JPH0468308A - Optical scanning device - Google Patents

Abstract

PURPOSE:To obtain an excellent ftheta characteristic, an excellent image formation characteristic, etc., with a relatively small optical element by using equal-speed scanning optical systems consisting of cylindrical mirrors, etc., for forming line images in the scanning direction. CONSTITUTION:The line image formation optical systems 2 and 4 which form line images nearby a deflecting surface in the scanning direction and have positive positive refracting power only in the direction perpendicular to the scanning direction are provided. Further, the device is equipped with equal-speed scanning optical systems 5 - 8 composed of a concave lens 5 which has negative refracting power, a 1st cylindrical mirror 6 which has positive refracting power only in the direction perpendicular to the scanning direction, and a cylindrical lens 7 which has positive refracting power only in the parallel direction, and a 2nd cylindrical mirror 8 which has positive refracting power only in the vertical direction. Consequently, the equal-speed scanning characteristic and image formation characteristic are obtained by using the inexpensive, relatively small optical element and the surface tilt error of the deflecting surface can be corrected.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a scanning optical device, and more particularly to a scanning optical device using a deflector such as a single rotating polygon mirror.

[Conventional technology]

As is well known, even if a deflector such as a single-rotation polygon mirror is machined with high precision, there will be some error in the parallelism between the rotation axis and the deflection surface. This error in the parallelism of the deflection surface is generally called a surface inclination error, and in a scanning optical device, the positional deviation of the light spot in the direction perpendicular to the scanning direction (sub-scanning direction) on the scanning surface is detected. cause it to grow.

Now, if the surface inclination error of the deflection surface is Δθ, and the focal length of the constant velocity scanning optical system that focuses the light beam deflected by the deflection surface onto the scanning surface is f, then the light spot focused on the scanning surface is The positional deviation amount Δd in the sub-scanning direction is expressed as Δd==2Δθ・f 0For example, when f=300mm, in order to make the positional deviation amount Δd 0.01mm or less, the surface tilt error Δθ
Deflectors such as single-rotation polygon mirrors are required to have very high processing accuracy of approximately 3 seconds or less. It is actually very difficult to manufacture such a highly accurate deflector.

Therefore, various scanning optical devices have been proposed in the past that optically correct the surface inclination error of the deflection surface of the deflector (hereinafter, this correction is referred to as surface inclination correction).

For example, in a conventional scanning optical device that performs surface tilt correction as shown in FIG. A line image parallel to the scanning direction is formed in the vicinity of the deflection surface of the rotating polygon mirror 84 by the cylindrical lens 83 which has positive refractive power only in the cylindrical lens 83 .

Next, the light beam reflected by the deflection surface of the rotating polygon mirror 84 forms a light spot on the scanning surface 87 via the fθ lens 85 and the cylindrical lens 86 having positive refractive power only in the direction perpendicular to the scanning direction. Image.

In such a conventional scanning optical device that performs surface tilt correction,
The fθ lens 85 provides an fθ characteristic, and since the deflection surface of the rotating polygon mirror 84 and the scanning surface 87 are in an optically conjugate relationship, the cylindrical lens 86
Accordingly, it is possible to correct the positional deviation of the light beam in the sub-scanning direction on the scanning surface 87 due to the surface tilt error of the deflection surface of the rotating polygon mirror 84.

[Problem to be solved by the invention]

However, in the above-described conventional scanning optical device that performs surface tilt correction, the rotating polygon mirror 84 is
The cylindrical lens 86 is required to have a large refractive power, and the cylindrical lens 86 is required to have a large refractive power. The direction in which the lens 86 is parallel to the scanning plane 87, that is, the cylindrical lens 86
The disadvantage is that the lens becomes very long in the longitudinal direction, making the scanning optical device expensive and large.

Further, it becomes necessary to correct the inclination of the image plane (field curvature) caused by the cylindrical lens 8G using the fθ lens 85, and there is a drawback that the design of the fθ lens 85 becomes complicated.

In view of the above-mentioned points, an object of the present invention is to be able to obtain good constant velocity scanning characteristics (hereinafter referred to as fθ characteristics) and imaging characteristics using an inexpensive and relatively small optical element, and to
It is an object of the present invention to provide a compact scanning optical device capable of correcting a positional shift of an optical stub V in the sub-scanning direction on a scanning surface caused by a surface inclination error of a deflection surface.

