JPH0545580A - Lens for optical scanning and optical scanning device - Google Patents

Abstract

(57) [Summary] (Correction) [Purpose] To realize high-performance optical scanning with small size and low cost. [Structure] A light beam from a light source Q is made into a light beam which is condensed by a first condensing optical system 2 toward a natural condensing point Q ′ set behind a surface 6 to be scanned. The light beam is imaged as a long line image LI in the main scanning corresponding direction by the second condensing optical system 7, and a constant angular velocity is obtained by the deflector having the deflection reflection surface 3 at or near the image formation position of the line image LI. And the deflected light beam is condensed by the optical scanning lens 5 as a light spot on the surface 6 to be scanned, and the surface 6 to be scanned is optically scanned at a substantially constant speed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical scanning lens and an optical scanning device.

[0002]

2. Description of the Related Art Optical scanning devices are widely known in connection with optical printers and digital copying machines.

In such an optical scanning device, there is a problem of how to realize a high performance, inexpensive and small device.

[0004]

SUMMARY OF THE INVENTION The present invention solves the above problems, realizes a small size and low cost, and is capable of performing optical scanning with good performance, and a novel optical scanning device and an optical scanning lens. For the purpose of provision.

[0005]

In this specification,
The "main scanning corresponding direction" is a virtual optical path (virtual optical path) obtained by linearly expanding the optical path from the light source to the surface to be scanned in the state where the deflected light beam is orthogonally incident on the surface to be scanned. Assuming that, on this virtual optical path, the direction corresponding to the main scanning direction is parallel, and the "sub-scanning corresponding direction" is the direction orthogonal to the virtual optical path and the main scanning corresponding direction on the virtual optical path. is there.

FIG. 1 (a) is a drawing of the optical scanning device of the present invention developed from a light source to a surface to be scanned along a virtual optical path so that the vertical direction corresponds to the main scanning direction. FIG. 6B is a diagram in which the state of being developed along the virtual optical path is drawn so that the vertical direction corresponds to the sub-scanning corresponding direction.

The optical scanning device of the present invention is shown in FIGS.
As shown in, “the light beam from the light source Q is not a light beam that is condensed by the first condensing optical system 2 toward the natural condensing point Q ′ set behind the scanned surface 6. The focused light flux is imaged by the second focusing optical system 7 as a long line image LI in the direction corresponding to the main scanning, and the deflector having the deflective reflection surface 3 at or near the image forming position of the line image LI. Is deflected at a constant angular velocity by the optical scanning lens 5, and the deflected light beam is condensed as a light spot on the surface 6 to be scanned by the optical scanning lens 5 to optically scan the surface 6 to be scanned at a substantially constant velocity. The "natural condensing point Q '" is a position where the condensing light flux by the first condensing optical system 2 is condensed only by its own condensing property. In FIG. 1A, reference numeral 4 indicates the locus of the natural condensing point Q ′ accompanying the deflection of the deflected light beam. Further, H indicates the front principal point of the optical scanning lens, and t indicates the distance from the front principal point H to the deflective reflection surface.

The "optical scanning lens" of claim 1 is provided between the deflector and the surface to be scanned in such an optical scanning device, and collects the deflected light beam as a light spot on the surface to be scanned. The lens has the following features.

FIG. 1C shows the lens shape in the deflection surface (a plane formed by sweeping the principal ray of the deflected light beam ideally deflected by the deflector) of the optical scanning lens of claim 1. FIG. 3D shows the lens shape in the plane orthogonal to the deflection (the plane including the lens optical axis and orthogonal to the deflection plane).

The lens surface on the deflector side of the optical scanning lens 5 has a concave shape obtained by rotating an aspherical shape in the deflecting surface with a straight line parallel to the main scanning corresponding direction and intersecting the optical axis as a rotation axis. , And the lens surface on the scanned surface side has a “radius:
It has a convex surface shape obtained by rotating an arc of R _2S with a straight line parallel to the sub-scanning corresponding direction and orthogonal to the optical axis at a radius of R _2M .

The radius of gyration of the aspherical surface of the lens surface on the deflector side (the distance on the optical axis between the rotation axis and the lens surface) is R _1S ,
The radius of curvature on the optical axis of the aspherical shape (the radius of curvature on the optical axis in the deflecting surface) and the conic constant are R _1M and K, respectively.
And the distance from the deflection start point of the deflector to the natural condensing point is S
Then, R _1S , R _1M , K, R _2S , R _2M and S are (I) −55.0 <R _1M /K<−15.0 (II) −0.3 <R _2M / S <−0.1 (III) 1.5 <R _1S / R _2S <2.5 is satisfied.

The optical scanning lens 5 of claim 1 can be formed of glass, of course, but it may be formed of plastic (claim 2).

