JP2002303810A - Optical scanner and image forming device using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an optical scanner by which high-definition printing is obtained a simple constitution by suppressing deviation in an image formation position in a main scanning direction due to wavelength fluctuation or/and the divergence of focus (specially image surface curvature movement in a subscanning direction) in the subscanning direction associated with environmental fluctuation and a color image forming device using it. SOLUTION: This scanner comprises a deflecting means to deflect a light beam emitted by a light source means and a scanning optical means to perform image formation on a surface to be scanned with the light beam deflected by the deflecting means, and the scanning optical means possesses at least one refractive surface and also at least one diffraction surface, and when the synthesizing power of the refractive surface in the main scanning direction is set as ϕr, and that of the diffraction surface in the main scanning direction is set as ϕd and the rate of change of the refractive index of the material of an optical device forming the refractive surface to the oscillating wavelength of the light source means is set as dn/dλ (/nm), the condition of -2.37×10<-3> (/ nm)<(ϕr/ϕd)×(dn/dλ)<-0.9×10<-3> (/nm) is satisfied.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical scanning device and an image forming apparatus using the same, and more particularly, to an image forming position shift (chromatic aberration of magnification) in the main scanning direction due to a wavelength variation, and / or an environmental variation (temperature change). It is suitable for devices such as a laser beam printer (LBP) and a digital copying machine, which suppress the accompanying defocus in the sub-scanning direction.

[0002]

2. Description of the Related Art Generally, an optical scanning device of this type reflects and deflects a light beam (light flux) emitted from a laser light source by a polygon mirror which is an optical deflector, and receives the light beam by scanning optical means (scanning optical system) having fθ characteristics. An image is formed as a light spot on the scanning surface.

A semiconductor laser or the like is frequently used as a laser light source. A divergent light beam emitted from the semiconductor laser 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 reflected and deflected by a polygon mirror rotating at a constant angular velocity, and is incident on the scanning optical means.
The scanning optical means has an fθ characteristic of scanning a light beam reflected and deflected at a constant angular velocity on a surface to be scanned arranged at a predetermined interval at a constant speed, so that a minute light spot is formed over the entire scanning area. There is a need for good correction of field curvature.

Further, since the polygon mirror has a processing error on the mirror surface (deflection surface) and a vibration of the rotating shaft, many scanning optical means scan in a direction perpendicular to the main scanning section, that is, in the sub-scanning section. A tilt correction function for correcting a positional shift is provided. For this reason, the scanning optical means is an anamorphic lens system having different imaging characteristics between the main scanning section (main scanning direction) and the sub-scanning section (sub-scanning direction).

Conventionally, the scanning optical means has been processed to have a toric surface and a cylindrical surface by a glass material, and an anti-reflection film is applied to this kind of glass lens by vapor deposition or the like. On the other hand, processing of a glass lens is difficult and costly. Therefore, in recent years, a plastic lens which has a low cost and can correct aberration with a free shape has been frequently used.

In addition, various demands have been made for a multi-beam optical scanning device for simultaneously forming a plurality of scanning lines with a plurality of light beams emitted from a plurality of laser light sources due to a demand for high speed.

FIG. 17 is a schematic view of a main part of a conventional multi-beam optical scanning apparatus of this kind. In FIG.
The respective light beams emitted from the light beams 1 and 82 are converted into substantially parallel light beams by the corresponding collimator lenses 83 and 84, and then combined by the combining optical element 85 into optical paths in the same direction. The combined two light beams form a long line image in the main scanning direction near the deflecting surface 87a of the polygon mirror 87 by a cylindrical lens 86 having a predetermined refractive power only in the sub-scanning direction, and then have scanning optics having fθ characteristics. Means (scanning optical system) 88 form light spots on the surface of the photosensitive drum 89 at different positions in the sub-scanning direction. As described above, since two scanning lines can be formed by one optical scanning, the speed can be remarkably increased as compared with the conventional optical scanning device.

Further, as a laser light source for a multi-beam optical scanning device, in addition to one using a plurality of separated light sources,
There is a monolithic multi-beam laser having many light emitting points. In the case of using this monolithic multi-beam laser, since a combining optical element is not required, simplification of an optical system and optical adjustment can be achieved.

A conventional semiconductor laser used as a laser light source is an infrared laser (eg, 780 nm) or a visible laser (eg, 675 nm).
Due to a demand for higher resolution, development of an optical scanning device that can obtain a minute spot shape using a short wavelength laser having an oscillation wavelength of 500 nm or less has been promoted.

An advantage of using a short-wavelength laser is that it is possible to achieve a small spot diameter which is about half of the conventional one while keeping the emission F-number of the scanning optical means at the same level as the conventional one. In order to use an infrared laser and make the spot diameter half of the conventional one,
The brightness of the scanning optical means must be approximately doubled. Since the depth of focus is proportional to the oscillation wavelength of the laser light source used and proportional to the square of the emission F number of the scanning optical means, when trying to obtain the same spot diameter, the depth of focus of the infrared laser is shorter than that of the short wavelength laser. Is about 1/2 or less.

[0011]

FIG. 18 is a schematic view of a main part of a conventional color image forming apparatus. In the figure, a plurality of optical scanning devices 211 to 214 are used simultaneously, and image information for each color is recorded on different photosensitive drums 221 to 224 to form a color image. In such a color image forming apparatus, since an image is formed by superposing a plurality of scanning lines, it is particularly important to reduce the scanning line deviation between the colors and the image density unevenness between the colors. Therefore, the optical scanning device must: (1) compensate for a change in imaging position (spot displacement) in the main scanning direction due to a wavelength variation of a light beam emitted from a semiconductor laser as a laser light source; )
It is required that the focus change in the sub-scanning direction, which has a particularly large effect, is compensated for due to environmental fluctuations such as a temperature rise, and the like (the focus change in the main scanning direction is originally small and often causes no problem). Even if the light source wavelength of the optical scanning device (the wavelength of the light beam emitted from the laser light source) and the use environment (especially the environmental temperature) fluctuate, as well as the optical performance within one optical scanning device, In addition, a configuration is required in which even if there is a difference between the light source wavelengths and the use environment of the plurality of optical scanning devices, there is no registration shift between the respective colors or image unevenness.

Further, even in a monochromatic optical scanning device using a multi-beam laser light source, jitter (fluctuation in the scanning line interval in the main scanning direction on the photosensitive drum surface) due to the wavelength difference between the plurality of laser light sources is solved. In order to minimize the wavelength difference between laser light sources, measures have been taken, such as selecting the laser light sources.

In order to correct the jitter (chromatic aberration of magnification) due to the wavelength difference between a plurality of laser light sources by the scanning optical means,
It requires a plurality of lenses having different dispersion characteristics. This is compared to scanning optical means that does not correct the chromatic aberration of magnification.
Generally, the number of sheets increases, the optical system becomes complicated, and the cost increases. Further, there is a limit to the wavelength selection of the laser light source, and it is difficult to completely match the wavelengths, and there is also a problem of the cost required for wavelength selection. In addition, when the semiconductor laser rises, image quality is degraded due to wavelength fluctuation called mode hopping. Therefore, even if it is not a color image forming apparatus or an optical scanning apparatus using a multi-beam laser light source, it is necessary to suppress jitter due to wavelength fluctuation as much as possible in order to improve the stability of image quality.

Further, in the case of a high-resolution optical scanning device in which the wavelength of the laser light source is shortened, there is a problem that the dispersion of the optical material is large as compared with the case where an infrared laser is used.

FIG. 19 is a sectional view of a main part of a general optical scanning apparatus using two plastic lenses as scanning optical means. In the figure, a light beam emitted from a laser light source 91 is converted into a substantially parallel light beam by a collimator lens 92, and is then deflected by a cylinder lens 94 having a predetermined refractive power only in the sub-scanning direction. An image is once formed in the sub-scanning direction near the (reflection surface) 95a. The light beam reflected and deflected by the polygon mirror 95 is scanned at a constant speed by the two refraction lenses 961 and 962 having fθ characteristics, and is imaged on the scanned surface 98 into a minute spot.

When such an optical scanning device is used, an infrared laser (780) conventionally used as a laser light source is used.
FIG. 20 is a graph showing calculated chromatic aberration of magnification in a short wavelength laser (408 nm) used for a high-resolution optical scanning device.

The graph in the figure is obtained by subtracting the image forming position in the main scanning direction at the reference wavelength from the image forming position in the main scanning direction when a wavelength difference of 1.5 nm is given, and plotting the result for each image height. (For example, an image forming position of 781.5 nm and 7
Difference from the image formation position of 80 nm). In this optical system using two plastic lenses of the same material, it is basically impossible to correct lateral chromatic aberration. Until now, the oscillation wavelength of the laser light source was long and the dispersion characteristics of the material were relatively low, so even if the chromatic aberration of magnification was not corrected by the scanning optical means, jitter was reduced by measures such as selecting the laser light source. It was done.

