scanning light is often bent in the sub-scanning direction due to the arrangement of each unit of the image forming apparatus. In the present embodiment, the light beam scanned horizontally by the polygon mirror 5 passes through the scanning imaging lenses 6 and 7, is bent once by the folding mirror 9 in the vertical direction, and is guided to the photosensitive drum 10.

The folding mirror 9 is generally formed by depositing a metal film on the surface of a glass base material. In this embodiment, aluminum is deposited as described above, and a sufficient amount of light can be obtained even when a light source of 500 nm or less is used. We have succeeded in securing.

In order to further increase the reflectance, it is effective to deposit a dielectric film thereon.

{Circle over (5)} FIG. 5 shows the spectral reflectance of a mirror having a MgF2 film and a ZrO2 film deposited on an aluminum film. Compared with the case of the single layer of the aluminum film shown in FIG. 2, the reflectance is increased by several%. Further, in order to produce a mirror with increased reflectance, it is preferable to alternately form a plurality of low refractive index films and high refractive index films.

Further, although the aluminum film is used in the present embodiment, the present invention is not limited to this. Any metal film that satisfies k> √ (−n ² + 18n−1) can exert its effect.

The scanning imaging lenses 6 and 7 used in the present embodiment may be made of glass or plastic, but in the case of a plastic lens, Lmax described in the fourth and fifth embodiments is used. −Lmin <3 · log ₁₀ 0.93 / S, S = log ₁₀ (1−3.55 × 10 ⁸ / λ ⁴ ), λ: It is preferable to use a lens that satisfies the wavelength (nm) of the light beam.

Or a lens that satisfies Lmax−Lmin <10.0 (mm) is preferably used.

In addition, at least one of a reflection mirror, a filter, and an optical thin film deposited on an optical member, which is a correction member for correcting unevenness in the light amount distribution of the sixth embodiment, may be used in the present embodiment.

{Circle around (2)} Further, an optical member having the reverse characteristic to the transmittance spectral characteristic of the optical resin of the seventh embodiment (for example, the reflectance b of the folding mirror) may be used. As an optical member having characteristics opposite to the transmittance spectral characteristics of the optical resin, a filter or an optical thin film deposited on an optical member may be used in addition to the folding mirror.

FIG. 6 is a perspective view of an optical scanning device according to a third embodiment of the present invention. This embodiment is different from the first and second embodiments in that a scanning imaging mirror 11 is used instead of the scanning imaging lens 7. As the scanning image forming mirror 11, a free-form surface mirror has recently been used in addition to a cylindrical mirror and a spherical mirror, with the improvement of plastic molding technology. An advantage of using the scanning image forming mirror 11 in the scanning image forming system is that the effect of the image forming lens and the effect of the return mirror are simultaneously provided. Therefore, the folding mirror described in the second embodiment can be eliminated, and cost reduction can be expected by reducing the number of parts.

The scanning imaging lens 6 used in the present embodiment may be made of glass or plastic, but in the case of a plastic lens, Lmax-Lmin described in the fourth and fifth embodiments. <3 · log ₁₀ 0.93 / S, S = log ₁₀ (1−3.55 × 10 ⁸ / λ ⁴ ), λ: It is preferable to use a lens that satisfies the wavelength (nm) of the light beam.

Or a lens that satisfies Lmax−Lmin <10.0 (mm) is preferably used.

In addition, at least one of a reflection mirror, a filter, and an optical thin film deposited on an optical member, which is a correction member for correcting unevenness in the light amount distribution of the sixth embodiment, may be used in the present embodiment.

{Circle around (2)} Further, an optical member having the reverse characteristic to the transmittance spectral characteristic of the optical resin of the seventh embodiment (for example, the reflectance b of the folding mirror) may be used. As an optical member having characteristics opposite to the transmittance spectral characteristics of the optical resin, a filter or an optical thin film deposited on an optical member may be used in addition to the folding mirror.

も Also in the present embodiment, a sufficient amount of light can be ensured by using an aluminum film for the scanning imaging mirror despite the use of a light source of 500 nm or less.

In addition, although an aluminum film is used in each of the embodiments, the present invention is not limited to this. If a metal film satisfies k> √ (−n2 + 18n−1), the effect can be exerted.

て Considering the reflectivity characteristics of FIGS. 2, 3 and 5, the lower limit of the wavelength of the light source used in the first to third embodiments of the present invention is preferably 380 nm or more.

The semiconductor laser 1, which is a light source used in the embodiment of the present invention, may be a multi-beam of two or more beams.

