JPH0772405A - Optical scanner - Google Patents

Abstract

PURPOSE:To provide the optical scanner capable of relieving the influence of the light intensity of the side lobe of the vessel beam and executing optical scanning with high accuracy by using a diaphragm member for limiting the beam diameter of the vessel beam. CONSTITUTION:The vessel beam emitted from a light source means 1 is made into the vessel beam having the intensity distribution approximately proportional to the square of a zero order vessel function of a first kind via a vessel beam forming means 3. The vessel beam is condensed by a condenser means 5 via the diaphragm member 4 for limiting the beam diameter and is made incident on a deflecting means 6. After the vessel beam is reflected and deflected by the deflecting means 6, the vessel beam is guided onto a surface 8 to be scanned via an imaging optical system to optically scan the surface 8 to be scanned and the surface is optically scanned.

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, a Bessel beam having a minute spot and a deep focal depth is used as a laser beam to optically scan a surface to be scanned 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 has generally been treated as a Gaussian beam and has been restricted by its propagation characteristics. However, in recent years the depth of focus has been very deep,
A Bessel beam (or non-diffractive beam) is attracting attention as a laser beam having a small spot diameter.

The characteristic of this Bessel beam is that the light intensity distribution in a cross section perpendicular to the propagation direction is proportional to the square of the 0th-order Bessel function of the first kind.

FIG. 7 shows a Japanese Patent Application No. 4-1376 filed by the present applicant.
It is a principal part schematic diagram of the optical system of the optical scanning device using the Bessel beam proposed by No. 45.

In the figure, a laser beam L71 which is light-modulated based on image information from a light source means 71 and emitted, is a plane A crossing its optical path by a Bessel beam generating means 72.
_It becomes a Bessel beam L72 having a center position of ₀ , is condensed on the plane A ₀ , and then diverges.

The diverging Bessel beam L72 is converged by a condenser lens 73, is incident on a reflecting surface (deflecting surface) of a rotary polygon mirror 74 as an optical deflector, and is then reflected and deflected.
An image is formed on the surface (scanned surface) of the rotating drum (photosensitive drum) D ₀ by the imaging lens 75 having the −θ characteristic, and an electrostatic latent image is formed on the photosensitive member (not shown) on the surface. There is.

In the figure, since the plane A ₀ and the surface of the rotary drum D ₀ are set in an optically substantially conjugate relationship, the Bessel beam is formed near the surface of the rotary drum D ₀ . Since this Bessel beam has a very deep depth of focus as described above, for example, even if the optical system has a field curvature,
Alternatively, the beam spot diameter does not change even if the position of the rotary drum D ₀ is slightly displaced in the optical axis direction, and thus a high-resolution optical scanning device is obtained.

[0008]

The cross-sectional intensity distribution of the Bessel beam formed near the surface (scanned surface) of the rotary drum D ₀ in the conventional optical scanning device shown in FIG. It is proportional to the square of the next Bessel function.

The light intensity of the portion other than the central spot of the Bessel beam, that is, the side lobe (diffraction ring) is relatively large. For this reason, when this Bessel beam is applied to an optical scanning device (recording device) as a recording beam, for example, the side lobe intensity is too high, and as a result, the image quality of a recorded image may deteriorate. there were.

According to the present invention, the laser beam is a Bessel beam and the beam diameter of the Bessel beam is limited by a diaphragm member, whereby the influence of the light intensity of the side lobes of the Bessel beam is alleviated and the image quality of a recorded image is improved. An object of the present invention is to provide an optical scanning device.

[0011]

The optical scanning device of the present invention comprises:
The laser beam emitted from the light source means is converted into a Bessel beam having an intensity distribution substantially proportional to the square of the 0th-order Bessel function of the first kind through the Bessel beam generating means, and the Bessel beam restricts the beam diameter. After being converged by the condensing means via the optical system, incident on the deflecting means, reflected and deflected by the deflecting means, the light is guided onto the surface to be scanned through the imaging optical system, and the surface to be scanned is optically scanned. It is characterized by doing so.

In particular, the diaphragm member is characterized in that it can be switched to different diaphragm diameters.

[0013]

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

In the figure, reference numeral 1 is a light source means, which is composed of, for example, a semiconductor laser. Reference numeral 2 is a collimator lens, which collimates a laser beam (light beam) emitted from the light source means 1 on the basis of image information after being modulated.

Reference numeral 3 denotes an axicon as Bessel beam generating means, which generates a Bessel beam B1 having an intensity distribution substantially proportional to the square of the 0th-order Bessel function of the first kind having a beam spot with a deep focal depth.