[Means to solve the problem]

A scanning optical device of the present invention is a scanning optical device that makes a light beam from a light source enter a deflection surface and deflects it, and scans the scanning surface with the deflected light beam. A line image forming optical system that forms a line image parallel to the scanning direction and has positive refractive power only in the direction perpendicular to the scanning direction, a concave lens that has negative refractive power in order from the deflection surface side, and a concave lens that has negative refractive power perpendicular to the scanning direction. a first cylindrical mirror having positive refractive power only in a direction parallel to the scanning direction, a cylindrical lens having positive refractive power only in a direction parallel to the scanning direction, and a second cylindrical mirror having positive refractive power only in a direction perpendicular to the scanning direction.
The present invention is characterized by comprising a constant velocity scanning optical system consisting of a cylindrical mirror.

[Effect]

In the scanning optical device of the present invention, a line image forming optical system having positive refractive power only in a direction perpendicular to the scanning direction forms a line image parallel to the scanning direction near the deflection surface using a light beam from a light source, A concave lens with negative refractive power and a cylindrical lens with positive refractive power only in the direction parallel to the scanning direction give negative distortion to the light beam in the direction parallel to the scanning direction to perform fθ correction. A first cylindrical mirror that has a positive refractive power only in a direction perpendicular to the scanning direction and a second cylindrical mirror that has a positive refractive power only in a direction perpendicular to the scanning direction correct the optical beam in the direction perpendicular to the scanning direction. to form an image on the scanning plane.

〔Example〕

Next, the present invention will be explained in detail with reference to the drawings.

1, 2, and 3 are a perspective view, a schematic plan view, and a schematic side view showing the configuration of the scanning optical device of the present invention.

This scanning optical device includes a semiconductor laser 1 as a light source, a collimation lens 2 that converts the laser light from the semiconductor laser 1 into a parallel light beam, and a line image parallel to the scanning direction near the deflection surface of a rotating polygon mirror 4. A first cylindrical lens 3 having positive refractive power only in a direction perpendicular to the scanning direction in which it is formed.
, a rotating polygon mirror 4 as a deflector, a concave lens 5 having negative refractive power, a first cylindrical mirror 6 having positive refractive power only in a direction perpendicular to the scanning direction, and a first cylindrical mirror 6 having positive refractive power only in a direction perpendicular to the scanning direction. It is composed of a second cylindrical lens 7 having positive refractive power only in the direction perpendicular to the scanning direction, a second cylindrical mirror 8 having positive refractive power only in the direction perpendicular to the scanning direction, and a scanning surface 9 scanned by the light spot. .

Next, the operation of the scanning optical device of this embodiment configured as described above will be explained.

The collimation lens 2 converts the laser light emitted from the semiconductor laser 1 into a parallel light beam.

The first cylindrical lens 3 causes the light beam made parallel by the collimation lens 2 to form a line image parallel to the scanning direction near the deflection surface of the rotating polygon mirror 4 .

The rotating polygon mirror 4 rotates at a constant angular velocity, and reflects and deflects a line image light beam formed near the deflection surface by the first cylindrical lens 3 by the deflection surface.

The concave lens 5 and the second cylindrical lens 7 apply negative distortion to the light beam deflected by the rotating polygon mirror 4 to perform fθ correction.

The first cylindrical mirror 6 reflects the light beam that has passed through the concave lens 5 at an angle of 90 degrees, and also performs surface tilt correction by having positive refractive power only in the direction perpendicular to the scanning direction.

The second cylindrical mirror 8 reflects the light beam that has passed through the second cylindrical lens 7 at an angle of 90 degrees, and has positive refractive power only in the direction perpendicular to the scanning direction, thereby correcting the surface tilt and scanning. A light spot is imaged onto surface 9.

