JP3129769B2 - Optical scanning device - Google Patents

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 used in an optical writing system such as a laser printer, a laser facsimile, a digital copying machine, and the like.

[0002]

2. Description of the Related Art An optical scanning device that deflects and scans light from a light source by various deflectors such as a rotary polygon mirror and an axial deflector such as a pyramidal mirror to scan a scanning surface of a medium to be scanned such as a photoconductor. Have been proposed and used in optical writing systems such as laser printers, laser facsimile machines, and digital copiers. As the axial deflector used for deflection scanning, a V-shaped mirror, a tenon-type mirror, and the like are known in addition to a pyramidal mirror. In addition, as a single-lens optical scanning lens, a coaxial aspheric surface is used to correct the field curvature in the main scanning direction, and in the sub-scanning direction, a long cylinder lens or a long toroidal lens is used to correct the field curvature. Or a type in which the optical scanning lens has an anamorphic shape and also corrects the sub-scanning direction at the same time.

[0003]

However, in a deflector such as a rotary polygon mirror used in an optical scanning device, there is a problem that a large deflection angle at the time of deflection scanning causes a field curvature. In order to correct the error, it is necessary to use an optical system such as an fθ lens, or to use a correction means such as mechanically driving a lens of the optical system before the deflector, thereby increasing the size and cost of the apparatus. Was a factor. Further, in the case of a deflector such as a pyramidal mirror, there is a disadvantage that the beam pitch changes in a normal use of the pyramidal mirror, and there is a problem that it is difficult to form a multi-beam. The present invention has been made in view of the above circumstances, and a first object of the present invention is to provide an optical scanning device capable of correcting a field curvature without using an fθ lens and capable of reducing the size and weight of the device. Is to provide.

When correcting the curvature of field in both the main scanning direction and the sub-scanning direction with a single fθ lens, the lens shape must be such that the first surface is corrected to correct the curvature of field in the sub-scanning direction. The barrel-shaped toroidal surface (BT surface) has a shape as shown in FIG. 11 in which the second surface is a normal toroidal surface (NT surface). At this time, since the first surface is concave with respect to the main scanning direction, it is difficult to correct the linearity. When a normal deflecting mirror using a flat mirror surface is used, the amount of curvature of field is reduced to some extent. However, there is a problem that the linearity is about ten and several percent at the maximum. When a deflector such as a polygon mirror having a curvature R or a tenon mirror having a curvature R is used, the field curvature can be corrected very well without using an fθ lens. However, in this case, the linearity is almost completely corrected. Since it is not possible, a rather electrical correction will be used. In addition, since the amount that can be corrected by electrical correction is about 30% at the maximum, there is a problem in that there is a limit in widening the angle of view or shortening the optical path length. Therefore, a second object of the present invention is to provide an optical scanning device capable of satisfactorily correcting field curvature and linearity by combining an axial deflector and an optical scanning lens.

[0005]

In order to achieve the first object, an optical scanning device according to a first aspect of the present invention comprises a light source device, a lens for focusing a light beam emitted from the light source device, and a scanner. The motor shaft has a mirror surface formed integrally with the shaft, and the mirror surface is a convex spherical or cylindrical mirror having a radius R disposed substantially in the vicinity of the rotation center of the shaft. And a scanning surface on which a light beam deflected by the deflector scans, and the distance L ₀ from the deflection point to the scanning surface when the rotation angle of the deflector is 0, and the rotation The mirror surface of the deflector is set such that the distance L from the deflection point to the scanning surface when the angle is θ is L ₀ = L.
The radius R and the L ₀ of, and having a relationship of R = {(1 / cosθ) + cosθ / (1 + cosθ) -1} L 0.

According to a second aspect of the present invention, there is provided an optical scanning device having a light source device, a lens for converging a light beam emitted from the light source device, and a mirror surface formed integrally with a scanner motor shaft. A deflector characterized in that the mirror surface is a two-sided mirror having a convex spherical shape having a radius R and disposed near the center of rotation of the shaft, and a light beam deflected by the deflector is A scanning surface for scanning, and a distance L ₀ from the deflection point to the scanning surface when the rotation angle of the deflector is ₀
And the radius L of the mirror surface of the deflector so that L ₀ = L from the deflection point to the scanning surface when the rotation angle is θ.
And R and the L _0, characterized in that it has a relationship of R = {(1 / cosθ) + cosθ / (1 + cosθ) -1} L 0.

According to a third aspect of the present invention, there is provided an optical scanning device, a light source device, an anamorphic lens group for converging a light beam emitted from the light source device, and a mirror surface formed integrally with the axis of the scanner motor. A deflector characterized in that the mirror surface is a two-sided mirror having a convex cylindrical surface having a radius R and disposed near the center of rotation of the shaft. A scanning surface on which the light beam scans, and a long cylindrical lens disposed between the scanning surface and the deflector and having power only in the sub-scanning direction. as the distance L ₀ from the deflection point to the scanning plane and the distance L from the deflection point when the rotation angle is θ until the scanning surface becomes L ₀ = L in time, the deflector
The radius R and the L ₀ of the mirror surface, and having a relationship of R = {(1 / cosθ) + cosθ / (1 + cosθ) -1} L 0.

According to a fourth aspect of the present invention, there is provided an optical scanning device, comprising: a light source device; a lens for converging a light beam emitted from the light source device; a cylindrical lens having power only in the sub-scanning direction; Wherein the mirror surface is a one- or two-surface mirror having a convex cylindrical surface with a radius R disposed substantially near the center of rotation of the shaft. And a barrel-shaped toroidal surface disposed between the scanning surface on which the light beam deflected by the deflector scans and the deflector and having a radius of curvature in the sub-scanning direction that decreases as the optical axis moves away from the main scanning direction. A long toroidal lens including a concave lens surface as
As the distance L from the deflection point when the rotation angle and the distance L ₀ to the scanning plane from the deflection point when the rotation angle of the deflector 0 θ until scanning surface becomes L ₀ = L, the Mira of deflector
The radius R and the L ₀ of the over surface, and having a relationship of R = {(1 / cosθ) + cosθ / (1 + cosθ) -1} L 0.

According to a fifth aspect of the present invention, there is provided an optical scanning device according to any one of the first, third, fourth , and fourth aspects, wherein the light source device includes a light source device. It is characterized by using an element for emitting two or more light beams.

