JPH10319317A - Scanning and image forming lens system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a scanning and image formation lens system constituted of two lenses which is stable with respect to parts tolerance fluctuation and assembling accuracy fluctuation. SOLUTION: This system is constituted by successively arranging first and second lenses 5A and 5B from an optical deflector 4 side to a surface 6 to be scanned side. As to a shape inside a deflecting surface, an incident side surface is convex on the optical deflector side, and an exit side surface is convex on the surface to be scanned side in terms of the lens 5A, and the incident surface side is concave on the optical deflector side, and the exit surface side is convex on the surface to be scanned side in terms of the lens 5B; both surfaces of the lens 5A are symmetrical to an optical axis, and both surfaces of the lens 5B inside the deflecting surface are non-circular shape; and when a distance on an optical axis from the exit side surface of the lens 5A to the incident side surface of the lens 5B is defined as D2 , and a focal distance with respect to the main scanning corresponding direction to an entire system is defined as (fm), the condition of 0.07<=D2 /fm<=0.30 is satisfied.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a scanning imaging lens system used in an optical scanning device.

[0002]

2. Description of the Related Art In an optical scanning apparatus, a scanning image forming lens system for converging a deflected light beam as a light spot on a surface to be scanned is provided by:
It is necessary to satisfactorily correct the constant velocity characteristics such as the fθ characteristic in order to secure the constant velocity of the optical scanning, and to satisfactorily correct the field curvature in order to suppress the fluctuation of the light spot diameter due to the image height. Also,
With the demand for lower cost and more compact optical scanning devices,
There is a need for a scanning imaging lens system that has a small number of lens components and can be realized at low cost. "Single lens made of plastic" has also been proposed as a scanning imaging lens system that can be realized at low cost and compact. However, plastic single lenses have environmental resistance, in which the optical performance changes due to the effects of temperature and humidity. There's a problem.

Japanese Patent Laid-Open Publication No. Hei 6-34900 discloses a plastic scanning lens system as a compact scanning imaging lens system.
Although a lens configuration is proposed, the distance between the two lenses is reduced for compactness, and the distance between the second lens disposed on the surface to be scanned and the surface to be scanned is increased. There is a disadvantage on top. That is, when the distance between the second lens and the surface to be scanned is increased, the imaging magnification of the scanning image forming lens system is increased. However, it is easily deteriorated significantly from “design performance”.

Japanese Patent Application Laid-Open No. 7-174999 proposes a scanning image forming lens system which is excellent in environmental resistance and excellent in performance and has a two-lens structure combining a glass lens and a plastic lens. However, the distance between the two lenses is very narrow, the distance between the lens on the surface to be scanned and the surface to be scanned tends to be large, and the optical magnification increases. is there.

That is, in using the scanning image forming lens system described in each of the above publications, it is necessary to set the tolerance of the optical arrangement to be quite strict, and the component accuracy and the assembly accuracy of the optical scanning device are high. Become.

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a two-element scanning imaging lens system which is excellent in compactness and is stable against fluctuations in component tolerances and fluctuations in assembly accuracy. Another object of the present invention is to realize a two-element scanning imaging lens system which is stable against component tolerance fluctuations and assembly accuracy fluctuations and has excellent environmental resistance.

[0007]

The scanning image forming lens system according to the present invention is arranged in a direction corresponding to the main scanning (on a virtual optical path in which the optical path from the light source to the surface to be scanned is linearly developed along the optical axis, A direction parallel to the main scanning direction, and a direction parallel to the sub-scanning direction on the virtual optical path is referred to as a sub-scanning direction). An optical deflector having a deflecting / reflecting surface in the vicinity of the image forming position deflects the light at a uniform angular velocity, and converges the deflected light beam as a light spot on the surface to be scanned by the scanning image forming lens system, so that the uniform velocity of the surface to be scanned is achieved. Scanning imaging lens system in an optical scanning device that performs effective optical scanning, in which first and second lenses are sequentially provided from the optical deflector side to the scanned surface side.

[0008] Assuming a deflected light beam ideally deflected by the optical deflector, a plane formed by sweeping the principal ray of the deflected light beam along with the deflection is called a "deflection surface". A plane orthogonal to the deflecting surface and parallel to the optical axis of the scanning and imaging lens system is called a “deflection orthogonal surface”. In addition,
The “light flux that forms a linear image long in the main scanning direction” in the vicinity of the deflecting reflection surface may be a parallel light flux or a weakly convergent or weakly divergent light flux in the main scanning corresponding direction.

In the scanning imaging lens system according to the present invention, the shape of the deflecting surface of the first lens is such that the incident side surface is convex toward the optical deflector,
The exit surface side is convex to the scanned surface side ", and the" second lens is concave on the incident surface side on the optical deflector side and convex on the exit surface side on the scanned surface side ". That is, the cross-sectional shape within the deflection surface is such that the first lens is “biconvex” and the second lens is “meniscus convex on the surface to be scanned”. The first lens has “both surfaces are symmetrical with respect to the optical axis, and one surface has an aspherical shape”, and the second lens has “at least one surface has a non-arcuate shape in a deflection surface”.

The distance on the optical axis from the exit side surface of the first lens to the entrance side surface of the second lens: D ₂ , and the focal length fm in the main scanning corresponding direction of the entire system are as follows: (1) 0.07 ≦ D ₂ /fm≦0.30 is satisfied (claim 1).

