JP2002277784A - Light deflector device, optical scanning method, optical scanner and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize multiplex reflecting deflection with a wide deflection angle at high speed where the skew of deflection light fluxes is effectively reduced in optical scanning. SOLUTION: An optical scanner is provided with a light deflector which deflects the light fluxes by reflection which are made incident from a direction being inclined concerning a surface which is orthogonally crossed with an axis by rotating or rocking a deflection reflecting surface 20A around the axis and >=1 fixed mirrors 20D and 20E which are arranged to face the deflection reflecting surface in the light deflector and performs reflection multiple times with the deflection reflecting surface. Inclination angles θ1 and θ2 with respect to the axis on a sub-scanning cross section in the >=1 fixed mirrors are fixed to effectively reduce the skew of the deflection light fluxes for optically scanning a surface to be 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 method, an optical scanning device for performing the optical scanning method, an optical deflecting device used in the optical scanning device, and an image forming apparatus using the optical scanning device. .

[0002]

2. Description of the Related Art An optical scanning apparatus is widely known in relation to an image forming apparatus such as an optical printer, a digital copying apparatus, and a facsimile apparatus. One of the objectives for improving the optical scanning device is to “increase the speed of optical scanning”.

As a method effective in increasing the speed of optical scanning, there is a multi-beam scanning method in which a plurality of scanning lines are optically scanned at once. However, in either a single-beam scanning method or a multi-beam scanning method, deflection of a deflected light beam is performed. By increasing the speed, it is possible to further increase the speed.

As a method of increasing the deflection speed of the deflected light beam, for example, it is conceivable to increase the rotation speed of a rotary polygon mirror. However, as the rotation speed increases, power consumption increases.
Noise and vibration are generated, and the durability of the optical deflector itself is deteriorated.

As a method of increasing the deflection speed, it is conceivable to increase the number of deflection reflection surfaces of the rotary polygon mirror to increase the number of deflections per rotation of the rotary polygon mirror. However, simply increasing the number of deflecting and reflecting surfaces inevitably increases the radius of the rotating polygonal mirror, and the coefficient of inertia of the rotating polygonal mirror is proportional to the square of the radius. Inevitably increases power consumption.

In order to avoid this, the number of deflecting and reflecting surfaces must be increased without increasing the radius of the rotary polygon mirror. However, in this case, the individual deflecting and reflecting surfaces are reduced, and the deflection angle of the deflected light beam is reduced. In order to secure the length of the optical scanning area required for optical scanning, it is necessary to increase the optical path length from the rotary polygon mirror to the surface to be scanned, which leads to an increase in the size of the optical scanning device. .

A well-known optical deflector other than the rotating polygon mirror is a "oscillating mirror". The oscillating mirror is combined with a fixed mirror, and the light beam is reflected a plurality of times between the fixed mirror and the oscillating mirror. A light deflecting method (hereinafter referred to as "multiple reflection deflecting" for the sake of convenience) for deflecting a light beam at a high speed and a wide deflection angle has been proposed (Japanese Patent Laid-Open No. 4-52618).

As a swinging mirror, a “micro swinging mirror capable of sine wave oscillation capable of high-speed deflection” has recently been developed in the field of micromachines. Scanning can be speeded up.

However, when the light beam is deflected by the multiple reflection deflection described in the above publication, "skew" described later occurs in the deflected light beam, and the wavefront aberration of the deflected light beam is deteriorated.
If the wavefront aberration of the deflected light beam deteriorates, it becomes impossible to form a good light spot on the surface to be scanned with a small diameter, and it is impossible to perform high-density and high-definition optical scanning.

[0010]

SUMMARY OF THE INVENTION It is an object of the present invention to realize a multiple reflection deflection with a wide deflection angle, a high speed, and an effective reduction of the skew of a deflected light beam in optical scanning.

[0011]

An optical deflector according to the present invention has an optical deflector and one or more fixed mirrors. The “optical deflector” rotates or swings a deflecting / reflecting surface about an axis, and reflects and deflects a light beam incident from a direction inclined with respect to a plane orthogonal to the axis. Therefore, the "shaft" is a rotation axis or a swing axis. The “fixed mirror” is arranged so as to face the deflecting / reflecting surface of the optical deflector, and reflects a light beam between the deflecting / reflecting surface a plurality of times.