According to another aspect of the present invention, there is provided an optical scanning device, comprising: a light source device; a lens for converging a light beam emitted from the light source device; A cylindrical lens for focusing only in the sub-scanning direction on a substantially deflecting surface of the device, and a single-lens optical scanning lens for condensing a light beam deflected by the deflector on a surface to be scanned; The mirror has one or more mirror surfaces formed integrally with the shaft of the scanner motor, and the mirror surface is a convex cylindrical surface having a radius R disposed substantially near the rotation center of the shaft. Further, the optical scanning lens is further characterized in that the first surface rotates the circular arc having a radius R _1m with the axis in the main scanning direction on the main scanning surface as a rotation axis and a radius R _1s. and a surface, the second surface around the sub-scanning direction of the axis passing through the optical axis of the arc of radius R _2s Diameter R is a surface rotated by _2m, characterized in that it is a optical scanning lens made substantially conjugate relationship between the deflecting surface and the scan surface in the sub-scanning direction.

The optical scanning lens has the following conditions.
6.5 <meet R _1m / R _2m <8.0, focused light by the lens for focusing the light beam,
Assuming that the distance between the convergence point in the main scanning direction and the deflection point when the light does not pass through the optical scanning lens is S , the following condition is satisfied : 0.4 <S / R <0.5. conditions, and satisfies the _{2.0 <R 1s / R 2s <} 3.0.

According to a seventh aspect of the present invention, there is provided an optical scanning device, comprising: a light source device; a lens for converging a light beam emitted from the light source device; A cylindrical lens that focuses only the light beam, and a single-lens optical scanning lens that focuses the light beam deflected by the deflector on the surface to be scanned. The axial deflector is integrated with the axis of the scanner motor. Characterized in that the mirror surface is a convex cylindrical mirror having a radius R disposed substantially in the vicinity of the center of rotation of the shaft. The optical scanning lens has a first surface formed by rotating a curve having an aspherical shape on a main scanning plane on an axis in a main scanning direction with a radius of R _{1 s} , and a second surface. rotates at a radius arc R _2s around the sub-scanning direction axis passing through the optical axis radius R _2m A surface, characterized in that it is a optical scanning lens which the deflecting surface and the scan surface in a substantially conjugate relationship in the sub scanning direction.

The shape of the aspheric surface to be rotated on the first surface of the optical scanning lens is determined by the curvature of the contact circle when the intersection of the first surface of the optical scanning lens with the optical axis is the coordinate origin. An equation using an aspheric coefficient with a radius of R _1m , x = {y ² / (R _1m + √ (R _1m ² − (1 + K) y ² ))}} + A ₂ y ²
+ A ₃ y ³ + A ₄ y ⁴ +..., A _fourth -order aspherical coefficient A ₄ is used, and the main scanning is performed when the light focused by the lens that condenses the light beam does not pass through the optical scanning lens. When the distance between the point converging in the direction and the deflection point is S, the optical scanning lens is
-4.0 × 10 ⁻⁶ [mm ⁻³ ] <(A ₄ × (R _1m / R _2m )) <
−0.3 × 10 ⁻⁶ [mm ⁻³ ] 0.4 <S / R <0.7 2.5 <R _1s / R _2s <3.5

[0014]

In the optical scanning device according to the present invention, the mirror is provided integrally with the shaft of the scanner motor of the deflector, so that the device can be reduced in size and weight, and the mirror surface has a radius of curvature. R spherical or cylindrical surface, deflector
Is the distance L ₀ from the deflection point to the scanning surface when the rotation angle of
And the distance L from the deflection point to the scanning surface when the rotation angle is θ,
Is the radius of the mirror surface of the deflector so that L ₀ = L.
And R and the L ₀ is, by having a relationship of R = {(1 / cosθ) + cosθ / (1 + cosθ) -1} L 0, without the use of fθ lens can correct curvature of field. In the optical scanning device according to the fifth aspect, each of the optical scanning devices according to the first to fourth aspects can be formed into a multi-beam. Claim 6 , Claim
7. In the optical scanning device according to item 7 , the mirror surface has a convex shape with a radius R.
The curvature of field and linearity can be satisfactorily corrected by the combination of the axial deflector, which is a cylindrical mirror , and the optical scanning lens.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the illustrated embodiments. 1A and 1B show an example of a deflector of the optical scanning device according to the first aspect. 1A and 1B, reference numeral 1 denotes a shaft of a cylindrical scanner motor, and a mirror surface 4 for deflection scanning is formed integrally with the shaft 1. The shaft 1 is rotatably supported by a bearing 2 fixed to a scanner motor body (not shown), and the shaft 1 has N, S
The magnet 3 whose poles are alternately magnetized is fixed,
The shaft 1 is driven by magnetic force from an electromagnetic coil (not shown) on the body side.
Is to be rotated. The mirror surface 4 formed integrally with the shaft 1 is a one-sided mirror having a convex spherical or cylindrical surface with a radius R and disposed substantially near the center of rotation of the shaft 1, as shown in FIG. Here, an example in which the mirror surface 4 is spherical is shown in FIG.
Shows examples of cylindrical surfaces. Here, in the optical scanning device of the present invention, the distance L ₀ from the deflection point to the scanning surface when the rotation angle of the deflector is ₀ and the distance L from the deflection point to the scanning surface when the rotation angle is θ so but the L ₀ = L, above
Serial and radius R and the L ₀ of the mirror surface of the deflector is, R = {(1 / cosθ ) + cosθ / (1 + cosθ) -1} but is characterized by having a relation of L _0, below, Figure 2 The reason will be described with reference to FIG.

In FIG. 2, the mirror surface M of the deflector 13 is a spherical surface or a cylindrical surface centered on C and rotates about Q. The scanning light beam from the light source 21 is incident on the point S via the lens 12 so as to be focused, is reflected by the mirror surface M, and forms an image at the point S ′. In the figure, S ₀ ′ is an image point when the deflection angle θ is zero. Here, assuming that the distance between S ₀ ′ and Q is L ₀ and the distance between the perpendicular foot lowered from point S ′ and Q is L, L = (cos 2θ / cos θ) K′R. R is the radius of curvature of the mirror surface M, K 'is QC
Is the distance from the perpendicular foot lowered from S 'to the extended line to Q, and the distance between QS is K ₀ , and the distance between Q and the perpendicular foot lowered from point S to the QC line is K. For example, K = K ₀ cos θ K ′ = K cos ² θ / (cos ² θ−2K), and is eventually expressed as L = K ₀ R cos θ cos 2θ / (cos θ−2 K ₀ ). Here, when the mirror surface M rotates around Q, the distance L when the rotation angle θ is equal to the distance L when θ = 0.
_{Since the} condition for being equal to ₀ is L = L ₀ = K ₀ R / (1-2K ₀ ), 1 / K ₀ = (R / L ₀ ) +2, and R = {(1 / cos θ) + cos θ / (1 + cos θ) −1} L ₀ . Therefore, if a mirror surface M composed of a spherical surface or a cylindrical surface having a radius of curvature R that satisfies the above equation is formed, the distance L at the rotation angle θ is equal to the distance L ₀ at θ = 0, and a correction lens is used. Thus, it is possible to correct the curvature of field on the scanning surface without any problem.