However, when the same optical system is used with a short-wavelength laser, the dispersion characteristics of the material are 4-8.
Since it is doubled (see FIG. 21), chromatic aberration of magnification occurs at about 20 μm in the peripheral portion of the image (see FIG. 20). This is about half the value of one dot in an image forming apparatus having a resolution of 600 dpi. Therefore, it is premised that an optical scanning device using a short wavelength laser of 500 nm or less corrects chromatic aberration of magnification.

However, even if a plurality of lenses having different dispersion characteristics are used for the scanning optical means as described above, the optical design itself is difficult due to the extremely large dispersion. Furthermore, since there are few materials having different dispersion characteristics in plastic lenses, it is difficult to correct lateral chromatic aberration using only plastic lenses.

In addition, as shown in FIG. 21, the refractive index of a general optical resin fluctuates due to a change in environmental temperature. FIG. 21 is a graph plotting the wavelength characteristics of the refractive index of ZEONEX E48R manufactured by Zeon Corporation in a 25 ° C. environment and a 40 ° C. environment. As can be seen from this graph, the refractive index of a general optical resin decreases as the environmental temperature increases. The amount is -8.9962E-5 / ° C at a wavelength of 780 nm, -8.000785E-5 / ° C at a wavelength of 408 nm, and 2 of optical glass.
The value is larger as the digit. E-5 represents 10 ^-5 .

Therefore, when the environmental temperature rises, the focus surface is farther away from the photosensitive drum surface than when the glass lens is used, and the spot diameter is enlarged on the photosensitive drum surface. .

According to the present invention, in an optical scanning device using a short wavelength light source of 500 nm or less and an image forming apparatus using the same, an image forming position shift (chromatic aberration of magnification) in a main scanning direction due to a wavelength variation, and / or an environmental variation ( It is an object of the present invention to provide an optical scanning device capable of suppressing a focus shift in the sub-scanning direction accompanying a temperature change or the like, and easily obtaining high-definition printing with a simple configuration, and an image forming apparatus using the same.

[0023]

According to a first aspect of the present invention, there is provided an optical scanning device, comprising: a deflecting unit for deflecting a light beam emitted from a light source unit; and connecting the light beam deflected by the deflecting unit onto a surface to be scanned. Scanning optical means for imaging, the scanning optical means having at least one refraction surface and at least one diffraction surface, the combined power of the refraction surface in the main scanning direction Φr, the main power of the diffraction surface The combined power in the scanning direction is Φd,
When the rate of change of the refractive index of the material of the optical element forming the refractive surface with respect to the oscillation wavelength of the light source means is dn / dλ (/ nm), -2.37 × 10 ⁻³ (/ nm) <(Φr / Φd) × (dn / dλ)
<−0.9 × 10 ⁻³ (/ nm).

According to a second aspect of the present invention, in the first aspect of the present invention, the scanning optical means comprises: -2.25 × 10 ⁻³ (/ nm) <(Φr / Φd) × (dn / d
λ) <-1.30 × 10 ⁻³ (/ nm).

According to a third aspect of the present invention, in the first or second aspect, the oscillation wavelength of the light source means is 380 nm to 500 nm.
nm.

According to a fourth aspect of the present invention, in the first, second or third aspect of the present invention, the light source means includes a gallium nitride-based blue-violet semiconductor laser.

According to a fifth aspect of the present invention, in any one of the first to fourth aspects of the present invention, the scanning optical unit corrects chromatic aberration of magnification in the main scanning direction.

According to a sixth aspect of the present invention, in the first aspect of the present invention, the scanning optical means has a single refracting element and a single diffractive element having a plane-shaped diffraction grating surface. It is characterized by having.

According to a seventh aspect of the present invention, in the sixth aspect, the refracting element and the diffractive element are made of a plastic material.

According to an eighth aspect of the present invention, in any one of the first to seventh aspects, the light source means includes a monolithic multi-beam laser having a plurality of light emitting points.

According to a ninth aspect of the present invention, in the first aspect of the present invention, the light source means has a plurality of laser light sources, and a plurality of light beams emitted from the plurality of laser light sources are beam-combined. And light is guided to the deflecting means.

According to a tenth aspect of the present invention, there is provided an optical scanning device, comprising: a deflecting means for deflecting the light beam emitted from the light source means; , The scanning optical means has at least one refraction surface and at least one diffraction surface, and the combined power of the refraction surface in the sub-scanning direction is ψr,
When the combined power of the diffraction surface in the sub-scanning direction is Δd and the change rate of the oscillation wavelength of the light source means with respect to the temperature is dλ / dt (nm / ° C.), 15.0 (° C./nm)<Δr/[Δd× (Dλ / dt)] <45.
0 (° C./nm).

In the eleventh aspect, in the tenth aspect, the scanning optical means includes: 18.0 (° C./nm)<ψr/[ψd×(dλ/dt)]<38.
0 (° C./nm).

According to a twelfth aspect of the present invention, in the tenth or eleventh aspect, the oscillation wavelength of the light source means is 380 nm to 380 nm.
It is characterized by being within the range of 500 nm.

According to a thirteenth aspect, in the tenth, eleventh, or twelfth aspect, the light source means includes a gallium nitride-based blue-violet semiconductor laser.

According to a fourteenth aspect of the present invention, in any one of the tenth to thirteenth aspects, the scanning optical means compensates for a focus position variation on the surface to be scanned due to a temperature variation. I have.

According to a fifteenth aspect of the present invention, in the invention according to any one of the tenth to fourteenth aspects, the scanning optical means has a single refracting element and a single diffractive element having a plane-shaped diffraction grating surface. It is characterized by having.

A sixteenth aspect of the present invention is characterized in that, in the fifteenth aspect, the refraction element and the diffraction element are made of a plastic material.

The invention according to claim 17 is characterized in that, in the invention according to any one of claims 10 to 16, the light source means includes a monolithic multi-beam laser having a plurality of light emitting points.

According to an eighteenth aspect of the present invention, in accordance with any one of the tenth to sixteenth aspects, the light source means has a plurality of laser light sources and combines a plurality of light beams emitted from the plurality of laser light sources. And light is guided to the deflecting means.

According to a nineteenth aspect of the present invention, there is provided an optical scanning device, comprising: a deflecting means for deflecting the light beam emitted from the light source means; , The scanning optical means has at least one refraction surface and at least one diffraction surface, and the combined power of the refraction surface in the main scanning direction is Φr,
The combined power of the diffraction surface in the main scanning direction is Φd, and the change rate of the refractive index of the material of the optical element forming the refractive surface with respect to the oscillation wavelength of the light source means is dn / dλ (/ nm). When the power is Δr, the combined power of the diffraction surface in the sub-scanning direction is Δd, and the change rate of the oscillation wavelength of the light source means with respect to the temperature is dλ / dt (nm / ° C.), -2.37 × 10 ⁻³ (/ nm) <(Φr / Φd) × (dn / dλ)
<−0.9 × 10 ⁻³ (/ nm) 15.0 (° C./nm)<Δr/[Δd×(dλ/dt)]<45.
0 (° C./nm).

According to a twentieth aspect of the present invention, in the nineteenth aspect, the scanning optical means comprises: -2.25 × 10 ⁻³ (/ nm) <(Φr / Φd) × (dn / d
λ) <− 1.30 × 10 ⁻³ (/ nm) 18.0 (° C./nm)<ψr/[ψd×(dλ/dt)]<38.
0 (° C./nm).

According to a twenty-first aspect, in the nineteenth or twentieth aspect, the oscillation wavelength of the light source is 380 nm to 5 nm.
It is characterized by being within the range of 00 nm.

According to a twenty-second aspect of the present invention, in the nineteenth, twentieth or twenty-first aspect, the light source means comprises a gallium nitride-based blue-violet semiconductor laser.

According to a twenty-third aspect of the present invention, in the first aspect of the present invention, the scanning optical means corrects lateral chromatic aberration in the main scanning direction, and adjusts the position of the auxiliary optical element on the surface to be scanned due to temperature fluctuation. It is characterized in that the focus position fluctuation in the scanning direction is compensated.

According to a twenty-fourth aspect of the present invention, in the invention according to any one of the nineteenth to twenty-third aspects, the scanning optical means has a single refracting element and a single diffractive element having a plane-shaped diffraction grating surface. It is characterized by having.

According to a twenty-fifth aspect, in the twenty-fourth aspect, the refracting element and the diffractive element are made of a plastic material.