Therefore, in the constant velocity scanning optical system, only the concave lens 5 and the second cylindrical lens 7 have refractive power in the scanning direction, and the other optical elements include the first cylindrical mirror 6 and the second cylindrical lens 7, which have refractive power only in the sub-scanning direction. Since there is only the second cylindrical mirror 8, there is no influence such as tilting of the image plane (field curvature), and the concave lens 5 and the second
The fθ characteristic can be determined only by designing the cylindrical lens 7. In addition, the lens system that determines the fθ characteristic is a concave lens 5.
and the second cylindrical lens 7 having positive refractive power (that is, a convex lens), fθ
The distance from the deflection surface to the concave lens 5 can be shortened in order to bring the characteristic distortion coefficient V to a value close to the standard V=2/3, and as a result, the scanning optical device can be made more compact. can. Furthermore, the concave lens 5 and the second
The cylindrical lens 7 is a plano-concave spherical lens and a plano-convex cylindrical lens (see second embodiment below).
Alternatively, it is also possible to configure a plano-concave cylindrical lens and a plano-convex cylindrical lens (see the fourth embodiment below), which facilitates lens processing and further reduces the cost of the scanning optical device.

In addition, in the sub-scanning direction, the light beam is imaged once near the deflection surface by the cylindrical lens 3,
After being deflected by the deflection surface, a light spot is imaged on the scanning surface 9 by the first linear mirror 6 and the second horizontal mirror 8, so that the deflection surface and the scanning surface 9 are optically connected. Since it is conjugate, even if there is some surface tilt error in the deflection surface, the positional shift of the light spot on the scanning surface 9 in the sub-scanning direction can be corrected. On the other hand, since the first solindrical lens 6 has positive refractive power only in the direction perpendicular to the scanning direction, the light beam incident on the second cylindrical lens 7 is close to a parallel light beam to some extent, The two-cylindrical lens 7 has almost no effect on imaging in the sub-scanning direction. In other words, concave lens 5. It is only necessary to consider the arrangement of the first cylindrical mirror 6 and the second cylindrical mirror 8 and the imaging based on the refractive power, which facilitates the design.

Further, since the configuration is such that the refractive power for focusing the light beam is distributed to the first cylindrical mirror 6 and the second cylindrical mirror 8, each optical element can be made small and inexpensive.

Hereinafter, specific embodiments of the scanning optical device of the present invention will be described.

However, in the following examples, as shown in FIGS. 2 and 3, rXl""rX6 is the radius of curvature (unit: mm) in the direction parallel to the scanning direction, and ryl to ryb are the radius of curvature in the direction perpendicular to the scanning direction. The radius of curvature in the direction (units are mm), n is the refractive index of the concave lens 5, n2 is the refractive index of the second cylindrical lens 7, do is the distance from the deflection surface to the first refractive surface of the concave lens 5 (units are mm) , d, to d6 represent the path # (in mm) between each refractive surface on the optical axis from the concave lens 5 to the scanning surface 9, respectively. In addition, f is the focal length in the scanning direction of the constant velocity scanning optical system (unit: mm), Fk is the F number of the uniform velocity scanning optical system, and 2θ is the total scanning angle (unit: degrees ('
)), fc is the focal length of the first cylindrical lens 3 in the direction perpendicular to the scanning direction (in mm), and λ is the wavelength used (in nm).

<First example> -f = 300mm FNn = 60 20 = 57
．． 2958°f c = 137.061mm λ-
780 nm・Lens data Distance d from the deflection surface to the first refractive surface of the concave lens 5, =
21.636 First refractive surface r of concave lens 5,, = −720,031r,, −720
,031d + = 15.924 n +
= 1.60910 Second refractive surface r of concave lens 5, lz = 1099.144 r −2=
1099.144d, = 37.029 Reflection surface r of first cylindrical mirror 6, 13=1 or y3-332.887d3=
10.385 REEL (90 degree reflection) first refractive surface of second cylindrical lens 7 r, I, = 0
0 r,, = ″)d4=
19.483 ng = 1.65947 second
The second refractive surface r-s-151 of the solin drill lens 7,
916r,, = ■d s =117.414 Reflection surface rX of second cylindrical mirror 8, = oor,, = -348,034d, =
209.329 REFL (90 degree reflection)
・Aberration coefficient when normalized to f=1 only in the direction parallel to the scanning direction Spherical aberration coefficient 1 = 12.40615 Comatic aberration coefficient n = -0,15612 Astigmatism coefficient III = -0,15182 Field curvature IV = 0.37192 Distortion aberration coefficient V = 0.61488 Petzval sum
P=0.52374 The astigmatism (AS) and linearity (L I N) of the scanning optical device of the first example are
Shown in Figures (a) and (b). In FIG. 4(a), AS indicates astigmatism in the sagittal direction, and ΔM indicates astigmatism in the meridional direction (the same applies hereinafter).