Next, FIG. 3 is a diagram showing a configuration example of the optical scanning device according to the first aspect as viewed in a cross section in the sub-scanning direction. In FIG. 3, reference numeral 11 denotes a laser diode (LD), and 12 denotes an LD11.
A lens 13 for converging the emitted divergent light, 13 is a deflector comprising a motor shaft 1 and a mirror surface 4 formed integrally with the shaft, and 14 is a photoconductor. In order to correct the field curvature, it is necessary to input a light beam from the optical axis direction, that is, the direction in which the deflection angle is 0, as described above. For this purpose, for example, in the configuration shown in FIG. 3, a light beam enters from a position slightly deviated from the main scanning plane in the sub-scanning direction. However, when the mirror surface 4 is spherical in the configuration of FIG. The surface curvatures coincide. When the mirror surface 4 is a cylindrical mirror having a curvature only in the main scanning direction, for example, an anamorphic lens group is used for the lens 12, and the deflector 13 and the photoconductor 1 are used.
For example, there is a means such as disposing a long cylindrical lens between the four and correcting the sub-scanning field curvature.

Next, FIG. 4 shows an example of the deflector of the optical scanning device according to the second aspect. In FIG. 4, reference numeral 1 denotes a shaft of a cylindrical scanner motor, and a mirror surface 4 for deflection scanning is formed integrally with the shaft 1. The shaft 1 is rotatably supported by a bearing 2 fixed to a scanner motor main body (not shown), and a magnet 3 having N and S poles alternately magnetized on the peripheral surface is fixed to the shaft 1. The shaft 1 is rotated by magnetic force from an electromagnetic coil (not shown) on the main body side. The mirror formed integrally with the shaft 1 is a mirrored surface 4 of two convex spherical surfaces having a radius R arranged substantially in the vicinity of the center of rotation of the shaft 1. As in the case of the deflector shown in FIG. 4, when the number of mirror surfaces is two, the influence of surface tilt must be taken into consideration. However, with two surfaces, it is difficult to obtain the accuracy of the mirror without a surface tilt correction optical system. Rather, costs are hardly high.

The optical scanning device according to the second aspect also has the relationship described with reference to FIG. 2, and the distance from the deflection point to the scanning surface when the rotation angle of the deflector is zero. as L ₀ and <br/> rotation angle and the distance L to the scanning plane from the deflection point when the θ becomes L ₀ = L, the radius R of the mirror surface of the deflector
And the above L ₀ is, R = {(1 / cosθ ) + cosθ / (1 + cosθ) -1} because it is characterized by having a relation of L _0, main and sub Tomo curvature is small. In the example shown in FIG. 4, the center of rotation of the mirror surface 4 does not exactly coincide with the center of rotation of the shaft 1. However, since the thickness of the mirror surface is very thin, the influence is small and the radius of curvature R is smaller than the above. With this relationship, the field curvature can be corrected. Although the use of two mirror surfaces 4 in this way has some problems such as the influence of surface tilt, this problem can be solved by increasing the processing accuracy of the mirror.
With a surface, two scans can be performed for one rotation of the mirror, so that the speed of deflection scanning can be increased.

Next, FIG. 5 shows an example of the deflector of the optical scanning device according to the third aspect. In FIG. 5, the same reference numerals as those in FIGS. 1 and 4 denote the same components. In the deflector shown in FIG. 5, the mirror surface 4 is a two-sided mirror having a convex cylindrical surface having a radius R and arranged in the vicinity of the center of rotation of the shaft 1. And the distance L ₀ from the deflection point to the scanning surface when the rotation angle of the deflector is _0, and the distance from the deflection point to the scanning surface when the rotation angle is θ. as L and becomes the L ₀ = L, the above-mentioned
The radius R and the L ₀ of the mirror surface of the deflector is characterized by having a relationship of R = {(1 / cosθ) + cosθ / (1 + cosθ) -1} L 0.

FIG. 6 is a diagram showing a configuration example of the optical scanning device according to the third aspect as viewed in a cross section in the sub-scanning direction. In FIG. 6, 21 is a laser diode (LD), 22 is LD2.
23, a lens for converging the divergent light emitted from 1
Is a cylindrical lens, 24 is a deflector having two mirror surfaces 4 integrally formed on the shaft 1 of the motor, 25 is a long cylindrical lens, and 26 is a photoconductor. In this example, since the mirror surface 4 of the deflector 24 has a cylindrical shape having a curvature only in the main scanning direction, an anamorphic optical system is provided. In the sub-scanning direction, an image is formed in the vicinity of the mirror surface 4 of the deflector 24, and a long cylindrical lens 25 between the deflector 24 and the photoreceptor 26 is used to reduce surface tilt. It has an optical system for correction. With such a configuration, it is possible to realize high-quality writing in which deflector having two mirror surfaces 4 causes a problem of surface tilt. In the optical scanning device shown in FIG. 6, the curvature of field in the sub-scanning direction is corrected by the long cylindrical lens 25. Further, when the surface tilt correction is not required, the beam diameter in the sub-scanning direction can be adjusted to various sizes by a combination of the cylindrical lens 23 and the long cylindrical lens 25.

Next, FIG. 8 is a diagram showing a configuration example of the optical scanning device according to claim 4 as viewed in a cross section in the sub-scanning direction. 8, reference numeral 21 denotes a laser diode (LD), and reference numeral 22 denotes an LD 21.
A lens for converting the emitted divergent light into a focused luminous flux,
Reference numeral 23 denotes a cylindrical lens having a curvature only in the sub-scanning direction, and reference numeral 24 denotes a motor shaft 1 and a mirror surface formed integrally with the shaft, the mirror surface being disposed near the rotation center of the shaft. FIG. 1 (b) is a deflector characterized in that the mirror is a one- or two-surface mirror having a convex cylindrical surface of R.
Alternatively, it is configured as shown in FIG. Also, 2
5 'is a long toroidal lens having a concave surface formed of a barrel-shaped toroidal lens, and 26 is a photoreceptor. In order to correct the field curvature, it is necessary to input a light beam from the optical axis direction, that is, the direction in which the deflection angle is 0, as described above. For this purpose, for example, in the configuration shown in FIG. 8, a light beam is incident from a position slightly deviated from the main scanning plane in the sub-scanning direction.
Since the mirror surface of the deflector 24 has a cylindrical shape having a curvature only in the main scanning direction, it becomes an anamorphic optical system, and has a curvature only between the focusing lens 22 and the deflector 24 in the sub-scanning direction. Using a cylindrical lens 23, the mirror surface 4 of the deflector 24 is
An image is formed in the vicinity, and an optical system for correcting surface tilt is formed by a long toroidal lens 25 ′ disposed between the deflector 24 and the photoconductor 26. Here, the long toroidal lens is used because the field curvature can be reduced and the light amount loss can be reduced as compared with using a long cylindrical lens having a curvature only in the sub-scanning direction. is there.

