JP2979754B2 - 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 an electrophotographic process in which an image is formed by optically scanning a surface to be scanned, which is an image carrier such as a photosensitive member or an electrostatic recording member. The present invention relates to an optical scanning device suitable for a device such as a laser beam printer, a color laser beam printer, a multi-color laser beam printer, etc.

[0002]

2. Description of the Related Art Conventionally, in an optical scanning device such as a laser beam printer, a light beam (laser beam) modulated on a surface of an image carrier through a rotary polygon mirror as disclosed in Japanese Patent Publication No. 62-36210. By performing optical scanning with a light beam, writing and reading of image information are performed.

FIG. 8 is a schematic view of a main part of a conventional optical scanning device. In FIG. 8, a light beam emitted from a light source unit 1 such as a semiconductor laser is converted into a parallel light beam by a collimator lens 2 and condensed by a cylindrical lens 83 having a refractive power only in the sub-scanning direction. Are linearly incident on the deflection reflection surface 4a. The collimator lens 2 and the cylindrical lens 83 constitute an imaging optical system. The light beam reflected and deflected by the deflecting / reflecting surface 4a is a lens 87 having a negative refractive power and a spherical surface constituting a scanning lens 87.
The light is guided on the surface to be scanned 89 by a lens 87b having a toric surface having different refracting powers in two directions orthogonal to a, thereby forming a spot. By rotating the deflector 4 in the direction of arrow 86 by the motor 85 about the rotation axis 82, the deflection scanning surface on the surface to be scanned 89 is optically scanned in the direction of arrow 90 (main scanning direction).

[0004] In many cases, aluminum (Al), plastic, glass, and the like are used as materials for the rotary polygon mirror. By applying a vapor deposition film to the reflection surface, the reflectance is increased and the surface is prevented from being oxidized.

[0005]

A semiconductor laser used in an optical scanning device generally emits a linearly polarized light beam due to its structure. The divergence angle of the light beam differs between the polarization direction and the direction perpendicular thereto.

When forming image information by optically scanning the surface of a photoreceptor, a spot in the main scanning direction in which a light beam is scanned by an optical deflector as disclosed in Japanese Patent Application Laid-Open No. 52-119331. The image quality is better when the diameter is set smaller than the spot diameter in the sub-scanning direction (the direction including the optical axis and orthogonal to the main scanning direction).

When the above two requirements are taken into consideration, if the aperture stop 3 shown in FIG. 1 described later is a circular aperture stop, the direction in which the divergence angle of the semiconductor laser is large (the direction orthogonal to the laser junction surface) is the scanning direction. When the aperture stop is set to, the spot diameter can be reduced to a small value, and in the case of a rectangular or elliptical aperture stop, it is advantageous in view of the efficiency of use of the laser.

That is, when a laser light source is used to arrange a laser light source so as to form a light beam having a spot shape that is long in the sub-scanning direction on the surface to be scanned, the polarization plane of the emitted light beam is changed in the sub-scanning direction due to the nature of the laser light source. It becomes a luminous flux that vibrates.
This light flux is incident on the deflection reflection surface of the optical deflector as S-polarized light.

In many cases, the reflection surface of a rotary polygon mirror as an optical deflector is provided with a reflection-enhancing film or the like by a vacuum deposition method. Differences in film thickness result in variations in reflection characteristics.

[0010] For this reason, it is necessary to use a high-precision vapor deposition facility, to reduce the effect by increasing the basic reflectivity by forming a multilayer film, or to perform the deposition by a special vapor deposition method. For this reason, the cost is increased and the degree of freedom of the film is reduced. In particular, S
In the case of incidence with polarized light, there is a problem that the dependency of the reflectance on the angle of incidence with respect to the error of the film thickness becomes large.

According to the present invention, when a polarized light beam from a laser light source is incident on a deflection reflecting surface of an optical deflector so as to be P-polarized light, and when aluminum is used as a material of the optical deflector,
When a film of aluminum oxide (Al ₂ O ₃ ) is formed on the reflecting surface to improve the reflectance, the variation in the reflectance due to the variation in the thickness of the aluminum oxide and the variation in the reflectance due to the incident angle are reduced. It is another object of the present invention to provide an optical scanning device capable of performing optical scanning on a surface to be scanned with a light beam having a uniform light amount with high accuracy.

