JP2001066532A - Optical scanner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain excellent image formation performance on a surface to be scanned by inclining a cylindrical lens by a specified amount while setting the optical axis of an incident optical system as a rotary shaft and making a line image formed on a deflection surface parallel with a main scanning direction. SOLUTION: A collimator lens 2 changes divergent luminous flux emitted from a semiconductor laser 1 to nearly parallel beams, and a diaphragm 3 has an aperture part consisting of a rectangle which is longer in the main scanning direction than in a subscanning direction and restricts the passing luminous flux. The cylindrical lens 4 has specified refractive power only in the subscanning direction and forms the luminous flux passing through the diaphragm 3 into an image as nearly the line image on the deflection surface 6a of a light deflector 6 on a main scanning cross section. By inclining the lens 4 by the specified amount while setting the optical axis L of the incident optical system 11 as the rotary shaft, the line image formed on the deflection surface 6a of the light deflector 6 is made parallel with the main scanning direction. A reflecting mirror 9 reflects the luminous flux transmitted through the lens 4 to the light deflector 6 side.

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 using an oblique incidence optical system, and more particularly, to a cylindrical lens or an optical scanning device in which a line image formed on a deflection surface of an optical deflector is parallel to a main scanning direction. And / or by inclining the stop by a predetermined amount with the optical axis of the incident optical system as the rotation axis, it is possible to obtain good imaging performance on the surface to be scanned. For example, an image forming apparatus such as a laser beam printer or a digital copier The present invention relates to a preferred optical scanning device.

[0002]

2. Description of the Related Art Conventionally, in an optical scanning device used for an image forming apparatus such as a laser beam printer or a digital copying machine, a light beam modulated and emitted from a light source means in accordance with an image signal is output to, for example, a rotating polygon mirror (polygon mirror). ) Is periodically deflected by an optical deflector, and focused on a photosensitive recording medium (photosensitive drum) surface in the form of a spot by an imaging optical system having fθ characteristics, and the surface is optically scanned to record an image. It is carried out.

FIG. 12 is a schematic view of a main part of a conventional optical scanning device.

In FIG. 1, a substantially parallel light beam emitted from a laser unit 121 enters a cylindrical lens 122 having a predetermined refractive power only in the sub-scanning direction. Of the substantially parallel light beams incident on the cylindrical lens 122, they are emitted as they are in a substantially parallel light state in the main scanning section. In the sub-scan section, the light is converged and formed as a substantially linear image on the deflecting surface 123a of the optical deflector 123 composed of a rotating polygon mirror. Then, the deflection surface 123 of the optical deflector 123
The light beam deflected and reflected at a is imaged on a photosensitive drum surface 126 as a surface to be scanned by an imaging optical system (fθ lens system) 127 having fθ characteristics, and the optical deflector 123 is turned to an arrow A.
The photosensitive drum surface 126.
Image information is recorded by optically scanning the upper part in the direction of arrow B (main scanning direction).

In recent years, along with downsizing of printers and the like,
Optical scanning devices are also required to be small and have high performance. In order to solve this problem, various methods have been proposed for reducing the size of the entire optical scanning device by, for example, bending the optical path by a return mirror. Accordingly, it is necessary to arrange the incident optical system at an angle to the plane perpendicular to the rotation axis of the optical deflector (hereinafter also referred to as “oblique incident optical system”), but avoid the scanning lens system and the optical deflector. In order for the light beam to enter the optical deflector, the incident light beam must be greatly inclined.

However, when the incident light beam is greatly inclined, the change in the inclination of the light beam caused by the deflecting reflection of the optical deflector becomes large depending on the image height, which causes problems such as deterioration of the spot and bending of the scanning line.

Therefore, in order to solve this problem, a folding mirror is used for the incident optical system, and the incident light beam is arranged so as not to avoid the optical deflector and the image forming optical system, and the oblique incident angle is reduced. Is required.

In the configuration of the oblique incidence optical system, if the return mirror is tilted in the sub-scanning section with respect to the deflection surface of the optical deflector, the light flux incident on the imaging optical system is tilted by the return mirror, and the reflected light is obstructed. A problem is that the spot on the scanning surface is adversely affected.

Therefore, conventionally, for example, Japanese Patent Publication No. 2659
As disclosed in Japanese Patent No. 137, it has been proposed to arrange the slits of the incident optical system at the same angle as the incident angle of the light beam on the optical deflector.