FIG. 9 shows an example of a long toroidal lens. In FIG. 9, d ₁ is the distance from the deflection point to the first surface of the long toroidal lens 25 ′, d ₂ is the distance from the second surface of the long toroidal lens 25 ′ to the scanning surface, and D is the long toroidal lens. 25 'is shown. Also, R _1s , R
_1m , R _2s and R _2m have the following meanings. The first surface of the long toroidal lens 25 ′ has a radius of curvature R _1m in the main scanning direction with the axis in the main scanning direction on the main scanning plane as a rotation axis and a radius R _1s.
The second surface is a toroidal surface obtained by rotating an arc having a radius R _2s with a radius R _2m about an axis in the sub-scanning direction passing through the optical axis. Also a long toroidal lens 2
The refractive index of 5 ′ is n. Next, in the optical scanning device using the long toroidal lens 25 ′, the R _1s ,
An embodiment in which R _1m , R _2s , and R _2m are specifically defined will be described. R indicates the radius of curvature of the mirror surface 4 of the deflector in the main scanning direction. In the following embodiments, R _1m , R _1s ,
The unit of R _2m , R _2s , D, d ₁ , d ₂ , and R is [mm].

(Example 1) R _1m R _1s R _2m R _2s D d ₁ d ₂ R n -700 -22.0 -700 -12.0 3 126.2 60 98.914 1.5721 (Example 2) R _1m R _1s R _2m R _2s D d ₁ d ₂ R n -700 -18.8 -700 -10.15 3 126.2 60 98.914 1.48519 (Example 3) R _1m R _1s R _2m R _2s D d ₁ d ₂ R n -1000 -18.9 -1000 -11.45 3 119.5 60 98.914 1.5721 (Example 4) R _1m R _1s R _2m R _2s D d ₁ d ₂ R n -900 -14.8 -900 -9.18 3 119.5 60 98.914 1.48519 (Example 5) R _1m R _1s R _2m R _2s D d ₁ d ₂ R n -500 -25.8 -500 -13.3 3 119.5 60 98.914 1.5721 Here, FIG. 10 shows the field curvature of each of the embodiments (1) to (5), and the dotted line indicates the main scanning direction. , The solid line indicates the amount of field curvature in the sub-scanning direction.

Next, FIG. 7 is a diagram showing a configuration example of the optical scanning device according to claim 5 as viewed in a cross section in the sub-scanning direction. In the optical scanning device shown in FIG. 7, an element that emits laser light from two points having a certain pitch in the sub-scanning direction is used as the light source device 21. The two beams emitted from the light source device 21 become focused light by the focusing lens 22, and are imaged on the mirror surface of the deflector 24 only in the sub-scanning direction by the cylindrical lens 23. Here, as the deflector 24, one having a cylindrical mirror surface 4 is used as an example, and the optical system is configured in the same manner as in FIG. The mirror surface of the deflector 24 and the surface of the photoreceptor 26 are conjugated by a long cylindrical lens 25. The lateral magnification is β, and the pitch of the two beams on the mirror surface of the deflector 24 is u. _1, when the pitch of the two beams on the photoreceptor surface and u _2, and has a u ₂ = .beta.u _1. In this example, an example in which the optical scanning device described in claim 3 is multi-beamed has been described. However, even if the optical scanning device described in claim 1, claim 2, or claim 4 is used, multi-beam formation is similarly performed. can do.

Next, the inventions of claims 6 and 7 will be described. When the fθ lens is used as the optical scanning lens, if the fθ lens is a single lens and the field curvature is to be corrected in both the main scanning direction and the sub scanning direction, the lens shape is as follows.
In order to correct the field curvature in the sub-scanning direction, the lens has a lens shape as shown in FIG. 11 in which the first surface is a barrel-shaped toroidal surface (BT surface) and the second surface is a normal toroidal surface (NT surface). At this time, since the first surface is concave with respect to the main scanning direction, it is difficult to correct the linearity. When a normal deflecting mirror using a flat mirror surface is used, the amount of curvature of field is reduced to some extent. However, there is a problem that the linearity is about ten and several percent at the maximum. In addition, as described above, when a deflector such as a tenon-type mirror having a mirror surface with a curvature of R is used, field curvature can be corrected very well without using an fθ lens. Therefore, the number of components can be reduced without using an fθ lens as a post-objective optical scanning device, and cost can be reduced. But,
Also in this case, since the linearity can hardly be corrected, a considerably electric correction is used. Also, since the maximum amount that can be corrected by electrical correction is about 30%,
Thus, there is a problem that there is a limit to widening the angle of view or shortening the optical path length.

Further, when the optical scanning lens has an anamorphic shape and also corrects the sub-scanning direction at the same time, when combined with an axial deflector, the mirror surface of the deflector has one or two mirror surfaces. Although the surface and the surface to be scanned do not have a conjugate relationship (a so-called surface tilt correction optical system), the anamorphic configuration is such that the paraxial focal lengths in the main scanning direction and the sub-scanning direction are almost equal. In this case, the curvature of field in the sub-scanning direction can be easily corrected more easily than using a surface tilt correction optical system, and since the number of deflecting mirrors is at most two, the tilting accuracy of the two surfaces can be improved by processing the deflecting mirror. There is a high possibility that you can get enough. However, from the viewpoint of cost merit, the cost of the deflecting mirror motor is very high.If the precision of the rotation unevenness of the motor and the processing accuracy of the mirror surface are strict, the cost will increase. There's a problem. In the case of an optical scanning lens having a surface tilt correction optical system using a normal BT surface and NT surface, correction of linearity is still slightly insufficient and electrical correction is required. If it is not necessary to perform a proper correction, the load on the drive circuit is reduced, which is preferable.