A diaphragm member 4 limits the beam diameter of the Bessel beam. In this embodiment, by limiting the beam diameter of the Bessel beam as will be described later, the side lobes of the Bessel beam are shielded. The influence of the light intensity of the side lobes is reduced. In this embodiment, the diaphragm member 4 can be switched to a diaphragm member having a different diaphragm diameter according to the optical characteristics of the optical system or the like.

Denoted at 5 is a condenser lens (condensing means) which is composed of a single lens and condenses the Bessel beam so that it is incident on the deflecting surface (reflecting surface) of the optical deflector 6 as the deflecting means. ing. The optical deflector 6 is composed of a rotary polygon mirror having four deflecting surfaces 6a to 6d, and is rotated at a constant speed in the direction of arrow C about a rotation axis O by a driving means (not shown) such as a motor. .

Reference numeral 7 denotes an f-θ lens (imaging optical system) as an image forming means, which is composed of two spherical lenses 7a and 7b, and the laser beam reflected and deflected by the optical deflector 6 is scanned. An image is formed near the surface 8. Scanned surface 8
Corresponds to the surface of the photoconductor drum in, for example, a copying machine or LBP.

The optical scanning device of this embodiment is of a so-called pre-objective scanning type in which the beam is deflected in front of the imaging lens 7, that is, on the side of the light source means 1.

In this embodiment, the laser beam emitted from the semiconductor laser 1 is converted into a plane wave by the collimator lens 2 and made incident on the axicon 3. Then, the laser beams emitted from the axicon 3 interfere with each other, and a laser beam of the first type 0 is generated in the vicinity of a plane (position) A crossing the optical path.
A Bessel beam B1 having an intensity distribution substantially proportional to the square of the next Bessel function is formed. At this time, the beam diameter of the Bessel beam B1 is limited by the diaphragm member 4 arranged on the plane A, and the Bessel beam B2 centered on the plane A is set.
Is formed. And the Bessel beam B2 is a plane A
Although it diverges as it goes away, it is converged by the condenser lens 5 and condensed in a substantially ring shape in the vicinity of the deflection surface (reflection surface) 6b of the rotary polygon mirror 6.

In the present embodiment, the plane A corresponds to the front focal position of the condenser lens 5, and the deflection surfaces 6a to 6d of the rotary polygon mirror 6 correspond to the rear focal position of the condenser lens 5. Is set.

The laser beam reflected and deflected by the rotary polygon mirror 6 is converged by the f-θ lens 7,
A Bessel beam B2 'is formed on the surface 8 to be scanned.

In this embodiment, the plane A and the surface 8 to be scanned are set in an optically substantially conjugate relationship.

Then, the rotary polygon mirror 6 is rotated in the direction of arrow C in the drawing to optically scan the surface to be scanned 8 in the main scanning direction with a minute spot diameter as shown by arrow D in the drawing, and the surface to be scanned 8 is scanned. The image is two-dimensionally optically scanned (recorded) by moving or rotating in the sub-scanning direction.

As described above, in this embodiment, the laser beam formed in the vicinity of the surface to be scanned is a non-diffractive beam, and the non-diffractive beam has a very deep focal depth as described above. Has a large curvature of field,
Alternatively, even if there is an error or variation in the arrangement position of the optical component, the image does not deteriorate, and a high-quality image can always be obtained.

Next, the effect of this embodiment when the diaphragm member 4 is used will be described with reference to FIGS.

FIG. 3A is an explanatory view showing a state of forming the Bessel beam when a diaphragm member is not used in the Bessel beam forming portion, and FIG. 3B is formed on the surface to be scanned at this time. FIG. 4A is an explanatory view showing the intensity pattern of the Bessel beam, and FIG. 4A is an explanatory view showing the state of the Bessel beam formation when the diaphragm member 4 is used in the Bessel beam forming portion as in the present embodiment. B) is an explanatory view showing the intensity pattern of the Bessel beam formed on the surface to be scanned at this time. In FIGS. 3 and 4, the same elements as those shown in FIG. 1 are designated by the same reference numerals.

As can be seen by comparing the intensity patterns of the Bessel beam as shown in FIGS. 3B and 4B, when the beam diameter of the Bessel beam is limited by the diaphragm member 4, the surface to be scanned is proportional to the limit. It can be seen that the beam diameter of the Bessel beam formed above (the diameter of the entire beam including the ring) is small. Each ring of the Bessel beam contains almost the same amount of light (light intensity), and if the diameter of the entire beam is reduced as shown in FIG. The impact can be mitigated. As a result, an image with less fog and higher contrast is obtained.