The optical scanning device according to a third aspect of the present invention is a first light source Q and a first light beam from the light source that is a convergent light beam that converges toward a natural condensing point Q ′ set behind the surface 6 to be scanned. The condensing optical system 2 and the light flux condensed by the first condensing optical system 2 are condensed in the sub-scanning corresponding direction to form a long line image L in the main scanning corresponding direction.
A second condensing optical system 7 for forming an image as I, a deflector having a deflecting / reflecting surface 3 in the vicinity of the image forming position of the line image LI, and a deflector for deflecting the reflected light flux at a constant angular velocity, and this deflector and It is provided between the scanning surface and the sub-scanning corresponding direction, and the deflection origin point by the deflector and the position of the scanned surface 6 have a geometrically-optically substantially conjugate relationship, and the deflected light flux is used as a light spot on the scanned surface. And a light scanning lens 5 for collecting light, and a "deflector"
However, as shown in FIG. 3 (a), a hozo-type mirror having one deflecting / reflecting surface 3a, or as shown in FIG. 3 (b),
The present invention is characterized in that the optical scanning lens 5 is a tenon mirror having two deflecting and reflecting surfaces 3a, and the optical scanning lens 5 is the optical scanning lens of claim 1.

As the light source Q, a semiconductor laser or LE
It is possible to use D, or a combination of these and a collimator lens so as to emit a parallel light flux. The light source Q and the first condensing optical system 2 or these and the second condensing optical system may be integrally configured.

The aspherical surface shapes are the above-mentioned R _1M , K and high-order aspherical surface coefficients A, B, C ,. ． X axis in the optical axis direction and Y axis in the direction orthogonal to the optical axis in the deflection plane, and the origin is at the intersection of the optical axis and the lens surface, it is well known that X = Y ² / {R _1M + √ [R _1M ² − (1 + K) Y ² ] + AY ²
+ BY ³ + CY ⁴ +. ． (The symbol: √ [] represents the square root of the quantity in []).

[0016]

As described above, in the optical scanning device of the present invention, the optical scanning lens is a single lens. In addition, the optical scanning device is configured to be able to correct "face tilt" in the deflector.
Further, since the deflector is a HOSO type mirror and its deflection reflection surface is coincident with or very close to the mirror rotation axis, the positional deviation between the deflection reflection surface and the line image due to the rotation of the deflection reflection surface is small, and The condition for correcting the field curvature in the sub-scanning corresponding direction in the scanning lens becomes lenient.

The above condition (I) concerning the optical scanning lens
(III) will be described. The condition (I) is a condition for favorably correcting the field curvature in the main scanning direction. The field curvature in the main scanning direction falls to the under side if the lower limit of the condition (I) is exceeded, and falls to the over side if the upper limit is exceeded, making good correction difficult. The condition (II) is also a condition for correcting the field curvature in the main scanning direction, and the field curvature in the main scanning direction falls to the over side if the lower limit of the condition (II) is exceeded and exceeds the upper limit. It falls to the under side, making good correction difficult. The condition (III) is a condition for correcting the field curvature in the sub scanning direction. The field curvature in the sub-scanning direction falls to the over side when the lower limit of the condition (I) is exceeded, and falls to the under side when the upper limit is exceeded, making good correction difficult.

[0018]

EXAMPLES Specific examples will be given below.

The optical scanning device is as shown in FIGS.
I will assume the one explained in accordance with. Further, as the deflector, it is assumed that the deflector is a tenon mirror having one deflecting / reflecting surface as shown in FIG. The horizontal mirror has a deflection reflection surface 3 formed on the rotation axis of the motor, and the rotation axis matches the deflection reflection surface.

In each embodiment, as shown in FIG. 2, the radius of curvature on the optical axis R _1M , the conic constant K, and the radius gyration R _1S in the deflecting surface of the deflector-side lens surface of the optical scanning lens 5,
The optical scanning lens 5 is specified and deflected by the curvature radii of the surface to be scanned: R _2M and R _2S , the refractive index of the material of the scanning lens 5: n, and the lens surface interval on the optical axis: d _1. A distance on the optical axis from the reflecting surface 3 to the deflector-side lens surface of the optical scanning lens 5: d ₀ , from the scanned surface side lens surface to the scanned surface 6
The position of the optical scanning lens 5 is specified by the distance D on the optical axis to the optical axis. Further, the state of the condensed light flux by the first condensing optical system is the distance from the deflective reflection surface to the natural condensing point Q ′:
Specified by S. The light source Q and the first and second focusing optical systems satisfy the above distance S, and in the sub-scanning corresponding direction,
It can be appropriately set so that the light flux forms a long line image in the direction corresponding to the main scanning at the position of the deflective reflection surface 3.