[0010]

However, according to the above-mentioned method, it is effective when the angle of incidence of the light beam on the return mirror is 45 degrees, but when the angle is other than that, the light is incident on the deflection surface of the optical deflector. There is a problem that it is difficult to correct the tilt of the beam. Further, since the incident angle of 45 degrees bends the optical path at a right angle, the light source is disposed farthest from the light beam incident on the optical deflector, which is very disadvantageous in terms of space. In practice, the turning angle is 45 due to space constraints.
It is necessary to set the angle to a value other than the degree, and a method for correcting the inclination of the light beam at this angle is required.

Further, according to the above construction, the line image formed in a line in the main scanning direction on the deflection surface of the optical deflector is tilted by the cylindrical lens, and in this state, the linear image is deflected by the optical deflector to the imaging optical system. When the incident light flux is incident, there is a problem that the wavefront aberration of the spot on the surface to be scanned is deteriorated, and the shape and size of the spot are deteriorated.

According to the present invention, in a light scanning apparatus using an oblique incidence optical system, a cylindrical lens or / and a stop are formed on a deflection surface of an optical deflector by inclining a predetermined amount about the optical axis of the incident optical system as a rotation axis. It is an object of the present invention to provide a compact optical scanning device capable of making a line image to be parallel to a main scanning direction, thereby obtaining good imaging performance on a surface to be scanned.

[0013]

According to a first aspect of the present invention, there is provided an optical scanning device, comprising: an incident optical system for causing a light beam emitted from a light source means to enter a deflection surface of an optical deflector obliquely in a sub-scan section; An image forming optical system for forming an image of the light beam deflected by the light deflector on the surface to be scanned. The incident optical system converts the light beam emitted from the light source means into a substantially parallel light beam. A collimator lens, a stop for restricting a substantially parallel light beam from the collimator lens, and a light beam passing through the stop is condensed by a cylindrical lens having power in the sub-scanning direction, and the light beam from the cylindrical lens is light-deflected. A folding mirror for entering the deflection surface of the vessel,
Wherein the line image formed on the deflection surface of the optical deflector is parallel to the main scanning direction by tilting the cylindrical lens with the optical axis of the incident optical system as a rotation axis. It is characterized by.

According to a second aspect of the present invention, in the first aspect of the present invention, the angle between the sagittal line of the cylindrical lens and the sub-scanning direction is γ, and the light beam emitted from the light source means is folded in the main scanning section by the folding mirror. The angle is α, and the inclination angle of the reflection surface and the deflection surface of the return mirror in the sub-scanning section is θ. When α ≠ 45 °, the angle γ is γ = −tan ⁻¹ {(tan α) × ( tanθ)}.

According to a third aspect of the present invention, in the first aspect of the present invention, the angle between the sagittal line of the cylindrical lens and the sub-scanning direction is β, and the light beam emitted from the light source means is reflected by the folding mirror in the main scanning section. When the angle is α, and the inclination angle of the reflecting surface and the deflecting surface of the return mirror in the sub-scanning section is θ, when α ≠ 45 °, the angle β is −1.3 × tan ⁻¹ ((tan α) × (tan θ )} ≦ β ≦ -0.7 × tan ^-1 {(t
anα) × (tan θ)}.

According to a fourth aspect of the present invention, in the second aspect of the present invention, the stop is tilted about the optical axis of the incident optical system as a rotation axis, and the tilt angle is a short distance passing through the center of the aperture of the stop. When the angle between the direction and the sub-scanning direction is γ, γ = −tan ⁻¹ {(tan α) × (tan θ)}.

According to a fifth aspect of the present invention, in the third aspect of the present invention, the stop is inclined about the optical axis of the incident optical system as a rotation axis, and the inclination angle is a short distance passing through the center of the aperture of the stop. When the angle between the direction and the sub-scanning direction is β, −1.3 × tan ⁻¹ {(tanα) × (tanθ)} ≦ β ≦ −0.7 × tan ⁻¹ {(t
anα) × (tan θ)}.

According to a sixth aspect of the present invention, in the fourth or fifth aspect, the deflecting direction of the light beam emitted from the light source means is tilted by the same angle as the tilt angle of the stop.

According to a seventh aspect of the present invention, in the first aspect of the present invention, the light beam emitted from the light source is incident on the deflection surface from substantially the center of the deflection angle of the light deflector.

According to an eighth aspect of the present invention, in the first aspect of the present invention, the light beam emitted from the light source is incident on the deflecting surface of the optical deflector in a state wider than the width of the deflecting surface in the main scanning direction. And

According to a ninth aspect of the present invention, in the first aspect of the present invention, at least some of the optical elements constituting the imaging optical system also constitute the incident optical system.

