JP3397638B2 - Optical scanning optical system and image forming apparatus using the same - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light scanning optical system and an image forming apparatus using the same, and particularly to a first optical system arranged on the light source means side of an optical deflector and a surface to be scanned. By providing a diffractive optical element in at least one of the second optical systems, it is suitable for high-definition printing in which aberration variation (focus variation) does not occur even when environmental variation (especially temperature variation) occurs in the apparatus. For example, it is suitable for an image forming apparatus such as a laser beam printer (LBP) and a digital copying machine.

[0002]

2. Description of the Related Art Conventionally, in a scanning optical system used in a laser beam printer, a digital copying machine or the like, a light beam which is light-modulated from a light source means in accordance with an image signal and is emitted is composed of, for example, a light composed of a rotating polygon mirror. A recording medium (photosensitive drum) which is photosensitive by a scanning optical element (imaging element) having an fθ characteristic, which is periodically deflected by a deflector.
An image is recorded by converging a spot on the surface and optically scanning the surface.

In this type of optical scanning optical system, a system in which a diffractive optical element is applied to the optical system is disclosed in, for example, Japanese Patent Laid-Open No.
It is proposed in Japanese Patent No. 125111. In this publication, an optical system is configured by a holographic fθ lens having power only in the main scanning direction and a cylindrical lens having power in the subscanning direction, and fθ characteristics, surface tilt correction, first-order diffracted light, and other orders are obtained. Separation of diffracted light is performed.

US Pat. No. 5,486,694 discloses an optical scanning optical system having a toric lens provided with a diffractive surface and having a surface tilt correction effect.

[0005]

[Patent Document 1] Japanese Unexamined Patent Application Publication No.
The cylindrical lens in the -125111 publication has a cost advantage over the conventional fθ lens in which a plurality of lenses are combined, for example, when the cylindrical lens is made of a glass material. It is more expensive than a plastic lens. On the other hand, if the cylindrical lens is made of a plastic material in order to keep the cost low, environmental shift, particularly temperature change, causes a focus shift in the sub-scanning direction. In order to prevent this, it suffices to bring the cylindrical lens close to the surface to be scanned, but then the cylindrical lens becomes large, and as a result, the entire apparatus becomes large and the cost becomes high. Will occur.

There is a problem in US Pat. No. 5,486,694 that no consideration is given to the deterioration of aberration caused by the change of the diffraction angle due to the wavelength variation of the laser light.

On the other hand, as the scanning optical element (fθ lens) in the scanning optical system, a plastic lens is mainly used because of the demand for cost reduction and compactness.

FIG. 8 is a schematic view of a main part of a conventional optical scanning optical system of this type. In the figure, the divergent light beam emitted from the light source means 81 is made into a substantially parallel light beam by the collimator lens 82, and the light beam (amount of light) is limited by the diaphragm 83 to form a cylindrical lens 84 having a predetermined refractive power only in the sub-scanning direction. It is incident. Within the main scanning cross section, the parallel light flux that has entered the cylindrical lens 84 is emitted as it is in the state of an optical parallel light flux. Further, in the sub-scanning cross section, they converge and form a substantially linear image on the deflecting surface (reflecting surface) 85a of the optical deflector 85 composed of a rotating polygon mirror (polygon mirror).

A scanning optical element (f.theta. Lens) 8 having the f.theta. Characteristic for the light beam deflected by the deflecting surface of the optical deflector 85.
Light is guided onto the photosensitive drum surface 87 as a surface to be scanned via 6 and the optical deflector 85 is rotated in the direction of arrow A, so that the photosensitive drum surface 87 is optically scanned in the direction of arrow B. . As a result, an image is recorded on the photosensitive drum surface 87, which is a recording medium. The collimator lens 82,
Each element of the diaphragm 83 and the cylindrical lens 84 constitutes one element of the first optical system L ₈₁ , and the fθ lens 86 constitutes one element of the second optical system L ₈₂ .