The "non-arc shape" is defined as a paraxial radius of curvature in the deflection surface: Rm, a conic constant: K, and higher-order coefficients: A, B,
C, D,. . The coordinates in the optical axis direction: X and the coordinates in the optical axis orthogonal direction (direction corresponding to main scanning): Y are expressed as follows: X = Y ² / [Rm + Rm√ ｛1− (1 + K) Y ² / Rm ² }] + AY ⁴ + BY ⁶ + CY ⁸ + DY ¹⁰ +. . . In the shape represented by (6), Rm, K, A, B, C,
D,. . And the shape specified. Higher order coefficients:
A, B, C, D,. Is determined such that “the power of Y increases sequentially by the square”. The shape obtained by rotating this “non-circular shape” around the X axis is the “aspherical shape”.

In the scanning imaging lens system according to the first aspect, the distance: D ₂ and the distance from the deflecting reflection surface to the surface to be scanned: L are as follows: (2) 0.05 ≦ D ₂ / L ≦ 0.20 can be satisfied (claim 2).

In the scanning imaging lens system according to claim 1 or 2, the distance on the optical axis from the exit side surface of the second lens to the surface to be scanned: D ₄ , and the focal length: fm are as follows: 0.6 ≦ D ₄ /fm≦0.9 can be satisfied (claim 3).

In the scanning imaging lens system according to the second or third aspect, the distance: D ₄ , L can satisfy the following condition: (4) 0.4 ≦ D ₄ /L≦0.7 (Claim 4).

In the scanning imaging lens system according to claim 1, the "shape of the second lens in the plane orthogonal to the deflection (shape in the direction corresponding to the sub-scanning)" is such that the incident side face is "the optical deflector side" Concave, and the emission side surface may be "convex to the surface to be scanned", that is, "meniscus convex to the surface to be scanned" (claim 5). In this case, the “surface having a non-circular shape in the deflecting surface” of the second lens means that “the radius of curvature in the deflecting orthogonal surface is continuously correlated with the shape in the main scanning corresponding direction and in the deflecting surface. Change "(claim 6).

That is, in the second lens, at least one surface has a non-circular shape in the deflecting surface, and the curvature of the surface having the non-circular shape in the deflecting orthogonal plane. The radius is continuously changed in the main scanning corresponding direction in relation to the non-arc shape. In this case, a line connecting the center of curvature in the plane orthogonal to the deflection of the lens surface in the main scanning corresponding direction generally has a curve different from the shape (non-circular shape) in the deflection surface of the lens surface. The radius of curvature in the plane orthogonal to the deflection is changed so as to improve the optical characteristics in the sub-scanning corresponding direction in correlation with the shape in the deflection plane, that is, according to the non-circular shape in the deflection plane. .

In the scanning imaging lens system according to the sixth aspect, the lateral magnification (the light beam height: H of the light beam incident on the H) in the direction orthogonal to the main scanning direction in the light beam height: H on the surface to be scanned. Assuming that the scanning lateral magnification is βs (H), this lateral magnification satisfies the following condition in the effective image area: (5) 0.95 ≦ | βs (H) / βs (0) | ≦ 1.05 (Claim 7).

In the scanning imaging lens system according to the sixth or seventh aspect, both the first and second lenses can be "formed of plastic" (claim 8).
The lens can be formed of "glass" and the second lens can be formed of "plastic".

Condition (1) relates to the "optical magnification", and the focal length (focal length in the deflecting surface) of the scanning imaging lens system in the main scanning corresponding direction: fm (light beam incident on the optical deflector is main scanning). When the beam is parallel with respect to the corresponding direction,
Longitudinal magnification in the main scanning corresponding direction, distance to be proportional to fm): sets forth the optimum range of D _2. When the value exceeds the upper limit of the condition (1), both the curvature of field in the main scanning direction and the constant velocity characteristic deteriorate. Particularly, the deterioration of the constant velocity characteristic becomes remarkable. If the lower limit is exceeded, the vertical magnification in the direction corresponding to the main scanning increases, and the component tolerance and the assembly tolerance become severe. Further, when at least one of the first and second lenses is formed of a plastic lens (claims 8 and 9), environmental resistance is also deteriorated.

The condition (2) is mainly based on a condition that mainly determines the size of the optical scanning device.
The optimum range of the distance: D _{2 to} “L” is determined. When the value exceeds the upper limit of the condition (2), as in the case of the condition (1), both the field curvature in the main scanning direction and the constant velocity characteristic deteriorate,
Particularly, the deterioration of the constant velocity characteristic becomes remarkable. If the lower limit is exceeded, the distance between the first and second lenses is reduced, the optical magnification is increased, the component tolerance and the assembly tolerance are tightened, the environmental resistance is deteriorated, or scanning from the deflecting reflective surface is performed. The distance to the surface increases, and the size of the optical scanning device increases.

The condition (3) defines an optimum range of the distance: D ₄ with respect to the focal length: fm. The condition (3) is premised on satisfying the condition (1) or the conditions (1) and (2). By satisfying the condition (3), only the condition (1) or (1), (2) is satisfied. ), Better performance can be realized than in the case where only ()) is satisfied.

When the value exceeds the upper limit of the condition (3), both the curvature of field in the main scanning direction and the constant velocity characteristic deteriorate, and the deterioration of the constant velocity characteristic becomes particularly remarkable. If the lower limit is exceeded, the vertical magnification in the direction corresponding to the main scanning becomes large, so that component tolerances and assembly tolerances become strict and environmental resistance deteriorates.