According to a tenth aspect of the present invention, in the optical scanning device, an incident optical system for causing a light beam emitted from the light source means to be incident obliquely on the deflection surface of the optical deflector in the sub-scanning section, and deflecting by the optical deflector. An image forming optical system for forming an image of the light beam on the surface to be scanned, and an optical scanning device having the collimator lens for converting the light beam emitted from the light source means into a substantially parallel light beam. A stop for restricting a substantially parallel light beam from the collimator lens, and a light beam passing through the stop is condensed by a cylindrical lens having power in the sub-scanning direction, and the light beam from the cylindrical lens is incident on a deflection surface of an optical deflector. A folding mirror, and a line image formed on the deflection surface of the optical deflector becomes parallel to the main scanning direction by tilting the stop with the optical axis of the incident optical system as a rotation axis. It is characterized in that there was Unishi.

According to an eleventh aspect of the present invention, in the invention of the tenth aspect, an angle between a short direction passing through the center of the aperture of the aperture and the sub-scanning direction is γ, and a light beam emitted from the light source means is reflected by the folding mirror. Is the angle of the main scanning section turned back at α, and the inclination angle of the reflection surface and the deflecting surface of the turning mirror in the sub-scanning section is θ. When α ≠ 45 °, the angle γ
Is characterized by γ = −tan ⁻¹ {(tan α) × (tan θ)}.

According to a twelfth aspect of the present invention, in the tenth aspect, an angle between a short direction passing through the center of the aperture of the aperture and the sub-scanning direction is β, and a light beam emitted from the light source means is reflected by the folding mirror. Is the angle of the main scanning section at which the reflection mirror is turned back at α, and θ is the inclination angle of the reflection surface and the deflection surface of the reflection mirror at the sub-scanning section. When α ≠ 45 °, the angle β
Is -1.3 × tan ^-1 {(tanα) × (tanθ)} ≦ β ≦ -0.7 × tan ^-1 {(t
anα) × (tan θ)}.

According to a thirteenth aspect, in the eleventh or twelfth aspect, the deflecting direction of the light beam emitted from the light source means is inclined by the same angle as the inclination angle of the stop.

According to a fourteenth aspect of the present invention, in the tenth aspect of the present invention, the light beam emitted from the light source is incident on the deflection surface from substantially the center of the deflection angle of the light deflector.

According to a fifteenth aspect of the present invention, in the tenth aspect of the present invention, the light beam emitted from the light source is incident on the deflecting surface of the optical deflector in a state wider than the width of the deflecting surface in the main scanning direction. And

A sixteenth aspect of the present invention is characterized in that, in the tenth aspect of the present invention, at least a part of the optical elements constituting the imaging optical system also constitutes the incident optical system.

[0029]

[First Embodiment] FIG. 1 is a top view of a main part of a first embodiment of the present invention, showing a state where each element is projected in a main scanning section. FIG. 2 is a side view of a main part of FIG. 1 and shows a state where each element is projected in a sub-scanning cross section. FIG. 3 is a developed view when developed in the main scanning direction along the light beam according to the first embodiment of the present invention, and FIG. 4 is a developed view when developed in the sub-scanning direction in FIG.

In this specification, a coordinate system as shown in FIG. 1 is taken with the optical axis of the incident optical system as the z-axis. An x, y, z coordinate system having an x-axis in the main scanning direction when the optical path is developed is used. The main scanning section is defined as an xz section, and the sub scanning section is defined as a yz section.

In the figure, reference numeral 1 denotes a light source means, which is composed of, for example, a semiconductor laser. A collimator lens 2 converts a divergent light beam emitted from the semiconductor laser 1 into a substantially parallel light beam. Reference numeral 3 denotes a stop (slit member), which has a rectangular opening longer in the main scanning direction than in the sub-scanning direction, and restricts a passing light beam (light amount).

Reference numeral 4 denotes a cylindrical lens (cylinder lens) having a predetermined refracting power only in the sub-scanning direction. (Reflection surface) 6a is formed as a substantially linear image.

In the present embodiment, by tilting the cylindrical lens 4 by a predetermined amount with the optical axis L of the incident optical system 11 described later as a rotation axis, a line image (deflection surface 6a) formed on the deflection surface 6a of the optical deflector 6 is formed. (Light flux incident on the main scanning direction) is parallel to the main scanning direction.

Numeral 9 denotes a folding mirror, which folds the light beam transmitted through the cylindrical lens 4 toward the optical deflector 6. In the present embodiment, the reflecting surface 9a of the return mirror 9 is disposed at an angle θ with respect to the sub-scan section in order to obtain a compact apparatus as a whole, and the light beam emitted from the light source means 1 is bent at an angle α ≠ 45 °. And is reflected to the optical deflector 6 side. It is desirable that the bending angle α be set to less than 45 °.