In the optical scanning optical system of this type, due to the demand for cost reduction and downsizing of the fθ lens as described above, the fθ lens is often constructed by only one plastic lens having an aspherical shape. There is. However, since the plastic material has the property that the refractive index changes with changes in the operating environment (especially temperature changes),
In these scanning optical systems, focus changes occur due to environmental changes. There is no problem because the current focus fluctuation amount is set so as not to affect the actual image,
When it is desired to reduce the spot diameter of the focused beam on the surface to be scanned for the purpose of high-definition printing, and for the purpose of further cost reduction and size reduction, the fθ lens is used as an optical deflector in order to make it smaller. When trying to bring them closer to each other, there is a problem that the above-mentioned focus fluctuation, especially the focus fluctuation in the sub-scanning direction becomes unacceptable.

In order to solve the above problems, the present invention provides at least one of a first optical system arranged on the light source means side and a second optical system arranged on the scanned surface side of the optical deflector. By providing a diffractive optical element in the optical system, a compact scanning optical system suitable for high-definition printing in which aberration fluctuation (focus change) does not occur even if environmental fluctuations (especially temperature fluctuations) occur in the apparatus, and images using the same An object is to provide a forming apparatus.

The optical scanning optical system according to the invention of claim 1 is a light source means.
The light flux emitted from the first optical system to the deflection means.
Light, and the light beam deflected by the deflecting means is refracted and diffracted.
An image is formed on the surface to be scanned through the second optical system that has,
In the optical scanning optical system for optically scanning the surface to be scanned,
The optical system of the
-Power in the sub-scanning direction of the diffraction part due to changes and environmental changes
-A change has occurred and the sub-scanning direction of the refraction part of the second optical system
Direction power and diffractive part power in the sub-scanning direction are φL and
And φB, 1.0 ≦ φL / φB ≦ 2.6 is satisfied. In the optical scanning optical system according to a second aspect of the invention, the light beam emitted from the light source means is first
Light is guided to the deflection means through the optical system of and is deflected by the deflection means.
The formed light flux is imaged on the surface to be scanned via the second optical system.
The optical scanning optical system that optically scans the surface to be scanned.
The second optical system has a refraction part and a diffraction part, and
Sub-running of the refraction part of the second optical system due to the change in the refractive index that occurs
Wave of light source means caused by power fluctuation in the scanning direction and temperature fluctuation
Power in the sub-scanning direction of the refracting portion of the second optical system due to long fluctuations
-Change due to wavelength fluctuation of light source means caused by temperature fluctuation
Due to the power change in the sub-scanning direction of the diffractive part of the second optical system
It is characterized by being corrected. The invention of claim 3 is the refracting portion of the second optical system in the invention of claim 1 or 2.
Is characterized by having a plastic lens
It The optical scanning optical system according to the invention of claim 4 radiates from the light source means.
The deflected light beam through the first optical system having the diffractive portion.
The light beam guided to the step and the light beam deflected by the deflecting means is rotated together with the refracting portion.
An image is formed on the surface to be scanned through the second optical system having a folded portion.
And an optical scanning optical system for scanning the surface to be scanned,
The refraction part of the second optical system has a plastic lens,
In the sub-scanning direction due to temperature fluctuations of the plastic lens
Aberration variation due to wavelength variation of the light source means due to the temperature variation
It is characterized in that the correction is made by the power change of the diffractive part of the first optical system and the power change of the diffractive part of the second optical system. The optical scanning optical system according to the invention of claim 5 is a light source.
Deflection means for deflecting the luminous flux emitted from the means through the first optical system
The light beam deflected by the deflecting means and diffracts to the refraction part.
An image on the surface to be scanned through a second optical system having
An optical scanning optical system for scanning the surface to be scanned,
The refraction part of the optical system of 2 has a plastic lens,
The sub-scanning direction convergence due to the temperature fluctuation of the plastic lens
The difference fluctuation is caused by the wavelength fluctuation of the light source means due to the temperature fluctuation.
The feature is that it is corrected by the power change at the fold.
It is a sign. According to a sixth aspect of the present invention, in the fifth aspect of the invention, the sub-scanning direction according to the temperature variation of the plastic lens
The aberration variation of the plastic lens is caused by the temperature variation.
Wavelength of light source means caused by changes in refractive index and temperature changes
Change due to the change in the refractive index of the plastic lens
Characterized by a change in power in the scanning direction
It The invention of claim 7 is the invention of claim 2, 4, 5 or 6, wherein the power of the diffractive portion in the second optical system is φB,
It is characterized in that the condition of 1.0 ≦ φL / φB ≦ 2.6 is satisfied when the power of the folded portion is φL .

