JPH04242215A - Optical scanner - Google Patents

Abstract

PURPOSE:To obtain the optical scanner which makes a highly accurate optical scanning while the plane tilt of reflecting surfaces of a rotary polygon mirror is corrected with simple constitution. CONSTITUTION:The optical scanner makes an optical scanning in a main scanning direction by guiding the luminous flux emitted by a light source 1 onto a scanned surface through an image formation optical system 5 after deflecting the luminous flux by a deflector 4 and also makes an optical scanning in two dimensions by moving or rotating the scanned surface in a subscanning direction. A grating lens 10 which is different in focal length mutually between main scanning section and subscanning section and in a rectangular or blazed surface shape is arranged between the light source 1 and deflector 4 to image the luminous flux from the light source on the reflecting surface of the deflector 4 linearly in the main scanning section.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical scanning device, and in particular corrects the inclination of a reflecting surface of a rotating polygon mirror as a deflector.
Electrophotography that corrects scanning unevenness (scanning deviation) in the sub-scanning direction of a surface to be scanned such as a photosensitive drum or photosensitive belt, and performs optical scanning on the surface to be scanned with high precision, for example, to form a high-quality image. The present invention relates to an optical scanning device that is suitable for devices such as laser beam printers, color laser beam printers, and multicolor laser beam printers that have processes.

0002

2. Description of the Related Art Conventionally, in an optical scanning device having this type of tilt correction function, a light beam modulated and emitted from a laser light source is rotated into a polygonal plane, as described in, for example, Japanese Patent Laid-Open No. 62-36210. Image information is written by deflecting the light using a deflector such as a mirror, guiding the light onto the surface to be scanned, and scanning the surface.

FIG. 13 is a schematic diagram of the main parts of a conventional optical scanning device of this type. In the figure, reference numeral 1 denotes a light source, which is composed of a semiconductor laser oscillator, etc., and is almost a point light source, emitting divergent laser light.

The diverging light beam from the light source 1 is converted into a parallel beam by a collimator lens 24 and guided to a cylinder lens 25. The cylinder lens 25 is arranged in a direction perpendicular to the rotational direction plane (plane perpendicular to the rotational axis or the main scanning plane, X-Y plane formed by the scanning beam over time) of the polygon mirror (rotating polygon mirror) 4 which is a deflector. (
Collimator lens 2 has light focusing power only in the sub-scanning direction
4 to the deflection reflection surface 4 of the polygon mirror 4.
The light is focused in the form of a focal line on point a. After this focal line beam is reflected by the deflection reflection surface 4a, it becomes a divergent beam again in the X-Z plane (sub-scanning direction plane) in the figure, and the fθ beam is formed by a spherical concave lens 5a and an anamorphic toric lens 5b.
The light is focused onto the photosensitive drum 8 by the lens 5.

The fθ lens 5 has a conjugate relationship between the deflection reflection surface 4a of the polygon mirror 4 and the photosensitive drum 8 in the X-Z plane, thereby forming a tilt correction system, and the deflection reflection surface of the polygon mirror 4 The scanning line deviation (pitch error) on the photosensitive drum 8 caused by the inclination angle of the photosensitive drum 4a, the inclination of the rotation axis, etc. is corrected in principle purely optically.

On the other hand, in the rotation direction plane (main scanning plane) of the polygon mirror 4, the scanning beam from the cylinder lens 25 enters the fθ lens 5 as parallel light, and is focused on the photosensitive drum 8. .

Due to the focusing performance of the fθ lens 5, the scanning beam is focused into a spot on the photoreceptor drum 8.
A linear scanning line is formed on the photosensitive drum 8 as the polygon mirror 4 rotates (main scanning). The photosensitive drum 8 rotates in the sub-scanning direction as shown by an arrow 8a in FIG. 13, and two-dimensional information is recorded on the photosensitive drum 8 by a scanning beam in conjunction with the main scanning. This recorded information is reproduced on a medium such as paper using, for example, a known electrophotographic process.

[0008]

[Problem to be Solved by the Invention] In a conventional optical scanning device, a light beam from a light source is focused into a linear image on the reflecting surface of a rotating polygon mirror using two lenses, a collimator lens and a cylindrical lens. , thereby correcting the inclination of the reflective surface.

In general, the collimator lens and cylindrical lens used at this time require strict precision in optical axis alignment and eccentricity during manufacture and assembly of both lenses.

For this reason, it has been proposed to use an anamorphic aspherical lens made of a glass mold that integrates the functions of both a collimator lens and a cylindrical lens to perform tilt correction. However, this anamorphic aspherical lens is difficult to manufacture and has problems in that sufficient accuracy cannot be obtained.