The inventions of claims 6 and 7 have been made in view of these circumstances, and the optical scanning lens 30 is shown in FIG.
The deflector has a mirror surface having a cylindrical surface shape, for example, as shown in FIG. 5 described above.
At this time, as described above, when a deflector is used as a post-objective deflector without using an fθ lens, focused light is incident on the deflector, and the scanning surface is deflected from the deflection point when the rotation angle of the deflector is zero. and the distance L to the scanning surface becomes L ₀ = L and the distance L ₀ up from the deflection point when the rotation angle θ
As described above, when a deflector having a cylindrical surface having a radius of curvature R having a relationship of R = {(1 / cos θ) + cos θ / (1 + cos θ) −1} L ₀ as a mirror surface is used, as described above, very well. Field curvature can be corrected. In this case, when the deflecting mirror surface is flat, the incident converging light draws an arc Q by deflection as shown in FIG. 12A, and the deflecting mirror surface has a curvature as shown in FIG. By doing so, the focal point is made flat on the scanning surface S. That is, when the deflecting mirror has a convex curvature, the deflecting mirror has an effect of correcting that the curvature of field is under. However, as described above, when a deflector having a curvature is used as a post-objective type, the curvature of field is corrected very well, but the linearity cannot be corrected much.

[0029] Therefore, according to claim 6, in the invention of claim 7, wherein, to correct the linearity by fθ lens with fθ lens as the optical scanning lens, and, utilizing the effect described above with reference to the deflection mirror having a curvature Thus, the field curvature is satisfactorily corrected. That is, a deflection mirror having a curvature is used as a pre-objective type. FIG. 13 shows the field curvature when the field curvature is corrected using a single fθ lens using a BT surface as the first surface and an NT surface as the second surface, and using a flat deflecting mirror as the deflector. And linearity. However, if the field curvature is corrected in this manner, the linearity becomes under-corrected and cannot be corrected. At this time, if parameters such as R of the lens are changed so as to reduce the linearity, the curvature of field in the main scanning largely falls toward the under side. At this time, it is possible to reduce the main scanning field curvature by using the field curvature correction operation of the deflecting mirror having the above-described curvature. The sub-scanning direction is
The deflecting surface and the surface to be scanned have a substantially conjugate relationship to perform surface tilt correction.

Here, in the optical scanning device according to the sixth aspect,
A light source device, a lens that converges the light beam emitted from the light source device, a cylinder lens that converges the converged light substantially only on the deflection surface of the axial deflector in the sub-scanning direction, and is deflected by the deflector. A single-lens optical scanning lens for condensing the luminous flux on the surface to be scanned, and the axial deflector is configured as shown in FIG.
As shown in FIG. 5 or FIG. 5, the scanner motor shaft 1 has one or more mirror surfaces 4 integrally formed with the shaft, and the mirror surface is arranged at a radius substantially in the vicinity of the rotation center of the shaft. R
Characterized in that it is a convex cylindrical mirror. The optical scanning lens has a shape as shown in FIG. 11, and the first surface rotates with an arc in the main scanning direction on the main scanning surface on a circular arc having a radius R _1m and a radius R _1s on the main scanning direction. The second surface is a surface obtained by rotating an arc having a radius R _2s around an axis in the sub-scanning direction passing through the optical axis with a radius R _2m , and the deflecting surface and the surface to be scanned in the sub-scanning direction. Is a light scanning lens that makes the relationship substantially conjugate.

Hereinafter, R _1s , R _1m ,
An example in which R _2s and R _2m are specifically defined will be described. still,
In this embodiment, in order to further correct the curvature of field in the sub-scanning direction, a position conjugate with the surface to be scanned is slightly closer to the light source than the deflecting surface. In this case, the surface tilt correction function is lower than when the deflecting surface and the surface to be scanned are accurately conjugated. However, in the case of a two- or one-surface deflecting mirror such as an axial deflecting mirror, there is not enough. There is a tilt correction function. In the embodiments described below, d ₀ is the distance between the lens surface on the deflection starting side and the deflection starting point, d ₁ and n are the lens surface spacing and refractive index of the optical scanning lens, and D is the scanning surface side lens. It represents the distance between the surface and the surface to be scanned. Further, the distance from the deflection starting point to the position of the naturally focused light point is S. FIG. 14 shows the curvature of field in each of the following embodiments. The dotted line indicates the curvature of field in the main scanning direction, and the solid line indicates the curvature of field in the sub-scanning direction. Also below
In the embodiment described above, S, R _1m , R _1s , R _2m , R _2s ,
The unit of D, d ₀ , d ₁ is [mm].

(Example 1) S = 79.2, R _1m = -500, R _{1s
= -47.0, R 2m = -70,} R 2s = -18.5, d 0 = 25.0, d 1 = 2
1.6, D = 120.0, n = 1.65, S / R = 0.495, R 1m / R 2m = 7.14, R 1s / R 2s = 2.5
4. The writing width is 225.3 and the linearity is 5.0% or less. FIG. 14A shows the field curvature of this embodiment. (Example _{2) S = 79.2, R 1m} = -500, R 1s = -54.0, R
_{2m = -73.0, R 2s = -19.5} , d 0 = 30.0, d 1 = 21.6, D =
120.0, n = 1.65, S / R = 0.466, R 1m / R 2m = 6.85, R 1s / R 2s = 2.7
7. The writing width is 221.7 and the linearity is 5.0% or less. FIG. 14B shows the field curvature of this embodiment. (Example _{3) S = 79.2, R 1m} = -500, R 1s = -54.0, R
_{2m = -81.0, R 2s = -21.8} , d 0 = 30.0, d 1 = 21.6, D =
120.0, n = 1.766, S / R = 0.466, R 1m / R 2m = 6.17, R 1s / R 2s = 2.4
8, writing width = 217.9, linearity = 4.0% or less. FIG. 14C shows the field curvature of this embodiment. (Example _{4) S = 79.2, R 1m} = -500, R 1s = -45.5, R
_{2m = -65.0, R 2s = -16.7} , d 0 = 25.0, d 1 = 21.6, D =
120.0, n = 1.5721 S / R = 0.483, R 1m / R 2m = 7.69, R 1s / R 2s = 2.7
2. The writing width is 232.2 and the linearity is 6.0% or less. FIG. 14D shows the field curvature of this embodiment.