According to an eighth aspect of the present invention, in the invention according to any one of the first to seventh aspects, the aberration variation is focus variation.
It is characterized by that. The invention of claim 9 relates to claims 1 to 8.
In the invention of any one of paragraphs 1, the diffractive portion has a lattice structure.
Is composed of a stepwise optical element. According to a tenth aspect of the invention, in the invention according to any one of the first to eighth aspects, the diffractive portion is a Fresnel-shaped light having a continuous grating structure.
It is characterized by consisting of scientific elements. The invention of claim 11 is the first aspect of the invention of any one of claims 1 to 10 .
The optical system of the above makes the light beam on the deflection surface of the deflection means in the main scanning direction.
It has the function of forming a long line image on the
I am trying. The invention of claim 12 is the invention of any one of claims 1 to 11, wherein the first optical system is a cylindrical
A lens, and a diffractive portion on the surface of the cylindrical lens.
It is characterized by having. The invention of claim 13 is the first optical element according to any one of claims 1 to 12.
The system has a collimator lens, and the collimator lens surface
It is characterized by having a diffractive part on the top. Claim 14
The invention according to any one of claims 1 to 13
Main scanning direction due to temperature fluctuation of the refraction part of the optical scanning optical system
Changes in the wavelength of the light source means due to the temperature change
The power of the diffractive part
It is characterized by. The invention of claim 15 is claims 1 to 1.
In the invention of any one of 4 above, the optical scanning optical system is
A light source means is provided, and the light source means is a semiconductor laser.
It is characterized by that.

[0014] The image forming apparatus of the invention of claim 16 according to claim
16. The optical scanning optical system according to any one of 1 to 15,
The feature is that the photosensitive drum surface is used as the surface to be scanned.
ing.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a sectional view of a main part in a main scanning direction (main scanning section) when a scanning optical system according to a first embodiment of the present invention is applied to an image forming apparatus such as a laser beam printer or a digital copying machine. Figure).

In the figure, reference numeral 1 denotes a light source means, which is composed of, for example, a semiconductor laser. A collimator lens 2 converts a divergent light beam (light beam) emitted from the light source means 1 into a substantially parallel light beam. An aperture stop 3 limits the passing light flux (light quantity) to shape the beam shape.

Reference numeral 4 is a diffractive optical element having a diffractive surface,
For example, a flat plate formed of a glass material or a plastic material is added to the flat surface on the side of the optical deflector 5 described later. The diffractive optical element 4 has a power (diffraction power) in the sub-scanning direction, and forms the light flux passing through the aperture stop 3 on the deflecting surface 5a of the optical deflector 5 as a substantially linear image in the sub-scanning cross section.

The diffractive optical element 4 in this embodiment has, for example, a binary diffractive optical element whose grating structure is a stepped diffractive grating formed by photoetching, or a Fresnel diffractive optical element which is a sawtooth diffractive grating formed by surface cutting. Etc. Each element of the collimator lens 2, the diaphragm 3, and the diffractive optical element 4 includes the first optical system L ₁
It constitutes one element.

Denoted at 5 is an optical deflector composed of, for example, a polygon mirror (rotary polygon mirror) as a deflecting means, 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 an fθ lens (scanning optical element) having an fθ characteristic, which is composed of a single lens made of a plastic material, and both lens surfaces in the main scanning direction of the single lens are aspherical. , Have different refractive powers in the main scanning direction and the sub-scanning direction. The fθ lens 6 forms a light beam based on the image information deflected by the optical deflector 5 on the photosensitive drum surface 7 that is the surface to be scanned and corrects the surface tilt of the deflecting surface of the optical deflector 5. The fθ lens 6 constitutes one element of the second optical system L ₂ .

In this embodiment, the divergent light beam emitted from the semiconductor laser 1 is converted into a substantially parallel light beam by the collimator lens 2, and the light beam (amount of light) is limited by the aperture stop 3 to enter the diffractive optical element 4. Diffractive optical element 4
The parallel light flux incident on the light exits as it is in the main scanning cross section. In the sub-scanning section, they converge and form a substantially linear image (longitudinal line image in the main scanning direction) on the deflection surface 5a of the optical deflector 5. Then, the light beam deflected by the deflecting surface 5a of the optical deflector 5 is guided onto the photosensitive drum surface 7 via the fθ lens 6, and the optical deflector 5 is rotated in the direction of arrow A so that the photosensitive drum surface 7 is rotated. The upper part is optically scanned in the direction of arrow B. As a result, an image is recorded on the photosensitive drum surface 7, which is the recording medium.