The present invention provides an optical scanning device that effectively corrects the inclination of the reflecting surface of a rotating polygon mirror with a simple configuration by using an appropriately configured grating lens, and that enables highly accurate optical scanning. purpose.

0012

[Means for Solving the Problems] The optical scanning device of the present invention includes:
After the light beam emitted from the light source is deflected by a deflector, it is guided onto the surface to be scanned through an imaging optical system to scan the light in the main scanning direction, and at the same time, the surface to be scanned is moved or rotated in the sub-scanning direction. In an optical scanning device that scans light two-dimensionally by moving, a grating lens having a rectangular or blazed surface shape and having different focal lengths in a main scanning section and a sub-scanning section is provided between the light source and the deflector. is arranged, and the light beam from the light source is imaged on the reflective surface of the deflector so as to form a linear image within the main scanning cross section.

In particular, the present invention is characterized in that the effective surface of the grating lens is elliptical, and that the grating lens is composed of a cylindrical grating lens with both surfaces perpendicular to each other.

[0014]

[Example] Fig. 1 is a schematic diagram of the main parts in the main scanning section of Embodiment 1 of the present invention, and Fig. 2 is an expanded view of the optical path in the sub-scanning section perpendicular to the main scanning section of Fig. 1 and including the optical axis. Schematic diagram of the main parts, Figure 3
2 is an explanatory plan view of a portion of FIG. 1. FIG.

In FIGS. 1 to 3, reference numeral 1 denotes a light source consisting of a semiconductor laser or the like, and the light beam emitted from the light source 1 is incident on a reflecting surface 4a of a rotating polygon mirror 4, which is a deflector, via a grating lens 10, which will be described later. do.

The grating lens 10 has different refractive powers in the main scanning section and the sub-scanning section. The light beam passing through the grating lens 10 becomes a parallel light beam in the main scanning section, and is set to form a substantially linear image on the surface of the reflecting mirror 4a in the sub-scanning section.

The rotating polygon mirror 4 is rotating at a constant speed in the direction of an arrow 4Q, and the light beam incident on the point P of the reflecting surface 4a of the rotating polygon mirror 4 is reflected and deflected and scanned in the main scanning cross section. The light enters the image optical system 5.

The imaging optical system 5 is composed of two lenses: a negative lens 5a made of a spherical system and a toric lens 5b having positive refractive power in both the main scanning section and the sub-scanning section. The light flux that has passed through the imaging optical system 5 forms an image on the surface of the photosensitive drum 8, which is the surface to be scanned, and optically scans the surface with a substantially uniform linear motion.

In FIG. 2, P indicates the reflection position of the reflection surface 4a of the rotating polygon mirror 5, and the light beam in the sub-scanning section is condensed approximately at this reflection position P via the grating lens 10, as described above. ing.

Here, since the reflection position P and the photosensitive drum 8 are set in an optically approximately conjugate relationship, for example, the reflection surface 4
Even if a is not parallel to the rotation axis 4P in the sub-scanning section and is tilted (that is, even if the surface is tilted), the light beam forms an image on the same scanning line on the photosensitive drum 8. In this way, a so-called system for correcting the surface inclination of the reflecting surface of the rotating polygon mirror 4 is constructed.

Next, the grating lens 10 of this embodiment
The configuration of is explained below. The grating lens 10 in FIG. 3 is a schematic diagram when viewed from the light source section 1 side in FIG. 1.

FIGS. 4 and 5 each show the grating lens 1.
1 is a main part schematic diagram of a main scanning section and a sub-scanning section of light source 1 and light source 1. FIG.

In FIG. 3, for convenience, the main scanning cross-sectional direction is shown as the y-axis, and the sub-scanning cross-sectional direction is shown as the z-axis. As shown in FIG. 3, the grating lens 10 has a structure in which a lens pattern having a rectangular or blazed surface shape is formed on the surface of a substrate 12.

Grating lens 1 in this embodiment
0, the annular boundary radius is different between the main scanning section and the sub-scanning section. That is, it has an elliptical shape with different focal lengths in the main scanning section and the sub-scanning section.

In the main scanning cross section (y cross section) of FIG. 4, the light beam emitted from the light source 1 is turned into a parallel light beam by the grating lens 10 and is incident on the reflecting surface 4a of the rotating polygon mirror 4.

On the other hand, in the sub-scanning section (z section) of FIG. 5, the light beam emitted from the light source 1 passes through the grating lens 1
0 and forms a linear image at a point P on the reflective surface 4a of the rotating polygon mirror 4.