FIG. 10 is a sectional view of a main part of an optical scanning device which best illustrates the features of the present invention. After the divergent light from the semiconductor laser 1 as a light source is converted into a substantially parallel light beam by the collimator lens 2, the light beam diameter is limited by the stop 3 so that a desired spot diameter is obtained. The semiconductor laser 1 used in the present embodiment is a gallium nitride based semiconductor laser, and its oscillation wavelength is 408 nm. Reference numeral 5 denotes a rotating polygon mirror (polygon mirror) that scans the light beam from the light source toward the surface to be scanned, and scans the reflected light from the polygon mirror 5 using the scanning and imaging lenses 6 and 7 to generate minute light over the entire scanning area. Form into spots. Further, the scanning imaging lenses 6 and 7 are required to have fθ characteristics for converting a constant angular velocity light beam deflected by the polygon mirror 5 into a constant distance velocity light beam. Further, the parallel light beam is once focused on the polygon mirror 5 in the sub-scanning direction by the cylindrical lens 4 and the polygon mirror 5 and the surface 8 to be scanned are brought into an optically conjugate relationship in the sub-scanning cross section. 5 can be corrected.

Here, the scanning imaging lenses 6 and 7 used will be described in detail. The scanning imaging lens 6 is a glass lens made of a glass material BSL-7 (manufactured by OHARA), and has an antireflection film deposited on the 6a and 6b surfaces through which the light beam passes. The scanning imaging lens 7 is an injection-molded plastic lens made of ZEONEX480 (manufactured by Zeon Corporation) which is an optical resin.

The transmittance of the optical member is considered to be divided into a surface reflection component P (reflection coefficient) and an internal transmittance τ.
Total transmittance T (λ) = P (λ) × τ (λ) (Equation 1)
The reflection coefficient P depends on the refractive index n (λ) of the optical member, and can be expressed by the following equation.
Reflection coefficient P (λ) = 2 · n (λ) / (n (λ) ² +1) (Equation 2)

Further, the internal transmittance depends on the thickness t of the optical member, and the following equation is established from Lambert's law.
Internal transmittance τ2 (λ) = τ1 (λ) ^{t2 / t1} (formula 3)
Since ZEONEX480 has a refractive index n (408 nm) of 1.5402 and a total transmittance at a thickness of 3 mm of T0 (408 nm) = 0.902 from the graph of FIG. 7, the internal transmittance is τ0 (408 nm) = 0. 987.

Assuming that the maximum ray passage distance of the plastic lens is Lmax and the minimum ray passage distance is Lmin,
τ1 (408 nm) = τ0 (408 nm) ^{Lmax / 3}
τ2 (408 nm) = τ0 (408 nm) ^{Lmin / 3}
T1 / T2 = τ1 (408 nm) / τ2 (408 nm) = τ0 (408 nm) ^{(Lmax−Lmin) / 3}
Therefore, the ratio of the transmittance depends on the difference in the light ray passage distance. In the present embodiment, since Lmax = 7.50 (mm) and Lmin = 3.21 (mm), T1 / T2 = 0.981, and the amount of light fluctuation due to internal absorption is suppressed to 1.9%. Is possible.

According to the results verified by the inventor,
Lmax-Lmin <3 · log ₁₀ 0.93 / S
If S = log ₁₀ (1−3.55 × 10 ⁸ / λ ⁴ ), and λ is the wavelength (nm) of the light beam, the amount of fluctuation in the amount of light due to internal absorption of the plastic lens can be suppressed to a practically small value. it can.

According to the results of verification by the inventor, if Lmax−Lmin <10.0 (mm), the fluctuation in the amount of light due to the internal absorption of the plastic lens can be suppressed to a practically sufficiently small value.

FIG. 11 is a diagram illustrating a fifth embodiment of the present invention. The difference from the fourth embodiment is that two injection-molded plastic lenses are used. In recent years, the cost of laser printers has been reduced and the cost of laser scanner units has been further reduced. The plastic lens is inexpensive and can form a free-form curved surface, which is impossible with a glass lens, so that it is superior to a glass lens from the viewpoint of aberration correction.

In this embodiment, by optimizing the shapes of the two plastic lenses, the polygon mirror and the surface to be scanned have a conjugate relationship, the scanning beam has fθ characteristics, and the field curvature is successfully corrected. are doing. However, by using two plastic lenses, the distance that light rays pass through the plastic lens is longer than when using one plastic lens as in the fourth embodiment.

