JPH04104213A - Lens for optical scanning and optical scanning optical system - Google Patents

Abstract

PURPOSE:To excellently compensate curvature of field in a main-scanning and a subscanning direction although single-lens constitution is employed by making an object-side surface concave and using a convex toroidal surface as an image-side surface. CONSTITUTION:The object-side surface in a deflecting surface is represented by an aspherical surface curve which has a radius R1m of on-axis curvature and a cone constant K, and the image-side surface has a radius R2m of curvature. In this surface, the object-side surface has the radius R1m of curvature and the image-side surface has the radius R4d2m of curvature; and the radius of on-axis curvature and radius of curvature satisfy large/small relations ¦R1m¦ > ¦R1a¦ and ¦R2m¦, and ¦R1m¦ > R2a¦ and ¦R1a¦ > ¦R2a¦ when R1m <0, R1a<0, and R2m<0. Then the object-side surface is a concave surface obtained by rotating the aspherical surface curve which has the radius R1m of on-axis curvature and the cone constant K and is in a plane of deflection around an axis which crosses the optical axis in the plane of deflection at right angles and is at a distance R1m from a light spherical curve on the optical axis. Further, the image-side surface is the convex toroidal surface obtained by rotating an arc which has a radius R2a and is in an orthogonal plane of deflection around an axis J which crosses the optical axis in the orthogonal plane of deflection at right angles and is at a distance R2m from the arc on the optical axis. Consequently, the curvature of field is excellently compensated in the main-scanning and subscanning directions.

Description

[Detailed description of the invention] [Industrial application fields] The present invention relates to an optical scanning lens and an optical scanning optical system.

[Prior Art] A focused light beam deflected at a constant angular velocity is further focused and imaged as a light spot on a surface to be scanned.

2. Description of the Related Art An optical scanning lens that optically scans a surface to be scanned at approximately constant speed is known.

[Problem to be solved by the invention] In an optical scanning device, if the field curvature of the optical scanning lens is not well corrected in the main and sub-scanning directions, the diameter of the optical spot will change depending on the image height of the optical spot. Achieves good optical scanning8
do not come.

It is difficult for the above-mentioned optical scanning lenses to satisfactorily correct the curvature of field in the main and sub-scanning directions at the same time.Usually, the curvature of field in the main scanning direction is corrected well, and the curvature of field in the sub-scanning direction is corrected well. This is corrected using a long cylinder lens or the like. For this reason, the number of optical system elements in the optical scanning optical system increases, leading to an increase in the complexity and cost of the optical scanning device.

The present invention was made in view of the above-mentioned circumstances, and
The object of the present invention is to provide a novel optical scanning lens that satisfactorily corrects field curvature in the main and sub-scanning directions despite having a single lens configuration, and an optical scanning optical system using this lens.

[Means for Solving the Problems] The optical scanning lens of the present invention further converges a focused light beam that is deflected at a constant angular velocity by a deflection reflection surface of an optical deflection device and forms an image as a light spot on a scanned surface. This is a lens for scanning the surface to be scanned with light at a substantially constant speed, and is configured as a single lens.

A plane formed by sweeping the principal ray of a convergent beam that is ideally deflected is called a "deflection plane", and a plane passing through the optical axis and perpendicular to the deflection plane is called a "deflection orthogonal plane".

In FIG. 2, (A) shows the shape within the deflection plane of the optical scanning lens of the present invention, that is, the cross-sectional shape by the deflection plane. In the deflection plane, the object side surface is an aspherical curve having an axial radius of curvature R1m and a conic constant K. The image side surface has a radius of curvature R2+a. The figure (B) shows the lens shape within the plane perpendicular to the deflection. In this plane, the object side surface has a radius of curvature R1m, and the image side surface has a radius of curvature R2n.
R2m< 0 and lR++++llR+a + R
2-1>IR2nl and 1r++, l>lr+z-1,
The magnitude relationship lR+->Rlm is satisfied.

As is clear from this, the optical scanning lens functions as a positive meniscus lens with its concave surface facing the object side (left side in FIG. 2) both in the deflection plane and in the plane orthogonal to the deflection plane.

The side surface of the object is an aspherical curve with a radius of curvature R1° on the optical axis and a conic constant K that lies within the deflection plane. It is a concave surface obtained by rotating around an axis.