According to a twenty-sixth aspect of the present invention, in any one of the nineteenth to twenty-fifth aspects, the light source means includes a monolithic multi-beam laser having a plurality of light emitting points.

According to a twenty-seventh aspect of the present invention, in any one of the nineteenth to twenty-fifth aspects, the light source means has a plurality of laser light sources and combines a plurality of light beams emitted from the plurality of laser light sources. And light is guided to the deflecting means.

According to a twenty-eighth aspect of the present invention, there is provided an optical scanning device comprising: a deflecting means for deflecting a light beam emitted from a light source means; and a scanning optical means for forming an image of the light beam deflected by the deflecting means on a surface to be scanned. , The oscillation wavelength of the light source means is in the range of 380 to 500 nm, and the scanning optical means is characterized in that chromatic aberration of magnification is corrected.

An optical scanning device according to a twenty-ninth aspect of the present invention is a light scanning device, comprising: a deflecting means for deflecting a light beam emitted from a light source means; and a scanning optical means for forming an image of the light beam deflected by the deflecting means on a surface to be scanned. , The oscillation wavelength of the light source means is in the range of 380 to 500 nm, and the focus position variation on the surface to be scanned due to the temperature variation of the optical scanning device is compensated. And

According to a thirtieth aspect of the present invention, there is provided an optical scanning device, comprising: a deflecting means for deflecting the light beam emitted from the light source means; and a scanning optical means for forming an image of the light beam deflected by the deflecting means on a surface to be scanned. , The oscillation wavelength of the light source means is in the range of 380 to 500 nm, the scanning optical means is corrected for chromatic aberration of magnification, and on the surface to be scanned due to temperature fluctuation of the optical scanning device. Is compensated for the focus position fluctuation.

According to a thirty-first aspect of the present invention, there is provided an image forming apparatus comprising: the optical scanning device according to any one of the first to thirty aspects; a photosensitive member disposed on the surface to be scanned; A developing device for developing the electrostatic latent image formed on the photoreceptor as a toner image by the generated light beam, a transfer device for transferring the developed toner image to a transfer material, and a transfer device for transferring the transferred toner image. And a fixing device for fixing to the transfer material.

According to a thirty-second aspect of the present invention, there is provided an image forming apparatus comprising: the optical scanning device according to any one of claims 1 to 30; and the optical scanning device which converts code data input from an external device into an image signal. And a printer controller that allows the user to input the data to the printer.

According to a thirty-third aspect of the present invention, there is provided a color image forming apparatus, comprising: a plurality of optical scanning devices each comprising the optical scanning device according to any one of the first to thirty aspects; And a plurality of image carriers that are arranged on the surface and form images of different colors from each other.

A color image forming apparatus according to a thirty-fourth aspect of the present invention has a printer controller for converting a color signal input from an external device into image data of a different color and inputting it to each optical scanning device. Features.

[0057]

[First Embodiment] FIG. 1 is a schematic view of a main part of a color image forming apparatus according to a first embodiment of the present invention.

In the figure, 11, 12, 13, and 14 are optical scanning devices, 21, 22, 23, and 24 are photosensitive drums as image carriers, 31, 32, 33, and 34 are developing devices, and 41 is a developing device. It is a conveyor belt. As will be described later, the color image forming apparatus according to the present embodiment performs the above-described optical scanning in which the change in the imaging position due to the wavelength change of the light beam (light flux) emitted from the laser light source and the change in the aberration due to the environmental change (temperature change) are suppressed. Four devices (11, 12, 13, 14) are arranged, each corresponding to each color of C (cyan), M (magenta), Y (yellow), and B (black). Image signals (image information) are recorded on the surfaces 22, 23, and 24, and a color image is printed at high speed.

Next, a description will be given of a method of satisfactorily correcting an imaging position change caused by a wavelength change of a laser light source and an aberration change caused by an environmental change, which are features of the present invention, and an optical element thereof.

FIG. 2 is a schematic view of a principal part showing one optical scanning device and an image carrier corresponding thereto, and FIG. 3 is a sectional view of a principal part in the main scanning direction of the optical system shown in FIG. Figure).

In FIGS. 2 and 3, reference numeral 1 denotes a light source means.
For example, it is composed of a gallium nitride-based blue-violet semiconductor laser (laser light source) having an oscillation wavelength of 408 nm. A collimator lens 2 converts a divergent light beam emitted from the laser light source 1 into a substantially parallel light beam. Reference numeral 3 denotes an aperture stop, which restricts a passing light beam (light amount). Reference numeral 4 denotes a cylindrical lens (cylinder lens) which has a predetermined power (refractive power) only in the sub-scanning direction, and converts a light beam passing through the aperture stop 3 into an optical deflector 5 to be described later in the sub-scan section. An image is formed as a substantially linear image on the deflection surface (reflection surface) 5a.

Reference numeral 5 denotes a light deflector as a deflecting means, for example, a polygon mirror (rotating polygon mirror), which is rotated at a constant speed in the direction of arrow A in the figure by a driving means (not shown) such as a motor.

Reference numeral 6 denotes a scanning optical unit (scanning optical system) having fθ characteristics, which has a refracting element (refracting lens) 61 and a diffractive element (diffraction lens) 62. The refracting element 61 is formed of a plastic toric lens having different powers in the main scanning direction and the sub-scanning direction, and has both lens surfaces 61a, 61a in the main scanning section of the toric lens 61.
Both 61b have an aspherical shape.

The diffractive element 62 is composed of a long composite optical element having different powers in the main scanning direction and the sub-scanning direction. The composite optical element 62 has a plane 62a on the incident side having a predetermined power only in the main scanning direction. (The sub-scanning direction is a plane), and the emission-side surface 62b is composed of a diffraction surface obtained by adding a diffraction grating 71 to the plane. Here, as the grating shape of the diffraction grating 71, for example, a Fresnel-like grating shape made of a sawtooth-like diffraction grating by surface ablation, or a step-like grating shape made by photo-etching is suitable. Although the composite optical element 62 in this embodiment is made of plastic manufactured by injection molding, the same effect can be obtained even if a diffraction grating is manufactured by replica on a glass substrate.

In this embodiment, the toric lens 61 is located on the polygon mirror 5 side from the midpoint between the rotation axis of the polygon mirror 5 and the surface 8 to be scanned, and the composite optical element 62 is located on the surface 8 to be scanned.
Is arranged. These optical elements have different powers in the main scanning direction and the sub-scanning direction as described above, and form an image of the deflected light beam from the polygon mirror 5 on the surface 8 to be scanned and a polygon mirror in the sub-scanning section. Of the deflection surface is corrected. Reference numeral 8 denotes the surface of the photosensitive drum that is the surface to be scanned.

In the color image forming apparatus of this embodiment, the latent images are respectively formed by the four optical scanning devices 11, 12, 13 and 14 using the light beams based on the respective modulation signals as described above. It is formed on 22, 23, and 24 surfaces. For example, C (cyan), M (magenta),
The latent images of Y (yellow) and B (black) are formed on the corresponding surfaces of the photosensitive drums 21, 22, 23, and 24, and thereafter,
A single full-color image is formed by multiple transfer onto a recording material.

As described above, a gallium nitride-based blue-violet semiconductor laser is used as the laser light source of the optical scanning device in this embodiment, and its oscillation wavelength is 408 nm. As described above, by shortening the wavelength of the laser light source, a spot diameter that is about half that of the related art is achieved. As a result, it is possible to further increase the resolution, and to form an image that is particularly excellent in gradation expression.

In this embodiment, a blue-violet semiconductor laser having an oscillation wavelength of a laser light source of 408 nm is used.
As in the embodiment described later, the oscillation wavelength of the laser light source may be in the range of 380 nm to 500 nm.

