JP3198751B2 - Optical scanning device - Google Patents

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 more particularly, to optically scan a surface to be scanned by using a Bessel beam having a small spot and a large depth of focus as a laser beam to record an image with high accuracy. The present invention relates to an optical scanning device suitable for, for example, a laser beam printer (LBP).

[0002]

2. Description of the Related Art Conventionally, a laser beam is generally treated as a Gaussian beam, and is subject to restrictions based on its propagation characteristics. However, in recent years the depth of focus is very deep,
A Bessel beam (or a non-diffractive beam) has attracted attention as a laser beam having a small spot diameter.

A characteristic of this Bessel beam is that the light intensity distribution in a section perpendicular to the propagation direction is proportional to the square of the first-order zero-order Bessel function.

FIG. 5 shows that the present applicant has previously filed Japanese Patent Application No. 4-1376.
It is a principal part schematic diagram of the optical system of the optical scanning device using the Bessel beam proposed in No. 45.

In FIG. 1, a laser beam L 51 emitted from a light source means 51 after being light-modulated based on image information is converted by a Bessel beam generating means 52 into a plane A crossing the optical path.
_The beam becomes a Bessel beam L52 centered at ₀ , and diverges after being focused on the plane A0.

The divergent Bessel beam L52 is converged by a condenser lens 53, is incident on a reflecting surface (deflecting surface) of a rotary polygon mirror 54 as an optical deflector, is reflected and deflected, and f
The imaging lens 55 having a -θ properties imaged on a rotating drum (photosensitive drum) D ₀ of the surface (surface to be scanned), to form an electrostatic latent image on the photosensitive body surface (not shown) I have.

In FIG. 1, since the plane A ₀ and the surface of the rotary drum D ₀ are set to have an optically conjugate relationship, the Bessel beam is formed near the surface of the rotary drum D ₀ . Since the Bessel beam has a very deep depth of focus as described above, for example, even if the optical system has a curvature of field,
Or the position of the rotary drum D ₀ is the beam spot diameter is not changed even slightly shifted in the optical axis direction, thereby had received optical scanning apparatus with a high resolution.

[0008]

[SUMMARY OF THE INVENTION Conventional cross-sectional intensity distribution of Bessel beams formed in the vicinity of the surface (surface to be scanned) of the rotary drum D ₀ in the optical scanning device of the first kind as described above 0
It is proportional to the square of the following Bessel function.

The intensity of the side lobe (diffraction ring) of this Bessel beam is 16% when the intensity of the peak of the center spot is 100%.
%, The intensity of the second side lobe is 9%, and the intensity of the third side lobe is 6%, and the light intensity of the side lobe is relatively large.

For this reason, when this Bessel beam is applied, for example, as a recording beam to an optical scanning device (recording device), the intensity of the side lobe is too large, and as a result, the image quality of the recorded image may be reduced. There was a problem.

According to the present invention, a laser beam is used as a Bessel beam, and a slit member having a predetermined shape is arranged near a surface to be scanned. It is an object of the present invention to provide an optical scanning device that improves the image quality of a recorded image by effectively shielding light.

[0012]

An optical scanning device according to the present invention comprises:
The laser beam emitted from the light source means is converted into a Bessel beam in which side lobes are formed concentrically via a Bessel beam generating means, and the Bessel beam is deflected by a deflecting means. An optical scanning device that guides light upward and optically scans the surface to be scanned, wherein the longitudinal direction is the main scanning direction at a small distance such that spots due to diffraction do not occur near the surface to be scanned. Arrange a slit member substantially matched to, mainly through the center spot of the vessel beam by the slit member,
Most of the side lobes are shielded from light, and a condenser lens is provided between the Bessel beam generating means and the deflecting means, and the Bessel beam formed on the front side of the deflecting means by the Bessel beam generating means Is formed on the surface to be scanned through the condenser lens and the imaging optical system, and a position where a Bessel beam is formed in front of the deflecting unit is set as a front focal position of the condenser lens. ,
It is characterized in that the deflecting means is arranged at a rear focal position of a condenser lens.

[0013]

1 and 2 are a main scanning sectional view and a sub-scanning sectional view of a first embodiment of the present invention.

In FIG. 1, reference numeral 1 denotes light source means, which is made of, for example, a semiconductor laser. Reference numeral 2 denotes a collimator lens, which converts a laser beam (light beam) emitted from the light source unit 1 based on image information into a parallel light beam.