The above-mentioned "aspherical curve" means the coordinate in the optical axis direction as X, the coordinate in the direction perpendicular to the optical axis as Y, the radius of curvature on the optical axis as R9, the conic constant, and the higher-order aspherical coefficient as A2+^3. When X=[
Y2/(R+ R-]+K Y")]+A2Y2+A
This is a curve represented by 3Y3+, , (1). The cross-sectional shape of the object side surface of the optical scanning lens of the present invention on the inside of the deflection plane is an aspherical curve obtained by dividing R in equation (1) by R3.

The image side surface is a circular arc with radius R2n that lies in the plane orthogonal to the deflection plane.
perpendicular to the optical axis in the plane orthogonal to deflection, and R on the optical axis from the above circular arc.
22n is a convex toroidal surface obtained by rotating around a separate axis.

When the distance from the deflection-reflection surface to the natural focal point of the focused light beam deflected by the deflection-reflection surface is S, the optical scanning lens of the present invention has the following formula: (I) −35,0(R1,/K < -1
3,0(II) -7,0X10'< S-
R,,<-2n5X10'(III) 1
．． The light scanning optical system according to claim 2, characterized by the condition 3<R+a/Rza<2.1, includes: "a light source device; and a focusing optical system that converges a light beam from the light source device."

a deflection device that deflects the focused light beam by the focusing optical system at a constant angular velocity; further focuses the focused light beam deflected by the deflection device to form an image as a light spot on the scanned surface;
An optical scanning lens that scans the surface to be scanned with light at approximately constant velocity.
has.

The optical scanning lens according to claim 1 is used as the optical scanning lens.

The optical scanning lens of the present invention has a so-called one-sided tilt of the polarizing reflection surface.
It does not have a stop to compensate for this. Therefore, as the deflection device of the optical scanning device, a "pyramidal mirror (deflection device fit, which is cut at a 45 degree inclination around the rotation axis and whose cut surface is a mirror surface)" that does not cause surface tilt is used (Claim 3). , or use a "rotating polygon mirror with good surface tilt accuracy" (Claim 4)
is preferable.

In addition, in the above, "the surface to be scanned is optically scanned at approximately constant speed" means that the deviation between the optical scanning achieved by the optical scanning lens according to the present invention and the ideal uniform stray optical scanning is caused by electrical This means that it can be corrected to the extent that

[Function] FIG. 1 schematically shows an example of the light scanning optical system of the present invention. That is, this figure is a diagram developed along the optical path from the light source device Q to the surface to be scanned 6, and drawn so that the main scanning direction corresponds to the vertical direction. As the light source device Q, a semiconductor laser is assumed.

The light flux from the light source device Q is converted into a focused light flux by a condensing lens 2 as a condensing optical system, and the light flux is converted into a condensed light flux by a condensing lens 2 as a condensing optical system.
and is deflected by rotating the direction of the deflection reflection surface by a deflection device. The deflected condensed light beam enters the optical scanning lens 5, but if the optical scanning lens 5 were not present, it would be condensed at the natural focal point Q', and due to the deflection, the natural focal point Q' would become an arc. If a pyramidal mirror is used as a deflection device to draw a close trajectory 4, the trajectory 4 becomes an arc.

The optical scanning lens 5 further focuses the incident focused light beam and forms an image on the scanned surface 7 as a light spot. As the focused light beam is deflected, the light spot moves substantially uniformly on the surface to be scanned 6 to perform optical scanning.

In this way, the optical scanning lens 5 is ideally configured to take the locus 4 of the natural condensing point Q' as the virtual light source object position, and to link this to the surface to be scanned 6 in a conjugate relationship.

Now, in order to satisfactorily correct field curvature in the main scanning direction, the optical scanning lens of the present invention employs a special concave surface obtained by rotating the aspherical curve J on the object side. It is obtained by rotating "an aspherical curve existing on the deflection plane, having a radius of curvature R on the optical axis and a conic constant K" around an axis perpendicular to the optical axis within the deflection plane. This axis of rotation and the side surface of the object are separated by R1+i on the optical axis.

Regarding this object side surface, Rlm and Nito satisfy condition (I). R1, (Since it is O,>0.