The shapes of the refraction surface and the diffraction surface of the toric lens 61 and the composite optical element 62 that constitute the scanning optical means 6 of the optical scanning device in this embodiment are as follows: . . An aspheric surface shape in which the main scanning direction can be expressed by a function up to the 10th order, an intersection point with the optical axis as an origin, an optical axis direction as an x axis, an axis orthogonal to the optical axis in a main scanning cross section as a y axis,
When the axis orthogonal to the optical axis in the sub-scanning section is the z-axis, the generatrix direction corresponding to the main scanning direction is

[0070]

(Equation 1)

(Where R is the radius of curvature, K, B4, B6,
B8 and B10 are aspherical coefficients. The sagittal direction corresponding to the sub-scanning direction (the direction including the optical axis and orthogonal to the main scanning direction) is

[0072]

(Equation 2)

[0073] Here, r '= r0 (1 + D2Y 2 + D4Y 4 + D6Y 6 + D8Y 8 + D10Y 10) ( where, r0 is the sagittal curvature radius on the optical axis, D2, D4, D6, D
8, D10 is the aspheric coefficient) (a) Diffraction surface. . . Main scanning direction is up to tenth order, the diffraction surface is the sub-scanning direction is expressed by a quadratic phase function varies with position in the main scanning direction φ = 2πm / λ [b2 Y 2 + b4 Y 4 + b6 Y 6 + b8 Y 8
^{+ B10 Y 10 + (d0 +} d1 Y + d2 Y 2 + d3 Y 3 +
^{d4 Y 4 + d5 Y 5 +} d6 Y 6) Z 2] ( where, phi is the phase function, m is the diffraction order, lambda is the wavelength used (408 nm), Y is the height from the lens optical axis, b2, b4, b6, b
8, b10, d0, d1, d2, d3, d4, d5, d6 are phase coefficients, Embodiment 1
-4 use + 1st order diffracted light).

In the present embodiment, by optimizing the power arrangement of the refraction surface and the diffraction surface constituting the scanning optical means 6,
In the main scanning direction, the change in the imaging position caused by the wavelength fluctuation of the laser light source, and in the sub-scanning direction, the environmental fluctuations of the apparatus (changes in temperature, humidity, and atmospheric pressure. The same can be said for the environmental fluctuations of the above.)

That is, in this embodiment, the chromatic aberration of magnification of the scanning optical means 6 is reduced by the toric lens (refractive element) 61 having a positive dispersion and the composite optical element (diffraction element) 62 having a negative dispersion in the main scanning direction. Compensation (magnification color compensation).

The power arrangement is such that the refractive surfaces 61a and 61b of the toric lens 61 and the refractive surface 62 of the composite optical element 62
The combined power of the a in the main scanning direction is Φr, the Abbe number of the material of the toric lens 61 is νr, the power of the diffraction surface 62b of the composite optical element 62 in the main scanning direction is Φd, and the Abbe number of the diffraction element 71 is νd. Then, it is desirable to satisfy the following equation: Φr / νr + Φd / νd = 0 (Equation 1)

Here, the Abbe number νr is as follows: νr = (n−1) / Δn = (n−1) / (dn / dλ) (Equation 2)

Using the above relational expression (Expression 2) and the fact that the dispersion characteristic of the diffraction element 71 changes linearly with wavelength,
(Equation 1) can be modified as follows.

(Φr / Φd) × (dn / dλ) = − (n−1) / λ (Equation 3) The range of the oscillation wavelength λ of the laser light source is 380 to 500 nm,
The range of the refractive index n of the general optical material is 1.45 to
Assuming 1.90, − (1.45-1) / 380 (nm) = − 1.18 × 10 ⁻³
(/nm)−(1.90−1)/380(nm)=−2.368×10
⁻³ (/nm)−(1.45-1)/500 (nm) = − 0.9 × 10 ⁻³ (/
nm) − (1.90−1) / 500 (nm) = − 1.8 × 10 ⁻³ (/
Therefore, the range that (Equation 3) can take is -2.37 × 10 ⁻³ (/nm)<(Φr/Φd)×(dn/dλ)<−0.9×10 ⁻³ (/ nm) .. (Equation 4). That is, in the present embodiment, the combined power of the refraction surface in the main scanning direction is Φr, and the combined power of the diffraction surface in the main scanning direction is Φr.
d, when the change rate of the refractive index of the material of the optical element forming the refraction surface with respect to the oscillation wavelength of the light source means is dn / dλ (/ nm), the condition of the above (Equation 4) is satisfied. Here, the combined power includes the case where there is only one refraction surface,
Also includes the case where there is one diffraction surface.

On the other hand, if the power of the diffraction grating is too strong, the grating pitch becomes narrow, the number of objects increases, and the processing difficulty increases. Therefore, it is desirable to keep the power of the diffraction grating within a certain range. In order to perform better chromatic aberration of magnification correction, (Expression 4) should be set to -2.25 × 10 ⁻³ (/ nm) <(Φr / Φd ) × (dn / dλ) <− 1.30 × 10 ⁻³ (/ nm) (Equation 4 ′) is preferably satisfied.

When the surface of the composite optical element 62 excluding the diffraction grating 71 has power, the power is treated as the power of the refraction surface.

Further, dn / dλ is the rate of change of the refractive index n of the material of the optical element (in this embodiment, the toric lens 61 or the composite optical element 62) forming the refraction surface with respect to the oscillation wavelength λ of the semiconductor laser 1 as described above. is there.

The conditional expression (Equation 4) represents the power ratio in the main scanning direction between the refractive surface of the toric lens 61 and the composite optical element 62 constituting the scanning optical means 6 and the diffraction surface of the composite optical element 62, This is related to the dispersion characteristics of the material, and if the conditional expression (Equation 4) is not satisfied, it is difficult to correct the change in the imaging position (chromatic aberration of magnification) in the main scanning direction on the surface 8 to be scanned due to the wavelength fluctuation of the semiconductor laser 1. It ’s not good because it ’s getting better.

On the other hand, in the sub-scanning direction, the change in the refractive index of the scanning optical means 6 due to the environmental change of the apparatus (particularly, the temperature rise) is compensated by the wavelength change of the semiconductor laser 1 also due to the environmental change.
It cancels out focus movement (temperature compensation).

Here, it is assumed that the optical scanning device is heated, for example, by the temperature t. By this temperature rise, the scanning optical means 6
The refractive index n of the material of the toric lens 61 is dn / dt
And the power change dψr (dn / dt) accompanying this is: d r (dn / dt) = ψr / (n−1) × (dn / dt) (Equation 5) n: refractive index of toric lens ト ー r : The combined power in the sub-scanning direction between the refractive surface of the toric lens and the refractive surface of the composite optical element.

On the other hand, as the temperature rises, the oscillation wavelength λ of the semiconductor laser 1 also changes by dλ / dt, and the power change dψr between the toric lens 61 and the composite optical element 62 accompanying this.
(Dλ / dt) and dψd (dλ / dt) are respectively: dψr (dλ / dt) = 1 / (n−1) · (dn / dλ) · (dλ / dt) · ψ r (Equation 6) Dψd (dλ / dt) = (1 / λ) · (dλ / dt) · ψd (Equation 7)

Here, in order to suppress a change in focus in the sub-scanning direction by raising the temperature, the following equation must be satisfied.

Dψr (dn / dt) + dψr (dλ / dt) + dψd (dλ / dt) = 0 (Equation 8)

[0089]

(Equation 3)

## EQU10 ##

Change rate (wavelength temperature characteristic) of the oscillation wavelength of a gallium nitride based blue-violet semiconductor laser with respect to each characteristic value and temperature of a general optical material (dλ / dt = 0.04 to
Considering that 0.06 nm / ° C.) has less change than the wavelength-temperature characteristics of the infrared laser, 15.0 (° C./nm)<Δr/[Δd×(dλ/dt)]<45.0 (° C./nm) nm) ・ ‥ (Equation 10)

Here, ψr: combined power of the refracting surface of the toric lens and the refracting surface of the composite optical element in the sub-scanning direction. Ψd: power of the diffractive surface of the composite optical element in the sub-scanning direction.

If the power of the diffraction grating is too strong, the grating pitch becomes narrow, the number of general objects increases, and the processing difficulty increases. Therefore, it is desirable to keep the power of the diffraction grating within a certain range, and to achieve better temperature compensation, (Equation 10) is calculated as follows: 18.0 (° C./nm)<ψr/[ψd×(dλ/dt) )] <38.0 (° C./nm) (Equation 10 ′) is preferably satisfied.

Here, dλ / dt is a rate of change of the oscillation wavelength λ of the semiconductor laser 1 with respect to the temperature t.

The conditional expression (Expression 10) represents the power ratio in the sub-scanning direction between the refractive surface of the toric lens 61 and the composite optical element 62 constituting the scanning optical means 6 and the diffraction surface of the composite optical element 62, It relates to the temperature characteristics of the light source,
If the conditional expression (Expression 10) is not satisfied, it becomes difficult to correct a change in focus in the sub-scanning direction due to an environmental change (temperature change) of the optical scanning device.

Table 1 shows the optical arrangement, the aspheric coefficient of the toric lens 61, and the composite optical element 62 in this embodiment.
Shows the aspheric coefficient and the phase term of.

[0097]

[Table 1]

The toric lens 61 in the present embodiment
Refracting surface of the composite optical element 62 and the composite optical element 62
The power ratio with respect to the diffraction surface is as follows: Main scanning direction: (Φr / Φd) × (dn / dλ) = − 1.7
3E-3 Sub-scanning direction: ψr / [ψd × (dλ / dt)] = 33.0, which satisfies the conditional expression (Expression 4) and the conditional expression (Expression 10), respectively.

