JPH0882739A - Optical system for optical scanning - Google Patents

Abstract

PURPOSE: To obtain a compact optical system for optical scanning which minimizes aberrations, such as curvature of field, and with which a high plane tilt correction effect of an optical deflector and optical performance high over a wide viewing angle are obtainable. CONSTITUTION: This optical system for optical scanning executes optical scanning by introducing the light beam emitted from a light source means 1 to a deflecting means 5 and introducing the light beam deflected and reflected by this deflecting means 5 onto a surface 9 to be scanned by an imaging means 10. This imaging means 10 is composed of three elements of lenses having respective refracting powers in sub-scanning cross sections; a first plastic lens 6 formed of a plastic material having a negative refracting power, a glass lens 7 formed of a glass material having a positive refracting power and a second plastic lens 8 formed of a plastic material having a positive refracting power.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical scanning optical system, and in particular, it guides a light beam emitted from a light source means onto a surface to be scanned, which is a recording medium surface, through an optical deflector such as a rotating polygon mirror. The present invention relates to an optical scanning optical system suitable for an apparatus such as a laser beam printer (LBP) or a digital copying machine, which records characters and information by optical scanning.

[0002]

2. Description of the Related Art Conventionally, an optical scanning optical system has been known which optically scans a surface to be scanned by using a light beam deflected and reflected by each reflection surface (deflection surface) of an optical deflector composed of a rotating polygon mirror. ,
For example, Japanese Examined Patent Publication No. 62-36210 and US Pat. No. 46.
Various proposals have been made in No. 39072.

The optical scanning optical system proposed in Japanese Examined Patent Publication No. 62-36210 has an f-position between the optical deflector and the surface to be scanned.
By providing an image-forming means for optical scanning having a θ characteristic and appropriately setting the refracting power of a toric lens which is one of the image-forming means, the reflecting surface of the optical deflector becomes parallel to the rotation axis. It corrects the angular error when falling down, so-called surface tilt.

That is, a toric lens is used to make the reflecting surface of the optical deflector and the surface to be scanned (the surface of the object to be irradiated) optically conjugate with each other to eliminate the adverse effect of the surface tilt. As a result, the traveling direction of the light beam reflected and deflected by the reflecting surface on the scanning surface is corrected to prevent unevenness in the pitch of the scanning lines.

Further, in the optical scanning optical system proposed in US Pat. No. 4,693,072, a cylindrical lens is arranged in the vicinity of the surface to be scanned of the scanning beam to reduce the influence of the surface tilt of the optical deflector.

[0006]

[Problems to be Solved by the Invention] Japanese Patent Publication No. 62-3621
The image forming means for optical scanning having the f- [theta] characteristic in the optical scanning optical system of Japanese Patent No. 0 is composed of a single lens composed of a spherical surface and a toric lens from the optical deflector side.

In order to maintain good optical performance in such a lens structure, the lens shape in the scanning section of the toric lens for aberration correction becomes close to a plano-convex shape. Further, the lens shape of the single lens composed of a spherical surface arranged between the toric lens and the optical deflector becomes close to a plano-concave shape or a biconcave shape. Generally, in order to widen the angle of view of the scanning range in such a lens shape, there is a limit naturally in aberration correction.

That is, with the above lens structure, if an attempt is made to achieve a wide angle of view of the scanning range while maintaining good optical performance, the lens thickness is inevitably increased and the size of the entire apparatus is increased. .

Further, since the toric lens is a special lens which is rotationally asymmetric, it is difficult to process it, which causes a cost increase.

In order to solve such a problem, it is conceivable to use a plastic toric lens or the like. As in the above-mentioned conventional example, a spherical single lens and a toric lens having a positive refractive power are sequentially arranged from the optical deflector side. In the configuration in which two lenses are arranged, the refractive power of the toric lens is stronger than the refractive power (power) of the entire system. For this reason, the influence of the power change of the lens made of a plastic material due to the environmental change cannot be ignored and problems such as focus shift on the surface to be scanned occur and the image output is adversely affected.