[0023] Condition (4), said distance: distance to L: defining an optimum range of D _4. The condition (4) is the condition (1), (2) or the condition (1), (2), (3)
Is satisfied. By satisfying the condition (4) together with these conditions, the performance can be further improved.

When the value exceeds the upper limit of the condition (4), both the curvature of field in the main scanning direction and the constant velocity characteristic deteriorate, and the deterioration of the constant velocity characteristic becomes particularly remarkable. If the lower limit is exceeded, the distance from the deflecting reflection surface to the surface to be scanned increases, and the size of the optical scanning device increases.

The “shape in the plane orthogonal to the deflection” of the second lens is
Since the rear principal point in the sub-scanning corresponding direction can be made closer to the surface to be scanned by defining the meniscus shape convex to the surface to be scanned as described in claim 5, the vertical magnification can be reduced. The lateral magnification is also reduced), the stability against component tolerance and assembly tolerance is improved, and the environmental resistance can be improved.

Further, by making the lens surface shape of the second lens as described in claim 6, fluctuations in magnification in the sub-scanning direction due to the height of the light beam are suppressed, and fluctuations in the light spot diameter in the sub-scanning direction are effectively reduced. By satisfying the condition (5), the fluctuation of the light spot diameter can be effectively reduced.

[0027] According to the eighth aspect of the present invention, the first and second modes are provided.
By forming both lenses from plastic, a scanning imaging lens system can be mass-produced at low cost. Further, as in the ninth aspect of the present invention, the scanning imaging lens is formed by forming the first lens having optical axis symmetry on both surfaces from glass, and forming the second lens having a complicated shape from plastic which is easy to mold. The system can be manufactured at low cost, and the first lens of the “biconvex shape”, which is easily affected by environmental changes when formed of plastic, is a glass lens. Can be enhanced.

[0028]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is an explanatory diagram showing an example of an optical scanning device using a scanning image forming lens system according to the present invention. A divergent laser beam emitted from a light source 1 which is a semiconductor laser is coupled by a coupling lens 2 into a “parallel beam” or “weakly convergent beam” or “weakly divergent beam”, and a cylinder lens. 3, the light is converged in the sub-scanning corresponding direction (the direction perpendicular to the drawing), and the deflecting / reflecting surface 4 of the optical deflector using the polygon mirror 4
An image is formed in the vicinity of A as a “long line image in the main scanning corresponding direction”. The cylinder lens 3 can be replaced by a concave cylinder surface mirror.

The light beam reflected by the deflecting / reflecting surface 4A is deflected at a constant angular velocity with the rotation of the polygon mirror 4 at a constant speed in the direction of the arrow, and the deflected light beam is a first lens 5A and a second lens of a "scanning and imaging lens system". 5B, the light is condensed as a light spot on the scanned surface 6 by the action of the scanning image forming lens system, and the scanned surface 6 is optically scanned at a constant speed, that is, substantially at a constant speed. In the figure, the area between points indicated by reference signs A ₀ and B ₀ is an “effective image area”.
And its length is the effective writing width: W.

The scanning image forming lens system is provided with first and second lenses 5A and 5B in order from the optical deflector side to the surface 6 to be scanned. The "shape in the deflecting surface" is shown in FIG. As shown, in the first lens 5A, the “incident side surface is convex toward the optical deflector side, and the exit surface side is convex toward the scanned surface 6 side”, and in the second lens 5B, “the incident surface side is concave toward the optical deflector side”. , The exit surface side is convex to the scanned surface 6 side. "

The first lens 5 has "optical axis symmetry" on both surfaces, and one of them has the above-mentioned aspherical shape. Therefore, the first lens 5 is a “biconvex lens”. Second lens 5
In B, at least one surface has a “non-arc shape” within the deflection surface (the surface shown in FIG. 1).

[0032]

EXAMPLES Specific examples will be described below.

Each embodiment satisfies the following conditions. Effective writing width: W: 216 mm, half angle of view: 44 degrees, working wavelength (light emission wavelength of light source): 780 nm. The luminous flux from the light source is
The light beam that is coupled into the “parallel light beam” by the coupling lens and enters the optical deflector is “parallel light beam in the main scanning corresponding direction”, and the “constant velocity characteristic” of the scanning imaging lens system is a known “fθ characteristic”. ".

In the following, as shown in FIG. 1, the radius of curvature (the paraxial radius of curvature in a non-circular or aspherical shape) in the deflection surface of the i-th lens surface counted from the optical deflector is Rm. _i (i = 1 to 4), the radius of curvature in the plane orthogonal to the deflection including the optical axis is Rs _i (i = 1 to 4), and the surface distance between the i-th lens surface and the (i + 1) -th lens surface is _Di. (i =
1-3), the j-th lens counted from the optical deflector side,
Let N _j (J = 1, 2) be the refractive index for the above used wavelength,
The distance on the optical axis from the deflecting reflection surface to the incident side surface of the first lens is D ₀ (i = 0), and the distance on the optical axis from the exit lens surface of the second lens to the surface to be scanned is D ₄ (i = 4).

The aspherical shape and aspherical shape (the paraxial radius of curvature: R, the conic constant: K, and the higher order aspherical coefficients: A, B, C,. And a numerical value representing the change in the radius of curvature in the main scanning direction in the plane perpendicular to the deflection direction, E and the numerical value following it mean “power”, and “E-9” means “10 9”, for example. Means
This number is over the previous number.