Note that “ ^Ex ” represents “× 10 ^−x ”.

FIG. 4 is an explanatory diagram showing a change in the imaging position in the main scanning direction due to a change in the wavelength of the semiconductor laser 1 in this embodiment.
It shows the difference between the image forming position when 5 nm and 5 nm are given.

FIG. 5 is an explanatory view showing paraxial aberration (field curvature in the main scanning direction and the sub-scanning direction) before and after the environmental change in the present embodiment, and the solid line indicates the characteristic (design value) before the environmental change.
And the broken line is the characteristic (effective value) when the temperature of the optical scanning device is increased by + 25 ° C.

In general, in a device that records image information for each color from a plurality of optical scanning devices on a plurality of photosensitive drums and forms a color image, registration deviation between the colors and image density unevenness between the colors are not visually noticeable. In order to achieve this, the imaging position deviation in the main scanning direction due to the wavelength fluctuation of the semiconductor laser is 10 μm or less, and the focus deviation in the main scanning direction and the sub-scanning direction due to the environmental fluctuation (temperature fluctuation) of the apparatus is ± 1.0 mm or less. It is necessary.

FIG. 4 shows that in the present embodiment, the imaging position shift due to the wavelength difference of +5 nm is 2 μm, which is suppressed to a level that does not cause any problem.

Similarly, it can be seen from FIG. 5 that the amount of focus movement in the sub-scanning direction at the time of raising the temperature by + 25 ° C. is 0.1 mm, which is suppressed to a level causing no visual problem together with the main scanning direction.

Although the description has been made mainly on the behavior at the time of temperature rise with respect to environmental fluctuations, the same effect as described above can be obtained also with other environmental fluctuations such as a temperature decrease.

In this embodiment, all of these environmental fluctuations are compensated for by plastic optical elements, thereby reducing the manufacturing cost by molding, and shortening the optical path length by correcting the high angle of view aberration using an aspherical surface. Can be achieved at the same time.

As described above, in the present embodiment, as described above, a short-wavelength laser is used as the light source means, and a spot diameter which is about half that of the conventional art is achieved, thereby enabling a high-resolution image forming apparatus excellent in gradation expression. A plastic toric lens 61 and a composite optical element 62 are used as the scanning optical means 6 to make it possible to correct chromatic aberration of magnification, which has conventionally been difficult to correct when using a short-wavelength laser with a plastic lens. It also compensates for focus shifts due to environmental changes,
A color image forming apparatus with less density unevenness between colors is realized with a simple configuration and at low cost.

[Embodiment 2] FIG. 6 shows Embodiment 2 of the present invention.
FIG. 3 is a cross-sectional view of a main part of the optical scanning device in the main scanning direction. In the figure, the same elements as those shown in FIG. 3 are denoted by the same reference numerals.

This embodiment differs from the first embodiment in that a monolithic multi-beam laser 51 having a plurality of light-emitting points (light-emitting portions) is used as a light source means.
As in the first embodiment, the imaging position shift (chromatic aberration of magnification) in the main scanning direction due to the wavelength difference of the light source means is compensated with high accuracy. Other configurations and optical functions are substantially the same as those of the first embodiment, and thus, similar effects are obtained.

That is, in the figure, reference numeral 51 denotes light source means, which is composed of a monolithic multi-beam laser (multi-semiconductor laser light source) having a plurality of light emitting points (two in this embodiment, but may be three or more). , Two light beams independently modulated (only one light beam is shown in the figure)
Are emitted.

Reference numeral 46 denotes scanning optical means as an optical element having fθ characteristics, and has a refracting element 63 and a diffractive element 64. The refracting element 63 is composed of a single plastic toric lens having different powers in the main scanning direction and the sub-scanning direction, and both lens surfaces 63a and 63b in the main scanning section of the toric lens 63 are both aspheric. Consists of

The diffraction element 64 is composed of a long composite optical element having different powers in the main scanning direction and the sub-scanning direction. The composite optical element 64 has an incident side surface 64a in the main scanning direction and the sub-scanning direction. The output side surface 64b is composed of a diffraction surface obtained by adding a diffraction grating 72 on a plane.

In this embodiment, the two light beams emitted from the multi-beam laser 51 are the same as those in the first embodiment.
Scanning is performed simultaneously on the surface 8 to be scanned in a state where the surface to be scanned 8 is separated by a certain amount in the sub-scanning direction.

Table 2 shows the optical arrangement, the aspheric coefficient of the toric lens 63, and the composite optical element 64 in this embodiment.
Shows the aspheric coefficient and the phase term of.

[0115]

[Table 2]

As in the first embodiment, a gallium nitride-based blue-violet semiconductor laser 51 is used as the light source means of the optical scanning device in this embodiment, and its oscillation wavelength is 408 nm. As described above, by shortening the wavelength of the laser light source, a spot diameter that is about half that of the related art is achieved. As a result, it is possible to further increase the resolution, and to form an image that is particularly excellent in gradation expression.

In the present embodiment, as in the first embodiment, by appropriately setting the power arrangement of the refracting surface and the diffractive surface constituting the scanning optical means 46, the main scanning direction is changed by the wavelength variation of the multi-beam laser 51. Changes in the imaging position caused by the change in the environment in the sub-scanning direction (especially temperature rise)
In the present embodiment, a change (jitter) in a scanning interval in the main scanning direction on the photosensitive drum surface 8 caused by a wavelength difference between a plurality of light emitting points can be compensated. ing.

The toric lens 63 in the present embodiment
Refracting surface of the composite optical element 64 and the composite optical element 64
The power ratio with respect to the diffractive surface is: Main scanning direction: (Φr / Φd) × (dn / dλ) = − 2.2
0E-3 Sub-scanning direction: ψr / [ψd × (dλ / dt)] = 24.3, which satisfies the conditional expression (Expression 4) and the conditional expression (Expression 10), respectively.

FIG. 7 is an explanatory view showing a change in the imaging position in the main scanning direction due to a change in the wavelength of the multi-beam laser 51 in the present embodiment. The difference between the initial wavelength of the multi-beam laser 51 and the wavelength difference of 1.5 nm and 5 nm is given. The difference from the imaging position in the case is shown.

FIG. 8 is an explanatory view showing paraxial aberration (field curvature in the main scanning direction and the sub-scanning direction) before and after the environmental change in the present embodiment, and the solid line is the characteristic (design value) before the environmental change.
And the broken line is the characteristic (effective value) when the temperature of the optical scanning device is increased by + 25 ° C.

As shown in FIG. 7, in this embodiment, the imaging position shift due to the wavelength difference of +5 nm is 2 μm. For example, in the case of a printer with a resolution of 600 dpi, the shift of the pixel (position) within about 1/20 pixel is suppressed. You can see that it is.

Similarly, it can be seen from FIG. 8 that the amount of focus movement in the sub-scanning direction at the time of raising the temperature by + 25 ° C. is 0.1 mm, and is suppressed to a level causing no visual problem together with the main scanning direction.

Although the description has been made mainly on the behavior at the time of temperature rise with respect to the environmental change, the same effect as described above can be obtained also in other environmental changes such as a temperature decrease.

In the present embodiment, all of these environmental fluctuations are compensated for by plastic optical elements, thereby reducing the manufacturing cost by molding and shortening the optical path length by correcting the high angle of view aberration using an aspherical surface. Can be achieved at the same time.

Also, as a feature of the present embodiment, since the chromatic aberration of magnification (change of the imaging position in the main scanning direction) is corrected with high accuracy, jitter can be reduced due to the wavelength difference between a plurality of light emitting points of the multi-beam laser 51. No.

As described above, in the present embodiment, a short-wavelength laser is used as a light source as described above, and a high-resolution image forming apparatus excellent in gradation expression can be realized by achieving a spot diameter which is about half that of a conventional one. A plastic toric lens 63 and a composite optical element 64 are used as the scanning optical means 46, and it is possible to correct the chromatic aberration of magnification, which has conventionally been difficult to correct when a short wavelength laser is used with a plastic lens. In addition, a jitter during use of the multi-beam laser 51 is suppressed, a focus shift due to environmental fluctuation is compensated, and a color image forming apparatus with less density unevenness between colors is realized with a simple configuration and at low cost.

In the present embodiment, the monolithic multi-beam laser 51 is used as the light source means. However, the present invention is not limited to this. For example, a plurality of laser light sources for emitting a single light beam are provided and emitted from the plurality of laser light sources. A configuration may be adopted in which the plurality of light beams thus formed are combined into an optical path in the same direction by a beam combining unit.