On the other hand, in the optical scanning optical system proposed in US Pat. No. 4,693,072, although there are few problems due to the above-mentioned environmental changes, for example, in a laser beam printer using an electrophotographic system, a process such as a developing device and a cleaner is performed. Since the optical device is arranged in close contact with the photoconductor drum, it is not preferable to arrange an optical element such as a cylindrical lens in the vicinity of the photoconductor drum because the structure becomes complicated and it is not preferable. Achieving optics becomes difficult.

Further, the structure in which the cylindrical lens is arranged in the vicinity of the photosensitive drum as described above is contaminated by toner,
It has a problem that it is easily affected by heat and ozone.

The applicant of the present invention has previously mentioned that the image forming means (scanning lens) arranged between the optical deflector and the surface to be scanned in JP-A-3-231218 is positive in order from the optical deflector side. The toric lens includes a spherical lens having a refractive power and a toric lens arranged near the surface to be scanned of the spherical lens and having a positive refractive power in both the main scanning section and the sub-scanning section. By configuring at least one lens surface of the main scanning section of as an aspherical surface,
We propose an optical scanning optical system with high performance, wide angle of view, miniaturization, and improved environmental resistance.

As described above, this optical scanning optical system is excellent in terms of high performance, wide angle of view, miniaturization, environmental resistance characteristics, etc., but only the main scanning section of the toric lens as an image forming means. The lens thickness of the spherical lens inevitably tended to be large because of the aspherical shape. Further, in order to further improve the performance, it was difficult with the above configuration.

According to the present invention, the image forming means comprises a first plastic lens made of a plastic material having a negative refracting power in the sub-scan section and a glass lens made of a glass material having a positive refracting power. And a second plastic lens made of a plastic material having a positive refracting power, the three lenses make it possible to suppress aberrations such as field curvature to be small, and to achieve a surface tilt correction effect of the optical deflector. An object of the present invention is to provide a compact optical scanning optical system capable of obtaining high-performance optical performance over a wide wide angle of view.

Another object of the present invention is to provide a low-cost optical scanning optical system having good environmental characteristics even if two of the three lenses forming the image forming means are made of a plastic material.

[0017]

According to the optical scanning optical system of the present invention, a light beam emitted from a light source means is guided to a deflecting means, and the light beam deflected and reflected by the deflecting means is covered by an image forming means. In an optical scanning optical system that guides light onto a scanning surface to perform optical scanning, the image forming unit has a positive plastic lens formed of a plastic material having a negative refractive power in a sub-scan section and a positive plastic lens having a positive refractive power. A glass lens made of a glass material having a refractive power and a second plastic lens made of a plastic material having a positive refractive power 3
It is characterized by being composed of one lens.

In particular, the image forming means is composed of the first plastic lens, the glass lens and the second plastic lens in this order from the deflecting means side, and the first plastic lens has a negative refracting power only in the sub-scan section. The glass lens is made up of a cylindrical lens, the glass lens is made up of an anamorphic lens having different positive refractive powers in the main scanning section and the sub-scanning section, and the second plastic lens is in the main scanning section and the sub-scanning section. Both are characterized by being made of a toric lens having a positive refractive power.

Further, the image forming means is composed of the glass lens, the first plastic lens and the second plastic lens in this order from the deflecting means side, and the glass lens has a cylindrical shape having a positive refractive power only in the sub-scan section. The first plastic lens is an anamorphic lens having a positive refractive power in the main scanning section and a negative refractive power in the sub scanning section, and the second plastic lens is in the main scanning section and the sub scanning section. It is characterized by being made of a toric lens having a positive refractive power in both of the cross sections.

Further, the focal lengths of the second plastic lens in the main-scan section and the sub-scan section are f _2a , f _2b , and
The maximum thickness of the second plastic lens in the optical axis direction is d
_MAX , f _{a is a} combined focal length in the main scanning cross section of the entire image forming means, and f _1b is a focal length in the sub scanning cross section of the first plastic lens (f _1b is a focal point in the air even with a cemented lens). When the distance between the second plastic lens and the surface to be scanned is L, 0.05 <f _a / f _2a <0.15 (1) 0.25 <f _2b / _{f a <0.75 ‥‥‥ (2)} 0.6 <L / f a <1 ‥‥‥ (3) d MAX / f 2b <0.1 ‥‥‥ (4) -1.5 <f 1b / F _2b <-0.5 ... (5) It is characterized by satisfying the condition.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a plan view (main-scan sectional view) of an essential part of an optical system according to a first embodiment of the present invention, and FIG. 2 is a sectional view (sub-scan sectional view) of a main part perpendicular to the main-scan section of FIG. Is.