Each element such as the collimator lens 2, the diaphragm 3, the cylindrical lens 4, and the return mirror 9 constitutes one element of the incident optical system 11, respectively.

Reference numeral 6 denotes an optical deflector, which comprises, for example, a rotating polygon mirror (polygon mirror) and is rotated at a constant speed in a direction indicated by an arrow A in the figure by driving means (not shown) such as a motor.

Reference numeral 12 denotes an image forming optical system having a light condensing function and fθ characteristics, and includes a single fθ lens (fθ lens system) 5;
A cylindrical mirror 7 having a predetermined refractive power only in the sub-scanning direction, and forms a deflected light beam from the optical deflector 6 on the surface 8 to be scanned; The tilt of the deflecting surface 6a is corrected by making the deflecting surface 6a and the scanned surface 8 have a substantially conjugate relationship. lens 5 also constitutes one element of the incident optical system 11. The fθ lens system may be composed of a plurality of lenses.

Reference numeral 8 denotes a photosensitive drum surface as a surface to be scanned.

In this embodiment, in the main scanning section shown in FIG. 1, a divergent light beam emitted from the semiconductor laser 1 is converted into a substantially parallel light beam by a collimator lens 2, and the light beam (light amount) is restricted by a stop 3. Incident on the cylindrical lens 4. The substantially parallel light beam incident on the cylindrical lens 4 exits as it is, passes through the fθ lens 5 via the return mirror 9, and enters the deflection surface 6a from substantially the center of the deflection angle of the optical deflector 6 (front incidence). ). At this time, the light beam incident on the light deflector 6 is incident on the deflecting surface 6a of the light deflector 6 in a state wider than the width of the deflecting surface 6a in the main scanning direction (overfield optical system). The light beam deflected and reflected by the deflecting surface 6 a of the optical deflector 6 is converged by passing through the fθ lens 5 again, and is guided onto the photosensitive drum surface 8 via the cylindrical mirror 7.

On the other hand, in the sub-scanning section shown in FIG. 2, a divergent light beam emitted from the semiconductor laser 1 is converted into a substantially parallel light beam by a collimator lens 2, and the light beam (light amount) is restricted by a stop 3 to form a cylindrical lens. 4 is incident. The substantially parallel light beam that has entered the cylindrical lens 4 converges, passes through the fθ lens 5 via the return mirror 9, and enters the deflection surface 6a of the optical deflector 6 at a predetermined angle (ε / 2). An image is formed on the deflection surface 6a as a substantially linear image (a linear image elongated in the main scanning direction) (oblique incidence optical system). The light beam deflected and reflected by the deflection surface 6a of the optical deflector 6 passes through the fθ lens 5 again, is converged by the cylindrical mirror 7, and is guided onto the photosensitive drum surface 8.
By rotating the optical deflector 6 in the direction of arrow R, the surface of the photosensitive drum 8 is moved in the direction of arrow S (main scanning direction).
Optical scanning. Thus, an image is recorded on the photosensitive drum surface 8 as a recording medium.

When the incident optical system 11 is configured as an oblique incidence optical system as in this embodiment, the deflecting surface 6a of the optical deflector 6
On the other hand, if the turning mirror 9 is tilted in the sub-scanning section, the light beam incident on the fθ lens 5 is tilted by the turning mirror 9 as described above, which causes a problem that the spot on the photosensitive drum surface 8 is adversely affected.

Here, the above problem will be described with reference to FIG. FIG. 11 is a cross-sectional view (sub-scanning cross-sectional view) of a main part of a conventional optical scanning device in the sub-scanning direction near a turning mirror.

In the figure, reference numeral 113 denotes a folding mirror, 1
Reference numeral 10 denotes a light beam before being incident on the return mirror 113;
Reference numerals 1-1, 111-2, and 111-3 denote light beams reflected by the reflecting mirror 113, 112-1, 112-2, and 11, respectively.
2-3 are the principal ray and the outermost ray (peripheral ray) in the light beam, respectively.
The reflection points 114, 115 and 116 are the positions of the reflection surfaces of the principal ray and the outermost ray in the light beam.