2nd Example> ・f=300mm Fft=60 2θ=57
．． 2958°f c = 137.06], mm λ
−780 nm・Lens data Distance d0 from the deflection surface to the first refractive surface of the concave lens 5 =
28.260 First refractive surface jX of concave lens 5: (X) f, I
= IXId I= 22.343 n
+ -1,63552 Second refractive surface r of concave lens 5 X! = 615.3B2 r , 2=
615.382d2=38.503 Reflection surface rX, -ωr, of the first cylindrical mirror 6, = -374,226d3=1
2.171 REFL (90 degree reflection) 2nd
First refractive surface rX4 of cylindrical lens 7 = 0
0 j,, = 00da
= 23.227 nt = 1.7
1230 Second refractive surface r- of second cylindrical lens 7
s= 173.968 r-s= ■d%
= 79.147 Reflection surface of second cylindrical mirror 8 r −b = oor yb = 376.545d,
= 240.252 REFL (90 degree reflection) - Aberration coefficient when normalized to f = 1 only in the direction parallel to the scanning direction Spherical aberration coefficient 1 = 9.32543 Comatic aberration coefficient n = -0,10811 Astigmatism Coefficient 1[1=-0,14784 field curvature
IV = 0.38005 distortion aberration coefficient
V = 0.62341 Petzval sum
P=0.52793 The astigmatism (AS) and linearity (LIN) of the scanning optical device of the second embodiment are shown in Fig. 5(a).
and (b).

<Third Example> -f = 300mm Fk-602θ-57,29
5+11°f c = 137.061mm λ-7
80 nm・Lens data Distance do from the deflection surface to the first refractive surface of the concave lens 5 =
21.187 First refractive surface r□ of concave lens 5 --353,414ry, = ■d, =
15.832 n, = 1.65947
The second refractive surface r, I, of the concave lens 5! 4810.991 r yz=
"dz = 27.681 Reflection surface r -3 of first cylindrical mirror 6 = "ry3 = 325
．． 587ds=10.385 REFL (90
degree reflection) 1st ff folding surface r of the second cylindrical lens 7
X4- ■ ry4=
■d4 = 17.671 nt = 1.712
30 Second refractive surface r xs of second cylindrical lens 7
-148,739r□-■d, = 126.908 Reflection surface r of second cylindrical mirror 8,, = oOr, 6 = -329,370a,
= 207.079 REFL (90 degree reflection) - Aberration coefficient when normalized to f = 1 only in the direction parallel to the scanning direction Spherical aberration coefficient 1 = 14.01009 Comatic aberration coefficient ff = -0,30391 Astigmatism Coefficient I[1= -0,13967 Field curvature IV= 0.33725 Distortion aberration coefficient V= 0.61966 Betzpearl sum
P=0.47692 The astigmatism (AS) and linearity (LIN) of the scanning optical device of the third embodiment are shown in Fig. 6 (
Shown in a) and (b).

<Fourth Example> ・f = 300mm F = 60 28 = 57.
2958”f C= 137.061mm λ-78
0nm・Lens data Distance between the deflection surface and the first refractive surface of the concave lens 5 do ""
21.175 First refractive surface rX of concave lens 5, = 00 ry,:
00d, -25,283n, = 1.6
3552 Second refractive surface r, lz of concave lens 5 = 626.837 r, =
-dt= 36.238 Reflection surface r of the first cylindrical mirror 6, 3= (1) ryz= 380.
532d3= 12.803 REFL(90
degree reflection) the first refractive surface f of the second lindrical lens 7
X4e 00 f,, -0
0d, = 24.254 1. =1.71
230 Second refractive surface r x of second cylindrical lens 7
s"' 174.347 r,, = 00
d, = 80.009 Reflection surface r□ of second cylindrical mirror 8 = ω ryb = 374.33
3d, =238.600 REFL (90
degree reflection)・Aberration coefficient when normalized to f=1 only in the direction parallel to the scanning direction Spherical aberration coefficient I-9,24469 Comatic aberration coefficient It = -0,12108 Astigmatism coefficient I [[= -0 , 14600 field curvature
IV = 0.38383 distortion aberration coefficient
V = 0.62016 pe, Tzhar sum P
= 0.52983 The astigmatism (As>) and linearity (LIN) of the scanning optical device of the fourth example are shown in FIGS. 7(a) and 7(b).