In the figure, reference numeral 1 is, for example, a semiconductor laser as a light source means. A collimator lens 2 collimates the light beam emitted from the light source means 1 into a parallel light flux. Three
Is an aperture stop, which adjusts the diameter of the passing light beam. Reference numeral 4 denotes a cylindrical lens, which has no refracting power in the main scanning cross section and has a predetermined refracting power in the sub scanning cross section. Reference numeral 5 denotes an optical deflector as a deflecting means, which is composed of, for example, a rotating polygon mirror, and rotates at a constant speed in the direction of arrow A.

Reference numeral 10 denotes an image forming means (fθ lens system) according to the present invention, which has no refracting power in the main scanning direction in order from the optical deflector 5 side and has a negative refracting power only in the sub-scanning direction. A cylindrical lens 6 as a first plastic lens formed of a plastic material, and a glass material having a positive refractive power in the main scanning direction and a positive refractive power different from the main scanning direction in the sub scanning direction. An anamorphic lens 7 formed as a glass lens, and a second plastic which is disposed near the surface to be scanned of the anamorphic lens 7 and is made of a plastic material having a positive refractive power in both the main scanning direction and the sub scanning direction. It is composed of three lenses, a toric lens 8 as a lens.

The arrangement order of the three lenses is not limited to this, and may be variously changed as shown in the embodiments described later.

The cylindrical lens 6 and the anamorphic lens 7 are formed in a lens shape for satisfactorily correcting the f-θ characteristic and the field curvature, and the toric lens 8 satisfactorily corrects the field curvature over a wide field angle. Therefore, the lens is formed in a concentric shape (the center of the radius of curvature of both lens surfaces of the toric lens 8 is in the vicinity of the reflection surface of the optical deflector 5) and both lens surfaces are formed of an aspherical shape.

Further, the cylindrical lens 6 has a negative refracting power in the sub-scanning direction as described above, and corrects the focus shift due to the temperature change of the toric lens 8 made of a plastic lens as described later. Reference numeral 9 is a photosensitive drum.

In this embodiment, the light beam emitted from the light source means 1 is made into a substantially parallel light beam by the collimator lens 2, and the parallel light beam is incident on the cylindrical lens 4 with the size of the light beam cross section being limited by the aperture stop 3. To do.

The cylindrical lens 4 causes the parallel light flux of the incident parallel light flux to be emitted as it is in the main scanning cross section, and is converged in the sub scanning cross section to be converged to the optical deflector 5.
It is formed on the reflecting surface 5a of the above as an almost linear image light flux. The reflection surface 5a of the optical deflector 5 reflects and deflects at high speed. The light beam reflected and deflected by the light deflector 5 passes through the cylindrical lens 6, the anamorphic lens 7 and the toric lens 8 so that its scanning linearity is corrected and an image is formed on the surface of the photosensitive drum 9 to form a substantially constant velocity linear line. The surface of the photosensitive drum 9 is optically scanned by the movement.

In FIG. 2, P indicates the position of the reflecting surface of the optical deflector 5, and in the sub-scanning cross section, the light beam is focused substantially on this reflecting surface position P as described above.

Here, the reflection surface position P and the photosensitive drum 9 are in a substantially optically conjugate positional relationship with respect to the image forming means 10. As a result, the light beam is focused on the same scanning line on the surface of the photosensitive drum 9 even if the reflecting surface is tilted in the sub-scanning section or so-called surface tilt occurs.
In this way, in this embodiment, the surface tilt of the optical deflector 5 is corrected.

As described above, in this embodiment, the image forming means (f.theta. Lens system) 10 is composed of the three lenses of the cylindrical lens 6, the anamorphic lens 7 and the toric lens 8 having the above-mentioned shapes, so that a predetermined lens is formed. After achieving sufficient imaging performance and achieving sufficient correction performance for surface tilt correction by providing an imaging relationship in the sub-scanning direction, focus movement (focus misalignment) in the sub-scanning direction, which is a technical problem in the past, is obtained. ) Is suppressed to a minute.