As described above, since the optical deflector "rotates or swings the deflecting and reflecting surface to deflect the light beam", a rotary polygon mirror or a swinging mirror can be used as the optical deflector. The “deflecting / reflecting surface facing the fixed mirror” is a deflecting / reflecting surface that actually deflects a light beam. When a rotating polygon mirror is used as an optical deflector, the deflecting / reflective surface is located at a position where a light beam from the light source side is incident. It is.

According to a first aspect of the present invention, there is provided an optical deflecting device, wherein one or more fixed mirrors are tilted with respect to the axis (rotation axis or swing axis) in the sub-scanning cross section, and the tilt angle is determined by the tilt angle. The skew of the deflected light beam that optically scans the surface is determined to be effectively reduced. "

The "sub-scan section" refers to a plane including the axis of the deflecting / reflecting surface of the optical deflector, that is, the axis including the rotation axis or swing axis and the "principal ray of the light beam from the light source incident on the deflecting / reflecting surface". To tell.

That is, in the multiple reflection deflection described in JP-A-4-52618, the fixed mirror is "parallel to the oscillation axis of the oscillation mirror" in the sub-scanning section.
Therefore, the skew is generated in the deflected light beam to degrade the wavefront aberration. In the optical deflector of the present invention, the fixed mirror moves the rotation axis or the swing of the deflected reflection surface in the sub-scan section. By tilting with respect to the moving axis, the skew in the deflected light beam is effectively reduced as described later.

The fixed mirror facing the deflecting reflection surface of the optical deflector may be one surface (claim 2) or two surfaces. When two fixed mirrors are used, these two fixed mirrors are arranged (arranged) in the sub-scanning direction. Also, when the fixed mirror surface is one surface or two surfaces, the incident light beam can be reflected at least three times between the deflecting / reflecting surface to be a deflected light beam.

In the optical deflecting device according to the third aspect, the inclination angles of the two fixed mirrors in the sub-scanning cross section are set to be opposite to each other, and the distance between the mirror surface and the deflecting reflection surface of each fixed mirror is In the sub-scanning cross section, it is possible to configure so as to increase toward the gap between the two, so that the deflected light beam is emitted from the gap.

In the optical deflecting device according to the fourth aspect,
The light flux first reflected by the deflecting reflection surface and incident on one of the fixed mirrors is reflected on the mirror surface of the one fixed mirror by one.
After being reflected once, the light can be incident on the mirror surface of the other fixed mirror via the deflecting reflection surface (claim 5).

Further, in the optical deflecting device according to the second or third aspect, while the incident light beam is reflected three times or more between the deflecting and reflecting surface, the moving direction of the reflecting position on the deflecting and reflecting surface is in the sub-scanning direction. The arrangement of each fixed mirror can be set so as to "reverse at" (claim 6).

In the optical deflector according to any one of the first to sixth aspects, it is possible to "emit the deflected light beam so as to make an angle with respect to the light beam incident on the deflective reflection surface in the sub-scan section". (Claim 7). This can completely prevent the deflected light beam from returning to the light source side.

In the optical deflecting device according to any one of the first to seventh aspects, the optical deflector may be a "micro oscillating mirror that oscillates at a high speed" (claim 8).

The optical scanning method according to the present invention comprises the steps of: "deflecting a light beam from a light source side by an optical deflector, guiding the deflected light beam to a surface to be scanned by a scanning image forming optical system, and forming a light spot; Optical scanning method for optically scanning a scanned surface ”.

The "scanning optical system" can be constituted by one or more lenses, or can be constituted by one or more image forming mirrors having an image forming function. It can also be constituted by a combination with one or more image forming mirrors.

According to a ninth aspect of the present invention, there is provided a light scanning method, wherein the light deflecting device according to the first aspect is used as the light deflecting device. An optical scanning method according to a tenth aspect is characterized in that the optical deflection device according to the second aspect is used as an optical deflection device.

An optical scanning method according to an eleventh aspect is characterized in that the optical deflection device according to any one of the third to sixth aspects is used as an optical deflection device. An optical scanning method according to a twelfth aspect is characterized in that the optical deflector according to the seventh aspect is used as an optical deflector.

According to a thirteenth aspect of the present invention, there is provided an optical scanning method, wherein the light deflector according to the eighth aspect is used as the light deflector. The optical scanning method according to any one of claims 9 to 13, wherein the light beam from the light source is coupled, the coupled light beam is focused by the line image forming optical system in the sub-scanning direction, and the light deflection is performed. In the vicinity of the position where the light is finally reflected by the deflecting / reflecting surface of the device, a long linear image is formed in the main scanning direction. " In this way, the tilting of the deflecting and reflecting surface when using a rotating polygon mirror as the optical deflector, and the eccentricity of the scanning axis in the sub-scanning direction due to the axial deviation of the oscillating axis when using the oscillating mirror as the optical deflector. Fluctuations "can be corrected.