As described above, in the optical scanning device according to the sixth embodiment, the mirror surface is a convex cylindrical mirror having a radius R disposed substantially near the center of rotation of the shaft. By using the deflector characterized by the above and the optical scanning lens having the above configuration, it is possible to correct the field curvature in both the main and sub and the linearity with a configuration in which the number of components of the optical system is small. In addition, since the optical system is a surface tilt correction optical system, the processing accuracy of the deflecting mirror and the accuracy of rotation unevenness of the motor can be reduced, and the cost of the deflector can be reduced.

Further, in the optical scanning device according to claim 6,
In the meantime, the optical scanning lens satisfies the following condition: 6.5 <R _1m / R _2m <8.0,
Assuming that the distance between the convergence point in the main scanning direction and the deflection point when the light does not pass through the optical scanning lens is S , the following condition is satisfied : 0.4 <S / R <0.5. The condition of 2.0 <R _1s / R _2s <3.0 is satisfied. When the lower limit of the above expression is exceeded, the linearity increases to the minus side, and the upper limit is exceeded. In this case, the linearity correction becomes insufficient. If the lower limit of the expression is exceeded, the field curvature of the main scanning falls to the under side, and if the upper limit is exceeded, the field curvature falls to the over side, and the spot diameter in the main scanning direction increases at each image height. Will be different. If the lower limit of the expression is exceeded, the curvature of field in the sub-scanning direction falls to the over side, and if the upper limit is exceeded, the image surface falls to the under side, so that astigmatism increases. Therefore, by satisfying the above conditions, the linearity is well corrected, and the spot diameter can be kept constant at each image height.

By the way, in the optical scanning device according to the sixth aspect, the first surface of the optical scanning lens is the BT surface and the second surface is the NT surface. Correction may be required. However, it is preferable that the electric correction is not performed because the load on the drive circuit is reduced. Therefore, in the optical scanning device according to the seventh aspect, the lens for optical scanning is such that the first surface has an aspherical curve as a rotation axis in the main scanning direction on the main scanning plane, and a radius R _1s The second surface is a surface obtained by rotating an arc having a radius R _2s with a radius R _2m around an axis in the sub-scanning direction passing through the optical axis, and the second surface is formed as a deflecting surface in the sub-scanning direction. It is an optical scanning lens having a substantially conjugate relationship with a scanning surface. That is, in the optical scanning lens of the present invention, the main scanning direction of the first surface is made aspherical, so that better linearity is corrected. FIG. 15 shows an example in which the curvature of field and the linearity are corrected when the aspherical shape in the main scanning direction is not used. In this case, the linearity can be corrected quite satisfactorily. Target correction is required.
The problem at this time is that the curve of the linearity when the linearity is corrected is slightly large.To reduce this curve, the curvature of the lens surface changes when the angle of view increases. It is effective to do so, so that the linearity can be further corrected by using an aspherical surface.

Further, in the optical scanning device according to the seventh aspect, the shape of the aspheric surface to be rotated on the first surface of the optical scanning lens is such that the intersection of the first surface of the optical scanning lens with the optical axis of the optical scanning lens. An equation using an aspherical coefficient with the radius of curvature of the contact circle at the coordinate origin as R _1m , x = {y ² / (R _1m + √ (R _1m ² − (1 + K) y ² ))} + A ₂ y ²
+ A ₃ y ³ + A ₄ y ⁴ +..., A _fourth -order aspherical coefficient A ₄ is used, and the main scanning is performed when the light focused by the lens that condenses the light beam does not pass through the optical scanning lens. When the distance between the point converging in the direction and the deflection point is S, the optical scanning lens is
-4.0 × 10 ⁻⁶ [mm ⁻³ ] <(A ₄ × (R _1m / R _2m )) <
-0.3 × 10 ⁻⁶ [mm ⁻³ ] 0.4 <S / R <0.7 2.5 <R _1s / R _2s <3.5 By satisfying 3.5, the linearity is well corrected. . Hereinafter, an embodiment in which R _1s , R _1m , R _2s , R _2m , A _4, etc. of the optical scanning lens in the optical scanning device according to claim 7 are specifically defined will be described. In the embodiments described below, d ₀ is the distance between the lens surface on the deflection starting point side and the deflection starting point, and d ₁ and n are the lens surface spacing and the refractive index of the optical scanning lens. Further, the distance from the deflection starting point to the position of the naturally focused light point is S. In the examples below,
S, R _1m , R _1s , R _2m , R _2s , d ₀ , d ₁ , R and
The unit of the effective writing width is [mm], and the fourth order aspherical coefficient
Unit of A ₄ is a [mm ^-3].

(Example 1) S = 119.2, R _1m = -650.0,
R _1s = -52.0, R _2m = -57.0, R _2s = -17.0, A ₄ = -1.50
/ 10 ⁷ , d ₀ = 25.0, d ₁ = 21.6, n = 1.572, R = 210.0
Effective writing width = 215.2, linearity = -1.2 to 2.3%,
It is. FIG. 16A shows the field curvature of this embodiment. (Example _{2) S = 84.2, R 1m} = -700.0, R 1s = -58.0,
R _2m = -68.0, R _2s = -19.6, A ₄ = -0.7 / 10 ⁷ , d ₀ = 30.
0, d ₁ = 21.6, n = 1.65, R = 170.0 Effective writing width = 216.0, linearity = −0.7 to 2.
2%. FIG. 16B shows the field curvature of this embodiment. (Example _{3) S = 189.2, R 1m} = -650.0, R 1s = -59.0,
R _2m = -80.0, R _2s = -22.3, A ₄ = -0.5 / 10 ⁷ , d ₀ = 30.
0, d ₁ = 21.6, n = 1.766, R = 400.0 Effective writing width = 217.4, linearity = −0.6 to 1.9%,
It is. FIG. 16C shows the field curvature of this embodiment. (Example _{4) S = 120.6, R 1m} = -1072.0, R 1s = -64.
8, R _2m = -56.3, R _2s = -19.0, A ₄ = -1.75 / 10 ⁷ , d ₀
= 26.0, d ₁ = 20.0, n = 1.572, R = 201.0 Effective writing width = 216.0, linearity = −1.4 to 1.4%,
It is. FIG. 16D shows the field curvature of this embodiment.

