JP3658439B2 - Scanning imaging lens and optical scanning device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a scanning imaging lens and an optical scanning device using the scanning imaging lens.
[0002]
[Prior art]
A substantially parallel light beam radiated from the light source device is a virtual image obtained by linearly developing the optical path from the light source to the scanned surface along the optical axis of the optical system by the line image imaging optical system. Considering the optical path, the direction corresponding to the virtual scanning path in parallel with the main scanning direction and the direction corresponding to the virtual scanning path in parallel to the sub scanning direction are referred to as “sub scanning corresponding direction”). An image is formed as a line image, deflected at an equiangular velocity by an optical deflector having a deflection reflection surface in the vicinity of the image formation position of the line image, and the deflected light beam is collected as a beam spot on the surface to be scanned by the imaging optical system. 2. Description of the Related Art Conventionally, an optical scanning device that performs light scanning at a constant speed on a surface to be scanned is widely known.
[0003]
The “scanning imaging lens” used as the “imaging optical system” in the optical scanning apparatus as described above is directed toward the surface to be scanned with a deflected light beam deflected at a constant angular velocity by an optical deflector such as a rotary polygon mirror. In addition to the “imaging function” for focusing, it is necessary to have an “fθ function” in order to make the movement of the beam spot on the scanned surface constant.
[0004]
Recently, in order to record “higher quality images with higher resolution” in optical scanning, as a scanning imaging lens, fθ characteristics, curvature of field in the main and sub scanning directions, beam diameter (beam spot on the scanned surface) There is a demand for a material in which the non-uniformity of the diameter of the material is well corrected.
[0005]
If the fθ characteristic is poor, the deviation from the constant speed of the optical scanning is large, “distortion” occurs in the recorded image, and if the nonuniformity of the beam diameter is not corrected well, the beam diameter fluctuates with the image height. Reduce the resolution of the recorded image. Also, when the curvature of field is not corrected well, the beam diameter fluctuates, causing a reduction in resolution.
[0006]
[Problems to be solved by the invention]
SUMMARY OF THE INVENTION In view of the above circumstances, an object of the present invention is to make it possible to satisfactorily correct the fθ characteristic and the field curvature in the main and sub scanning directions over the entire effective scanning region in the scanning imaging lens.
[0007]
Another object of the present invention is to make it possible to perform a good correction over the entire effective scanning region of the nonuniformity of the beam diameter as well as the fθ characteristic and the curvature of field in the main and sub scanning directions in the scanning imaging lens.
[0008]
Another object of the present invention is to enable effective prevention of distortion of a recorded image and a decrease in resolution in an optical scanning device.
[0009]
[Means for Solving the Problems]
The “scanning imaging lens” of the present invention forms a substantially parallel light beam into a line image that is long in the direction corresponding to the main scanning, and is provided with a constant angular velocity by an optical deflector having a deflection reflection surface in the vicinity of the imaging position of the line image. Is a scanning imaging lens used as an imaging optical system in an optical scanning device that deflects optically, condenses as a beam spot on a scanned surface by an imaging optical system, and optically scans the scanned surface at a constant speed .
[0010]
As shown in FIG. 1, the scanning imaging lens of the present invention is “from the optical deflector 3 side toward the scanned surface 8 side, the first lens 5 as the first group and the second lens 6 as the second group. , “A third group of three elements in which the third lens 7 as the third group is arranged”.
[0011]
The light beam deflected by the optical deflector 3 is imaged as a “line image long in the main scanning direction” in the vicinity of the deflecting reflection surface 4 and condensed as a beam spot on the scanned surface 8 by the scanning imaging lens. Therefore, the scanning imaging lens has a “geometrical optically conjugate relationship” between the position of the scanned surface 8 and the position of the deflecting reflecting surface 4 in the sub-scanning corresponding direction (direction orthogonal to the drawing of FIG. 1). Thus, it has a so-called “surface tilt correction function” and makes the movement of the beam spot, which is the imaging point of the light beam deflected at a constant angular velocity constant, so that it has the “fθ function” in the main scanning corresponding direction.
[0012]
2. The scanning imaging lens according to claim 1, wherein the first lens 5 as the first group has a "refractive spherical surface" on the deflecting / reflecting surface 4 side and a "plane" on the scanned surface 8 side, and has a "negative refractive power". have.
[0013]
The second lens 6 in the second group has a “deflection cylinder surface having a curvature only in the sub-scanning corresponding direction” on the side of the deflecting reflection surface 4 and a “convex spherical surface” on the surface to be scanned. This is an anamorphic lens having a negative refractive power in the sub-scanning corresponding direction.