Reference numeral 3 denotes an axicon as a Bessel beam generating means. The laser beam is perpendicularly incident on the axicon 3. The axicon 3 generates a Bessel beam B1 having an intensity distribution substantially proportional to the square of the zeroth-order Bessel function of the first kind having a beam spot with a large depth of focus, and side lobes of the Bessel beam are formed concentrically. ing.

A condensing lens (condensing means) 4 condenses the Bessel beam and makes it incident on a deflecting surface (reflection surface) of an optical deflector 5 as a deflecting means. The optical deflector 5 is composed of a rotating polygonal mirror having four deflecting surfaces 5a to 5d, and is rotated at a constant speed in the direction of arrow C about the rotation axis O by a driving means such as a motor (not shown). .

Reference numeral 6 denotes an f-.theta. Lens (imaging optical system) as imaging means, which comprises two spherical lenses 6a and 6b, and a laser beam (Bessel beam) reflected and deflected by the optical deflector 5. ) Is formed near the surface 8 to be scanned. The scanned surface 8 corresponds to a photosensitive drum surface in a copying machine, an LBP, or the like, for example.

Reference numeral 7 denotes a slit member which is arranged in the vicinity of the surface 8 to be scanned with a small distance d such that a spot is not blurred due to diffraction. The slit member 7 is provided such that the longitudinal direction of the opening substantially coincides with the main scanning direction.

In this embodiment, as will be described later, the opening 7a of the slit member 7 allows the center spot of the Bessel beam to pass mainly, and the light shielding portion 7b shields most of the side lobe portion from light.

FIG. 3 shows the slit member 7 shown in FIGS.
3 is an enlarged explanatory view when a part of is viewed from the f-θ lens side, and shows the positional relationship between the opening 7a of the slit member 7 and the Bessel beam.

As shown in the figure, the opening 7a of the slit member 7 is formed to extend long in the main scanning direction, and is formed without affecting optical scanning. Further, in the sub-scanning direction, the beam is formed so as to mainly pass the beam at the center and to shield most of the other portions from light by the light shielding portion 7b.

In this embodiment, a part of the side lobe reaches the surface to be scanned, but the light intensity of the side lobe at this time is much weaker than the intensity of the peak of the center spot. The scan is hardly affected.

In this embodiment, as shown in FIG. 1, a laser beam emitted from a semiconductor laser 1 is converted into a plane wave by a collimator lens 2 and vertically incident on an axicon 3. The laser beams emitted from the axicon 3 interfere with each other to form a Bessel beam B1 having an intensity distribution substantially proportional to the square of the first-order zero-order Bessel function near a plane (position) A crossing the optical path. . Although the Bessel beam B1 diverges as it moves away from the plane A, it is converged by the condenser lens 4 and converges in a substantially ring shape near the deflection surface (reflection surface) 5b of the rotary polygon mirror 5.

In this embodiment, the plane A corresponds to the front focal position of the condenser lens 4, and the deflecting surfaces 5a to 5d of the rotary polygon mirror 5 correspond to the rear focal position of the condenser lens 4. Is set as follows.

The laser beam reflected and deflected by the rotary polygon mirror 5 is converged by the f-θ lens 6,
A Bessel beam B2 is formed near the slit member 7. Note that the plane A and the position of the slit member 7 are set to have an optically conjugate relationship.

As shown in FIG. 3, most of the side lobes S _{1 to} S _N are formed by the slit member 7.
The light shielding by the shielding portion 7b, only a part of the central spot S ₀ and the side lobe S ₁ to S _N reaches the scanned surface through an opening 7a of the slit member 7. As a result, an optical scanning device with extremely high resolution is obtained. At this time, part of the side lobes reaches the surface to be scanned. However, as described above, the light intensity of the side lobes is very weak, so that the image quality of the recorded image is hardly reduced due to the influence.

FIG. 4 shows the slit member 7 shown in FIGS.
FIG. 5 is a sub-scan sectional view showing a state of a beam spot formed in the vicinity.

In the figure, the side lobe S _{1 of} the spots S ₀ , S _{1 to} S _N forming the Bessel beam B2 is shown.
ＳS _N is largely shielded by the light shielding portion 7b of the slit member 7, and the center spot S ₀ mainly passes through the opening 7a of the slit member 7 and reaches the surface 8 to be scanned. .