Example 1 S = 495.0, R _1M = -364.2, R _1S = -37.
6, K = 13.0, R _2M = −79.7, R _2S = −17.
6, d ₀ = 34.1, d ₁ = 28.5, D = 141.3,
n = 1.5721 Value of conditional expression R _1M /K=-28.0, R _2M /S=-0.161, R _1S
/ R _2S = 2.13 Write width: 215.9, linearity: 16.0% or less Example 2 S = 693.6, R _1M = -341.4, R _1S = -39.
5, K = 16.0, R _2M = −74.7, R _2S = −17.
3, d ₀ = 32.0, d ₁ = 26.7, D = 121.8,
n = 1.5721 Value of conditional expression R _1M /K=-21.34, R _2M /S=-0.108, R
_1S / R _2S = 2.284 Write width: 216.009, linearity: 15.5%
Hereinafter, Example 3 S = 337.0, R _1M = −326.4, R _1S = −27.
4, K = 6.0, R _2M = −85.3, R _2S = −15.
8, d ₀ = 31.6, d ₁ = 26.3, D = 117.0,
n = 1.5721 Value of conditional expression R _1M /K=−54.4, R _2M /S=−0.253, R
_1S / R _2S = 1.73 Write width: 216.1, Linearity: 20.6%
Hereinafter, Example 4 S = 419.2, R _1M = −366.8, R _1S = −26.
5, K = 10.0 R _2M = −85.9, R _2S = −15.9, d ₀ = 31.
4, d ₁ = 26.2, D = 132.1, n = 1.572
1 Value of conditional expression R _1M /K=-36.68, R _2M /S=-0.205, R
_1S / R _2S = 1.666 write width: 219.2, linearity: 17.3%
Example 5 S = 500.6, R _1M = -465.7, R _1S = -36.
_{1, K = 29, R 2M} = -81.5, R 2S = -17.
7, d ₀ = 34.9, d ₁ = 29.1, D = 146.7,
n = 1.5721 The value of the conditional expression R _1M /K=−16.058, R _2M /S=−0.163,
R _1S / R _2S = 2.04 Write width: 216.0, Linearity: 14.1%
The field curvature of each example is shown in FIG. 4 below. The broken line represents the main scanning direction, and the solid line represents the field curvature in the sub scanning direction. In each of the embodiments, the field curvature in the main / sub scanning direction is corrected well. In addition, the linearity is also within the range in which electrical correction is possible if it is about the above-mentioned embodiment.

[0022]

As described above, according to the present invention, a novel optical scanning lens and an optical scanning device using this lens can be provided. Since this optical scanning lens is a single lens, it can be manufactured at low cost. In particular, if you use plastic as a material and mold it, it can be realized at a very low price.
The cost and size of the optical scanning device can be reduced.

Further, since the optical scanning device of the present invention has the surface tilt correction function, extremely good optical scanning can be realized regardless of the axis deviation due to the rotation of the deflector-shaped mirror. Further, because of the above-described surface tilt correction function, the accuracy of the deflecting reflection surface of the deflector-type mirror is relaxed, and the cost of the deflector can be reduced.

[Brief description of drawings]

FIG. 1 is a diagram for explaining the present invention.

FIG. 2 is a diagram for explaining an example.

FIG. 3 is a diagram for explaining a deflector.

FIG. 4 is a diagram showing field curvature for each example.

[Explanation of symbols]

 Q light source 2 first condensing optical system 3 deflection reflection surface 5 optical scanning lens 6 surface to be scanned 7 second condensing optical system Q'natural condensing point

Claims (3)

[Claims] 1. A light flux from a light source is made into a light flux which is condensed toward a natural light condensing point set behind a surface to be scanned by a first condensing optical system. An image is formed as a long line image in the main scanning corresponding direction by the second condensing optical system, and is deflected at a constant angular velocity by a deflector having a deflecting / reflecting surface at the image forming position of the line image or in the vicinity thereof. An optical scanning device for converging a light beam as a light spot on a surface to be scanned by an optical scanning lens to optically scan the surface to be scanned at a substantially constant speed. A lens for condensing a light beam as a light spot on the surface to be scanned, wherein the lens surface on the deflector side rotates an aspherical shape with a straight line parallel to the main scanning corresponding direction and intersecting the optical axis as a rotation axis. The surface of the lens to be scanned has a radius of: The arc _2S, as an axis the straight line perpendicular to the parallel optical axes in the sub-scanning direction, radius has a convex shape obtained by rotating by R _2M, of the lens surface of the deflector-side, the radius of rotation When R _{1S is} the radius of curvature on the optical axis of the aspherical shape and the conic constant is R _1M and K, and the distance from the deflection start point of the deflector to the natural condensing point is S, then (I) −55.0 <R _{1M /K<-15.0 (II) -0.3 <R} 2M / S <-0.1 (III) 1.5 < a satisfies the R _1S / R _2S <2.5 condition: Optical scanning lens. 2. The optical scanning lens according to claim 1, wherein the lens material is plastic. 3. A light source device, a first condensing optical system for converting a light beam from the light source device into a converging light beam converging toward a natural condensing point set behind a surface to be scanned, and the first condensing optical system. A second condensing optical system that condenses the converging light beam by the condensing optical system in the sub-scanning corresponding direction and forms an image as a long line image in the main scanning corresponding direction, and deflects it near the image forming position of the line image. A deflector which has a reflecting surface and deflects the reflected light beam at a constant angular velocity, and is arranged between this deflector and the surface to be scanned. It has a geometrically-optically substantially conjugate relationship, and has an optical scanning lens for converging a deflected light beam as a light spot on the surface to be scanned, and the deflector has one or two deflecting / reflecting surfaces. Type mirror, wherein the optical scanning lens is the optical scanning lens according to claim 1. Wherein, the optical scanning device.