[0014]
The third lens 7 in the third group is an anamorphic lens having a “flat surface” on the deflecting / reflecting surface 4 side, a “toric surface” on the scanned surface side, and “stronger positive refractive power” in the sub-scanning direction. is there.
[0015]
The total focal length of the entire system in the main scanning-corresponding direction of the scanning imaging lens is f _M , and the “distance on the optical axis from the deflection start point to the surface on the deflection reflecting surface side of the first group” is D ₀ . When these are the conditions:
(1) 0.07 <D ₀ / f _M <0.50
Satisfied.
[0016]
The above-mentioned “starting point of deflection” is the “intersection between the optical axis of the scanning imaging lens and the deflecting reflecting surface” when the image height of the light spot is 0, and the “line image” is designed in the length direction. The center of the image is imaged at the origin of this deflection.
[0017]
The material of the first to third lenses constituting the scanning imaging lens according to claim 1, wherein is selectable appropriately depending on the design, but is of course to be able to configure the scanning imaging lens with two or more materials The first to third groups can be made of the same material (claim 2).
[0018]
The optical scanning device according to the present invention “forms a substantially parallel light beam emitted from the light source device as a long line image in the direction corresponding to the main scanning by the line image forming optical system, and in the vicinity of the image forming position of the line image. Optical scanning that deflects the beam at a constant angular velocity by an optical deflector having a deflecting reflecting surface and focuses the deflected light beam as a beam spot on the surface to be scanned by the imaging optical system to perform constant speed optical scanning of the surface to be scanned. The scanning imaging lens according to claim 1 or 2 is used as an imaging optical system (Claim 3) .
[0019]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows an embodiment of an optical scanning device according to the present invention.
[0020]
The light source device 1 is a laser light source that emits a “substantially parallel light flux”.
[0021]
The substantially parallel light beam from the light source device 1 is converged only in the sub-scanning corresponding direction (direction orthogonal to the drawing) by the cylinder lens 2 which is a line image imaging optical system, and is deflected by the polygon mirror 3 which is an optical deflector. An image formed as a “line image long in the main scanning direction” is formed in the vicinity of the reflecting surface 4, and the reflected light beam due to the deflecting reflecting surface 4 is “scanned imaged as a deflected light beam deflected at a constant angular velocity as the polygon mirror 4 rotates. It enters the lens ”and is focused as a beam spot on the surface to be scanned 8 by the action of the lens, and the surface to be scanned 8 is optically scanned.
[0022]
In addition to the cylinder lens, a “concave cylinder mirror” can be used as the line image imaging optical system 2, and a rotating dihedral mirror, a rotating single mirror or the like is used in addition to the illustrated polygon mirror as the optical deflector. Can do.
[0023]
As described above, when the “scanning imaging lens” of the present invention is used in an optical scanning device, the position of the surface to be scanned 8 and the position of the deflection reflecting surface 4 in the sub-scanning corresponding direction are “substantially geometrically optical. Accordingly, the optical scanning device according to claim 4 has a function of correcting “surface tilt” in the optical deflector.
[0024]
The “scanning imaging lens” according to claim 1 or 2 enables favorable correction of the fθ characteristic and the curvature of field in the main / sub-scanning direction by the configuration thereof. -Good correction of "non-uniform beam diameter" in the sub-scanning direction is possible.
[0025]
As described above, the scanning imaging lens of the present invention has “a surface with an infinite curvature radius in the main scanning direction” in each group. That is, in the first group, the lens surface on the scanned surface side is a “flat surface”, and in the second group, the surface on the deflection reflecting surface side is “a concave cylinder surface having a curvature only in the sub-scanning corresponding direction”. In the third group, the surface on the deflection reflection surface side is a “plane”.
[0026]
In particular, by combining the shape of the second and third groups in the main scanning correspondence direction (the lens cross-sectional shape in the plane including the optical axis and the main scanning correspondence direction) with a combination of “straight line and arc”, “main scanning” The “refractive power in the corresponding direction” is relatively increased to enable correction of “field curvature in the main scanning direction”, and “inexpensive glass material” having a relatively low refractive index can be used.
[0027]
Further, the surface of the second group on the deflecting / reflecting surface side should be “a concave cylinder surface having a curvature only in the sub-scanning direction”, and the surface of the third group on the scanned surface side should be “toric surface”. This makes it possible to correct “field curvature in the sub-scanning direction”.
[0028]
Condition (1) is a condition for maintaining a good beam diameter. When the lower limit value exceeds 0.07, “beam diameter fluctuation in the sub-scanning direction” increases, and when the upper limit value exceeds 0.50, “ “Beam diameter fluctuation in the main scanning direction” becomes large, and outside the range of condition 1, it is difficult to satisfactorily suppress the fluctuation of the beam diameter due to design parameters such as the curvature of the lens surface, the lens thickness, and the air gap.