[0012]

An optical scanning device according to the present invention comprises:
In an optical scanning device that deflects a linearly polarized light beam emitted from a light source unit by an optical deflector and guides the light to a surface to be scanned through a scanning lens to optically scan, the optical deflector rotates the reflecting mirror. Alternatively, the light beam is deflected by vibration, and the reflecting mirror is made of a material containing Al as a main component.
_{A 2} O ₃ layer is formed, and a light beam of linearly polarized light from the light source unit is incident on the deflecting / reflecting surface in a substantially P-polarized state.

Particularly, in the present invention, the Al
The range of the optical thickness nd of the ₂ O ₃ layer is λ / 11.1 to λ / 5.0 or λ / 4.11 to λ / 2.89, where λ is the wavelength of the light beam from the light source unit. λ / 1.73
To λ / 1.47 or λ / 1.28 to λ / 1.20, that the Al ₂ O ₃ layer provided on the deflecting / reflection surface is formed by anodic oxidation, The portion has a semiconductor laser, and is characterized in that the effective F number on the light emitting side of the semiconductor laser in the main scanning section is 4 or more.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a schematic view of a main part of a first embodiment in which the present invention is applied to a laser beam printer. FIG. 3 is a diagram for explaining functions in a main scanning section parallel to the bundle plane.

In FIG. 1, a divergent light beam (light beam) emitted from a light source unit 1 (for example, a semiconductor laser or the like) is converted into a parallel light beam by a collimator lens 2, and the polarization direction is changed through a diaphragm 3 in a main scanning section (light deflection as described later). P is applied to the deflecting / reflecting surface 4a of the optical deflector 4 composed of a rotating polygon mirror so as to be parallel to the inside of a plane formed by the light beam deflected by the
The light is incident as a polarized light beam.

That is, the incident light flux on the deflecting / reflecting surface of the rotary polygon mirror is P-polarized light, and the polarization direction is parallel to the reflection cross section (a plane including incident light, reflected light, and refracted light). In other words, the polarization direction of the light beam emitted from the semiconductor laser and incident on the rotary polygon mirror is parallel to the deflecting surface.

The light beam incident on the deflecting / reflecting surface 4a is reflected and deflected by the deflecting / reflecting surface 4a, and has a f-.theta.
Incident on The light beam incident on the scanning lens 5 is condensed and forms a light spot on the surface 6 to be scanned. Then, the optical deflector 4 is optically scanned on the main scanning surface of the scanned surface 6 as indicated by an arrow 6a by rotating the optical deflector 4 about a rotation axis 4b by a motor in a direction of an arrow 4c.

In this embodiment, the effective scanning angle of the light beam is 2ω as shown in FIG. The f-θ lens 5 corrects the f-θ characteristics of the deflected light beam, forms an image on the scanning surface 6, and scans the beam linearly.

Here, the angle between the light beam before entering the rotary polygon mirror 4 and the center of the effective deflection angle (scan angle) 2ω is defined as α as shown in FIG.

Here, the incident angle and the reflection angle of the light beam with respect to the normal to the deflecting / reflecting surface 4a of the rotary polygon mirror 4 in the effective scanning change with the rotation of the rotary polygon mirror, and the range of change is (α-ε). ) / 2 to (α + ε) / 2. Here, the number of surfaces of the rotating polygon mirror is 6,
If ε = 45 ° and α = 65 °, the incident angle θ with respect to the deflecting reflection surface as shown in FIG. 2 changes between 10 ° and 55 ° between these angles.

Here, the semiconductor laser of the first embodiment is linearly polarized, and is incident on the deflecting reflection surface of the rotary polygon mirror with a P-polarized component.

Therefore, the divergence angle (FF) of the semiconductor laser
Narrow direction of the angle theta ₁₁ of P) is in the main scanning direction. The F number FNo of the collimator lens 2 in the main scanning direction with respect to the aperture stop 3 is set to 5.5. Rotating polygon mirror 4
Is mainly made of aluminum, and a film of aluminum oxide Al ₂ O ₃ is formed on the surface of the mirror surface (reflection surface), and the optical film thickness is set to 108 nm.