When the lower limit of condition (I) is exceeded, the curvature of field in the main scanning direction falls to the under side, and when the upper limit is exceeded, it falls to the over side.

Therefore, the range of condition (1) is appropriate.

A toroidal surface is used on the image side to properly correct field curvature in the sub-scanning direction.

In the lens surface configuration of the present invention, the image side surface has the effect of imparting a strong focusing tendency to a convergent light beam whose focusing tendency has been weakened at the object side surface in the sub-scanning direction.

That is, the image side surface has the effect of bringing the imaging position of the light spot closer to the optical scanning lens side. In general, as the deflection angle increases, the curvature of the image side surface in the sub-scanning direction becomes stronger, and as described above [effect of bringing the imaging position of the light spot closer to the optical scanning lens side].
When the deflection angle increases, the natural focal point approaches the scanned surface, and this tends to cause a large negative field curvature in the sub-scanning direction. Therefore, in the present invention, a toroidal surface whose curvature tends not to increase in the sub-scanning direction as the deflection angle increases is employed on the image side surface.

Regarding the image side surface, condition (II) is satisfied.

When the lower limit of condition (II) is exceeded, the field curvature in the sub-scanning direction falls to the underside, and when the upper limit is exceeded, the field curvature falls to the overside. Therefore, the range of condition (II) is appropriate.

Condition (III) is a condition for improving astigmatism.

When the lower limit of condition (III) is exceeded, the optical spot imaging position in the sub-scanning direction shifts toward the optical scanning lens, and when the upper limit is exceeded, it shifts toward the opposite side. Therefore, outside the range of condition (III), astigmatism becomes large.

[Example code] Specific examples will be given below.

As shown in Figure 3, the radius of curvature of the side surface of the object in the deflection plane (corresponding to the main scanning direction) is 11 + - (radius of curvature on the optical axis).
R1 in the plane perpendicular to the deflection (corresponding to the sub-scanning direction).

The radius of curvature of the image side surface is R21 in the deflection plane, R2n is in the plane perpendicular to the deflection, the lens thickness on the optical axis is d8, the refractive index of the lens material is n, and the optical axis between the deflection reflection surface 3 and the object side surface is The upper distance is d. , the distance on the optical axis between the image side surface and the surface to be scanned is D.

Further, as explained with reference to FIG. 1, the distance from the position of the deflecting reflection surface to the natural light convergence point Q' is defined as S. The light source device side from the deflection reflection surface can be configured as appropriate to realize the given S. Note that a pyramidal mirror is assumed as the deflection device in each embodiment.

Example 1 s=990. o d,=30.0R'
7==-400,ORt,"-82nOd,=15.O
n=1.5721R1,=-aa,o R1-=-4
2nOD = 124.594 Conic constant of object side: = 2
8.0 Condition value R1, /=-14,29,5-Rx,=-6,7x
10', R1, /Rz, = 1.95 effective main scanning length: 21
6.6. Linearity: 17.3% or less Example 2 S = 390.0 da = 30.0R
'i-"-320, ORt-"-55, 2dt"15.
o rFl, 5721R2-"-82n5Rz-"-
38, OD = 126.041 Conic constant of the object side: =
11.0 Condition value Rt, /=-29,09,SR,,=-3,2x
10', R, , /Rt, = 1.45 effective main scanning length: 21
7.7. Linearity: 23.8% or less Example 3 S=790.0 d. =30.0Ri'
, knee 400. OR,,=-72n2d,:15. On
=1.5721Rz,”-70,OR2-”-40,O
D "124.092 Conic constant of object side: = 25.0 Condition value Rt, / to = -16,0, s-R,, = -s, sX 1
0', Rt, /Rz, = 1.81 effective main scanning length: 216
．． 6. Linearity: I7.8% or less Example 4 S=630. Odo”30.0 Rj, Knee 320.OR,,=-69,Od,=15.
o n=1.5721R2n=-70,OR,,=-
40,0D=124.195 Conic constant of object side:=1
0.0 Condition value R,,/bar=-32.0, 5-R2n=-4,4XI
O', R, , /R□=1.725 Effective main scanning length: 218
．． 7. Linearity: 20.6% or less Example 5 S = 790.0 d, = 30.0 R'
i-”-320,ORt-”-72n2d,=ts,o
n=1.5721Rz-”-68,0Rx-”-4
0,40=225.892 Conic constant of object side:=13
．． 0 Condition value R1yo/to = -24,6, S-R,, = -5,4xlO
', Rt, /R2n=1.79 Effective main scanning length: 214.
O, linearity: 19.6% or less FIGS. 4 to 8 show field curvature diagrams for Examples 1 to 5, respectively (the broken line indicates the main scanning direction, and the solid line indicates the sub scanning direction).