[0029]
Within the range of condition (1), fluctuations in the beam diameter can be satisfactorily suppressed in both the main and sub scanning directions.
[0030]
【Example】
Hereinafter, five specific examples regarding the scanning imaging lens according to claims 1 and 2 will be given .
[0031]
As shown in FIG. 1, in each embodiment, the radius of curvature of the i-th lens surface counted from the optical deflector 3 side is R _{ix in} the main scanning corresponding direction, and R _iy (i = 1 to 6), the surface distance on the optical axis between the i-th lens surface and the (i + 1) -th lens surface is D _i (i = 1 to 5), and the first point from the deflection starting point of the optical deflector 3 The distance on the optical axis to the second lens surface is D ₀ (i = 0), and the distance on the optical axis from the surface of the third group on the scanned surface side to the scanned surface 8 is D ₆ (i = 6). ).
The refractive index with respect to the wavelength used (the oscillation wavelength of the LD) of the j-th lens counted from the deflection start side is N _j (j = 1 to 3).
[0032]
f _M represents the focal length of the entire system in the main scanning correspondence direction, f _S represents the combined focal length of the entire system in the sub scanning correspondence direction, and 2θ represents the effective deflection angle (unit: degree). Throughout all the examples, the optical deflector is a polygon mirror 3 having ten deflecting reflection surfaces as shown in FIG. 1, and has an inscribed circle radius of 32 mm, an incident light beam on the deflecting reflecting surface 4, an optical axis of the scanning imaging lens, and the like. The oscillation angle of the light source device 1 is 325 nm.
[0033]
Example 1
f _M = 330, f _S = 66.498, 2θ = 44.3
i R _ix R _iy D _i j N _j
0 24.932
1 −60.0 −60.0 11.908 1 1.48163
2 ∞ ∞ 9.158
3 ∞ -25.0 13.9779 2 1.48163
4 -76.611 -76.611 9.784
5 ∞ ∞ 11.255 3 1.48163
6 -171.558-23.855 402.818
Parameter value of conditional expression: D ₀ / f _M = 0.076
[0034]
Example 2
f _M = 330, f _S = 85.062, 2θ = 44.3
i R _ix R _iy D _i j N _j
0 52.026
1 -129.09 -129.09 11.604 1 1.48163
2 ∞ ∞ 15.651
3∞-71.0 18.423 2 1.48163
4 −133.571 −133.571 4.622
5 ∞ ∞ 14.9 3 1.48163
6 -203.44 -34.57 372.488
Parameter value of conditional expression: D ₀ / f _M = 0.158.
[0035]
Example 3
f _M = 330, f _S = 124.872, 2θ = 44.3
i R _ix R _iy D _i j N _j
0 162.61
1-1429.8-1429.8 7.754 1 1.48163
2 ∞ ∞ 1.396
3 ∞-131.0 24.72 2 1.48163
4 -235.121 -235.121 1.675
5 ∞ ∞ 18.62 3 1.48163
6 -363.55 -53.62 324.472
Parameter value of conditional expression: D ₀ / f _M = 0.493.
[0036]
Example 4
f _M = 200, f _S = 67.245, 2θ = 61.9
i R _ix R _iy D _i j N _j
0 61.511
1 -543.19 -543.19 6.732 1 1.48163
2 ∞ ∞ 13.248
3 ∞ -64.5 14.468 2 1.48163
4 -142.212 -142.212 0.532
5 ∞ ∞ 13.151 3 1.48163
6 -199.28 -28.06 200.027
Parameter value of conditional expression: D ₀ / f _M = 0.308.
[0037]
Example 5
f _M = 200, f _S = 73.355, 2θ = 61.9
i R _ix R _iy D _i j N _j
0 79.257
1 -600.435 -600.435 7.563 1 1.48163
2 ∞ ∞ 5.593
3 ∞ -74.5 16.713 2 1.48163
4-132.972 -132.972 5.83
5 ∞ ∞ 14.227 3 1.48163
6 -221.499 -32.38 194.646
Parameter value of conditional expression: D ₀ / f _M = 0.396.
[0038]
FIG. 2 shows the field curvature and the fθ characteristic regarding the first embodiment.
FIG. 3 shows the field curvature and the fθ characteristic regarding the second embodiment.
FIG. 4 shows the field curvature and the fθ characteristic regarding the third embodiment.
FIG. 5 shows the field curvature and the fθ characteristic regarding the fourth embodiment.
FIG. 6 shows the field curvature and the fθ characteristic regarding the fifth embodiment.
[0039]
FIG. 7 shows the change in the beam diameter according to the image height regarding the first embodiment.
FIG. 8 shows changes in the beam diameter depending on the image height in the second embodiment.