Here, the principle of correction of focus fluctuation in the sub-scanning direction in this embodiment will be described with reference to FIG. FIG. 2 is a sectional view of an essential part of the optical system of the present embodiment in the sub-scanning direction.
In the figure, the same elements as those shown in FIG. 1 are designated by the same reference numerals.

Here, it is assumed that the temperature of the scanning optical system rises due to the influence of environmental changes. If the fθ lens 6 is made of a plastic material, the refractive index of the plastic material generally decreases as the temperature rises, so the focus position in the sub-scanning direction fluctuates from point P to point Q in the figure. It causes out of focus.

However, the semiconductor laser 1 as a light source has a characteristic that its oscillation wavelength becomes longer as the temperature rises. When the oscillation wavelength becomes long, the diffractive optical element 4
Since the diffraction angle diffracted by becomes large, the optical deflector 5 originally
The linearly imaged light flux at the point R near the deflection surface is linearly imaged at the point S on the semiconductor laser 1 side of the point R as shown in FIG. Then, the focus position, which has changed to the point Q due to the decrease in the refractive index of the fθ lens 6, is returned to the point P again.

Based on the above principle, in the present embodiment, the powers of the diffractive optical element 4 and the f.theta. The focus variation (aberration variation) in the scanning direction can be almost completely corrected by utilizing the wavelength variation of the semiconductor laser 1.

Tables 1 and 2 show the optical arrangement, the aspherical coefficient of the fθ lens 6 and the phase term of the diffractive optical element 4 in this embodiment.

[0027]

[Table 1]

[0028]

[Table 2] The diffractive surface 4a of the diffractive optical element 4 in the present embodiment is configured on the optical deflector 5 side, the phase function is φ (y, z), the intersection with the optical axis is the origin, and the optical axis direction is the x-axis. , Where the axis orthogonal to the optical axis in the main scanning plane is the y axis and the axis orthogonal to the optical axis in the sub scanning plane is the z axis,

[0029]

[Equation 1] It is expressed by

The lens shape of the fθ lens 6 is such that the origin is at the intersection of each lens surface and the optical axis, the optical axis direction is the x-axis, the axis orthogonal to the optical axis in the main scanning plane is the y-axis, and the sub-scan is performed. When the axis orthogonal to the optical axis in the plane is the z-axis, the main scanning sectional shape is

[0031]

[Equation 2] It is expressed by In addition, R is a radius of curvature, K, B _{4 to} B
₁₀ is an aspherical coefficient. Here, when the value of y is positive, the lens shape is calculated using ku and B ₄ u to B ₁₀ u with the subscript u as the aspherical surface coefficient, and when the value of y is negative, The lens shape is calculated using kl, B ₄ l-B ₁₀ l with the subscript 1 as the spherical coefficient.

In the sub-scanning section, the radius of curvature continuously changes, and the radius of curvature r'where the lens coordinate is y on the main scanning plane is r '= r (1 + D
₂ y ² + D ₄ y ⁴ + D ₆ y ⁶ + D ₈ y ⁸ + D ₁₀ y ¹⁰ ). In addition, r is a radius of curvature on the optical axis, and D _{2 to} D ₁₀ are respective coefficients. Here, when the value of y is positive, the radius of curvature r ′ is calculated using D ₂ u to D ₁₀ u with the subscript u as a coefficient, and when the value of y is negative, the subscript is used as a coefficient. The radius of curvature r ′ is calculated using D ₂ l to D ₁₀ l with l.

FIG. 3 is an aberration diagram showing the field curvature in the sub-scanning direction before and after the temperature rise of this embodiment, the solid line shows the characteristics at room temperature,
The dotted line shows the characteristics when a temperature rise of 25 ° C. occurs. From this figure, it can be seen that there is almost no focus change in the sub-scanning direction before and after the temperature rise.