In the optical scanning method according to the present invention, an appropriate optical deflector according to any one of claims 1 to 8 is used as an optical deflector. The light beam incident from a direction inclined with respect to the plane orthogonal to the swing is reflected and deflected, so that the deflected light beam itself also inclines with respect to the plane orthogonal to the axis, and this inclination of the deflected light beam is This causes the scanning line (moving locus of the light spot) on the scanning surface to bend.

Such bending of the scanning line may be caused by shifting (shifting in the sub-scanning direction) or tilting (tilting of the optical axis in the sub-scanning direction) by a lens or an imaging mirror included in the scanning and imaging optical system. However, as an effective method, in the optical scanning method according to any one of claims 9 to 14, in order to correct the curvature of the scanning line, "the vertex of the sagittal line of the lens surface is corrected. One or more lenses in which a series of lines are curved in the sub-scanning direction can be used for the scanning imaging optical system. "

The optical scanning device according to the present invention is arranged such that "a light beam from a light source side is deflected by an optical deflector, and the deflected light beam is guided to a surface to be scanned by a scanning image forming optical system to form a light spot. An optical scanning device that performs optical scanning of the surface to be scanned by the optical scanning device described above.

An optical scanning device according to a sixteenth aspect is characterized in that the optical deflection device according to the first aspect is used as an optical deflection device. An optical scanning device according to a seventeenth aspect uses the optical deflection device according to the second aspect as an optical deflection device.

An optical scanning device according to an eighteenth aspect uses the optical deflection device according to any one of the third to sixth aspects as an optical deflection device. An optical scanning device according to a nineteenth aspect uses the optical deflection device according to the seventh aspect as an optical deflection device.

An optical scanning device according to a twentieth aspect is characterized in that the optical deflection device according to the eighth aspect is used as an optical deflection device. An optical scanning device according to any one of claims 16 to 20, wherein a coupling lens for coupling a light beam from a light source and a light beam coupled by the coupling lens are focused in a sub-scanning direction. A line image forming optical system that forms a long line image in the main scanning direction in the vicinity of the position where the light is finally reflected by the deflecting reflection surface of the deflector may be provided.

The scanning image forming optical system of the optical scanning device according to any one of claims 16 to 21 may be configured such that "a line connecting the sagittal vertices of the lens surface is formed in order to correct the bending of the scanning line. It has one or more lenses that are curved in the sub-scanning direction ”.

The optical scanning device according to the present invention (claim 16)
To 22) can be implemented not only as a single beam scanning device, but also as a multi-beam scanning device. The optical scanning method of the present invention (claims 9 to 15)
It can be implemented as a single beam scanning method or a multi-beam scanning method.

An image forming apparatus according to the present invention is an "image forming apparatus for forming an image by optically scanning a photosensitive medium", wherein the optical scanning according to any one of claims 16 to 22 is used for optically scanning a photosensitive medium. A scanning device is used (claim 23).

As the "photosensitive medium", various known ones can be used. For example, an image can be formed by using a chromogenic photographic paper, which develops color by heat, as a photosensitive medium, optically scanning the photographic paper, and developing a color using "heat energy" by a light spot.

Depending on the photosensitive medium, a latent image is formed on the photosensitive medium by optical scanning, and an image can be formed by visualizing the latent image.
In this case, for example, a silver salt film can be used as the photosensitive medium. The latent image formed by optical scanning on the silver halide film is developed and processed according to the "normal silver halide photography process".
Fixing can be performed. Such an image forming apparatus includes:
It can be implemented as an optical plate making device or an optical drawing device.

As the photosensitive medium, a "photoconductive photosensitive member" can be used. In this case, the latent image is formed as an electrostatic latent image, visualized as a toner image, and the toner image is "finally carried on a sheet-shaped recording medium".
5).

When a known zinc oxide photosensitive paper is used as the photoconductive photoreceptor, the toner image formed on the zinc oxide photosensitive paper can be fixed as it is, using the zinc oxide photosensitive paper as a sheet-shaped recording medium. .

When a photoconductive photoreceptor that can be used repeatedly is used, the toner image formed on the photoreceptor is transferred to a sheet-like recording medium such as transfer paper or an OHP sheet (a plastic sheet for an overhead projector). Transfer directly or through an intermediate transfer medium such as an intermediate transfer belt,
By fixing, a desired image can be obtained.