[Embodiment 3] FIG. 9 shows Embodiment 3 of the present invention.
FIG. 4 is a cross-sectional view of a main part of the optical scanning device in the main scanning direction. In the figure, the same elements as those shown in FIG. 6 are denoted by the same reference numerals.

This embodiment differs from the second embodiment in that the oscillation wavelength of the monolithic multi-beam laser 51 as the light source means is set to 440 nm. Other configurations and optical functions are substantially the same as those of the second embodiment, and the same effects are obtained.

Table 3 shows the optical arrangement, the aspheric coefficient of the toric lens 63, and the composite optical element 64 in this embodiment.
Shows the aspheric coefficient and the phase term of. (However, the wavelength used in the phase function is 440 nm.)

[0131]

[Table 3]

In this embodiment, as in Embodiment 2 described above, by appropriately setting the power arrangement of the refracting surface and the diffractive surface constituting the scanning optical means 46, the main scanning direction varies with the wavelength variation of the multi-beam laser 51. Changes in the imaging position caused by the change in the environment in the sub-scanning direction (especially temperature rise)
In addition, in the present embodiment, a change (jitter) in the scanning interval in the main scanning direction on the photosensitive drum surface 8 caused by a wavelength difference between a plurality of light emitting points can be compensated. ing.

The toric lens 63 in the present embodiment
Refracting surface of the composite optical element 64 and the composite optical element 64
The power ratio with respect to the diffraction surface is as follows: Main scanning direction: (Φr / Φd) × (dn / dλ) = − 1.8
2E-3 Sub-scanning direction: ψr / [ψd × (dλ / dt)] = 24.4, which satisfies the conditional expression (Expression 4) and the conditional expression (Expression 10), respectively.

FIG. 10 is an explanatory diagram showing a change in the imaging position in the main scanning direction due to a change in the wavelength of the multi-beam laser 51 in the present embodiment. The difference between the initial wavelength of the multi-beam laser 51 and the wavelength difference of 1.5 nm and 5 nm is given. The difference from the imaging position in the case is shown.

FIG. 11 is an explanatory diagram showing paraxial aberrations (field curvature in the main scanning direction and the sub-scanning direction) before and after the environmental change in the present embodiment, and the solid line is a characteristic (design value) before the environmental change. The dashed line indicates the characteristic (effective value) when the temperature of the optical scanning device is increased by + 25 ° C.

As shown in FIG. 10, in this embodiment, the deviation of the imaging position due to the wavelength difference of +5 nm is 2 μm. You can see that it is.

Similarly, it can be seen from FIG. 11 that the amount of focus movement in the sub-scanning direction at the time of raising the temperature by + 25 ° C. is 0.1 mm, and is suppressed to a level causing no visual problem together with the main scanning direction.

Although the description has been made mainly on the behavior at the time of temperature rise with respect to the environmental change, the same effect as described above can be obtained also in other environmental change such as a temperature decrease.

In the present embodiment, all of these environmental fluctuations are compensated for by plastic optical elements, thereby reducing the manufacturing cost by molding and shortening the optical path length by correcting a high angle of view aberration using an aspherical surface. Can be achieved at the same time.

As described above, in this embodiment, a short-wavelength laser is used as the light source as described above, and a fine spot diameter is achieved as compared with the conventional art, thereby enabling a high-resolution image forming apparatus excellent in gradation expression. A plastic toric lens 63 and a composite optical element 64 are used as the optical means 46, and it is possible to correct chromatic aberration of magnification, which has conventionally been difficult to correct when a short wavelength laser is used with a plastic lens. In addition, a jitter during use of the multi-beam laser 51 is suppressed, a focus shift due to environmental fluctuation is compensated, and a color image forming apparatus with less density unevenness between colors is realized with a simple configuration and at low cost.

[Embodiment 4] FIG. 12 is a sectional view of a main portion of an optical scanning device according to Embodiment 4 of the present invention in the main scanning direction. In the figure, the same elements as those shown in FIG. 6 are denoted by the same reference numerals.

This embodiment differs from the second embodiment in that the oscillation wavelength of the monolithic multi-beam laser as the light source means is 480 nm. Other configurations and optical functions are substantially the same as those of the second embodiment, and the same effects are obtained.

Table 4 shows the optical arrangement, the aspheric coefficient of the toric lens 63, and the composite optical element 64 in this embodiment.
Shows the aspheric coefficient and the phase term of. (However, the wavelength used in the phase function is 480 nm.)

[0144]

[Table 4]

In this embodiment, as in Embodiment 2 described above, by appropriately setting the power arrangement of the refracting surface and the diffractive surface constituting the scanning optical means 46, the main scanning direction varies with the wavelength variation of the multi-beam laser 51. Changes in the imaging position caused by the change in the environment in the sub-scanning direction (especially temperature rise)
In addition, in the present embodiment, a change (jitter) in the scanning interval in the main scanning direction on the photosensitive drum surface 8 caused by a wavelength difference between a plurality of light emitting points can be compensated. ing.

The toric lens 63 in the present embodiment
Refracting surface of the composite optical element 64 and the composite optical element 64
The power ratio with respect to the diffractive surface in the main scanning direction is (Φr / Φd) × (dn / dλ) = − 1.6.
8E-3 Sub-scanning direction: ψr / [ψd × (dλ / dt)] = 22.9, which satisfies the conditional expression (Expression 4) and the conditional expression (Expression 10), respectively.

FIG. 13 is an explanatory diagram showing a change in the imaging position in the main scanning direction due to a change in the wavelength of the multi-beam laser 51 in the present embodiment. The difference between the initial wavelength of the multi-beam laser 51 and the wavelength difference of 1.5 nm and 5 nm is given. The difference from the imaging position in the case is shown.

FIG. 14 is an explanatory view showing paraxial aberration (field curvature in the main scanning direction and the sub-scanning direction) before and after the environmental change in the present embodiment, and the solid line indicates the characteristic (design value) before the environmental change. The dashed line indicates the characteristic (effective value) when the temperature of the optical scanning device is increased by + 25 ° C.

As shown in FIG. 13, in this embodiment, the imaging position deviation due to the wavelength difference of +5 nm is 2 μm. For example, in the case of a printer with a resolution of 600 dpi, the deviation of the pixel (position) within about 1/20 pixel is suppressed. You can see that it is.

Similarly, it can be seen from FIG. 14 that the amount of focus movement in the sub-scanning direction at the time of raising the temperature by + 25 ° C. is 0.1 mm, and is suppressed to a level causing no visual problem together with the main scanning direction.

Although the description has been made mainly on the behavior at the time of temperature rise with respect to the environmental fluctuation, the same effect as described above can be obtained also in other environmental fluctuations such as a temperature decrease.

In this embodiment, all of these environmental fluctuations are compensated for by plastic optical elements, thereby reducing the manufacturing cost by molding, and shortening the optical path length by correcting the high angle of view aberration using an aspherical surface. Can be achieved at the same time.

As described above, in the present embodiment, a short-wavelength laser is used as the light source means as described above, and a fine spot diameter is achieved compared to the conventional art, thereby enabling a high-resolution image forming apparatus excellent in gradation expression. A plastic toric lens 63 and a composite optical element 64 are used as the optical means 46, and it is possible to correct chromatic aberration of magnification, which has conventionally been difficult to correct when a short wavelength laser is used with a plastic lens. In addition, a jitter during use of the multi-beam laser 51 is suppressed, a focus shift due to environmental fluctuation is compensated, and a color image forming apparatus with less density unevenness between colors is realized with a simple configuration and at low cost.

In each of the embodiments, the scanning optical means is constituted by two optical elements of a single refractive element (toric lens) and a single diffractive element (composite optical element). However, the present invention is not limited to this. A single optical element including a refractive surface and a diffractive surface, or three or more optical elements including a refractive surface and a diffractive surface may be used.

In each embodiment, both of the conditional expressions (Expression 4) and the conditional expression (Expression 10) are satisfied. However, only one conditional expression may be satisfied.

In each embodiment, the change in the focus position in the sub-scanning direction on the surface to be scanned due to the environmental fluctuation of the apparatus is compensated for by the power change between the refraction surface and the diffraction surface and the wavelength change of the light source means. The focus position change in the scanning direction is also compensated for by the power change between the refraction surface and the diffraction surface and the wavelength change of the light source means.