In the figure, the light beam 110 incident on the return mirror 113 has a width in the main scanning direction, but is not inclined with respect to the main scanning direction, so that it has the same height in the sub-scanning cross section as shown in FIG. It is in. In the turning mirror 113, the principal ray is reflected at the reflection point 112-1, and the outermost rays are reflected at the reflection points 112-2 and 112-3, respectively. As a result, a difference occurs in the optical path length, and the respective reflected light beams 111-1, 111-2, and 111-3 have different heights in the sub-scanning direction as shown in FIG. Accordingly, the light beam is inclined in the main scanning direction, and in the optical system shown in FIG. 1, the light beam incident on the fθ lens 5 is inclined (that is, the line image formed on the deflecting surface 6a of the optical deflector 6 is shifted with respect to the main scanning direction). Optical performance is degraded.

In this embodiment, the line image formed on the deflecting surface 6a of the optical deflector 6 is tilted in the main scanning direction by tilting the cylindrical lens 4 at an angle γ about the optical axis L of the incident optical system 11 as a rotation axis. In contrast, good image forming performance is obtained on the surface 8 to be scanned by making the surfaces parallel to each other.

At this time, the angle (tilt angle) between the sagittal line of the cylindrical lens 4 and the sub-scanning direction is γ, the angle of the main scanning section at which the light beam emitted from the semiconductor laser 1 is turned by the turning mirror 9 is α, Reflecting surface 9 of mirror 9
The angle of inclination between the sub-scanning section a and the deflecting surface 6a in the sub-scanning section is θ. When α ≠ 45 °, the angle γ is γ = −tan ⁻¹ {(tan α) × (tan θ)}.

FIG. 5 is a cross-sectional view of a main part in the main scanning direction near the turning mirror according to the present embodiment, FIG. 6 is a cross-sectional view of a main part in the sub-scanning direction of FIG. 5, and FIG. FIG. 8 is a perspective view of a main part showing a cylindrical lens and a stop of the incident optical system of the present embodiment in the scanning direction. 5, 6, 7, and 8, the same elements as those shown in FIGS. 1 and 2 are denoted by the same reference numerals.

In the drawing, 53 is a light beam incident on the return mirror, 53-1 is a principal ray of the light beam incident on the return mirror 9 and a principal ray of the light beam reflected by the return mirror 9.
3-2.53-3 are the outermost rays of the light beam incident on the return mirror 9 and the outermost rays of the light beam reflected by the return mirror 9, 9-1 is the reflection point of the principal ray, 9-2, 9- Numeral 3 denotes a reflection point of the outermost ray, and 61, 62 and 63 denote positions of reflection surfaces of the principal ray and the outermost ray, respectively. 81 is the main scanning direction,
82 is a sub-scanning direction, 83 is a sagittal line, and 84 is a short direction.

In the present embodiment, as shown in FIG. 7, the principal ray 53 of the light beam 53
-1 is a reflection point 9-1 on the return mirror 9, and the outermost rays 53-2 and 53-3 are reflection points 9 on the return mirror 9, respectively.
-2 and 9-3. Therefore, as shown in FIG.
Reference numerals 4 denote light beams having the same height, and the deflecting surface 6 of the optical deflector 6
The light beam incident on a becomes a light beam parallel to the main scanning direction. That is, the line image formed on the deflection surface 6a of the optical deflector 6 is parallel to the main scanning direction.

As described above, in the present embodiment, as described above, the cylindrical lens 4 is inclined by the angle γ with the optical axis L of the incident optical system 11 as the rotation axis, so that the angle γ
In this case, the inclination of the light beam generated by the folding mirror 9 can be canceled, thereby the fθ lens 5
Drum surface 8 by minimizing the rotational component of the light beam incident on
A good spot is formed on the top.

In the present embodiment, the cylindrical lens 4 is inclined at an angle γ about the optical axis L of the incident optical system 11 as a rotation axis as described above. However, the present invention is not limited to this. Any level that does not cause a problem is fine. For example, assuming that the angle between the sagittal line 83 of the cylindrical lens 4 and the sub-scanning direction 82 is β, the angle β is -1.3 × tan ^-1 {(tanα) × (tanθ)} ≦ β ≦ -0.7 × tan ^{− 1} {(t
anα) × (tanθ)}. Thus, the beam spot on the photosensitive drum surface 8 can be formed into a beam shape having no practical problem.

In this embodiment, as shown in FIG. 8, the stop 3 may be inclined by a predetermined amount with the optical axis L of the incident optical system 11 as a rotation axis, similarly to the cylindrical lens 4. The inclination angle of the stop 3 at this time is the same as the inclination angle γ of the cylindrical lens 4 when the angle formed between the short direction 84 passing through the center of the opening 3a of the stop 3 and the sub-scanning direction 82 is γ. = −tan ⁻¹ {(tan α) × (tan θ)}. Alternatively, assuming that the angle between the short direction 84 passing through the center of the opening 3a of the stop 3 and the sub-scanning direction 82 is β, the same as the inclination angle β of the cylindrical lens 4 is -1.3 × tan ^-1 {(tanα) × (tanθ)} ≦ β ≦ -0.7 × tan ^-1 {(t
anα) × (tan θ)}.