These image forming apparatuses can be implemented as digital copiers, optical printers, optical plotters, facsimile machines and the like.

Hereinafter, in order to explain the above-mentioned "skew of the deflected light beam", a description will be given of a "comparative example" with respect to an embodiment described later. 1A and 1B show the optical arrangement of the optical scanning device of the comparative example. FIG. 1A shows a state viewed from the sub-scanning direction, and FIG. 1B shows a state viewed from the main scanning direction. The plane in the figure (b) is the “sub-scan section”.

The divergent laser beam emitted from the semiconductor laser 10 as a light source is converted by the coupling lens 12 into a beam form suitable for the subsequent optical system. The light beam form of the light beam emitted from the coupling lens 12 can be a “parallel light beam”, a “weakly focused light beam”, or a “weakly divergent light beam”. Is a collimating function, which converts the incident divergent light beam into a substantially parallel light beam.

When passing through the opening of the aperture 14, the parallel light beam is blocked at the light beam peripheral portion and "beam-shaped". The beam-shaped light beam (parallel light beam) is condensed only in the sub-scanning direction by the cylindrical lens 16, is converged only in the sub-scanning direction, is incident on the incident mirror 18, is reflected, and is incident on the optical deflector 20. Be deflected.

The light beam deflected by the light deflector 20 is reflected by a mirror 22 (shown in FIG. 1B), passes through two lenses 24 and 26 constituting a scanning image forming optical system, , 26 converge on the scanned surface 28 as a light spot. Then, this light spot optically scans the scanned surface 28. The scanned surface 28 is substantially a photosensitive surface of a photosensitive medium.

The incident mirror 18 and / or the mirror 22 can be omitted depending on the layout of the optical system.

FIG. 1C shows an optical deflecting device 20. The light deflecting device 20 includes an oscillating mirror 20A, a driving device 20B that oscillates the oscillating mirror 20A at high speed, and a fixed mirror 20C. Swing mirror 20A
Is a “deflection reflection surface”. The fixed mirror 20C is, of course, fixed to the device space.

The light beam reflected by the incident mirror 18 is
When the light is incident on a plane perpendicular to the oscillation axis of the oscillating mirror 20A at an angle (the angle of inclination with respect to the plane at this time is referred to as “the angle of incidence on the deflecting reflecting surface”), the light flux reflected by the deflecting reflecting surface Repeats reflection between the fixed mirror 20C and the deflecting / reflecting surface. That is, the light beam "multiple reflects" between the deflecting reflection surface of the oscillating mirror 20A and the fixed mirror 20C.

FIG. 1D shows the multiple reflection in the sub-scanning direction. Since the mirror surface of the fixed mirror 20C is set parallel to the swing axis of the swing mirror 20C, the incidence angle and the reflection angle in the sub-scanning direction do not change during multiple reflection, and after a predetermined number of reflections. As shown, the light is reflected by the deflecting / reflecting surface 20A to become a deflecting light beam.

On the other hand, the multiple reflection in the main scanning direction is as shown in FIG. In FIG. 1E, the deflecting / reflecting surface is inclined with respect to the fixed mirror 20C due to the swing of the swing mirror 20A. Therefore, as the reflection by multiple reflection is repeated, the incident angle and the reflection in the main scanning direction are repeated. The angle gradually increases, and the light beam finally reflected by the deflecting reflection surface becomes a deflecting light beam having a large deflection angle.

That is, in the main scanning direction, the deflection angle of the reflected light beam due to the inclination of the deflecting / reflecting surface is amplified by multiple reflection. As described above, in the multiple reflection deflection, even if the swing angle of the deflection reflection surface of the swing mirror 20A is minute,
A large deflection angle can be given to the deflected light beam. When the swing angle is small, the swing cycle can be shortened and the swing frequency can be increased. Therefore, the number of times of deflection of the deflected light beam can be increased, and the speed of optical scanning can be increased.

Hereinafter, "skew" in the above-mentioned deflection light beam will be described. Skew is simply a "torsion of the light beam". A description will be given based on a specific example.

In the optical scanning device of the comparative example shown in FIG. 1, the light beam from the semiconductor laser 10 is converted into a parallel light beam by the coupling lens 12 and then shaped by the aperture 14 as described above. The aperture shape of the aperture is a rectangular shape, and its size is 1. in the main scanning direction.
35 mm and 0.5 mm in the sub-scanning direction.