[Image Forming Apparatus] FIG. 15 is a sectional view of a main portion in the sub-scanning direction showing an embodiment of the image forming apparatus of the present invention. In the figure, reference numeral 104 denotes an image forming apparatus. Code data Dc is input to the image forming apparatus 104 from an external device 117 such as a personal computer. The code data Dc is converted into image data (dot data) Di by the printer controller 111 in the apparatus. This image data Di is input to the optical scanning unit 100 having the configuration shown in the first to fourth embodiments.
The optical scanning unit 100 outputs image data.
A light beam 103 modulated according to Di is emitted, and the light beam 103 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 115. Then, along with this rotation, the photosensitive surface of the photosensitive drum 101 moves in the sub-scanning direction orthogonal to the main scanning direction with respect to the light beam 103. Above the photosensitive drum 101, a charging roller 102 for uniformly charging the surface of the photosensitive drum 101 is provided so as to contact the surface.
The surface of the photosensitive drum 101 charged by the charging roller 102 is irradiated with a light beam 103 scanned by the optical scanning unit 100.

As described above, the light beam 103 is
The light is modulated based on the image data Di, and by irradiating the light beam 103, an electrostatic latent image is formed on the surface of the photosensitive drum 101. This electrostatic latent image is further moved from the irradiation position of the light beam 103 to the photosensitive drum 101.
Is developed as a toner image by a developing device 107 disposed so as to contact the photosensitive drum 101 on the downstream side in the rotation direction of the photosensitive drum 101.

The toner image developed by the developing device 107 is transferred below the photosensitive drum 101 onto a sheet 112 as a material to be transferred by a transfer roller 108 disposed so as to face the photosensitive drum 101. The sheet 112 is stored in a sheet cassette 109 in front of the photosensitive drum 101 (right side in FIG. 15), but can be fed manually. At the end of the paper cassette 109, the paper feed roller 1
10 are provided, and the paper 1 in the paper cassette 109 is provided.
12 to the transport path.

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

Although not shown in FIG. 15, the print controller 111 performs not only the above-described data conversion, but also a motor 115 and other components in the image forming apparatus, and a polygon motor in an optical scanning unit to be described later. And so on.

[Color Image Forming Apparatus] FIG. 16 is a schematic view of a main part of a color image forming apparatus according to an embodiment of the present invention. This embodiment is a tandem type color image forming apparatus in which four optical scanning devices are arranged and image information is recorded in parallel on the surface of a photosensitive drum as an image carrier. In FIG.
Reference numeral 60 denotes a color image forming apparatus; 11, 12, 13, and 14 each represent an optical scanning device having any of the configurations shown in the first to fourth embodiments; 21, 22, 23, and 24 each represent a photosensitive drum as an image carrier; , 31, 32, 33 and 34 are developing units, and 51 is a conveyor belt.

In FIG. 16, the color image forming apparatus 60
From an external device 52 such as a personal computer.
(Red), G (green), and B (blue) color signals are input. These color signals are converted into image data (dot data) of C (cyan), M (magenta), Y (yellow), and B (black) by the printer controller 53 in the apparatus. These image data are input to the optical scanning devices 11, 12, 13, and 14, respectively. From these optical scanning devices, light beams 41, 42, 43, 4 modulated in accordance with each image data are output.
4 are emitted, and the photosensitive drum 2 is
The photosensitive surfaces 1, 22, 23, and 24 are scanned in the main scanning direction.

The color image forming apparatus of this embodiment is composed of four optical scanning devices (11, 12, 13, 14), each of which is C (cyan), M (magenta), Y (yellow),
An image signal (image information) corresponding to each color of B (black) is provided on the photosensitive drums 21, 22, 23, and 24 in parallel.
Is recorded, and a color image is printed at a high speed.

The color image forming apparatus of this embodiment uses the four light scanning devices 11, 12, 13, and 14 to form latent images of respective colors by using the light beams based on the respective image data as described above. 21, 22, 23, 2
It is formed on four surfaces. Thereafter, multiple transfer to a recording material is performed to form one full color image.

As the external device 52, for example, a CCD
A color image reading device provided with a sensor may be used. In this case, the color image reading apparatus and the color image forming apparatus 60 constitute a color digital copying machine.

[0168]

According to the present invention, as described above, in an optical scanning apparatus using a short wavelength light source of 500 nm or less and an image forming apparatus using the same, at least one refracting surface and at least one By optimizing the power arrangement of the diffractive surface in the main scanning direction and / or the sub-scanning direction, it is possible to compensate for image position shift in the main scanning direction due to wavelength fluctuation (chromatic aberration of magnification) or / and environmental fluctuation (temperature change, etc.). To achieve an optical scanning device capable of suppressing out-of-focus in the sub-scanning direction (especially, curvature of field in the sub-scanning direction) and easily obtaining high-definition printing with a simple configuration, and an image forming apparatus using the same. be able to.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a main part of a color image forming apparatus according to a first embodiment of the present invention.

FIG. 2 is a main part schematic diagram showing the optical scanning device shown in FIG. 1 and an image carrier corresponding thereto.

FIG. 3 is a sectional view of a main part of the scanning optical unit shown in FIG. 2 in the main scanning direction.

FIG. 4 is a diagram showing a change in an imaging position in a main scanning direction due to a wavelength change in the first embodiment of the present invention.

FIG. 5 is a diagram showing a change in field curvature due to a wavelength change in the first embodiment of the present invention.

FIG. 6 is a sectional view of a main part of a scanning optical unit in a main scanning direction according to a second embodiment of the present invention.

FIG. 7 is a diagram illustrating a change in an imaging position in a main scanning direction due to a change in wavelength according to the second embodiment of the present invention.

FIG. 8 is a diagram illustrating a change in curvature of field due to a change in wavelength according to the second embodiment of the present invention.

FIG. 9 is a sectional view of a main part of a scanning optical unit in a main scanning direction according to a third embodiment of the present invention.

FIG. 10 is a diagram showing a change in an imaging position in a main scanning direction due to a wavelength change in Embodiment 3 of the present invention.

FIG. 11 is a diagram showing a change in field curvature due to a wavelength change in the third embodiment of the present invention.

FIG. 12 is a sectional view of a main part in a main scanning direction of a scanning optical unit according to a fourth embodiment of the present invention.

FIG. 13 is a diagram illustrating a change in an imaging position in the main scanning direction due to a change in wavelength according to the fourth embodiment of the present invention.

FIG. 14 is a diagram illustrating a change in curvature of field due to a change in wavelength according to the fourth embodiment of the present invention.

FIG. 15 is a sub-scan sectional view showing an embodiment of the image forming apparatus of the present invention.

FIG. 16 is a schematic diagram of a main part of a color image forming apparatus according to an embodiment of the present invention.

FIG. 17 illustrates a conventional multi-beam optical scanning device.

FIG. 18 is a schematic view of a main part of a conventional color image forming apparatus.

FIG. 19 is a sectional view of a main part of a conventional optical scanning device in a main scanning direction.

FIG. 20 is a diagram showing a change in an imaging position in a main scanning direction due to a change in wavelength in a conventional scanning optical unit.

FIG. 21 is a diagram showing a refractive index wavelength characteristic of an optical resin.

[Explanation of symbols]

 1, 51 light source means 2 collimator lens 3 stop 4 cylindrical lens 5 deflection means 6, 46 scanning optical means 61, 63 refraction element 62, 64 diffraction element (composite Optical elements) 71, 72 {Diffraction grating 8} Scanned surface 11, 12, 13, 14 Optical scanning device 21, 22, 23, 24 Image carrier (photosensitive drum) 31, 32, 33, 34 {developing device 41} conveyer belt 51 {multi-beam laser 52} external device 53 {printer controller 60} color image forming device 100 optical scanning device 101 photosensitive drum 102 charging roller 103 light beam 104 image forming device 107 developing device 108 transfer roller 109 paper cassette 110 paper feed roller 111 printer controller 112 transfer material (paper) 113 Fixing roller 114 Pressure roller 115 Motor 116 Discharge roller 117 External device

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (reference) G02B 13/00 G02B 13/08 5C072 13/08 13/18 5F073 13/18 H01S 5/323 610 H01S 5 / 323 610 H04N 1/036 A H04N 1/036 B41J 3/00 D 1/113 H04N 1/04 104A F-term (reference) 2C362 AA03 AA13 BA51 BA52 BA58 BA86 CA22 CA39 2H045 BA22 BA23 CA04 CA34 CA55 CA67 CB22 2H049 AA04 AA14A AA39 AA43 AA55 AA64 2H087 KA19 LA22 NA08 NA14 PA02 PA17 PB02 QA03 QA12 QA18 QA22 QA38 QA41 RA05 RA07 RA08 RA13 RA46 UA01 5C051 AA02 CA07 DA02 DB02 DB22 DB24 DB30 DC01 DC04 DC07 EA01 DA03 HA19 DA01 DA02A QA14 XA01 XA05 5F073 BA07 CA02 EA05