Further, the deflection direction (far field pattern) of the light beam emitted from the semiconductor laser 1 may be inclined by the same angle as the inclination angle of the stop 3.

Embodiment 2 FIG. 9 shows Embodiment 2 of the present invention.
FIG. 3 is a schematic diagram of a main part of the diaphragm of FIG. 8, the same elements as those shown in FIG. 8 are denoted by the same reference numerals.

This embodiment is different from the first embodiment in that the stop (slit member) 3 is tilted by a predetermined amount with the optical axis L of the incident optical system 11 as the rotation axis without tilting the cylindrical lens 4. Accordingly, the far field pattern (deflection direction) of the light beam emitted from the semiconductor laser 1 as the light source means is inclined by the same angle as the inclination angle of the stop 3. Other configurations and optical functions are substantially the same as those of the first embodiment, and thus, similar effects are obtained.

That is, in the drawing, reference numeral 93 denotes a far field pattern on the stop 3.

Generally, the far field pattern of a semiconductor laser is wider in the main scanning direction than in the sub scanning direction.
Therefore, a desired spot diameter and light amount can be achieved by using a wide far-field pattern for those who want to reduce the light flux.

In this embodiment, the stop 3 is tilted by a predetermined amount with the optical axis L of the incident optical system 11 as the rotation axis, and the far field pattern 93 is tilted by the same angle as the tilt angle of the stop 3 accordingly. The light beam can be effectively used, and the spot diameter and the light amount can be set to desired values.

In this embodiment, the angle (inclination angle) between the short direction 84 passing through the center of the opening 3a of the stop 3 and the sub-scanning direction 82 is γ, and the light beam emitted from the semiconductor laser 1 is folded back by the mirror 9. The angle of the main scanning section is α, the inclination angle of the reflecting surface 9a and the deflecting surface 6a of the folding mirror 9 in the sub-scanning section is θ, and when α ≠ 45 °, the angle γ
Is γ = −tan ⁻¹ {(tanα) × (tanθ)}. Further, in this embodiment, the far field pattern (deflection direction) of the light beam emitted from the semiconductor laser 1
93 is inclined by the same angle as the inclination angle γ of the diaphragm 3.

In the present embodiment, at this angle γ, the inclination of the light beam generated by the turning mirror 9 can be canceled, and the rotation component of the light beam incident on the fθ lens 5 can be minimized to be favorable on the photosensitive drum surface 8. Forming a spot.

In this embodiment, a laser unit fixing the semiconductor laser 1 and the aperture 3 are provided integrally,
The direction of the far field pattern 93 of the semiconductor laser 1 is made to coincide with the tilt direction of the stop 3 in advance, and by tilting the laser unit with respect to the optical axis L of the incident optical system 11, the tilt amount of the stop 3 and the semiconductor laser The inclination amount of the far field pattern 93 is made to match.

In the present embodiment, the stop 3 is tilted at an angle γ with the optical axis L of the incident optical system 11 as the rotation axis as described above. It is good if it is not at a level. For example, a short direction 84 passing through the center of the opening 3a of the stop 3 and a sub-scanning direction 82
And β is an angle of −1.3 × tan ⁻¹ {(tanα) × (tanθ)} ≦ β ≦ −0.7 × tan ⁻¹ {(t
anα) × (tanθ)}. Thereby, the beam spot on the surface 8 to be scanned can be formed into a beam shape having no practical problem.

At this time, the direction of deflection of the light beam emitted from the semiconductor laser 1 may be inclined by the same angle as the inclination angle β of the stop 3.

In this embodiment, as the diaphragm 3 is tilted, the direction of deflection of the light beam from the semiconductor laser 1 also changes.
The diaphragm 3 was inclined by the same angle as the inclination angle of the diaphragm 3,
Only may be.

FIG. 10 is a graph showing the inclination angle of the incident optical system in the first and second embodiments. The graph in the figure shows the inclination angle θ between the reflecting surface of the folding mirror and the sub-scanning section.
Embodiment 1 in which the angle α at which the light beam from the semiconductor laser is turned by the turning mirror is changed to 5 °,
2 shows the range of the tilt angle of the second optical system. In the range shown in the figure, the inclination of the light beam can be suppressed to a small value, whereby a good spot can be formed on the surface to be scanned.