The first embodiment, which is mentioned first, is described in claims 1 to 7,
9 is a specific embodiment of the scanning imaging lens system described in No. 9. The unit of the radius of curvature / surface interval is “mm”.

[0037] Example _{1 i Rm i Rs i D i} j N j 0 47.273 1 583.174 583.174 25.000 1 1.511 2 -97.266 -97.266 15.265 3 -3440. 264-59.603 6.000 21.524 4-432.139-21.486 124.537.

Lens surface shape “Lens surface shape on the incident side of the first lens” Aspherical shape convex on the optical deflector side Paraxial radius of curvature: R = Rm ₁ = Rs ₁ = 583.174, K = −24. 9262, A = 4.8589E-9, B = 3.6254E-12, C = -1.0225E-
15 "first lens on the exit side of the lens surface shape" of the convex surface to be scanned side spherical curvature _{radius: R = Rm 1 = Rs 1} = -97.266 "lens surface shape of the incident side of the second lens" deflecting surface Inner shape: Non-arc shape concave on the optical deflector side Paraxial radius of curvature: R = Rm ₃ = −3400.264, K = 76.7762, A = −1.5236E−8, B = −5.6835E -12, C = 2.8183E-
17 Shape in the plane orthogonal to deflection: radius of curvature in the plane orthogonal to deflection at the position of distance y from the optical axis in the main scanning direction: Rs
(y) is a polynomial: R _S (y) = R _S0 + ay ² + by ⁴ + cy ⁶ + dy ⁸ + ey ¹⁰ + + fy ¹² + gy ¹⁴ +. . . In (7), R _S0 , a, b,. . . Given.

R _S0 = −59.603 (radius of curvature on the optical axis), a = −8.8685E−3, b = 2.0121E−
5, c = -2.1373E-8, d = 8.4173E-1
2, e = -1.2065E-15
.

"Lens surface shape of the exit side surface of the second lens" Shape in the deflecting surface: non-circular shape convex to the scan surface side Paraxial radius of curvature: R = Rm ₄ = -432.139, K = -66 .5580, A = -3.8648E-8, B = 6.3101E-12, C = -6.7028E-
16. Shape in the plane orthogonal to the deflection: The change in the radius of curvature in the plane orthogonal to the deflection in the main scanning direction is represented by (+) on the optical scanning start side and (-) on the end side with respect to the optical axis. ) the shape of the side _{(y> 0), R S} (y) = R S0 + a (+) y 2 + b (+) y 4 + c (+) y 6 + d (+) y 8 + e (+) y 10 + .. (7+) The shape on the (−) side (y <0) is R _S (y) = R _S0 + a (−) y ² + b (−) y ⁴ + c (−) y ⁶ + d (−) y ⁸ + E (−) y ¹⁰ + .. (7−).

R _S0 = −21.486 (radius of curvature on the optical axis), a (+) = − 1.1476E−3, b (+) = 7.8192
E-7, c (+) =-8.1181E-10, d (+) = 2.717
4E-13, e (+) =-3.6322E-17 a (-) =-1.3372E-3, b (-) = 1.2765
E-6, c (-) =-1.2961E-9, d (-) = 4.5396
E-13, e (-) =-5.9599E-17
.

[0042] fm = 143.4, L = 218.075 conditional expressions (1) to (4) the value D ₂ /fm=0.106,D ₂ /L=0.070,D ₄ / f of each parameter
m = 0.868, D ₄ /L=0.571
.

| Βs (H) / βs (0) in conditional expression (5)
| To H H -108 -81 -40 0 40 81 108 | βs (H) / βs (0) | 0.96 0.98 0.99 1.0 0.99 0.97 0.95 FIG. 2 shows the field curvature relating to the first embodiment (the broken line indicates the main scanning direction). ,
The solid line indicates the fθ characteristic which is a constant velocity characteristic in the sub-scanning direction).
The curvature of field is extremely good in the main and sub-scanning directions, and fθ
The characteristics are also very good.

In the following Examples 2 to 12, only the shape within the deflection plane is given. The shape in the sub-scanning corresponding direction can be set in the same manner as in the first embodiment.

[0045] Example _{2 i Rm i D i j N} j 0 43.080 1 552.950 20.000 1 1.511 2 -93.574 20.574 3 -576.202 6.000 2 1.524 4 -265.745 116.088.

Lens surface shape in the deflection surface "Lens surface shape on the incident side of the first lens" Non-arc shape convex on the optical deflector side Paraxial radius of curvature: Rm ₁ = 552.950, K = -82.3618 , A = -9.9832E-10, B = 7.2173E-12, C = -1.1812E-
15 “Lens surface shape on the exit side of the first lens” Arc shape convex on the scanned surface side Curvature radius: Rm ₂ = −93.574 “Lens surface shape on the entrance side surface of the second lens” Concave on the optical deflector side Radius of curvature: Rm ₃ = −576.202 “Lens surface shape of the exit side surface of the second lens” Non-arc shape convex to the scanned surface side Paraxial radius of curvature: Rm ₄ = −265.745, K = −27.7855, A = −1.0115E−7, B = 1.8872E−11, C = −9.5083E−
16.

[0047] fm = 139.1, L = 205.742 conditional expressions (1) to (4) the value D ₂ /fm=0.148,D ₂ /L=0.100,D ₄ / f of each parameter
m = 0.834, D ₄ /L=0.564
.