As described above, in this embodiment, the diffractive optical element 4 is used in place of the cylindrical lens (see FIG. 8) which has been conventionally used as one element of the first optical system, and the diffractive optical element 4 is used. By appropriately setting the power (diffraction power) in the sub-scanning direction and the power (refractive power) in the sub-scanning direction of the fθ lens 6, the focus change in the sub-scanning direction due to the temperature change of the device can be prevented. Laser 1
It is effectively corrected by utilizing the wavelength variation of. This makes it possible to obtain a scanning optical system that is resistant to environmental changes and that is suitable for high-definition printing in a compact size and at a low cost.

FIG. 4 is a sectional view of the main part in the main scanning direction when the scanning optical system according to the second embodiment of the present invention is applied to an image forming apparatus. In the figure, the same elements as those shown in FIG. 1 are designated by the same reference numerals.

This embodiment differs from the first embodiment in that a diffractive optical element is added to the lens surface on the optical deflector side of the fθ lens forming the second optical system to form the first optical system. Each element is composed of a collimator lens, a diaphragm, and a cylindrical lens as in the conventional configuration (see FIG. 8). Other configurations and optical actions are substantially the same as those in the first embodiment, and the same effect is obtained.

That is, in the figure, reference numeral 46 designates the second optical system L _42.
Fθ lens, which is composed of an aspherical single lens formed of a plastic material, and has power (diffraction power) in the sub-scanning direction on the lens surface (first surface) Ra of the single lens on the optical deflector 5 side. Is formed by adding a diffractive optical element 48 having
Is represented by the same formula as in the first embodiment described above.

That is, the diffractive surface 48a of the diffractive optical element 48 added to the first surface Ra of the fθ lens 46 has a phase function of φ (y, z), and the intersection of the first surface Ra and the optical axis is defined as When the origin is set, the optical axis direction is the x axis, the axis orthogonal to the optical axis in the main scanning plane is the y axis, and the axis orthogonal to the optical axis in the sub scanning plane is the z axis.

[0039]

[Equation 3] It is expressed by

A cylindrical lens 44 constitutes one element of the first optical system L ₄₁ , and has a predetermined refractive power in the sub-scanning direction.

Here, the principle of correction of focus variation in the sub-scanning direction in this embodiment will be described.

Now, when the scanning optical device in this embodiment is at the environmental temperature t ° C., the refractive index of the fθ lens 46 is n, and the oscillation wavelength of the semiconductor laser 1 is λ.

If the temperature dependence coefficient of the refractive index of the fθ lens 46 is dn / dt and the temperature dependence coefficient of the wavelength of the semiconductor laser 1 is dλ / dt, the wavelength dependence coefficient of the refractive index of the fθ lens 46 is dn / dλ. Refractive index n ′ of fθ lens 46 and wavelength λ ′ of semiconductor laser 1 when it changes by Δt
Respectively

[0044]

[Equation 4] Is represented.

On the other hand, the power φ _B of the diffractive optical element 48 formed on the first surface Ra of the fθ lens 46 is equal to the power φ _B of the diffractive surface 48a.
If the lattice spatial frequency at the upper ray passing point is H,

[0046]

[Equation 5] It is represented by.

Therefore, the radius of curvature of the first surface Ra of the fθ lens 46 in the sub-scan section on the optical axis is r ₁ , and the second surface Rb is
Let r ₂ be the radius of curvature of the sub-scanning cross section on the optical axis, and assume that a thin system is used for the sake of simplicity and that the power of the diffractive optical element 48 and the power of refraction exist at the same position.
The power φ _{t in} the sub-scanning direction of the fθ lens 46 at the environmental temperature t ° C. is expressed by the following equation.

[0048]

[Equation 6] On the other hand, the fθ lens 4 when the environmental temperature changes by Δt
The power φ _t ′ of 6 in the sub-scanning direction is expressed by the following equation.

[0049]

[Equation 7] In principle, if the power of the fθ lens 46 in the sub-scanning direction is kept constant irrespective of the environmental temperature, focus fluctuation in the sub-scanning direction does not occur in principle.