As described above, in the optical scanning device according to the seventh embodiment, the mirror surface is a convex cylindrical mirror having a radius R disposed substantially near the center of rotation of the shaft. By using the deflector characterized by the above and the optical scanning lens having the above-described configuration, the configuration is such that the number of parts of the optical system is small, the primary and secondary components correct the field curvature, and the optical scanning lens has the By using an aspherical shape in one main scanning direction, the linearity can be corrected better than when a normal BT surface is used, and the linearity can be corrected to a level that does not require electrical correction. is there. Further, since the surface tilt correction optical system is used, it is possible to reduce the processing accuracy of the deflecting mirror and the accuracy of rotation unevenness of the motor, thereby reducing the cost of the deflector. Further, in the optical scanning lens of the optical scanning device according to claim 7 , when the value exceeds the lower limit of the conditional expression, the linearity increases to the minus side,
If the upper limit is exceeded, linearity correction will be insufficient. When the value exceeds the lower limit of the expression, the field curvature of the main scanning falls to the under side, and when the value exceeds the upper limit, it falls to the over side, and the spot diameter in the main scanning direction greatly differs at each image height. When the value exceeds the lower limit of the expression, the field curvature in the sub-scanning direction falls to the over side, and when the value exceeds the upper limit, it falls to the under side, so that astigmatism increases. Therefore,
By satisfying the conditions of ( 7 ) and ( 7 ), the linearity is corrected well, and the spot diameter can be kept constant at each image height.

[0039]

As described above, in the optical scanning device according to the first aspect, the mirror is provided integrally with the shaft of the scanner motor of the deflector, so that the device can be reduced in size and weight and the mirror surface can be further reduced. Is a spherical or cylindrical surface with a radius of curvature R
From the deflection point when the rotation angle of the deflector is 0 to the scanning surface.
From the deflection point to the scanning surface when the distance L ₀ and the rotation angle are θ at
Of the deflector so that the distance L at the point becomes L ₀ = L.
The radius R and the L ₀ of the error surface, by having a relationship of R = {(1 / cosθ) + cosθ / (1 + cosθ) -1} L 0, without the use of fθ lens, correct curvature of field it can. In the optical scanning device according to the second aspect, the same operation and effect as those of the optical scanning device according to the first aspect can be obtained, and further, high-speed writing can be performed by using two mirror surfaces. Claim 3
In the optical scanning device described above, the same operation and effect as those of the optical scanning device according to claim 1 can be obtained, and writing with higher image quality can be performed by using an optical system as a tilt correction optical system. Alternatively, it is possible to use an optical system in which the beam diameters in the main scanning direction and the sub-scanning direction are different.
Further, in the optical scanning device according to the fourth aspect, the first and second aspects of the invention are the same.
The same operation and effect as those of the optical scanning device described in Item 3 are obtained, and
By using a long toroidal lens having a concave toroidal barrel shape, the field curvature can be made smaller than when a long cylindrical lens is used, and the loss of light quantity can be reduced. When the number of mirror surfaces is two, the speed of the optical scanning device can be increased. In the optical scanning device according to the fifth aspect,
The same operation and effect as those of the optical scanning devices described in 2, 3, and 4 can be obtained, and each optical scanning device can be formed into a multi-beam, so that higher-speed writing can be performed.

Further, in the optical scanning device according to the present invention, a combination of an axial deflector having a mirror surface having a cylindrical mirror with a convex radius R and an optical scanning lens for correcting linearity is provided. By this, the field curvature and linearity can be satisfactorily corrected, and the conditions
By doing so, the linearity can be better corrected, and the spot diameter can be kept constant at each image height. Further, in the optical scanning device according to the seventh aspect, the same operation and effect as those of the optical scanning device according to the sixth aspect are obtained, and the aspherical shape is used in the main scanning direction of the first surface of the optical scanning lens. As a result, the linearity can be more favorably corrected. Also, the conditions
By doing so, the linearity can be better corrected, and the spot diameter can be kept constant at each image height.

[Brief description of the drawings]

FIG. 1 is a perspective view of an essential part showing an example of a deflector of an optical scanning device according to claim 1, wherein FIG.
(b) shows an example in which the mirror surface is a cylindrical surface.

FIG. 2 is an explanatory diagram of deflection scanning by the deflector.

FIG. 3 is a diagram showing a configuration example of the optical scanning device according to claim 1 in a cross section in the sub-scanning direction.

FIG. 4 is an essential part perspective view showing an example of a deflector of the optical scanning device according to the second embodiment.

FIG. 5 is a perspective view of an essential part showing an example of a deflector of the optical scanning device according to the third embodiment.

FIG. 6 is a diagram showing a configuration example of the optical scanning device according to claim 3 in a cross section in the sub-scanning direction.

FIG. 7 is a diagram showing a configuration example of the optical scanning device according to claim 5 in a cross section in the sub-scanning direction.

FIG. 8 is a diagram showing a configuration example of the optical scanning device according to claim 4 in a cross section in the sub-scanning direction.

FIG. 9 is a diagram showing a long toroidal lens of the optical scanning device according to claim 4 in a cross section in a main scanning direction and a sub scanning direction.

FIG. 10 shows embodiments (1) to (4) of the optical scanning device according to claim 4;
It is a figure showing the curvature of field of (5).

FIG. 11 is a perspective view showing an example of the shape of an optical scanning lens used in the optical scanning device according to claims 6 and 7 ;

FIG. 12 is an explanatory diagram showing a difference in light condensing position at the time of deflection scanning by a deflector having a flat mirror surface and a deflector having a curved surface.

FIG. 13 is a diagram illustrating field curvature and linearity when field curvature is corrected using a deflector having a flat mirror surface and a single fθ lens having a BT surface as a first surface and an NT surface as a second surface. It is.

FIG. 14 is a diagram illustrating curvature of field in Examples 1 to 4 of the optical scanning device according to claim 6 ;

FIG. 15 is a diagram showing field curvature and linearity in the optical scanning device according to claim 6;

FIG. 16 is a diagram illustrating curvature of field in Examples 1 to 4 of the optical scanning device according to claim 7 ;

[Explanation of symbols]

 1, a scanner motor shaft 2, a bearing 3, a magnet 4, M, a mirror surface 11, 21, a light source device 22, a focusing lens 13, 24,. .. Deflectors 14, 26 ... Medium to be scanned 23 ... Cylindrical lens 25 ... Long cylindrical lens 25 '... Long toroidal lens 30 ... Optical scanning lens

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Hirotsuka 1-3-6 Nakamagome, Ota-ku, Tokyo, Ricoh Co., Ltd. (56) References JP-A-1-169522 (JP, A) JP-A-63-188112 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G02B 26/10

Claims (7)