Next, the features of the lens configuration of the cylindrical lens 6, the anamorphic lens 7 and the toric lens 8 which form the image forming means 10 will be described.

The cylindrical lens 6, the anamorphic lens 7 and the toric lens 8 in this embodiment.
The three lenses have negative, positive, and positive refracting powers in the sub-scanning direction, respectively. The cylindrical lens 6 and the toric lens 8 are made of plastic material, and the anamorphic lens 7 is made of glass material. There is.

By adopting such a lens structure, in this embodiment, the focus fluctuation of the toric lens 8 having a positive refractive power caused by the change of the refractive index of the plastic material due to the temperature fluctuation or the like causes the cylindrical lens having a negative refractive power. Canceled by 6.

The total refracting power of the image forming means 10 in the sub-scanning direction requires a positive refracting power for finite image formation in order to form a surface tilt correction optical system.

In the present embodiment, the positive refracting power in the sub-scanning direction is mainly borne by the anamorphic lens 7 made of a glass material, and the focus fluctuation of the plastic lens made of a plastic material which easily causes focus fluctuation is corrected as described above. And it is canceled by the negative refracting power.

Therefore, the miniaturization of the focus fluctuation amount, which cannot be sufficiently obtained by the method of suppressing the focus fluctuation by suppressing the positive refracting power of the toric lens as small as possible, is performed by the image forming means 10 as in the present embodiment. By properly configuring the lens structure, the focus movement can be corrected almost completely.

Further, in the present embodiment, since the focus variation is suppressed only inside the image forming means 10, the focus variation is made minute without breaking the finite image formation relationship which constitutes the tilt correction optical system. Therefore, there is an advantage that the deterioration of the tilt correction performance is not seen at all as compared with the correction means outside the imaging means which is considered as another method.

FIGS. 3 and 4 are explanatory views showing the field curvature and the f-θ characteristic on the surface to be scanned in the optical scanning range according to the first embodiment of the present invention. As shown in FIGS. 3 and 4, good field curvature and f-θ characteristics are obtained over a wide field angle range in the main scanning section.

In the present embodiment, the aberration of the entire scanning cross section is satisfactorily corrected, the focus shift on the surface to be scanned due to the influence of environmental changes and the like, and the widening of the angle of view of the optical scanning range are facilitated. Should satisfy the following conditions.

That is, the focal lengths of the toric lens as the second plastic lens in the main scanning section and the sub-scanning section are f _2a and f _2b , the maximum thickness of the toric lens in the optical axis direction is d _MAX , and the image forming means is formed. (Fθ lens) f _a is the composite focal length in the main scanning section of the entire system (cylindrical lens, anamorphic lens, toric lens), and the focal point in the sub scanning section of the first plastic lens having a negative refractive power in the sub scanning section. When the distance is f _1b (f _1b is the focal length in the air even in the case of a cemented lens) and the distance between the toric lens and the surface to be scanned is L, 0.05 <f _a / f _2a < 0.15 ・ ・ ・ (1) 0.25 <f _2b / f _a <0.75 ‥‥ (2) 0.6 <L / f _a <1 ‥‥‥ (3) d _MAX / _{f 2b <0.1 ‥‥‥‥ (4)} -1 5 <it is to satisfy _{f 1b / f 2b <-0.5 ‥‥‥‥} (5) following condition.

Generally, if the refracting power of the main scanning section of the toric lens is made too strong, it becomes difficult to satisfactorily correct the field curvature in the scanning direction, that is, the meridional direction, while maintaining a good f-θ characteristic. . For this reason, it is preferable that the refractive power of the toric lens in the main scanning cross section be as weak as possible.

In consideration of the above, the conditional expression (1) has the focal lengths f _2a and f ₂ in the main scanning section of the toric lens.
The ratio to the combined focal length f _a in the main scanning cross section of the θ lens overall system is appropriately set. Exceeding the lower limit of conditional expression (1) and making the focal length f _2a too large is advantageous for aberration correction, but the toric lens approaches the surface to be scanned (photosensitive drum surface) side, and the overall size of the apparatus becomes large. Is coming.

On the other hand, if the focal length f _2a becomes too small beyond the upper limit of conditional expression (1), it is advantageous for downsizing the entire apparatus, but both f-θ characteristics and field curvature are balanced. It's not good because it becomes difficult to maintain it.