As described above, in this embodiment, the grating lens 10 is arranged at a focal length (
The light beam emitted from the light source 1 is formed into a linear image on the reflecting surface 4a of the rotating polygon mirror 4. As a result, the surface inclination of the reflecting surface of the rotating polygon mirror 4 is corrected in the same manner as described above.

Next, the grating lens 10 of this embodiment
A specific numerical example of the configuration will be shown below.

As shown in FIG. 6, grating lens 1
The m-th annular boundary radius rm from the optical axis x of 0 can be approximated by assuming that the focal length is f and the wavelength of the light beam from the light source 1 is λ. Here, the focal length fy of the main scanning section is fy = 14
．． 86 mm, the focal length fz of the sub-scanning section is fz = 1
If the diameter is 1.86 mm and the wavelength λ is λ = 780 nm, it becomes an ellipse with an eccentricity of 0.45, and the radius ry of the main scanning cross section is r1y = 152.26μ, r2y = 215.33μ.
It becomes...

Furthermore, the radius rz of the sub-scanning section is r1z=1
36.02μ, r2z=192.36μ.

Here, if the F number Fy of the main scanning section of the grating lens 10 is Fy = 4.5, and the F number Fz of the sub scanning section is Fz = 4, m = 11.
8, and the annular boundary radius pitch at the periphery is 7.05μ in the main scanning section and 6.31μ in the sub-scanning section.

In Example 1, the grating lens 10 was constructed by forming an elliptical grating lens on one side of the substrate 12 as shown in FIGS. 3 to 5, but the grating lens according to the present invention has such a construction. It is not limited to.

For example, as shown in FIGS. 7 to 9, one surface of the substrate 12 is provided with a circular grating lens 8 as shown in FIG.
1, the other surface may be a cylinder grating lens 91 shown in FIG. 9, and both surfaces may be formed of grating lenses as shown in FIG.

According to this, as in the first embodiment, the light beam from the light source 1 can be formed into a linear image on the reflecting surface of the rotating polygon mirror. Further, as shown in FIGS. 10 to 12, cylindrical grating lenses 111 and 121 having different focal lengths may be formed orthogonally on both sides of the substrate 12 to obtain the same effect as described above.

[0035]

According to the present invention, by disposing a grating lens having a rectangular or blazed surface shape with different focal lengths in the main scanning section and the sub-scanning section as described above between the light source and the deflector, With a simple configuration, it is possible to effectively correct the inclination of the reflecting surface of a rotating polygon mirror, thereby achieving an optical scanning device that enables highly accurate optical scanning.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of main parts of a main scanning cross section of Embodiment 1 of the present invention.

FIG. 2 is a schematic diagram of main parts of a sub-scanning cross section of Embodiment 1 of the present invention.

FIG. 3 is a front view of the grating lens in FIG. 1.

4 is a main scanning cross-sectional view of the grating lens in FIG. 1. FIG.

FIG. 5 is a sub-scanning cross-sectional view of the grating lens in FIG. 1.

6 is an enlarged explanatory view of a portion of the grating lens in FIG. 1. FIG.

FIG. 7 is a cross-sectional view of Example 2 of the grating lens according to the present invention.

FIG. 8 is a schematic diagram of one side of Example 2 of the grating lens according to the present invention.

FIG. 9 is a schematic diagram of the other surface of Example 2 of the grating lens according to the present invention.

FIG. 10 is a cross-sectional view of Example 3 of the grating lens according to the present invention.

FIG. 11 is a schematic view of one side of Example 3 of the grating lens according to the present invention.

FIG. 12 is a schematic diagram of the other surface of Example 3 of the grating lens according to the present invention.

FIG. 13 is a schematic diagram of the main parts of a conventional optical scanning device.

[Explanation of symbols]

1 Light source part 2
4 Collimator lens 25 Cylindrical lens 4 Rotating polygon mirror (
Deflector) 5 Imaging optical system 5a
Spherical concave lens 5b Toric lens
8 Scanning surface 10 Grating lens

Claims (3)

[Claims] Claim 1: After a light beam emitted from a light source is deflected by a deflector, the light beam is guided onto a surface to be scanned through an imaging optical system to perform optical scanning in the main scanning direction, and at the same time, the surface to be scanned is scanned in a sub-scanning direction. In an optical scanning device that scans light two-dimensionally by moving or rotating in a direction, the surface shape between the light source and the deflector has a rectangular or An optical scanning device characterized in that a blazed grating lens is disposed, and a light beam from the light source is imaged on a reflective surface of the deflector so as to form a linear image within a main scanning cross section. 2. The optical scanning device according to claim 1, wherein the effective surface of the grating lens has an elliptical shape. 3. The optical scanning device according to claim 1, wherein the grating lens is a cylindrical grating lens with both surfaces perpendicular to each other.