Therefore, assuming that equations (1) and (2) are equal, finally

[0051]

[Equation 8] The power φ _B of the diffractive optical element (diffraction part) 48 of the fθ lens 46 with the diffraction order as the first order is

[0052]

[Equation 9] The power φ _L of the fθ lens 46 other than the diffractive optical element (refraction portion) is

[0053]

[Equation 10] Equation (3) is

[0054]

[Equation 11] Therefore, if the power φ _B of the diffractive portion and the power φ _{L of the} refractive portion of the fθ lens 46 are determined so as to satisfy this equation,
It is possible to almost completely correct the focus fluctuation due to the change in the environmental temperature.

Here, dλ / dt, dn / dt, dn /
Considering the actual possible value of dλ, when the power of the diffractive portion of the fθ lens 46 in the sub-scanning direction is φ _B and the power of the refracting portion in the sub-scanning direction is φ _L , 1.0 ≦ φ _L / φ _B ≦ 2.6 ····················· (5) It is desirable to set each power.

Conditional expression (5) relates to the ratio between the power of the refracting portion and the power of the diffracting portion which compose the fθ lens 46. If the conditional expression (5) is not satisfied, the sub-scanning due to the environmental change of the apparatus will occur. It is not good because it becomes difficult to correct the focus change in the direction.

In the present embodiment, φ _L / φ _B = 1.171 and conditional expression (5) is satisfied.

Tables 3 and 4 show the optical arrangement, the aspherical coefficient of the fθ lens 46 and the diffractive optical element 4 in this embodiment.
8 shows the phase term of 8.

[0059]

[Table 3]

[0060]

[Table 4] FIG. 5 is an aberration diagram showing the field curvature in the sub-scanning direction before and after the temperature rise of this embodiment. The solid line shows the characteristics at room temperature, and the dotted line shows 25 ° C.
The characteristics when the temperature rises are shown. From this figure, it can be seen that there is almost no focus change in the sub-scanning direction before and after the temperature rise.

As described above, in this embodiment, as described above, the diffractive optical element 48 is added to the lens surface Ra of the fθ lens 46 which is the second optical system L ₄₂ on the optical deflector 5 side, and the fθ lens 46 of the fθ lens 46 is added. By appropriately setting the power of the diffractive portion in the sub-scanning direction (diffraction power) and the power of the refraction portion in the sub-scanning direction (diffraction power), the focus change in the sub-scanning direction due to the temperature fluctuation of the device can be prevented. The wavelength variation of the laser 1 is used for good correction. This makes it resistant to environmental changes,
Moreover, the scanning optical system suitable for high-definition printing is compact,
And it can be obtained at low cost.

FIG. 6 is a sectional view of the main part in the main scanning direction when the scanning optical system according to the third embodiment of the present invention is applied to an image forming apparatus. In the figure, the same elements as those shown in FIG. 4 are designated by the same reference numerals.

The present embodiment differs from the second embodiment described above in that a diffractive optical element is added to one surface of a cylindrical lens which constitutes one element of the first optical system. Other configurations and optical actions are substantially the same as those in the first embodiment, and the same effect is obtained.

That is, in the figure, 64 is the first optical system L.
₆₁ is a cylindrical lens constituting one element, and the lens surface on the light source means 1 side of the cylindrical lens 64 is constituted by a cylindrical surface having a predetermined power in the sub-scanning direction, and the lens surface on the optical deflector 5 side (planar surface). ) Is added with a diffractive optical element 68 having a power (diffraction power) in the sub-scanning direction. Reference numeral 46 is an fθ lens similar to that of the second embodiment.

In this embodiment, the above-described first embodiment is used.
The focus change in the sub-scanning direction due to the temperature change of the apparatus is utilized by using both the correction principle of the focus change in the sub-scanning direction described in 1) and the correction principle of the focus change in the sub-scanning direction described in the second embodiment. Corrected well. As a result, in the present embodiment, the cylindrical lenses 64 and f
The power of each diffractive portion (diffractive optical element) of the θ lens 46 in the sub-scanning direction can be set to a small value, and as a result, the grating pitch of each diffractive optical element 68, 48 can be increased, which is extremely advantageous in manufacturing. Be advantageous.

Tables 5 and 6 show the optical arrangement, the aspherical coefficient of the fθ lens 46, the shape of the cylindrical lens 64, and the phase terms of the diffractive optical elements 68 and 48 in this embodiment.