FIG. 3 shows the field curvature in the main scanning direction and the fθ characteristic according to the second embodiment. Field curvature in the main scanning direction, fθ
The characteristics are also very good.

[0049] Example _{3 i Rm i D i j N} j 0 43.830 1 1358.299 20.000 1 1.511 2 -86.003 14.537 3 -1966.471 6.000 2 1.524 4 -429.779 123.308.

Lens surface shape in the deflection surface "Lens surface shape on the entrance side of the first lens" Non-arc shape convex on the optical deflector side Paraxial radius of curvature: Rm ₁ = 1358.299, K = -1633.42 , A = -9.9970E-9, B = -3.9935E-13, C = -6.5790E-
16 "Lens surface shape on the exit side of the first lens" Arc shape convex on the scanned surface side Curvature radius: Rm ₂ = -86.003 "Lens surface shape on the incident side surface of the second lens" Concave on the optical deflector side Radius of curvature: Rm ₃ = −1966.471 “Lens surface shape of the exit side surface of the second lens” Non-arc shape convex to the scanned surface side Paraxial radius of curvature: Rm ₄ = −429.779, K = -4.0528, A = 2.4888E-8, B = 9.5216E-13, C = -3.1562E-
16.

[0051] fm = 140.4, L = 207.675 conditional expressions (1) to (4) the value D ₂ /fm=0.104,D ₂ /L=0.070,D ₄ / f of each parameter
m = 0.778, D ₄ /L=0.594
.

FIG. 4 shows the field curvature in the main scanning direction and the fθ characteristic according to the third embodiment. Field curvature in the main scanning direction, fθ
The characteristics are also very good.

[0053] Example _{4 i Rm i D i j N} j 0 42.673 1 518.258 20.000 1 1.511 2 -91.273 28.752 3 -561.567 6.000 2 1.524 4 -286.559 107.947.

Lens surface shape in the deflection surface "Lens surface shape on the incident side of the first lens" Non-arc shape convex on the optical deflector side Paraxial radius of curvature: Rm ₁ = 518.258, K = −180.673 , A = 4.2655E-9, B = 8.9702E-12, C = -1.8217E-
15 “Lens surface shape on the exit side of the first lens” Arc shape convex on the scan surface side Curvature radius: Rm ₂ = −91.273 “Lens surface shape on the entrance side surface of the second lens” Concave on the optical deflector side Radius of curvature: Rm ₃ = −561.567 “Lens surface shape of the exit side surface of the second lens” Non-arc shape convex to the scanned surface side Paraxial radius of curvature: Rm ₄ = −286.559, K = −29.9696, A = −1.1553E−7, B = 1.7679E−11, C = −7.7279E−
16.

[0055] fm = 139.2, L = 205.372 conditional expressions (1) to (4) the value D ₂ /fm=0.207,D ₂ /L=0.140,D ₄ / f of each parameter
m = 0.776, D ₄ /L=0.526
.

FIG. 5 shows the field curvature and fθ characteristics in the main scanning direction according to the fourth embodiment. Field curvature in the main scanning direction, fθ
The characteristics are also very good.

[0057] Example _{5 i Rm i D i j N} j 0 43.187 1 520.572 20.000 1 1.511 2 -91.515 37.869 3 -647.625 6.000 2 1.524 4 -360.896 103.324.

Lens surface shape in the deflection surface "Lens surface shape on the incident side of the first lens" Non-arc shape convex on the optical deflector side Paraxial radius of curvature: Rm ₁ = 520.572, K = -342.575 , A = 6.1453E-9, B = 9.2237E-12, C = −2.1114E−
15 “Lens surface shape on the exit side of the first lens” Arc shape convex on the scanned surface side Radius of curvature: Rm ₂ = −91.515 “Lens surface shape on the incident side surface of the second lens” Concave on the optical deflector side Radius of curvature: Rm ₃ = −647.625 “Lens surface shape of the exit side surface of the second lens” Non-arc shape convex to the scanned surface side Paraxial radius of curvature: Rm ₄ = −360.896, K = -35.320, A = -1.2198E-7, B = 1.7199E-11, C = -7.3454E-
16.

[0059] fm = 144.2, L = 210.380 conditional expressions (1) to (4) the value D ₂ /fm=0.263,D ₂ /L=0.180,D ₄ / f of each parameter
m = 0.717, D ₄ /L=0.391
.

FIG. 6 shows the field curvature and the fθ characteristic in the main scanning direction according to the fifth embodiment. Field curvature in the main scanning direction, fθ
The characteristics are also very good.

[0061] Example _{6 i Rm i D i j N} j 0 47.257 1 546.219 23.467 1 1.511 2 -96.641 21.491 3 -553.459 6.935 2 1.524 4 -239.641 115.575.

Lens surface shape in the deflection surface “Lens surface shape on the entrance side of the first lens” Non-arc shape convex on the optical deflector side Paraxial radius of curvature: Rm ₁ = 546.219, K = −35.6261 , A = 4.1877E-10, B = 4.3422E-12, C = -1.0617E-
15 "Lens surface shape on the exit side of first lens" Arc shape convex on the scanned surface side Curvature radius: Rm ₂ = -96.641 "Lens surface shape on the incident side surface of the second lens" Concave on the optical deflector side Radius of curvature: Rm ₃ = −533.459 “Lens surface shape of the exit side surface of the second lens” Non-arc shape convex to the scanned surface side Paraxial radius of curvature: Rm ₄ = −239.641, K = -19.5827, A = -9.8076E-8, B = 1.9787E-12, C = -1.1271E-
15.