(57) [Claims] A light source device, a lens for converging a light beam emitted from the light source device, and a mirror surface formed integrally with a shaft of a scanner motor, the mirror surface being a rotation center of the shaft. It has a deflector characterized by being a convex spherical or cylindrical mirror having a radius R disposed substantially in the vicinity thereof, and a scanning surface on which a light beam deflected by the deflector scans. Then, the distance L ₀ from the deflection point to the scanning surface when the rotation angle of the deflector is ₀ and the distance L from the deflection point to the scanning surface when the rotation angle is θ are L ₀ = L. ,
The radius R and the L ₀ of the mirror surface of the deflector, R = {(1 / cosθ ) + cosθ / (1 + cosθ) -1} optical scanning apparatus characterized by having a relation of L _0. 2. A light source device, a lens for converging a light beam emitted from the light source device, and a mirror surface formed integrally with the shaft on a shaft of the scanner motor, the mirror surface being a center of rotation of the shaft. A deflector characterized by being a convex spherical spherical opposed mirror having a radius of R disposed substantially in the vicinity thereof;
A scanning surface on which a light beam deflected by the deflector scans, a distance L ₀ from a deflection point to a scanning surface when the rotation angle of the deflector is 0, and a deflection point when the rotation angle is θ The radius R of the mirror surface of the deflector and the above L ₀ are determined by the following equation: R = {(1 / cos θ) + cos θ / (1 + cos θ) −1} so that the distance L from the scanning surface to the scanning surface becomes L ₀ = L. optical scanning apparatus characterized by having a relation of L _0. 3. A light source device, an anamorphic lens group for converging a light beam emitted from the light source device, and a mirror surface formed integrally with a shaft of a scanner motor, wherein the mirror surface is formed of an axis. A deflector characterized by being a convex cylindrical surface-like two-sided mirror having a radius R disposed near the center of rotation; and a scanning surface on which a light beam deflected by the deflector scans. A long cylindrical lens disposed between the scanning surface and the deflector and having power only in the sub-scanning direction, and having a length from the deflection point to the scanning surface when the rotation angle of the deflector is 0. a distance L ₀ from the deflection point when the rotation angle θ as the distance L to the scanning surface becomes L ₀ = L, and the radius R and the L ₀ of the mirror surface of the deflector, R = { Optical scanning characterized by having a relationship of (1 / cos θ) + cos θ / (1 + cos θ) −1} L ₀ apparatus. 4. A light source device, a lens for converging a light beam emitted from the light source device, a cylindrical lens having power only in the sub-scanning direction, and a mirror surface formed integrally with the axis of the scanner motor. A deflector characterized in that the mirror surface is a one- or two-surface mirror having a convex cylindrical surface with a radius R disposed substantially in the vicinity of the center of rotation of the shaft, and the mirror is deflected by the deflector. Elongate toroidal lens including a barrel-shaped toroidal surface as a concave lens surface, which is disposed between the scanning surface on which the light beam scans and the deflector and has a radius of curvature in the sub-scanning direction that decreases as the optical axis moves away from the main scanning direction. And the distance L ₀ from the deflection point to the scanning surface when the rotation angle of the deflector is ₀ and the distance L from the deflection point to the scanning surface when the rotation angle is θ are L ₀ = L. So that the mirror of the deflector An optical scanning device, wherein the surface radius R and the above L ₀ have a relationship of R = {(1 / cos θ) + cos θ / (1 + cos θ) −1} L ₀ . 5. The method of claim 1, claim 2, claim 3, or claim 4.
The optical scanning device according to any one of claims 1 to 3, wherein an element that emits two or more light beams is used for the light source device. 6. A light source device, a lens for converging a light beam emitted from the light source device, a cylinder lens for converging the converged light on a substantially deflection surface of an axial deflector only in a sub-scanning direction, and A single-lens optical scanning lens for condensing the light beam deflected by the deflector on the surface to be scanned, wherein the axial deflector is formed on one or more surfaces integrally formed with the axis of the scanner motor. Having a surface mirror surface, wherein the mirror surface is a convex cylindrical mirror having a radius R disposed substantially in the vicinity of the center of rotation of the shaft, and the optical scanning lens further comprises: The first surface is a surface rotated by an arc of radius R _1m with the axis in the main scanning direction on the main scanning surface as a rotation axis at a radius of R _1s , and the second surface is an arc of radius R _2s passing through the optical axis. is a surface obtained by rotating a radius R _2m around the sub-scanning direction axis, the deflection surface in the sub scanning direction Characterized in that the査面an optical scanning lens made substantially conjugate relationship, and, the optical scanning lens, the following condition, 6.5 <meet R _1m / R _2m <8.0, Focused light by a lens that focuses the light beam,
Assuming that the distance between the convergence point and the deflection point in the main scanning direction when the light does not pass through the optical scanning lens is S, the following condition: 0.4 <S / R <0.5 is satisfied. An optical scanning device satisfying the following condition: 2.0 <R _1s / R _2s <3.0. 7. A light source device, a lens for converging a light beam emitted from the light source device, a cylinder lens for converging the condensed light substantially on the substantially deflecting surface of the axial deflector only in the sub-scanning direction, A single-lens optical scanning lens for condensing the light beam deflected by the deflector on the surface to be scanned, wherein the axial deflector is formed on one or more surfaces integrally formed with the axis of the scanner motor. Having a surface mirror surface, wherein the mirror surface is a convex cylindrical mirror having a radius R disposed substantially in the vicinity of the center of rotation of the shaft, and the optical scanning lens further comprises: the main scanning direction of the axis of the first surface of the curve forming the aspherical shape on the main scanning plane to the rotation axis, a shape obtained by rotating a radius R _1s, light the arc of the second surface radius R _2s is a surface obtained by rotating a radius R _2m around the sub-scanning direction of the axis passing through the axis, the sub-scanning direction odor The optical scanning lens is characterized in that the deflecting surface and the surface to be scanned are substantially conjugated with each other, and the shape of the rotating aspheric surface on the first surface of the optical scanning lens is the optical scanning lens. the radius of curvature of the osculating circle when an intersection between the optical axis of the first surface of the lens was coordinate origin as R _{1 m,} using the non-spherical coefficient ^{equation, x = {y 2 / (} R 1m + √ (R 1m ² − (1 + K) y ² ))) + A ₂ y ²
+ A ₃ y ³ + A ₄ y ⁴ +..., A _fourth -order aspherical coefficient A ₄ is used, and the main scanning is performed when the light focused by the lens that condenses the light beam does not pass through the optical scanning lens. When the distance between the point converging in the direction and the deflection point is S, the optical scanning lens is
-4.0 × 10 ⁻⁶ [mm ⁻³ ] <(A ₄ × (R _1m / R _2m )) <
-0.3 * 10 < ^-6 > [mm < ^-3 >] The optical scanning device which satisfies 0.4 <S / R <0.7 2.5 < _R1s / _R2s <3.5.