In the present embodiment, the thickness of each plastic lens is set so as to satisfy the above-mentioned conditional expression regarding the difference in the light ray passage distance. In the present embodiment, Lmax = L10 + L20 and Lmin = L11 + L21. As a result, the maximum value of the total light beam passing distance of the two plastic lenses (material: ZEONEX480) is Lmax = 18.10 (mm), the minimum value of the total light beam passing distance is Lmin = 12.33 (mm), T1 / T2 = 0.076, and the amount of fluctuation in the amount of light due to internal absorption can be suppressed to 2.4% even though two plastic lenses are used.

FIG. 12 is a sectional view of a sub-scanning system of an optical scanning device according to a sixth embodiment of the present invention. The scanning optical system used here uses two scanning image forming lenses, and at least one uses a plastic lens.

Here, attention is paid to the difference in the incident angle i incident on the return mirror 9 at each scanning angle. For example, when the ray passage distance of the plastic lens at the scanning center is longer than that at the scanning end (the fourth embodiment) In such a case, by designing the reflectivity of the return mirror to decrease as the angle of incidence i increases (see FIG. 13), it is possible to further suppress the fluctuation of the total light amount distribution on the surface to be scanned. It becomes possible.

The vertical axis in FIG. 13 is a reflectance ratio (%) when the reflectance at an incident angle of 60 ° is taken as a denominator and an arbitrary incident angle is used as a numerator.

上 記 In addition to the folding mirror, as a correction member for correcting the unevenness in the light amount distribution, an optical thin film deposited on a filter or an optical member has the above-mentioned effect.

FIG. 14 is a graph showing the spectral characteristics of the optical resin and the mirror for explaining Example 7 of the present invention. As mentioned above, the semiconductor laser, which is the light source, has a temperature characteristic of the oscillation wavelength, which inevitably causes a wavelength change under the use environment. Therefore, optical characteristics such as transmittance and reflectance of optical components used in the scanning optical system are required. Is required to have little change near the oscillation wavelength of the laser.

Here, a PC (polycarbonate) manufactured by Teijin Chemicals Limited will be described as an example.
A semiconductor laser used as a light source is a gallium nitride-based semiconductor laser, and its oscillation wavelength is 408 nm. Assuming that there is a wavelength variation of ± 10 nm around 408 nm in the use environment, the variation in the amount of light due to the optical resin is about 1.0% as shown by the resin transmittance a in FIG. However, by using an optical member having a characteristic reverse to the transmittance spectral characteristic of the optical resin (for example, the reflectance b of the folding mirror), the total light quantity variation rate c can be suppressed to about 1/20 of that. As an optical member having characteristics opposite to the transmittance spectral characteristics of the optical resin, in addition to the folding mirror, a filter or an optical thin film deposited on the optical member has the above effect.

The optical resins used in Examples 4 to 7 are only examples of the resin material. The present invention is not limited to a part of optical resins, but has the same effect on other optical resins when transmittance becomes worse due to internal absorption as the wavelength becomes shorter.

、 Considering the reflectance characteristics shown in FIGS. 14 and 15, the lower limit of the wavelength of the light source used in Examples 4 to 7 of the present invention is preferably 380 nm or more.

The number of plastic lenses constituting the scanning optical system used in the fourth to seventh embodiments of the present invention may be three or more.

The semiconductor laser 1, which is the light source used in the fourth to seventh embodiments of the present invention, may be a multi-beam of two or more beams. If the synthetic optical system has a positive power in the main scanning direction and the sub-scanning direction (to form an image on the surface to be scanned), the plastic lens alone may have a positive power or a negative power.

FIG. 7 is a cross-sectional view of a main part of an image forming apparatus using the optical scanning device of the present invention in the sub-scanning direction. Code data Dc is input to the image forming apparatus 100 from an external device 200 such as a personal computer. The code data Dc is converted into image data (dot data) Di by the printer controller 121 in the image forming apparatus 100. This image data Di is input to the optical scanning unit 120 having the configuration shown in the first to seventh embodiments. The light scanning unit 120 emits a light beam Lb modulated in accordance with the image data Di, and the light beam Lb scans the photosensitive surface of the photosensitive drum 101 in the main scanning direction.

The photosensitive drum 101, which is an electrostatic latent image carrier (photoconductor), is rotated clockwise by a motor 105. Then, with this rotation, the photosensitive surface of the photosensitive drum 101 moves in the sub-scanning direction perpendicular to the main scanning direction with respect to the light beam Lb. Above the photosensitive drum 101, a charging roller 102 for uniformly charging the surface of the photosensitive drum 101 is provided so as to be in contact with the surface. The surface of the photosensitive drum 101 charged by the charging roller 102 is irradiated with a light beam Lb scanned by the optical scanning unit 120.