However, making the beam diameter of the entire Bessel beam smaller corresponds to the fact that the depth of focus becomes shallower in proportion thereto, so it is not preferable to make the aperture diameter of the aperture member too small.

Therefore, in this embodiment, a plurality of diaphragm members having suitable diaphragm diameters suitable for the purpose are prepared in consideration of the optical characteristics of the optical system and the photosensitive drum, and the appropriate diaphragm diameter is selected from them. The diaphragm member is selected according to its optical characteristics and mounted on the apparatus.

As a method of arbitrarily changing the aperture diameter, other than the above-mentioned method, for example, as shown in FIGS. 5A and 5B, one rod-shaped or arc-shaped aperture member 4 having a different diameter is used. A plurality of aperture holes may be provided, and an appropriate aperture hole may be selected and switched according to the optical characteristics of the optical system.

Next, a further effect of the diaphragm member 4 that occurs when the axicon 3 is used as a means for generating a Bessel beam will be described with reference to FIG. In FIG.
The same elements as those shown in are given the same reference numerals.

In the figure, 9 is the apex of the conical surface of the axicon 3,
Reference numeral 10 denotes scattered light emitted from the apex 9 of the conical surface.

In the figure, most of the plane wave incident on the axicon 3 becomes a conical wave when exiting the axicon 3 to form a Bessel beam. The light is scattered by and is emitted as scattered light 10.

At this time, if the diaphragm member 4 is not provided, the scattered light 10 reaches the surface to be scanned and becomes a flare to reduce the contrast, or interferes with the Bessel beam on the surface to be scanned to cause a central error. It was also a cause of lowering the intensity of the spot.

On the other hand, when the diaphragm member 4 is provided in the vicinity of the plane A as in this embodiment, a considerable part of the scattered light 10 can be blocked by the diaphragm member 4, whereby the flare and the central spot described above can be obtained. It is possible to prevent a decrease in strength.

In the present embodiment, the case where the present invention is applied to a rotationally symmetric optical system is shown. However, the present invention is also applicable to a rotationally asymmetric optical system having a surface tilt correction function as in the above-mentioned embodiments. Can be applied.

Further, although the present embodiment is applied to the pre-objective scanning type optical scanning device using the f-θ lens, it may be applied to the post-objective scanning type optical scanning device not using the f-θ lens. It is possible to obtain the same effect as that of the above-described embodiment.

Further, the condensing means in the present embodiment does not necessarily have to be constituted by a single lens, and may be a lens system constituted by a plurality of lenses, for example.

Further, in this embodiment, an axicon is used as a means for generating a Bessel beam. However, instead of the axicon, for example, an optical system using a thin ring aperture and a lens, or an optical performance equivalent to that of the axicon is used. You may use the diffraction grating etc. which have.

Further, although the rotary polygon mirror is used as the deflector in this embodiment, the present invention can be applied in the same manner as the above-mentioned embodiments even if it is a single-faced mirror such as a galvano mirror.

[0042]

According to the present invention, when the Bessel beam is used to optically scan the surface to be scanned as described above, a diaphragm member is provided in the vicinity of the central portion where the Bessel beam is formed. The effect of the light intensity of the lobe can be mitigated, and the surface to be scanned can be optically scanned with a minute spot having a higher contrast, thereby achieving an optical scanning device capable of improving the performance of the device. be able to.

[Brief description of drawings]

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

FIG. 2 is a sub-scan sectional view of the first embodiment of the present invention.

FIG. 3 is an explanatory diagram for explaining the effect of the diaphragm according to the first embodiment of the present invention.

FIG. 4 is an explanatory diagram for explaining the effect of the diaphragm according to the first embodiment of the present invention.

FIG. 5 is an explanatory view of a diaphragm member having a plurality of diaphragm holes.

FIG. 6 is an explanatory diagram for explaining an effect when a diaphragm member is used in a system using an axicon.

FIG. 7 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 Aperture member 5 Condensing means 6 Deflection means 7 Imaging optical system 8 Scanned surface

Claims (2)

[Claims] 1. A laser beam emitted from a light source means is made into a Bessel beam having an intensity distribution substantially proportional to the square of the 0th-order Bessel function of the first kind through the Bessel beam generating means, and the Bessel beam has a beam diameter. The light is condensed by the condensing means through the diaphragm member for restricting the incident light, is made incident on the deflecting means, is reflected and deflected by the deflecting means, and then is guided to the surface to be scanned through the imaging optical system to be scanned. An optical scanning device characterized in that the surface is optically scanned. 2. The optical scanning device according to claim 1, wherein the diaphragm members can be switched to different diaphragm diameters.