[0067]

[Table 5]

[0068]

[Table 6] FIG. 7 is an aberration diagram showing the curvature of the bay surface in the sub-scanning direction before and after the temperature rise of the present embodiment. The solid line shows the characteristics at room temperature, and the dotted line shows 25 ° C.
The characteristics when the temperature rises are shown. From this figure, it can be seen that there is almost no focus change in the sub-scanning direction before and after the temperature rise.

As described above, in this embodiment, as described above, the first
By providing diffractive optical elements in both the optical system L ₆₁ and the second optical system L ₄₂ , it is possible to set the grating pitch of each diffractive optical element to a large value, which makes it very easy to manufacture scanning optics. The system can be configured. Although the diffractive optical element is added to one surface of the cylindrical lens 64 in the present embodiment, the present invention is not limited to this, and the diffractive optical element may be added to one surface of the collimator lens 2. good.

In Embodiments 2 and 3 described above, the diffractive optical element is added to at least one surface of the optical element constituting each optical system, but the present invention is not limited to this, and the diffractive optical element may be independently provided in the optical path. It may be configured.

Further, in each of the embodiments, the correction method for the focus change in the sub-scanning direction due to the temperature change of the apparatus has been described. Of course, the focus change in the main scanning direction is also diffracted in the main scanning direction. It can be easily corrected by using the diffractive optical element.

[0072]

According to the present invention, as described above, at least one of the first optical system arranged on the light source means side and the second optical system arranged on the scanned surface side of the optical deflector. A diffractive optical element is installed on the device to change the environment of the device (especially temperature change)
Aberration fluctuations (focus changes) in the sub-scanning direction due to fluctuations are corrected by power fluctuations of the diffractive optical element and wavelength fluctuations of the semiconductor laser, so compact scanning suitable for high-definition printing that is not affected by environmental fluctuations An optical system and an image forming apparatus using the same can be achieved.

In particular, when the diffractive optical element is provided in the second optical system, the power of each element is appropriately set so as to satisfy the above-mentioned conditional expression (5), so that it is not affected by environmental fluctuation. A compact scanning optical system suitable for fine printing and an image forming apparatus using the same can be achieved.

[Brief description of drawings]

FIG. 1 is a sectional view of a main part in a main scanning direction according to a first embodiment of the present invention.

FIG. 2 is an explanatory diagram illustrating a principle of correcting focus variation in the sub-scanning direction according to the first embodiment of the present invention.

FIG. 3 is a diagram showing field curvature in the sub-scanning direction according to the first embodiment of the present invention.

FIG. 4 is a sectional view of a main part in a main scanning direction according to a second embodiment of the present invention.

FIG. 5 is a diagram showing field curvature in the sub-scanning direction according to the second embodiment of the present invention.

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

FIG. 7 is a diagram showing field curvature in the sub-scanning direction according to the third embodiment of the present invention.

FIG. 8 is a schematic view of a main part of a conventional scanning optical system.

[Explanation of symbols]

1 Light Source Means (Semiconductor Laser) 2 Collimator Lens 3 Aperture Stops 4, 48, 68 Diffractive Optical Element 5 Deflection Means (Polygon Mirror) 6,46 Image Forming Means (fθ Lens) 7 Scanned Surface (Photosensitive Drum Surface) 44, 64 Cylindrical lenses L ₁ , L ₄₁ , L ₆₁ First optical system L ₂ , L ₄₂ Second optical system

Claims (16)