FIG. 3 shows an incident angle 1 used by the rotary polygon mirror.
The calculation value of the angle dependence of the reflectance of the deflecting reflection surface in the range of 0 ° to 55 ° is shown. As shown in the figure, in the present embodiment, the angle dependency is about 0.3%, which indicates good performance. The state of the change in the reflectance with respect to the change in the film thickness is relatively gentle. For comparison, FIG. 4 shows how the reflectance of the reflecting surface changes with respect to the change in the film thickness at the maximum, minimum, and center of the incident angle of the P-polarized light.

FIG. 5 shows a change in reflectance with respect to a change in film thickness when the S-polarized light is used for the deflecting and reflecting surface under the same conditions.
Shown in As is clear from the change in the curve, the place where the angle dependency of the reflectance is small is where the film thickness is 163 nm and 286 nm.
FIG. 4 shows that the change in the reflectance with respect to the film thickness exists around nm.
It is smaller when used with P-polarized light indicated by.

When a semiconductor laser is used as P-polarized light with respect to the deflecting and reflecting surface of the optical deflector, the angle (FFP angle) diverged from the light emitting portion of the semiconductor laser is set to be narrow. When the FFP angle varies and the ratio of the light amount distribution on the aperture stop changes, the spot diameter on the scanning surface changes. Therefore, when the FFP angle of the semiconductor laser in the main scanning direction is in a range of 7 ° to 20 ° (an angle that becomes 50% of the maximum light amount), the F number in the main scanning direction on the semiconductor laser side is set to 4 or more. This reduces a change in the spot in the main scanning direction on the scanning surface depending on the FFP angle.

Al ₂ O ₃ deposited on the Al reflecting surface
As shown in FIG. 4, in the case of the first embodiment,
08 nm (0.14λ, λ = 780 nm). As a condition of the incident angle with respect to the deflecting reflection surface, a range α = 40 ° to 90 °, ω = 25 ° which is usually used for the angles α and ω in FIG.
At ６０60 °, the angle of incidence with respect to the normal to the reflecting surface is 0 ° to 75
Used in some of the ° range. Thus, the optical thickness of the aluminum oxide Al ₂ O ₃ film was changed from λ / 11.1 to
By setting it in the range of λ / 5.0 (λ: used wavelength), the dependency of the reflectance on the incident angle is small, and the influence of the change in the reflection characteristic on the variation in the film thickness is reduced. still,
When the optical film thickness is 40 nm or less, the effect of Al ₂ O _{3 as} a protective film is weakened.

As a method of forming a film of aluminum oxide on the surface of aluminum, a method of vacuum evaporation is generally used, but in this embodiment, a film of anodization is preferable. The anodization method uses 20
A film having a thickness of 0 nm or less has a large effect in principle when the cost is considered over the film formation time. In the case of the anodizing method, when the film is formed, the shape of the reflecting mirror or when a large number of workpieces are arranged, a large number of workpieces are arranged, and uneven current density occurs partially. Is generated, but it is possible to apply to such a method. Next, various numerical values as the second embodiment of the present invention will be described. The configuration is the same as the embodiment of FIG. In this embodiment, α = 90 °, ω = 54 °, wavelength λ = 780 nm, the incident angle range to the reflecting mirror 4a is 18 ° to 72 °, and the material of the reflecting mirror is Al in the arrangement of each element in FIG. On the reflection surface, Al ₂ O ₃ is deposited, and the optical film thickness at this time is 90 nm (0.115λ).
FIG. 6 shows the angle dependence of the reflectance of P-polarized light in this embodiment.

FIG. 7 shows how the reflectivity of the deflecting reflecting surface changes with respect to the change in the optical thickness (nd) of the anodic oxide film for P-polarized light. The vertical axis represents the reflectance Rp of the P component, and the horizontal axis represents the optical thickness (nd) of the anodic oxide film.

Here, the variation in the reflectance of the P-polarized light component is 5
% Of the optical film thickness (nd) in the region of 70%
m to 156 nm (λ / 11.1 to λ / 5.0) or 190 nm to 270 nm (λ / 4.11 to λ / 2.8)
9) or 451 nm to 531 nm (λ / 1.73 to
λ / 1.47) or 609 nm to 650 nm (λ /
1.28 to λ / 1.20).

Further, the variation in the reflectance of the P-polarized light component is 3%.
The range of the optical film thickness (nd) in the region is 83 nm.
~ 110 nm (λ / 9.4 ~ λ / 7.09) or 2
16 nm to 243 nm (λ / 3.61 to λ / 3.21)
Alternatively, 479 nm to 510 nm (λ / 1.63 to λ /
1.53).