Claims (34)

[Claims] 1. An optical scanning device comprising: a deflecting unit that deflects a light beam emitted from a light source unit; and a scanning optical unit that forms an image of the light beam deflected by the deflecting unit on a surface to be scanned. The scanning optical means has at least one refracting surface and at least one diffractive surface, the combined power of the refracting surface in the main scanning direction Φr, the combined power of the diffracting surface in the main scanning direction Φd, and the oscillation wavelength of the light source means. When the rate of change of the refractive index of the material of the optical element forming the refraction surface is dn / dλ (/ nm), -2.37 × 10 ⁻³ (/ nm) <(Φr / Φd) × (dn / d)
λ) <-0.9 × 10 ⁻³ (/ nm). 2. The scanning optical means comprises: -2.25 × 10 ⁻³ (/ nm) <(Φr / Φd) × (dn / d
2. The optical scanning device according to claim 1, wherein the following condition is satisfied: λ) <− 1.30 × 10 ⁻³ (/ nm). 3. An oscillation wavelength of said light source means is 380 nm or more.
The optical scanning device according to claim 1, wherein the optical scanning device is within a range of 500 nm. 4. The optical scanning device according to claim 1, wherein said light source means includes a gallium nitride-based blue-violet semiconductor laser. 5. The scanning optical unit according to claim 1, wherein the chromatic aberration of magnification in the main scanning direction is corrected.
The optical scanning device according to claim 1. 6. The scanning optical means according to claim 1, wherein said scanning optical means includes a single refracting element and a single diffractive element having a plane-shaped diffraction grating surface. 1
Item 6. The optical scanning device according to Item 1. 7. The optical scanning device according to claim 6, wherein the refraction element and the diffraction element are made of a plastic material. 8. The optical scanning device according to claim 1, wherein said light source means includes a monolithic multi-beam laser having a plurality of light emitting points. 9. A light source device comprising: a plurality of laser light sources; a plurality of light beams emitted from the plurality of laser light sources being combined by a beam combining means and guided to the deflecting means. The optical scanning device according to claim 1. 10. An optical scanning device comprising: deflecting means for deflecting a light beam emitted from a light source means; and scanning optical means for forming an image of the light beam deflected by the deflecting means on a surface to be scanned. The scanning optical means has at least one refracting surface and at least one diffractive surface, the combined power of the refracting surface in the sub-scanning direction is Δr, the combined power of the diffractive surface in the sub-scanning direction is Δd, and the oscillation of the light source means with respect to temperature. The rate of change of the wavelength is dλ / dt (nm /
° C), 15.0 (° C / nm) <ψr / [ψd × (dλ / dt)] <45.
An optical scanning device satisfying a condition of 0 (° C./nm). 11. The scanning optical means includes: 18.0 (° C./nm)<ψr/[ψd×(dλ/dt)]<38.
The optical scanning device according to claim 10, wherein a condition of 0 (° C / nm) is satisfied. 12. An oscillation wavelength of the light source means is 380 nm.
2. The method according to claim 1, wherein the wavelength is within a range of about 500 nm.
12. The optical scanning device according to 0 or 11. 13. The optical scanning device according to claim 10, wherein said light source means comprises a gallium nitride-based blue-violet semiconductor laser. 14. The optical scanning device according to claim 10, wherein the scanning optical unit compensates for a focus position variation on a surface to be scanned due to a temperature variation. 15. The scanning optical means according to claim 10, wherein said scanning optical means includes a single refracting element and a single diffractive element having a plane-shaped diffraction grating surface. Item 2. The optical scanning device according to item 1. 16. The apparatus according to claim 1, wherein the refracting element and the diffractive element are made of a plastic material.
6. The optical scanning device according to claim 5. 17. The optical scanning device according to claim 10, wherein said light source means includes a monolithic multi-beam laser having a plurality of light emitting points. 18. A light source device comprising a plurality of laser light sources, a plurality of light beams emitted from the plurality of laser light sources being combined by a beam combining means, and guided to the deflecting means. The optical scanning device according to claim 10. 19. An optical scanning apparatus comprising: a deflecting unit that deflects a light beam emitted from a light source unit; and a scanning optical unit that forms an image of the light beam deflected by the deflecting unit on a surface to be scanned. The scanning optical means has at least one refracting surface and at least one diffractive surface, the combined power of the refracting surface in the main scanning direction Φr, the combined power of the diffracting surface in the main scanning direction Φd, and the oscillation wavelength of the light source means. The rate of change of the refractive index of the material of the optical element forming the refractive surface is dn / dλ (/ nm), the combined power of the refractive surface in the sub-scanning direction is Δr, the combined power of the diffraction surface in the sub-scanning direction is Δd, When the change rate of the oscillation wavelength of the light source means is dλ / dt (nm / ° C.), -2.37 × 10 ⁻³ (/ nm) <(Φr / Φd) × (dn / dλ)
<−0.9 × 10 ⁻³ (/ nm) 15.0 (° C./nm)<Δr/[Δd×(dλ/dt)]<45.
An optical scanning device satisfying a condition of 0 (° C./nm). 20. The scanning optical means, wherein -2.25 × 10 ⁻³ (/ nm) <(Φr / Φd) × (dn / d
λ) <− 1.30 × 10 ⁻³ (/ nm) 18.0 (° C./nm)<ψr/[ψd×(dλ/dt)]<38.
20. The optical scanning device according to claim 19, wherein a condition of 0 (° C./nm) is satisfied. 21. An oscillation wavelength of the light source means is 380 nm.
2. The method according to claim 1, wherein the wavelength is within a range of about 500 nm.
21. The optical scanning device according to 9 or 20. 22. The optical scanning device according to claim 19, wherein said light source means comprises a gallium nitride based blue-violet semiconductor laser. 23. The scanning optical unit according to claim 13, wherein the chromatic aberration of magnification in the main scanning direction is corrected, and the focus position fluctuation in the sub-scanning direction on the surface to be scanned due to temperature fluctuation is compensated. 23. The optical scanning device according to any one of 19 to 22. 24. The scanning optical device according to claim 19, wherein the scanning optical means has a single refracting element and a single diffractive element having a plane-shaped diffraction grating surface. Item 2. The optical scanning device according to item 1. 25. The refraction element and the diffraction element are made of a plastic material.
5. The optical scanning device according to 4. 26. The optical scanning device according to claim 19, wherein said light source means includes a monolithic multi-beam laser having a plurality of light emitting points. 27. A light source device comprising: a plurality of laser light sources; a plurality of light beams emitted from the plurality of laser light sources being combined by a beam combining means, and guided to the deflecting means. The optical scanning device according to any one of claims 19 to 25. 28. An optical scanning device comprising: deflecting means for deflecting a light beam emitted from a light source means; and scanning optical means for forming an image of the light beam deflected by the deflecting means on a surface to be scanned. An optical scanning device wherein the oscillation wavelength of the light source means is in the range of 380 to 500 nm, and the scanning optical means has corrected chromatic aberration of magnification. 29. An optical scanning device comprising: deflecting means for deflecting a light beam emitted from a light source means; and scanning optical means for forming an image of the light beam deflected by the deflecting means on a surface to be scanned. An optical scanning device, wherein an oscillation wavelength of the light source means is in a range of 380 to 500 nm, and a focus position variation on a surface to be scanned due to a temperature variation of the optical scanning device is compensated. 30. An optical scanning device comprising: a deflecting unit that deflects a light beam emitted from a light source unit; and a scanning optical unit that forms an image of the light beam deflected by the deflecting unit on a surface to be scanned. The oscillation wavelength of the light source means is in the range of 380 to 500 nm, the scanning optical means corrects for chromatic aberration of magnification, and compensates for focus position fluctuation on the surface to be scanned due to temperature fluctuation of the optical scanning device. An optical scanning device, comprising: 31. An optical scanning device according to claim 1, further comprising: a photoconductor disposed on the surface to be scanned.
A developing device for developing an electrostatic latent image formed on the photoreceptor by the light beam scanned by the optical scanning device as a toner image, a transfer device for transferring the developed toner image to a transfer material, and a transfer device An image forming apparatus, comprising: a fixing device for fixing the formed toner image to a transfer material. 32. An optical scanning device according to claim 1, 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. An image forming apparatus comprising: 33. Each of claims 1 to 30
A plurality of optical scanning devices comprising the optical scanning device according to the item, and a plurality of image carriers that are arranged on the surface to be scanned of each optical scanning device and form images of different colors from each other. Color image forming apparatus. 34. A color image according to claim 33, further comprising a printer controller for converting a color signal input from an external device into image data of a different color and inputting the data to each optical scanning device. Forming equipment.