[0066]

According to the present invention, in the optical scanning device using the oblique incidence optical system as described above, the cylindrical lens and / or the stop are tilted by a predetermined amount with the optical axis of the incident optical system as the rotation axis, thereby obtaining the light. A compact optical scanning device capable of making a line image formed on a deflecting surface of a deflector parallel to a main scanning direction, thereby obtaining good imaging performance on a surface to be scanned. be able to.

[Brief description of the drawings]

FIG. 1 is a top view of a main part according to a first embodiment of the present invention.

FIG. 2 is a side view of a main part of the first embodiment of the present invention.

FIG. 3 is a developed view when developed in a main scanning direction along a light beam according to the first embodiment of the present invention.

FIG. 4 is a developed view when developed in a sub-scanning direction along a light beam according to the first embodiment of the present invention.

FIG. 5 is a main scanning cross-sectional view near the turning mirror according to the first embodiment of the present invention.

FIG. 6 is a cross-sectional view in the sub-scanning direction near the turning mirror according to the first embodiment of the present invention.

FIG. 7 is a sub-scanning cross-sectional view near the turning mirror according to the first embodiment of the present invention.

FIG. 8 is a perspective view of a main part of a main part of the incident optical system according to the first embodiment of the present invention.

FIG. 9 is a schematic view of a main part of a slit according to a second embodiment of the present invention.

FIG. 10 is a graph showing a tilt angle of an incident optical system according to the first and second embodiments of the present invention.

FIG. 11 is a sub-scanning cross-sectional view near a turning mirror of a conventional optical scanning device.

FIG. 12 is a schematic diagram of a main part of a conventional optical scanning device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Light source means 2 Collimator lens 3 Aperture 3a Opening 4 Cylindrical lens 5 fθ lens 6 Optical deflector 7 Cylindrical mirror 8 Scanning surface 11 Incident optical system 12 Imaging optical system 81 Main scanning direction 82 Sub scanning direction 83 Child line 84 Transverse direction 93 Far field pattern (deflection direction)

[Procedure amendment]

[Submission date] December 15, 2000 (200.12.
15)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0036

[Correction method] Change

[Correction contents]

Reference numeral 6 denotes an optical deflector, which comprises, for example, a rotating polygon mirror (polygon mirror) and is rotated at a constant speed in a direction indicated by an arrow R in the figure by driving means (not shown) such as a motor.

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0040

[Correction method] Change

[Correction contents]

On the other hand, in the sub-scanning section shown in FIG. 2, a divergent light beam emitted from the semiconductor laser 1 is converted into a substantially parallel light beam by a collimator lens 2, and the light beam (light amount) is restricted by a stop 3 to form a cylindrical lens. 4 is incident. The substantially parallel light beam that has entered the cylindrical lens 4 converges, passes through the fθ lens 5 via the return mirror 9, and enters the deflection surface 6a of the optical deflector 6 at a predetermined angle (ε / 2). An image is formed on the deflection surface 6a as a substantially linear image (a linear image elongated in the main scanning direction) (oblique incidence optical system). The light beam deflected and reflected by the deflection surface 6a of the optical deflector 6 passes through the fθ lens 5 again, is converged by the cylindrical mirror 7, and is guided onto the photosensitive drum surface 8.
By rotating the optical deflector 6 in the direction of arrow R, the photosensitive drum surface 8 is optically scanned in the direction of arrow S (main scanning direction). Thus, an image is recorded on the photosensitive drum surface 8 as a recording medium.

[Procedure amendment 3]

[Document name to be amended] Drawing

[Correction target item name] Figure 2

[Correction method] Change

[Correction contents]

FIG. 2

Claims (16)