Although a rotary polygon mirror has been described as an example of the optical deflector, the present invention can be similarly applied to a mirror having only one surface such as a galvanometer mirror.

According to the optical deflector of the present invention shown in the above-described embodiment, the linearly polarized light beam from the laser light source is made to enter the deflecting and reflecting surface of the optical deflector so as to become P-polarized light. When aluminum is used as the material of the container, a film of aluminum oxide (Al ₂ O ₃ ) is formed on the reflection surface to improve the reflectance. It is possible to achieve an optical scanning device capable of reducing the variation and the variation of the reflectance due to the incident angle, and scanning the surface to be scanned with a uniform amount of light with high accuracy.

In the case of this P-polarized light incidence, the range of the optical thickness (nd) of aluminum oxide is 70 nm to 156 nm (λ
/11.1 to λ / 5.0) or 190 nm to 270
nm (λ / 4.11 to λ / 2.89) or 451n
m to 531 nm (λ / 1.73 to λ / 1.47) or 609 nm to 650 nm (λ / 1.28 to λ / 1.2)
0).

[0034]

According to the present invention, as described above, the polarized light beam from the laser light source is incident on the deflecting / reflecting surface of the optical deflector so as to become P-polarized light, thereby using aluminum as the material of the optical deflector. Then, when a film of aluminum oxide (Al ₂ O ₃ ) is formed on the deflecting / reflecting surface to improve the reflectance, the variation in the reflectance due to the variation in the thickness of the aluminum oxide and the variation in the reflectance due to the incident angle. Thus, it is possible to achieve an optical scanning device capable of performing high-precision optical scanning with a uniform amount of light on the surface to be scanned by reducing the number of scans.

[Brief description of the drawings]

FIG. 1 is a schematic view of a main part of a first embodiment of the present invention.

FIG. 2 is an explanatory diagram of an incident angle and a reflection angle.

FIG. 3 is an explanatory diagram of a reflectance characteristic with respect to an incident angle of a reflection surface according to the present invention.

FIG. 4 is an explanatory diagram of a reflectance characteristic with respect to a change in a film thickness of a reflection surface according to the present invention.

FIG. 5 is an explanatory diagram of a reflectance characteristic with respect to a change in the thickness of S-polarized light.

FIG. 6 is an explanatory diagram of a reflectance characteristic with respect to an incident angle of a reflecting surface according to a second embodiment of the present invention.

FIG. 7 is an explanatory diagram of a reflectance characteristic with respect to a change in the thickness of P-polarized light.

FIG. 8 is a schematic view of a main part of a conventional optical scanning device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Light source part 2 Collimator lens 3 Aperture 4 Optical deflector 5 Scanning lens 6 Scanned surface 4a Deflection reflection surface

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Shiro Higashikozono 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (58) Field surveyed (Int.Cl. ⁶ , DB name) G02B 26 / Ten

Claims (4)

(57) [Claims] An optical deflector for deflecting a linearly polarized light beam emitted from a light source by an optical deflector, and then guiding the light to a surface to be scanned via a scanning lens to optically scan the light; Deflects a light beam by rotation or vibration of a reflecting mirror, the reflecting mirror is made of a material mainly composed of Al, and an Al ₂ O ₃ layer is formed on a deflecting reflecting surface thereof. A light beam of linearly polarized light from the optical scanning device is incident on the deflecting reflection surface in a substantially P-polarized state. 2. The range of the optical thickness nd of the Al ₂ O ₃ layer provided on the reflection surface is λ / 11.1 to λ / 5.0, where λ is the wavelength of the light beam from the light source unit. λ / 4.1
1 to λ / 2.89 or λ / 1.73 to λ / 1.47
2. The optical scanning device according to claim 1, wherein the wavelength is from λ / 1.28 to λ / 1.20. 3. The optical scanning device according to claim 1, wherein the Al ₂ O ₃ layer provided on the deflection reflection surface is formed by an anodic oxidation method. 4. The optical scanning device according to claim 1, wherein said light source unit has a semiconductor laser, and an effective F-number on a light emitting side of said semiconductor laser in a main scanning section is 4 or more. apparatus.