In the figure, the distance d between the slit member 7 and the surface 8 to be scanned is set to a small value such that the center spot S ₀ is not blurred by diffraction.

In this embodiment, by rotating the rotary polygon mirror 5, the surface 8 to be scanned is optically scanned with a minute spot in the main scanning direction, and the surface 8 to be scanned is moved or rotated in the sub scanning direction. By moving the image, the image is optically scanned (recorded) two-dimensionally.

As described above, in this embodiment, the laser beam formed near the surface to be scanned is a non-diffracting beam (Bessel beam), and the non-diffracting beam has a very large depth of focus as described above. For example, even if the field curvature of the optical system is large, or if there is an error or fluctuation in the arrangement position of the optical component, the image does not deteriorate, and a high-quality image can always be obtained.

In this embodiment, the case where the present invention is applied to a rotationally symmetric optical system has been described. However, the present invention is also applicable to a rotationally asymmetric optical system having a surface tilt correcting function, for example. Can be applied to

In this embodiment, an axicon is used to generate a Bessel beam as a means for generating a Bessel beam. However, the present invention is not limited to this forming method, and has, for example, a pupil filter and an optical action equivalent to that of the axicon. A Bessel beam may be formed using a diffraction grating or the like.

Further, in this embodiment, the distance d between the slit member and the surface to be scanned is set to a small distance which does not cause blurring of the spot due to diffraction. And may be configured integrally.

For example, when the surface to be scanned is a photosensitive drum, the photosensitive drum unit and the slit member may be integrally formed. This can prevent spot blurring due to diffraction.

Further, in the present embodiment, the width of the slit member in the sub-scanning direction is formed to be narrow such that only the center spot S ₀ passes. However, this width is adjusted to the sensitivity characteristic of the surface to be scanned, and the center spot S _{0 is formed.} And a width as wide as it passes through and several diffraction rings. In this case, the distance d between the slit member and the surface to be scanned can be set larger.

In this embodiment, the slit member is used as a means for shielding the side lobe portion. However, the present invention can be applied to any optical member capable of effectively shielding the side lobe portion. The same can be applied.

[0038]

According to the present invention, when optical scanning is performed on a surface to be scanned by using a Bessel beam as described above, most of the side lobe portions of the Bessel beam are formed in a predetermined shape provided near the surface to be scanned. By effectively shielding light with a slit member having a portion, it is possible to optically scan the surface to be scanned with only a small spot having a large depth of focus and a large light intensity, thereby improving the performance of the apparatus. Optical scanning device that can be achieved.

[Brief description of the drawings]

FIG. 1 is a main scanning sectional view of a first embodiment of the present invention.

FIG. 2 is a cross-sectional view in the sub-scanning direction according to the first embodiment of the present invention.

FIG. 3 is an explanatory diagram showing a positional relationship between a slit member and a Bessel beam according to the first embodiment of the present invention.

FIG. 4 is an explanatory diagram showing a state of a spot near a slit member according to the first embodiment of the present invention.

FIG. 5 is a schematic view of a main part of an optical system of a conventional optical scanning device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Light source means 2 Collimator lens 3 Bessel beam generation means (axicon) 4 Condensing means 5 Deflection means 6 Imaging optical system 7 Slit member 8 Scanning surface

Continuation of front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G02B 26/10

Claims (1)

(57) [Claims] 1. A laser beam emitted from a light source means is converted into a vessel beam in which side lobes are formed concentrically via a Bessel beam generating means, and after the Bessel beam is deflected by a deflecting means, an image forming optical system is formed. An optical scanning device that guides light onto a surface to be scanned through an optical scanning device and optically scans the surface to be scanned, wherein the optical scanning device is disposed at a small distance such that a spot blur due to diffraction does not occur near the surface to be scanned. A slit member whose direction is substantially coincident with the main scanning direction is arranged, the slit member allows the center spot of the Bessel beam to pass mainly, and most of the side lobe portion is shielded from light. A condenser lens is provided between the Bessel beam generating means and the deflecting means, and the Bessel beam formed by the Bessel beam generating means on the front side of the deflecting means is provided to the condenser lens and And forming a position where a Bessel beam is formed on the front side of the deflecting means at a front focal position of a condenser lens, wherein the deflecting means An optical scanning device, wherein is disposed at a rear focal position of a condenser lens.