[Claims] An incident optical system for causing a light beam emitted from a light source to enter a deflection surface of an optical deflector in an oblique direction in a sub-scanning cross section; and a light beam deflected by the optical deflector on a surface to be scanned. An optical scanning device having an imaging optical system for forming an image, wherein the incident optical system converts a light beam emitted from the light source means into a substantially parallel light beam, and a substantially parallel light beam from the collimator lens. A restricting mirror, and a folding mirror that converges a light beam passing through the diaphragm with a cylindrical lens having power in the sub-scanning direction and causes the light beam from the cylindrical lens to enter a deflection surface of an optical deflector. By tilting the cylindrical lens about the optical axis of the incident optical system as a rotation axis, a line image formed on the deflection surface of the optical deflector is parallel to the main scanning direction. An optical scanning device characterized by the above-mentioned. 2. The angle between the sagittal line of the cylindrical lens and the sub-scanning direction is γ, the angle of the main scanning section at which the light beam emitted from the light source means is turned by the turning mirror is α, and the reflection surface of the turning mirror is The angle of inclination in the sub-scan section with respect to the deflection surface is θ, and when α ≠ 45 °, the angle γ
2. The optical scanning device according to claim 1, wherein γ = −tan ⁻¹ {(tan α) × (tan θ)}. 3. An angle between the sagittal line of the cylindrical lens and the sub-scanning direction is β, an angle of a main scanning section at which the light beam emitted from the light source is turned by the turning mirror is α, and a reflection surface of the turning mirror is When the inclination angle in the sub-scan section with respect to the deflection surface is θ, when α ≠ 45 °, the angle β
Is -1.3 × tan ^-1 {(tanα) × (tanθ)} ≦ β ≦ -0.7 × tan ^-1 {(t
2. The optical scanning device according to claim 1, wherein the following condition is satisfied: anα) × (tan θ)}. 4. The stop is tilted about the optical axis of the incident optical system as a rotation axis, and the tilt angle is the angle between a short direction passing through the center of the aperture of the stop and the sub-scanning direction. 3. The optical scanning device according to claim 2, wherein γ = −tan ⁻¹ {(tan α) × (tan θ)}. 5. The stop is tilted about the optical axis of the incident optical system as a rotation axis, and the tilt angle is an angle formed by a short direction passing through the center of the opening of the stop and the sub-scanning direction. -1.3 × tan ^-1 {(tanα) × (tanθ)} ≦ β ≦ -0.7 × tan ^-1 {(t
4. The optical scanning device according to claim 3, wherein the following condition is satisfied: anα) × (tan θ)}. 6. The optical scanning device according to claim 4, wherein a deflection direction of a light beam emitted from said light source means is tilted by the same angle as a tilt angle of said stop. 7. The optical scanning device according to claim 1, wherein a light beam emitted from said light source means is incident on a deflection surface from substantially a center of a deflection angle of said optical deflector. 8. The optical scanning device according to claim 1, wherein a light beam emitted from said light source means is incident on said deflecting surface of said optical deflector in a state wider than a width of said deflecting surface in a main scanning direction. 9. The optical scanning device according to claim 1, wherein at least a part of the optical elements constituting the image forming optical system also constitutes the incident optical system. 10. An incident optical system for causing a light beam emitted from a light source means to enter a deflection surface of an optical deflector in an oblique direction in a sub-scanning cross section, and a light beam deflected by the optical deflector on a surface to be scanned. An imaging optical system for forming an image, wherein the incident optical system converts a light beam emitted from the light source means into a substantially parallel light beam, and a substantially parallel light beam from the collimator lens. A restricting aperture, and a folding mirror that condenses the light flux passing through the aperture with a cylindrical lens having power in the sub-scanning direction and causes the light flux from the cylindrical lens to be incident on a deflection surface of an optical deflector; A light beam characterized in that a line image formed on a deflecting surface of the optical deflector is parallel to a main scanning direction by tilting the stop with the optical axis of the incident optical system as a rotation axis. Scanning device. 11. An angle between the short direction passing through the center of the aperture of the aperture and the sub-scanning direction, γ, and an angle of a main scanning section at which a light beam emitted from the light source means is turned by the turning mirror, is α. When the inclination angle between the reflecting surface and the deflecting surface of the folding mirror in the sub-scanning section is θ, and α ≠ 45 °,
11. The optical scanning device according to claim 10, wherein the angle γ is γ = −tan ⁻¹ {(tan α) × (tan θ)}. 12. An angle between a short direction passing through the center of the aperture of the aperture and the sub-scanning direction is β, and an angle at which a light beam emitted from the light source means is turned by the turning mirror is α.
The inclination angle between the reflection surface of the folding mirror and the sub-scanning section is θ
When α ≠ 45 °, the angle β is −1.3 × tan ⁻¹ {(tanα) × (tanθ)} ≦ β ≦ −0.7 × tan ⁻¹ {(t
The optical scanning device according to claim 10, wherein the following condition is satisfied: anα) x (tanθ)}. 13. The optical scanning device according to claim 11, wherein a deflection direction of a light beam emitted from said light source means is tilted by the same angle as a tilt angle of said stop. 14. The optical scanning device according to claim 10, wherein the light beam emitted from said light source means enters the deflection surface from substantially the center of the deflection angle of said optical deflector. 15. The optical scanning device according to claim 10, wherein a light beam emitted from said light source means is incident on said deflecting surface of said optical deflector in a state wider than a width of said deflecting surface in a main scanning direction. 16. The optical scanning device according to claim 10, wherein at least a part of the optical elements constituting the imaging optical system also constitutes the incident optical system.