That is, the beam shaped beam becomes a parallel beam having a rectangular beam cross section of 1.35 mm × 0.5 mm in the main and sub scanning directions.

Hereinafter, data after the incident mirror 18 will be described.

Angle of incidence on the deflecting reflecting surface (mirror surface of the oscillating mirror 20A): 19.4 degrees Effective deflection angle of the deflecting reflecting surface: 3.71 degrees Distance between the deflecting reflecting surface and the fixed mirror: 0.3 mm Number of reflections on the surface: 5 times
.

Data surface number on the optical path from the deflecting reflection surface to the surface to be scanned Rm Rs DN 1 ∞ ∞ 10.2 (5th reflection deflecting reflection surface) -35.2 11.74 (the exit surface of the lens 24) 4 75.84 -12.95 2.56 1.52677 (the entrance surface of the lens 26) 5 151.23 -5.36 29.3 (the exit surface of the lens 26).

Here, Rm: paraxial radius of curvature in the main scanning direction Rs: paraxial radius of curvature in the sub-scanning direction N: wavelength used: refractive index at 665 nm D: surface spacing

Surface numbers: 2, 3, 4, 5
The coordinates in the main scanning direction are Y, and the coordinates in the sub-scanning direction are Z (Y, Z
Is the axis corresponding to the optical axis), and the depth in the optical axis direction is X, and X (Y, Z) = (1 / Rm) · Y ^ 2 / {1 + √ (1- (1+ Km) ・ (1 / Rm) ^ 2 ・ Y ^ 2)} ＋ a4 ・ Y ^ 4 + a6 ・ Y ^ 6 + ・ ・ ・ ・ ・ ・ ・ + Cs (Y) ・ [Z-Z0 (Y)] ^ 2 / {1+ {{1-Cs (Y) ^ 2 [Z-Z0 (Y)] ^ 2}} (1) Here, Cs (Y) = 1 / Rs + b2 · Y ^ 2 + b4 · Y ^ 4 + b6 · Y ^ 6 + ··· Z0 (Y) = d0 + d2 · Y ^ 2 + d4 · Y ^ 4 + d6 · Y ^ 6 + ··· is there. In the above equation, for example, "Y ^ 6" is "Y to the sixth power".
Represents

Using the above equations, the respective surfaces of the lenses 24 and 26 are specified as follows.

Surface number 2 (incident side surface of lens 24) Km = 1.85E + 02, a4 = -3.0E-06, a6 = -2.905E-09, a8 = -3.4E-11,
a10 = 5.0E-12 b2 = 3.95E-04, b4 = -9.533E-07, b6 = 1.906E-09, b8 = 1.57E-1
0, b10 = -3.37E-13, b12 = 4.326E-15 d0 = 0, d2 = 0, d4 = 0, ... Surface number 3 (exit surface of lens 24) Km = -1.93E-01, a4 = 2.91E-06, a6 = 1.375E-09, a8 = -5.348E-1
2, a10 = 2.535E-14 b2 = -3.253E-04, b4 = 2.14E-07, b6 = 5.939E-09, b8 = 2.108E-
11, b10 = 1.117E-13, b12 = 1.201E-15 d0 = 0, d2 = 0, d4 = 0, ... surface number 4 (incident side surface of lens 26) Km = -1.39E + 01, a4 = -1.102E-06, a6 = -9.881E-10, a8 = 1.072E
-12, a10 = 2.258E-15, a12 = -1.035E-18, a14 = -1.427E-23 b2 = -5.281E-06, b4 = 1.462E-08, b6 = -3.916E-11, b8 = 3.006E
-13, b10 = 5.198E-16, b12 = 4.551E-18 d0 = 0, d2 = 0, d4 = 0, ... Surface number 5 (exit side of lens 26) Km = -6.91E + 01, a4 = -2.188E-06, a6 = 4.3228E-10, a8 = 2.7814
E-12, a10 = -1.214E-15, a12 = 7.686E-19, a14 = 4.073E-22 b2 = -1.0E-04, b4 = 5.5E-07, b6 = 1.5E-10, b8 = 2.0 E-12, b12 =
2.0E-18 d0 = 0, d2 = 0, d4 = 0, ... In the above notation, for example, "E-10" is "10 to the -10th power"
And this number is multiplied by the previous number.

The lenses 24 and 26 are tilted counterclockwise with respect to the light beam toward the central image height. The incident side surface of the lens 24 is shifted by 0.3 mm in the upward direction in FIG. 1 (positive side in the Z direction) with respect to the light beam heading toward the central image height, and the incident side surface of the scanning lens 26 is shifted toward the central image height. On the other hand, it is shifted by 1.1 mm in the upward direction (positive side in the Z direction) in FIG.