FIG. 9 shows the change in the beam diameter according to the image height related to Example 3.
FIG. 10 shows changes in the beam diameter according to the image height in the fourth embodiment.
FIG. 11 shows changes in the beam diameter depending on the image height in the fifth embodiment.
In the field curvature diagram, the broken line relates to the main scanning direction, and the solid line relates to the sub-scanning direction.
[0040]
As is clear from these drawings, in each of the examples, the field curvature is corrected well in both the main and sub-scanning directions, and the variation in the beam diameter is small.
Since each embodiment does not use an aspherical surface for each group, it is easy to manufacture the first to third lenses. In each embodiment, since the first to third groups are made of the same material ( claim 2 ), the manufacture is easy and the cost can be reduced.
[0041]
【The invention's effect】
As described above, according to the present invention, a novel scanning imaging lens and an optical scanning device can be provided.
[0042]
The scanning imaging lens according to claim 1 can satisfactorily correct the field curvature and the fθ characteristic in the main and sub scanning directions.
[0043]
The scanning imaging lens according to claim 1 is also capable of satisfactorily correcting the curvature of field and the fθ characteristic in the main and sub scanning directions, and can effectively reduce the variation of the beam diameter on the surface to be scanned. .
[0044]
In the scanning imaging lens according to the second aspect, since the first to third groups are made of the same material, the design and manufacture are easy, and the cost can be reduced.
[0045]
The optical scanning device according to claim 3 can realize good optical scanning.
[Brief description of the drawings]
FIG. 1 is a diagram showing a lens configuration of a scanning imaging lens according to the present invention and an optical arrangement of an optical scanning device using the scanning imaging lens.
2 is a diagram of field curvature and fθ characteristics related to Example 1. FIG.
3 is a diagram of field curvature and fθ characteristics related to Example 2. FIG.
FIG. 4 is a diagram of field curvature and fθ characteristics related to Example 3.
FIG. 5 is a diagram of field curvature and fθ characteristics related to Example 4;
6 is a diagram of field curvature and fθ characteristics regarding Example 5. FIG.
7 is a graph showing changes in beam diameter according to the angle of view in Embodiment 1. FIG.
FIG. 8 is a diagram showing a change in the beam diameter according to the angle of view in the second embodiment.
FIG. 9 is a graph showing changes in the beam diameter depending on the angle of view in the third embodiment.
FIG. 10 is a graph showing changes in the beam diameter according to the angle of view in the fourth embodiment.
FIG. 11 is a graph showing changes in the beam diameter according to the angle of view in the fourth embodiment.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Light source device 2 Line image imaging optical system 3 Optical deflector 4 Deflection reflective surface 5 1st group 6 2nd group 7 3rd group 8 Surface to be scanned

Claims (3)

A substantially parallel light beam is formed into a line image that is long in the main scanning direction, deflected at an equiangular velocity by an optical deflector having a deflecting reflection surface in the vicinity of the image forming position of the line image, and covered by a scanning imaging lens. A scanning imaging lens in an optical scanning device that collects light as a beam spot on a scanning surface and optically scans the surface to be scanned at a constant speed,
The first to third groups are sequentially arranged from the optical deflector side to the scanned surface side, and have an fθ function in the main scanning corresponding direction.
The first group has a concave spherical surface on the deflection reflecting surface side, a flat surface on the scanned surface side, and a first lens having negative refractive power,
The second group has a concave cylinder surface having a curvature only in the direction corresponding to the sub-scanning on the deflecting reflection surface side, and a convex spherical surface on the surface to be scanned, and has a positive refractive power in the direction corresponding to the main scanning. An anamorphic second lens with negative refractive power in the corresponding direction,
Group 3 plane deflecting reflective surface side has a toric surface on the surface to be scanned side, Ru anamorphic third lens der having a strong positive refractive power by the sub-scanning direction, in three groups three-element Yes,
_Assuming that the total focal length of the entire system in the main scanning correspondence direction is f _M and the distance on the optical axis from the deflection start point to the surface on the deflection reflecting surface side of the first group is D ₀ , these are the conditions:
(1) 0.07 <D ₀ / f _M <0.50
A scanning imaging lens characterized by satisfying The scanning imaging lens according to claim 1.
A scanning imaging lens, wherein the first to third groups are made of the same material. An optical deflector that forms a substantially parallel light beam emitted from a light source device as a long line image in the main scanning direction by a line image imaging optical system, and has a deflecting reflection surface in the vicinity of the line image forming position. An optical scanning device that performs constant-speed optical scanning of the scanned surface by deflecting the deflected light beam as a beam spot on the scanned surface by an imaging optical system,
An optical scanning apparatus using the scanning imaging lens according to claim 1 or 2 as an imaging optical system.

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