Conditional expression (2) relates to the ratio of the focal length f _2b in the sub-scan section of the toric lens to the combined focal length f _a in the main-scan section of the entire fθ lens system, particularly in the sagittal direction (in the sub-scan section). This is to satisfactorily correct the field curvature in the direction perpendicular to the optical axis).

The focal length f exceeds the upper limit of conditional expression (2).
_{If 2b} becomes too large, it will be advantageous for aberration correction, but the toric lens will approach the surface to be scanned (photoreceptor drum surface) side, and the size of the entire device will increase.

If the lower limit of conditional expression (2) is exceeded and the focal length f _2b becomes too small, it becomes difficult to correct the field curvature in the meridional direction and the sagittal direction in a well-balanced manner, which is not preferable. The conditional expression (3) is related to the ratio of the distance L between the toric lens and the surface to be scanned and the combined focal length f _a in the main scanning cross section of the fθ lens overall system, when the lower limit value of the conditional expression (3) is exceeded ( That is, L <0.6f _a (the case of L <0.6fa) becomes large, and the face tilt correction effect becomes small.

If the refractive power of the toric lens exceeds the upper limit of conditional expression (3) (that is, L> f _a ) and the refractive power of the toric lens becomes too strong, the toric lens is made of a plastic material by taking advantage of cost. In such a case, the amount of focus shift on the surface to be scanned due to the influence of environmental fluctuations is out of the allowable range, which is not good.

Conditional expression (4) relates to the ratio between the maximum thickness d _MAX of the toric lens in the optical axis direction and the focal length f _2b in the sub-scan section of the toric lens. This is not preferable because it is difficult to prevent the out-of-focus on the surface to be scanned due to moisture absorption of the toric lens, and it becomes difficult to mold the toric lens with plastic.

Conditional expression (5) relates to the ratio of the focal length f _2b of the toric lens in the sub-scan section to the focal length f _1b of the first plastic lens in the sub-scan section, and By appropriately defining the ratio of the focal lengths of the toric lens in the sub-scan section, the focus movement of the plastic lens in the sub-scan section can be canceled. That is, in general, the refractive power of the toric lens in the sub-scanning cross section is positive. Therefore, by setting the refractive power of the first plastic lens in the sub-scanning cross section to be negative, the direction of the focus movement of each plastic lens can be changed. By reversing the direction, the focus movement in the sub-scan section can be miniaturized.

If the upper limit value and the lower limit value of the conditional expression (5) are exceeded, it becomes difficult to reduce the focus movement amount in the sub-scan section and it becomes impossible to perform good aberration correction. Absent.

Next, numerical examples of the image forming means according to the present invention will be shown. Numerical Examples 1 to 4 are numerical examples after the optical deflector 5 of Examples 1 to 4 of the present invention in order.

In each numerical example, the radii of curvature in the main scanning section of the cylindrical lens are R ₁ and R ₂ , the radii of curvature in the sub-scanning section are R ₁ ′ and R ₂ ′, and the radii of curvature in the main scanning section of the anamorphic lens are R. ₃ , R ₄ ,
The radii of curvature in the sub-scan section are R ₃ ′ and R ₄ ′, and the radii of curvature in the main-scan section of the toric lens are R ₅ and R ₅ .
₆ , the radii of curvature in the sub-scan section are R ₅ ′ and R ₆ ′, and the distances between the lens surfaces are D _{1 to} D ₆ .

The refractive indices of the cylindrical lens, the anamorphic lens and the toric lens at the wavelength of 675 nm are represented by N ₁ , N ₂ and N ₃ , respectively. The B~D is shown below x-y height of the lens surface in the plane y and the distance x between the relation ^{x = y 2 / R [1+} {1- (1 + A) (y / R) 2}
^1/2] + By A shows the aspherical coefficients of each order of ^{4 + Cy 6 + Dy 8 +} ········.

Each numerical example and each conditional expression (1) to
Table 1 shows the relationship with (5).

In the image forming means in Numerical Embodiment 2 as Embodiment 2 of the present invention, a cylindrical lens having a positive refracting power is formed of a glass material (glass lens) only in the sub-scan section, and the cylindrical lens in the main-scan section is positive. , An anamorphic lens having a negative refractive power in the sub-scan section is formed of a plastic material (first plastic lens), and a toric lens having a positive refractive power in both the main-scan section and the sub-scan section is formed of a plastic material (the first plastic lens). 2 plastic lens), the anamorphic lens has a negative refractive power in the sub-scanning cross section.