[0063] fm = 139.8, L = 214.907 conditional expressions (1) to (4) the value D ₂ /fm=0.154,D ₂ /L=0.100,D ₄ / f of each parameter
m = 0.828, D ₄ /L=0.439
.

FIG. 7 shows the field curvature and the fθ characteristic in the main scanning direction according to the sixth embodiment. Field curvature in the main scanning direction, fθ
The characteristics are also very good.

[0065] Example _{7 i Rm i D i j N} j 0 47.935 1 279.682 25.000 1 1.511 2 -108.637 30.160 3 -278.047 8.000 2 1.524 4 -173.879 104.334.

Lens surface shape in the deflection surface "Lens surface shape on the incident side of the first lens" Non-arc shape convex on the optical deflector side Paraxial radius of curvature: Rm ₁ = 279.682, K = -20.0872 , A = 2.0701E-8, B = 1.3398E-11, C = -1.6790E-
15 "first lens on the exit side of the lens surface shape" of the convex surface to be scanned side arc-shaped curvature radius: Rm ₂ = -108.637, the optical deflector side "lens surface shape of the incident side surface of the second lens" Concave arc shape Radius of curvature: Rm ₃ = −278.047 “Lens surface shape of the exit side surface of the second lens” Non-arc shape convex to the scanned surface side Paraxial radius of curvature: Rm ₄ = −173.879, K = -8.4709, A = -1.0003E-7, B = 1.6969E-11, C = 2.2040E-
16.

[0067] fm = 139.1, L = 215.429 conditional expressions (1) to (4) the value D ₂ /fm=0.271,D ₂ /L=0.140,D ₄ / f of each parameter
m = 0.750, D ₄ /L=0.484
.

FIG. 8 shows the field curvature and the fθ characteristic in the main scanning direction according to the seventh embodiment. Field curvature in the main scanning direction, fθ
The characteristics are also very good.

[0069] Example _{8 i Rm i D i j N} j 0 49.513 1 424.198 25.000 1 1.511 2 -97.192 39.490 3 -455.524 8.000 2 1.524 4 -221.642 97.387.

Lens surface shape in the deflection surface “Lens surface shape on the entrance side of the first lens” Non-arc shape convex on the optical deflector side Paraxial radius of curvature: Rm ₁ = 424.198, K = −33.0506 , A = -2.8930E-8, B = 3.2923E-12, C = -5.9831E-
16 “Lens surface shape on the exit side of the first lens” Arc shape convex on the scanned surface side Curvature radius: Rm ₂ = −97.192, “Lens surface shape on the incident side surface of the second lens” On the optical deflector side Concave arc shape Radius of curvature: Rm ₃ = −455.524 “Lens surface shape of the exit side surface of the second lens” Non-arc shape convex to the scanned surface side Paraxial radius of curvature: Rm ₄ = −221.642, K = -13.4612, A = -8.4264E-8, B = 1.2091E-11, C = -6.80884E-
16.

[0071] fm = 139.4, L = 219.390 conditional expressions (1) to (4) the value D ₂ /fm=0.283,D ₂ /L=0.180,D ₄ / f of each parameter
m = 0.699, D ₄ /L=0.444
.

FIG. 9 shows the field curvature and the fθ characteristic in the main scanning direction according to the eighth embodiment. Field curvature in the main scanning direction, fθ
The characteristics are also very good.

[0073] Example _{9 i Rm i D i j N} j 0 45.269 1 523.189 25.000 1 1.511 2 -95.100 14.872 3 -329.921 6.000 2 1.524 4 -196.877 121.310.

Lens surface shape in the deflection surface “Lens surface shape on the entrance side of the first lens” Non-arc shape convex on the optical deflector side Paraxial radius of curvature: Rm ₁ = 523.189, K = −31.8209 , A = -1.0783E-9, B = 6.3452E-12, C = -1.0348E-
15 “Lens surface shape on the exit side of the first lens” Arc shape convex on the scan surface side Curvature radius: Rm ₂ = −95.100 “Lens surface shape on the entrance side surface of the second lens” Concave on the optical deflector side Non-arc shape Paraxial radius of curvature: Rm ₃ = −329.921, K = 8.7719, A = −5.00043E−8, B = −1.2518E−12, C = −2.2230E−
16 "second lens lens surface shape of the exit surface of the" surface to be scanned side in a convex arcuate curvature _{radius: Rm 4 = -196.877 fm = 139.5} , L = 212.451 conditional expressions (1) to ( values of the parameters _{4) D 2 /fm=0.107,D 2 /L=0.070,D 4} / f
m = 0.870, D ₄ /L=0.571
.

FIG. 10 shows the field curvature in the main scanning direction and the fθ characteristic according to the ninth embodiment. Curvature of field in the main scanning direction, f
The θ characteristics are also very good.

[0076] Example _{10 i Rm i D i j N} j 0 49.698 1 660.078 25.000 1 1.511 2 -88.464 15.266 3 -256.743 6.000 2 1.524 4 -186.233 122.118.