(57) [Claims] 1. A light beam emitted from a light source means is converted into a first optical beam.
The light is guided to the deflecting means through the system and is deflected by the deflecting means.
The light beam is projected through a second optical system having a refraction part and a diffraction part.
Optical scanning that forms an image on the scanning surface and optically scans the surface to be scanned.
In the inspection optical system, The second optical system operates in the sub-scanning direction of the refraction part due to environmental changes.
In the sub-scanning direction of the diffraction part due to power changes and environmental changes
Power change is occurring, The power of the refraction part of the second optical system in the sub-scanning direction and the diffraction part
When the powers in the sub-scanning direction are φL and φB, respectively, 1.0 ≤ φL / φB ≤ 2.6 An optical scanning optical system characterized by satisfying the following condition. 2. A light beam emitted from a light source means for the first optical
The light is guided to the deflecting means through the system and is deflected by the deflecting means.
The light flux is imaged on the surface to be scanned through the second optical system,
In an optical scanning optical system for optically scanning the surface to be scanned, The second optical system has a refraction part and a diffraction part, The bending of the second optical system due to the change of the refractive index caused by the temperature change
Light caused by power change and temperature change in the sub-scanning direction
Sub-scanning of refraction section of second optical system due to wavelength variation of source means
Directional power change is the wavelength of the light source means caused by temperature fluctuations
Power in the sub-scanning direction of the diffraction part of the second optical system due to fluctuations
Optical scanning optics characterized by being corrected by changes
system. 3. The refracting portion of the second optical system is made of plastic.
It has a lens, Claim 1 or Claim 2 characterized by the above-mentioned.
The optical scanning optical system according to. 4. A diffracting portion is provided for the light flux emitted from the light source means.
The light is guided to the deflection means via the first optical system for
A second beam having a refraction part and a diffraction part
An image is formed on the surface to be scanned through the optical system, and the surface to be scanned is imaged.
An optical scanning optical system for scanning, The refraction part of the second optical system has a plastic lens, In the sub-scanning direction due to temperature fluctuations of the plastic lens
Aberration variation due to wavelength variation of the light source means due to the temperature variation
The power change of the diffractive part of the first optical system and the second Optics
The fact that it is corrected by the power change of the diffractive part
Characteristic optical scanning optical system. 5. A light beam emitted from a light source means for the first optical system.
The light is guided to the deflecting means through the system and is deflected by the deflecting means.
The light beam is transmitted through a second optical system having a refracting portion and a diffracting portion.
Optical scanning that forms an image on the scan surface and scans the scan surface
An optical system, The refraction part of the second optical system has a plastic lens, In the sub-scanning direction due to temperature fluctuations of the plastic lens
Aberration variation due to wavelength variation of the light source means due to the temperature variation
The fact that it is corrected by the power change of the diffractive part
Characteristic optical scanning optical system. 6. Along with a temperature change of the plastic lens
The aberration variation in the sub-scanning direction is caused by the temperature variation
Light caused by change in refractive index and temperature change of stick lens
Of the refractive index of the plastic lens due to the wavelength variation of the source means
Change caused by power change in the sub-scanning direction
The optical scanning optical system according to claim 5, which is characterized in that. 7. The power of the diffractive portion in the second optical system
When φB and the power of the refraction part are φL, 1.0 ≦ φL / φB ≦ 2.6 The following conditions are satisfied:
The optical scanning optical system according to claim 4, claim 5, or claim 6. 8. The aberration variation is focus variation.
8. The light traveling according to any one of claims 1 to 7, characterized in that
Inspection optics. 9. The diffractive portion is an optical device having a staircase grating structure.
9. An element according to any one of claims 1 to 8, characterized by comprising an element.
The optical scanning optical system according to item 1. 10. The diffractive portion has a continuous grating structure.
A flannel-shaped optical element.
8. The optical scanning optical system according to any one of items 8. 11. The first optical system is a deflector of the deflecting means.
A machine that forms a light beam on the surface as a line image that is long in the main scanning direction.
It has a function, Any one of Claims 1-10 characterized by the above-mentioned.
The optical scanning optical system according to item 1. 12. The first optical system comprises a cylindrical carlene.
And a diffractive portion on the surface of the cylindrical lens.
It described in any one of Claims 1-11 characterized by the above.
Optical scanning optical system. 13. The first optical system comprises a collimator lens.
And having a diffractive portion on the collimator lens surface.
The light traveling according to any one of claims 1 to 12, characterized in that
Inspection optics. 14. A temperature variation of a refraction portion of the optical scanning optical system.
The change in the hint in the main scanning direction due to the
Corrected by the power change of the diffractive part due to the wavelength fluctuation of the means
Any of claims 1 to 13 characterized in that
The optical scanning optical system according to item 1. 15. The optical scanning optical system includes a light source means.
The light source means is a semiconductor laser.
Optical scanning optics according to any one of claims 1 to 14.
system. 16. The method according to any one of claims 1 to 15.
Optical scanning optical system and the photosensitive drum surface as the surface to be scanned.
An image forming apparatus characterized by being used.