Numerical Example 3 as Example 3 of the present invention shows a case where the cylindrical lens and the anamorphic lens are independently configured in the configuration of Numerical Example 1.

Numerical Embodiment 4 as Embodiment 4 of the present invention shows a case where the cylindrical lens and the anamorphic lens are independently configured in the construction of Numerical Embodiment 2.

[Numerical Example 1] Focal length of the entire system 289.519 Maximum scanning angle 57.697 Deflection point to R1 surface 115.387 R ₁ = ∞ D ₁ = 4.93676 R ₁ ′ = −224.797 N ₁ = 1.521794 R ₂ = ∞ D ₂ = 0 R ₂ ′ = 71.2486 R ₃ = ∞ D ₃ = 11.4823 R ₃ ′ = 71.2486 N ₂ = 1.794120 R ₄ = −255.222799 _{D 4 = 12.836 R 4 '=} -255.22799 R 5 = -514.326 D 5 = 7.32891 N 3 = 1.521794 A = -7.58593 B = -1.49836 × 10 -7 C = 1.06599 × 10 ⁻¹¹ D = 5.34848 × 10 ⁻¹⁶ R ₅ ′ = −21.6494 R ₆ = −376.415 D ₆ = 276.976 A = −1.976 B = −1.29611 × 10 ^{-7 = 7.57283 × 10 -12 D = 6.90737} × 10 -16 R 6 '= -18.7449 [ Numerical Example 2] focal length 289.552 maximum scan angle 57.697 deflection point ~R1 surface of the entire system 102.424 R ₁ = ∞ D ₁ = 4.38968 R ₁ ′ = −268.5578 N ₁ = 1.79412 R ₂ = ∞ D ₂ = 0 R ₂ ′ = −54.937 R ₃ = ∞ D ₃ = _{13.15786 R 3 '= -54.937 N 2} = 1.521794 R 4 = -169.61224 D 4 = 15 R 4' = -169.61224 R 5 = -830.33014 D 5 = 8.23572 N ₃ = 1.521794 A = 7.82869 B = -1.87969 × 10 ⁻⁷ C = 1.14113 × 10 ⁻¹¹ D = 4.60277 × 10 ⁻¹⁶ R ₅ ′ = −20.9914 R ₆ = − 502.457 D ₆ = 274.308 A = -1.74477 B = -1.615 * 10 < ^-7 > C = 5.4401 * 10 < ^-12 > D = 8.38833 * 10 < ^-16 > R < ₆ '> =-18.3699 [Numerical Example] 3] focal length 289.572 maximum scan angle 57.697 deflection point ~R1 surface of _{101.997 R 1 = ∞ D 1 =} 5.57578 R 1 '= -476.254 N 1 = 1.521794 R 2 = ∞ D ₂ = 2.35 R ₂ ′ = 44.0319 R ₃ = ∞ D ₃ = 15.0 R ₃ ′ = 57.201 N ₂ = 1.79412 R ₄ = −251.43 D ₄ = 25. _{01 R 4 '= -251.43 R 5} = 1657.64 D 5 = 5.96 N 3 = 1.521794 A = -2.96118 B = -1.82276 × 10 -7 C = 1.01369 × 10 ^-11 D = 6.11519 × 10 ^-16 R ₅ ′ = −1 ^{_{9.01 R 6 = -9.49193 × 10 4}} D 6 = 264.793 A = 6.14821 × 10 4 B = -1.7533 × 10 -7 C = 1.00502 × 10 -11 D = 5. 65132 × 10 ⁻¹⁶ R ₆ ′ = −16.62 [Numerical Example 4] Focal length of the entire system 289.550 Maximum scanning angle 57.697 Deflection point to R1 surface 104.027 R ₁ = ∞ D ₁ = 4. 23 R ₁ ′ = −402.324 N ₁ = 1.79412 R ₂ ═∞ D ₂ ═3 R ₂ ′ = −58.21 R ₃ ═∞ D ₃ = 19.92 R ₃ ′ = −56.85 N _{2 = 1.521794 R 4 = -167.09 D} 4 = 15 R 4 '= -167.09 R 5 = 1668.31 D 5 = 7.43 N 3 = 1.521794 A = -16.6987 B = ^{-1.34299 × 10 -7 C = 9.42626 ×} 10 -12 D = 3. _{^{3539 × 10 -16 R 5 '=}} -18.76 R 6 = -1.49903 × 10 4 D 6 = 271.515 A = 1.06397 × 10 4 B = -1.11969 × 10 -7 C = 5 .62941 × 10 ^-12 D = 5.92525 × 10 ^-16 R ₆ ′ = −17.11