Lens surface shape in the deflection surface “Lens surface shape on the entrance side of the first lens” Arc shape convex on the optical deflector side Curvature radius: Rm ₁ = 660.0078 “Lens surface on the exit side of the first lens Shape "Non-arc shape convex to the surface to be scanned side Paraxial radius of curvature: Rm ₂ = −88.484 K = −0.25185, A = 2.4427E-8, B = 7.9818E-12, C = 4 .6606E-
16 "second lens lens surface shape of the incident side of" the optical deflector concave on the side of the arc-shaped curvature radius: Rm ₃ = -256.743 "lens surface shape of the exit surface of the second lens" scanned surface side in a convex Non-circular shape of paraxial radius of curvature: Rm ₄ = −186.233 K = −0.74107, A = 2.2082E−8, B = −1.8372E−12, C = 2.3868E−
16.

[0078] fm = 140.6, L = 218.082 conditional expressions (1) to (4) the value D ₂ /fm=0.109,D ₂ /L=0.070,D ₄ / f of each parameter
m = 0.868, D ₄ /L=0.560
.

FIG. 11 shows the field curvature and fθ characteristics in the main scanning direction according to the tenth embodiment. Curvature of field in the main scanning direction,
The fθ characteristics are also very good.

[0080] Example _{11 i Rm i D i j N} j 0 49.564 1 1103.859 25.000 1 1.511 2 -85.866 15.424 3 -1768.715 6.000 2 1.524 4 -518.088 124.360.

Lens surface shape in the deflecting surface “Lens surface shape on the entrance side of the first lens” Arc shape convex on the optical deflector side Curvature radius: Rm ₁ = 1103.859 “Lens surface on the exit side of the first lens Shape] Non-arc shape convex to the surface to be scanned Paraxial radius of curvature: Rm ₂ = −85.866 K = −0.26906, A = 1.8955E−8, B = 4.9998E−12, C = 1 .2244E-
15 “Lens surface shape on the incident side surface of the second lens” Non-arc shape concave on the optical deflector side Paraxial radius of curvature: Rm ₃ = −1768.715 K = −133.066, A = −2.2037E-8 , B = 2.4164E-12, C = −1.0015E−
16 "Lens surface shape of the exit side surface of the second lens" An arc shape convex on the surface to be scanned side Curvature radius: Rm ₄ = −518.088.

[0082] fm = 143.2, L = 220.348 conditional expressions (1) to (4) the value D ₂ /fm=0.108,D ₂ /L=0.070,D ₄ / f of each parameter
m = 0.868, D ₄ /L=0.564
.

FIG. 12 shows the field curvature and the fθ characteristic in the main scanning direction according to the eleventh embodiment. Curvature of field in the main scanning direction,
The fθ characteristics are also very good.

[0084] Example _{12 i Rm i D i j N} j 0 48.264 1 367.282 25.000 1 1.511 2 -116.236 15.489 3 -972.743 6.000 2 1.524 4 -277.218 126.522.

The lens surface shape in the deflecting surface "Lens surface shape on the entrance side of the first lens" Arc shape convex on the optical deflector side Curvature radius: Rm ₁ = 366.282 "The lens surface on the exit side of the first lens" Shape "Non-arc shape convex to the surface to be scanned side Paraxial radius of curvature: Rm ₂ = -116.236 K = -0.15516, A = -7.7737E-8, B = 4.5621E-13, C = -1.5929E-
15 “Lens surface shape on the incident side surface of the second lens” Non-arc shape concave on the optical deflector side Paraxial radius of curvature: Rm ₃ = −972.743 K = 154.477, A = −5.5872E-8, B = −3.3842E-12, C = −8.6679E−
16 “Lens surface shape of the exit side surface of the second lens” Non-arc shape convex to the surface to be scanned Paraxial radius of curvature: Rm ₄ = −277.218 K = −17.0968, A = −2.9810E-8 , B = 1.79898E-12, C = −8.4356E−
16.

[0086] fm = 146.0, L = 221.275 conditional expressions (1) to (4) the value D ₂ /fm=0.106,D ₂ /L=0.070,D ₄ / f of each parameter
m = 0.767, D ₄ /L=0.572
.

FIG. 13 shows the field curvature and fθ characteristics in the main scanning direction according to the twelfth embodiment. Curvature of field in the main scanning direction,
The fθ characteristics are also very good.

As described above, in Examples 2 to 12, only the lens shape in the deflecting surface is given, and only the field curvature in the main scanning direction and the fθ characteristic are shown. As is clear from the figures of each field curvature and the fθ characteristic, both the field curvature in the main scanning direction and the fθ characteristic are extremely good. The curvature of field in the sub-scanning direction can be satisfactorily corrected by optimizing the lens shape in the deflecting surface using the above-described equations (7), (7+), and (7-).

[0089]

As described above, according to the present invention, a novel scanning imaging lens system can be realized. Claims 1-4
The scanning imaging lens system of the described invention can very well correct the field curvature in the main scanning direction and the constant velocity characteristics such as the fθ characteristic,
In addition, stability against component tolerance and assembly tolerance is high, and when one or more of the first and second lenses is formed of a plastic lens, environmental resistance is high.

According to a fifth aspect of the present invention, the rear principal point of the scanning image forming lens system can be made closer to the surface to be scanned in a direction orthogonal to the main scanning corresponding direction, and the longitudinal magnification can be effectively reduced. Accordingly, requirements for environmental fluctuations, assembly errors, and component tolerances can be relaxed.