As described above, the light beam Lb is modulated based on the image data Di, and by irradiating the light beam Lb, an electrostatic latent image is formed on the surface of the photosensitive drum 101. This electrostatic latent image is developed as a toner image by a developing device 103 arranged so as to be in contact with the photosensitive drum 101 further downstream in the rotation direction of the photosensitive drum 101 than the irradiation position of the light beam Lb.

(4) The toner image developed by the developing device 103 is transferred below the photosensitive drum 101 by a transfer roller 104 disposed so as to face the photosensitive drum 101 onto a sheet 111 serving as a transfer material. The sheet 111 is stored in the sheet cassette 106 in front of the photosensitive drum 101 (right side in FIG. 7), but can be fed manually. A paper feed roller 107 is disposed at an end of the paper cassette 106 and feeds the paper 111 in the paper cassette 106 to a transport path.

{Circle around (4)} As described above, the sheet 111 onto which the unfixed toner image has been transferred is further conveyed to the fixing device behind the photosensitive drum 101 (left side in FIG. 7). The fixing device includes a fixing roller 108 having a fixing heater (not shown) therein and a pressure roller 109 arranged so as to be in pressure contact with the fixing roller 108, and the sheet 111 conveyed from the transfer unit. Is heated while being pressed by the pressure contact portion between the fixing roller 108 and the pressure roller 109, thereby fixing the unfixed toner image on the sheet 111. Further, a paper discharge roller 110 is disposed behind the fixing roller 108, and discharges the fixed paper 111 to the outside of the image forming apparatus 100.

Although not shown in FIG. 7, the print controller 121 controls not only the above-described data conversion but also control of the motor 105 and other components in the image forming apparatus 100 and the polygon motor in the optical scanning unit 120. I do.

FIG. 2 is a sectional view of a main part of the optical scanning device according to the first embodiment of the invention. The figure which shows the spectral reflectance of an aluminum mirror. The figure which shows the spectral reflectance of aluminum + alumina + protective film (dielectric film). FIG. 9 is a sectional view of a main part of an optical scanning device according to a second embodiment of the invention. The figure which shows the spectral reflectance of an aluminum + dielectric film. FIG. 9 is a perspective view of an optical scanning device according to a third embodiment of the present invention. FIG. 2 is a cross-sectional view of a main part of the image forming apparatus according to the present invention in the sub-scanning direction. The figure which shows the spectral reflectance of a copper mirror. The figure which shows the spectral reflectance of copper + alumina + SiO2. FIG. 2 is a sectional view of a main part of the optical scanning device according to the first embodiment of the invention. FIG. 9 is a sectional view of a main part of an optical scanning device according to a second embodiment of the invention. FIG. 9 is a sectional view of a sub-scanning system of an optical scanning device according to a third embodiment of the present invention. The figure which shows the reflectance ratio angle characteristic of a return mirror. FIG. 4 is a diagram illustrating a reflectance wavelength characteristic of a folding mirror. FIG. 4 is a diagram illustrating transmittance wavelength characteristics of a typical optical resin.

Explanation of reference numerals

DESCRIPTION OF SYMBOLS 1 Semiconductor laser 2 Collimator lens 3 Aperture 4 Cylindrical lens 5 Polygon mirror 6, 7 Scanning imaging lens 8 Scanned surface 9 Folding mirror 10 Photosensitive drum 11 Scanning imaging mirror

Claims (4)

A deflection optical system that deflects the light beam from the light source, and a scanning imaging lens system that forms an image of the light beam from the deflection optical system on the surface to be scanned.
The wavelength of the light source is 500 nm or less,
The scanning image forming lens system has at least one plastic lens, and when the maximum value of the total ray passing distance according to the deflection angle of the plastic lens from the optical axis is Lmax, and the minimum value is Lmin,
Lmax-Lmin <10mm
An optical scanning device characterized by satisfying the following. The optical scanning device according to claim 1, wherein the light source is a gallium nitride blue-violet semiconductor laser. The optical scanning device according to claim 1, a photosensitive member disposed on a surface to be scanned of the optical scanning device, and an electrostatic member formed on the photosensitive member by a light beam scanned by the optical scanning device. A developing device for developing a latent image as a toner image, a transfer device for transferring the developed toner image to a transfer material, and a fixing device for fixing the transferred toner image to the transfer material are provided. Image forming apparatus. 5. The image forming apparatus according to claim 4, further comprising a printer controller that converts code data input from an external device into an image signal and inputs the image signal to the optical scanning device.

Images