Note that the scanning optical device with the above configuration selectively changes only the light spot diameter in the sub-scanning direction without changing the light spot diameter in the scanning direction by moving the position of the second cylindrical mirror 8 parallel to the optical axis. It is possible to change it.

Further, it is also possible to make the refractive power of the first cylindrical mirror 6 in the direction perpendicular to the scanning direction and the refractive power of the second cylindrical mirror 8 in the direction perpendicular to the scanning direction the same, and in this case, In manufacturing the cylindrical mirror, it is sufficient to cut cylindrical mirrors with the same curvature and use them for both, making it possible to manufacture the scanning optical device at a lower cost.

By the way, in the above embodiment, the rotating polygon mirror 4 is used as a deflector.
Although the case where the deflector is used has been described, it goes without saying that the present invention is similarly applicable to the case where the deflector is a rotating mirror or the like.

〔Effect of the invention〕

As explained above, according to the present invention, a line image having positive refractive power only in the direction perpendicular to the scanning direction is formed in the vicinity of the deflection surface by the light beam from the light source. The optical system is arranged such that, in order from the deflection surface side, a concave lens having negative refractive power, a first cylindrical mirror having positive refractive power only in the direction perpendicular to the scanning direction, and a first cylindrical mirror having positive refractive power only in the direction parallel to the scanning direction. By using a constant velocity scanning optical system consisting of a cylindrical lens with a refractive power of This has the effect that a scanning optical device having good fθ characteristics and imaging characteristics for scanning and correcting surface tilt errors of the deflection surface can be realized compactly using inexpensive and relatively small optical elements.

[Brief explanation of the drawing]

1 is a perspective view showing the configuration of the scanning optical device of the present invention, FIG. 2 is a schematic plan view of the scanning optical device of FIG. 1, and FIG. 3 is a schematic side view of the scanning optical device of FIG. Figure 4 (a) and (
b) is a diagram showing the astigmatism and linearity, respectively, of the scanning optical device of the first embodiment, and FIGS. 5(a) and (b,) are diagrams showing the astigmatism and linearity of the scanning optical device of the second embodiment, respectively. 6(a) and (b) are diagrams showing astigmatism and linearity, respectively, of the scanning optical device of the third embodiment. FIG. 7(a) and (b) are diagrams showing the astigmatism and linearity, respectively. Diagrams showing astigmatism and linearity of the scanning optical device of the fourth embodiment, FIG. 8 is a plan view showing an example of a conventional scanning optical device, and FIG. 9 is a side view of the scanning optical device of FIG. 8. It is a diagram. In the figure, 1... Semiconductor laser, 2... Collimation lens, 3... First cylindrical lens, 4... Rotating polygon mirror (deflector), 5... Concave lens, 6... First cylindrical mirror 7...second cylindrical lens, 8...second cylindrical mirror 9...scanning surface.

Claims (2)

[Claims] (1) In a scanning optical device in which a light beam from a light source is incident on a deflection surface and is deflected, and the scanning surface is scanned by the deflected light beam, the light beam from the light source causes a beam to be caused near the deflection surface in a direction parallel to the scanning direction. A line image forming optical system having a positive refractive power only in the direction perpendicular to the scanning direction to form a line image, a concave lens having a negative refractive power only in the direction perpendicular to the scanning direction, and a concave lens having a negative refractive power in order from the deflection surface side. a first cylindrical mirror having a refractive power of
A constant velocity scanning optical system comprising a cylindrical lens having a positive refractive power only in a direction parallel to the scanning direction and a second cylindrical mirror having a positive refractive power only in a direction perpendicular to the scanning direction. scanning optical device. (2) The scanning optical device according to claim 1, wherein the concave lens is a cylindrical lens having negative refractive power only in a direction parallel to the scanning direction.