In each embodiment, the curvature of field in the main and sub-scanning directions is corrected in an extremely well-balanced manner. The linearity is also good and within a range that can be sufficiently corrected electrically. In the above embodiment, all the high-order aspherical coefficients in the aspherical curve that defines the object surface are O, but if you use the aspherical curve using these high-order coefficients, you can correct the field curvature more precisely. can be done.

[Effects of the Invention] As described above, according to the present invention, a novel optical scanning lens and device can be provided.

Since this light scanning lens/light scanning optical system has the above-described configuration, it is possible to satisfactorily correct field curvature in the main and sub-scanning directions and realize good light scanning even though it is a single lens structure.

[Brief explanation of drawings]

FIG. 1 is a diagram for explaining a light scanning optical system of the present invention, FIG. 2 is a diagram for explaining a light scanning lens of the present invention, and FIG. 3 is a diagram for explaining an embodiment. FIGS. 4 to 8 are field curvature diagrams for each embodiment. 301. Polarized reflective surface, 501. Optical scanning lens, 608
．． 34 causes and behind the scenes - Example 4) Anzu 5 (9JE:);! =・ノ Z) 6 times heather (Torako P) δ)

Claims (1)

[Claims] 1. A focused light beam deflected at a constant angular velocity by a deflection reflecting surface of a light deflection device is further focused and imaged as a light spot on a surface to be scanned, so that the surface to be scanned is moved at a substantially constant velocity. It is a lens for optically scanning light, and is configured as a single lens.The surface formed by sweeping the principal ray of a converged beam that is ideally deflected is the deflection surface, and the surface that passes through the optical axis and is orthogonal to the deflection surface. When is the plane orthogonal to deflection, the radius of curvature on the optical axis of the object side surface in the deflection plane: R_1_m, the radius of curvature of the image side surface: R_2_
m, radius of curvature of the object side in the plane orthogonal to deflection: R_1
_n, radius of curvature of image side surface: R_2_n, R_1_m<
0, R_1_n<0, R_2_m<0, R_2_n<0
So |R_1_m|>|R_1_n|, |R_2_m|>
|R_2_n| and |R_1_m|>|R_2_m|,
Satisfying the magnitude relationship of |R_1_n|>|R_2_n|, the object side surface has an aspherical curve existing in the deflection plane with a radius of curvature R_1_m on the optical axis and a conic constant K, and is perpendicular to the optical axis in the deflection plane. It is a concave surface obtained by rotating around an axis R_1_n apart on the optical axis from the aspherical curve, and the image side surface is obtained by rotating an arc with radius R_2_n in the plane orthogonal to deflection to the plane orthogonal to the optical axis in the plane orthogonal to deflection. , R on the optical axis from the above circular arc
It is a convex toroidal surface obtained by rotating around an axis _2_m apart, and when the distance from the deflection-reflection surface to the natural convergence point of the focused beam deflected by this deflection-reflection surface is S, (I )-35.0<R_1_m/K<-13.0(II
)-7.0×10^4<S・R_2_m<-2.5×1
0^4(III)1.3<R_1_n/R_2_n<2.
An optical scanning lens characterized by satisfying the following condition. 2. A light source device, a focusing optical system that converts the light beam from this light source device into a focused light beam, a deflection device that deflects the focused light beam by this focusing optical system at a constant angular velocity, and a focused light beam deflected by this deflection device. The light scanning lens further comprises a light scanning lens that focuses the light to form a light spot on the surface to be scanned and scans the light on the surface to be scanned at a substantially uniform speed, the light scanning lens being the light scanning lens of claim 1. An optical scanning optical system characterized in that it is a lens for use. 3. The optical scanning optical system according to claim 2, wherein the deflection device is a pyramidal mirror. 4. The optical scanning optical system according to claim 2, wherein the deflection device is a rotating polygon mirror with good surface tilt accuracy.