[0060]

[Table 1]

[0061]

According to the present invention, as described above, the image forming means has a first plastic lens formed of a plastic material having a negative refracting power in the sub-scan section, and a glass having a positive refracting power. A glass lens made of a material and a second plastic lens made of a plastic material having a positive refractive power are used to form three lenses, so that a field curvature or the like can be prevented over a wide field angle optical scanning range. Compact optical scanning optics that can satisfactorily correct aberrations, has a large effect of correcting surface tilt of the optical deflector, reduces the amount of focus movement in the sub-scanning direction, and provides good optical performance in aberration correction. The system can be achieved.

Further, according to the present invention, the image forming means 3 is constructed.
By forming two lenses out of one lens with a plastic material, cost reduction can be achieved at the same time.

[Brief description of drawings]

FIG. 1 is a plan view of a main part of a first embodiment of the present invention (main scanning sectional view).

FIG. 2 is a sectional view of a main part (sub-scan sectional view) perpendicular to the main-scan sectional view of FIG.

FIG. 3 is an aberration diagram illustrating field curvature of Example 1 of the present invention.

FIG. 4 is an aberration diagram illustrating an f-θ characteristic according to the first embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Light source means 2 Collimator lens 3 Aperture stop 4 Cylindrical lens 5 Deflection means 6 1st plastic lens 7 Glass lens 8 2nd plastic lens 9 Scanned surface (photosensitive drum) 10 Imaging means

Claims (4)

[Claims] 1. An optical scanning optical system which guides a light beam emitted from a light source means to a deflecting means, and guides the light beam deflected and reflected by the deflecting means onto a surface to be scanned by an image forming means for optical scanning. In the system, the image forming unit includes a first plastic lens formed of a plastic material having a negative refractive power in a sub-scan section, and a glass lens formed of a glass material having a positive refractive power. An optical scanning optical system comprising three lenses, a second plastic lens made of a plastic material having a positive refractive power and a second plastic lens. 2. The image forming means includes the first plastic lens, the glass lens, and the second lens in order from the side of the deflecting means.
The first plastic lens is a cylindrical lens having a negative refracting power only in the sub-scan section, and the glass lens has a positive refracting power different in the main-scan section and the sub-scan section. 2. The optical scanning device according to claim 1, wherein the second plastic lens is a toric lens having a positive refractive power in both the main scanning section and the sub-scanning section. Optical system. 3. The image forming means comprises the glass lens, the first plastic lens and the second lens in order from the side of the deflecting means.
The glass lens is composed of a plastic lens, the glass lens is a cylindrical lens having a positive refractive power only in the sub-scan section, and the first plastic lens is positive in the main-scan section and negative in the sub-scan section. 2. The light according to claim 1, comprising an anamorphic lens having a power, and the second plastic lens being a toric lens having a positive refractive power both in the main scanning cross section and in the sub scanning cross section. Scanning optics. 4. The focal lengths in the main-scan section and the sub-scan section of the second plastic lens are f _2a and f _2b , respectively, and the maximum thickness of the second plastic lens in the optical axis direction is d.
_MAX , f _{a is a} combined focal length in the main scanning cross section of the entire image forming means, and f _1b is a focal length in the sub scanning cross section of the first plastic lens (f _1b is a focal point in the air even with a cemented lens). Where L is the distance between the second plastic lens and the surface to be scanned, 0.05 <f _a / f _2a <0.15 0.25 <f _2b / f _a <0.75 _{0.6 <L / f a <1} d MAX / f 2b <0.1 -1.5 < claims 1, characterized by satisfying the f _1b / f _2b <-0.5 condition: 3 optical scanning optical system.