In the scanning image forming lens system according to the present invention, the variation in magnification in the sub-scanning direction due to the height of the light beam is suppressed while satisfactorily correcting the curvature of field in the main and sub-scanning directions and the uniform velocity characteristics. In addition, it is possible to effectively reduce the variation of the light spot diameter in the sub-scanning direction, and the scanning imaging lens system according to the seventh aspect of the invention can effectively reduce the variation of the light spot diameter.

Further, the scanning imaging lens system according to the present invention can be mass-produced at low cost, and the scanning imaging lens system according to the ninth invention can manufacture the scanning imaging lens system at low cost.
The environment resistance can be further improved than in the case of the invention of claim 8.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining a scanning image forming lens system according to the present invention, and shows a lens shape of a first embodiment.

FIG. 2 is a diagram illustrating field curvature in the main and sub-scanning directions and fθ characteristics according to the first embodiment.

FIG. 3 shows field curvature and fθ in the main scanning direction according to the second embodiment.
It is a figure showing a characteristic.

FIG. 4 shows the field curvature and fθ in the main scanning direction according to the third embodiment.
It is a figure showing a characteristic.

FIG. 5 shows the field curvature and fθ in the main scanning direction according to the fourth embodiment.
It is a figure showing a characteristic.

FIG. 6 shows the field curvature and fθ in the main scanning direction according to the fifth embodiment.
It is a figure showing a characteristic.

FIG. 7 shows field curvature and fθ in the main scanning direction according to the sixth embodiment.
It is a figure showing a characteristic.

FIG. 8 shows field curvature and fθ in the main scanning direction according to the seventh embodiment.
It is a figure showing a characteristic.

FIG. 9 shows the field curvature and fθ in the main scanning direction according to the eighth embodiment.
It is a figure showing a characteristic.

FIG. 10 shows the field curvature and f in the main scanning direction according to the ninth embodiment.
FIG. 9 is a diagram illustrating a θ characteristic.

FIG. 11 is a diagram illustrating field curvature in the main scanning direction and fθ characteristics according to the tenth embodiment.

FIG. 12 is a diagram illustrating field curvature in the main scanning direction and fθ characteristics according to an eleventh embodiment.

FIG. 13 is a diagram illustrating field curvature in the main scanning direction and fθ characteristics according to a twelfth embodiment.

[Explanation of symbols]

 4 Polygon mirror 5A First lens 5B Second lens 6 Scanned surface

Claims (9)

[Claims] An optical deflector having a deflecting / reflecting surface in the vicinity of an image forming position of the line image deflects a light beam formed into a long linear image in the main scanning direction at a uniform angular velocity. A scanning image forming lens system in an optical scanning device for converging a light spot on a surface to be scanned by an image lens system as a light spot and performing uniform optical scanning on the surface to be scanned. The first lens and the second lens are sequentially arranged on the side, and the shape of the deflecting surface of the first lens is such that the incident side surface is convex on the optical deflector side, the exit surface side is convex on the scanned surface side, The second lens has an incident surface side concave to the optical deflector side, an emission surface side convex to the surface to be scanned, the first lens has optical axis symmetry on both surfaces, and one surface is aspherical, In the second lens, at least one surface has a non-circular shape in the deflection surface, and the second lens has a second shape from the exit side surface of the first lens. The distance on the optical axis reaching the incident side surface of the two lenses: D ₂ , and the focal length in the main scanning corresponding direction of the entire system: fm satisfies the condition: (1) 0.07 ≦ D ₂ /fm≦0.30 A scanning imaging lens system, characterized in that: 2. The scanning imaging lens system according to claim 1, wherein a distance on the optical axis from the exit side surface of the first lens to the entrance side surface of the second lens is D ₂ , and a distance from the deflecting reflection surface to the surface to be scanned is D2. A scanning imaging lens system, wherein the distance: L satisfies the following condition: (2) 0.05 ≦ D ₂ /L≦0.20. 3. The scanning imaging lens system according to claim 1, wherein a distance on the optical axis from the exit side surface of the second lens to the surface to be scanned is D ₄ , and a focal length of the entire system in the main scanning corresponding direction. : Fm
The following conditions are satisfied: (3) 0.6 ≦ D ₄ /fm≦0.9. 4. The scanning imaging lens system according to claim 2, wherein a distance on the optical axis from the exit side surface of the second lens to the surface to be scanned is D ₄ , and a distance from the deflecting reflection surface to the surface to be scanned. : L is
Condition: (4) A scanning imaging lens system characterized by satisfying 0.4 ≦ D ₄ /L≦0.7. 5. The scanning imaging lens system according to claim 1, wherein the shape of the second lens in the plane orthogonal to the deflection is such that the incident side is concave on the optical deflector side, and the exit side is A scanning imaging lens system, which is convex toward the surface to be scanned. 6. The scanning imaging lens system according to claim 5, wherein the surface of the second lens having a non-circular shape in the deflecting surface has a radius of curvature in the deflecting orthogonal surface that is continuous in the main scanning corresponding direction. To
And a scanning imaging lens system, which changes in correlation with the shape in the deflection surface. 7. The scanning image forming lens system according to claim 6, wherein the beam magnification on the surface to be scanned: H in the direction orthogonal to the main scanning direction: βs (H) is within the effective image area. Wherein: (5) a scanning imaging lens system, wherein 0.95 ≦ | βs (H) / βs (0) | ≦ 1.05 is satisfied. 8. The scanning imaging lens system according to claim 6, wherein both the first and second lenses are formed of plastic. 9. The scanning imaging lens system according to claim 6, wherein the first lens is formed of glass and the second lens is formed of plastic.