Here, the skew in the deflected light beam will be described. FIG. 2A shows a light beam cross-sectional shape of a light beam (parallel light beam) immediately after beam shaping by the aperture 14. This light beam cross-sectional shape is the same as the opening shape of the aperture 14. The light beam is then condensed in the sub-scanning direction by the cylindrical lens 16, reflected by the incident mirror 18 and incident on the deflecting and reflecting surface of the oscillating mirror 20 </ b> A of the optical deflector 20 while converging. Are reflected multiple times.

When this multiple reflection is performed, ray tracing of rays passing through the four corners (indicated by black circles) of the light beam cross-sectional shape shown in FIG. It looks like this. FIG. 2B shows a ray tracing result when the deflecting reflecting surface and the fixed mirror are parallel. At this time,
The deflected light beam forms a light spot at an image height of 0 on the surface to be scanned.

In FIG. 2B, reference numeral 2-1 denotes a light beam cross-sectional shape on the deflecting reflection surface (a light beam passing through four corners in FIG. (Beam cross-sectional shape surrounded by a circle). Hereinafter, FIG.
Symbols 2-2, 2-3, 2-4, 2-5 in (b)
Indicates the light beam cross-sectional shape at the first to fourth reflection positions of the fixed mirror in multiple reflection, and reference numeral 2-6 indicates the light beam cross-sectional shape at the reflection position when the light beam is finally reflected by the deflecting reflection surface and becomes a deflected light beam. Is shown.

As can be seen from FIG.
Since the light beam from the side enters while being focused in the sub-scanning direction, the width of the light beam cross-section in the sub-scanning direction gradually decreases at the time of multiple reflection, and at the position where it is finally reflected by the deflecting reflective surface, An image is formed as a long line image in the scanning direction (light beam cross-sectional shape 2-6 in FIG. 2A).

As shown in FIG. 2A, for the image height of the light spot: 0, no "skew" occurs in the deflected light beam.

FIG. 2C shows a change in the cross-sectional shape of the light beam when the deflected light beam optically scans the peripheral image height. Reference numerals 2-11, 2-12, 2-13, 2-14, 2-15,
The light beam cross-sectional shapes indicated by 2-16 correspond to the light beam cross-sectional shapes 2-1 to 2-6 in FIG.

Referring to FIG. 2 (c), the cross section of the deflected light beam heading toward the peripheral image height gradually rotates clockwise as the reflection is repeated during multiple reflection in the light deflector. I understand. The rotation (twist) of this light beam is skew. The skew in the direction opposite to that of FIG. 2B (counterclockwise) is generated in the deflected light beam directed to the peripheral image height opposite to the image height: 0.

The cause of the skew is that when the incident angle from the incident mirror to the swinging mirror is not 0 and the image height of the light spot is other than 0, "the deflecting reflecting surface and the fixed mirror are not parallel". Another problem is that the optical path length of a light beam passing through the four corners of the light beam cross section changes.

As described above, when the optical path lengths of the light beams become uniform in the same light beam, the wavefront aberration of the deflected light beam is deteriorated. The deterioration of the wavefront aberration affects the spot diameter of the light spot formed on the surface to be scanned. That is, when the wavefront aberration deteriorates as the image height of the light spot increases from 0 to the peripheral image height, the “beam thickening” in which the spot diameter gradually increases from the image height: 0 to the peripheral image height is reduced. Will occur.

FIG. 3 is a diagram for explaining beam thickening. FIG. 3A shows the “change in spot diameter in the main scanning direction with respect to the defocus amount” of the light spot on the surface to be scanned, with the center image height (image height: 0) and the peripheral image height (image height: 25.7).
mm). FIG. 3A shows the change in the spot diameter in the sub-scanning direction with respect to the defocus amount of the light spot on the surface to be scanned, as the center image height (image height: 0).
And the peripheral image height (image height 25.7 mm).

As is clear from the figure, in both the main and sub-scanning directions, the light spot has a small spot diameter and a large depth margin when the image height is 0, but the beam becomes thick at the peripheral image height, and the beam system against defocusing occurs. Fluctuations have also increased.

[0074]

FIG. 4 shows only a characteristic portion of an optical scanning device according to an embodiment of the present invention. The difference from the optical scanning device example (comparative optical scanning device) shown in FIG. 1 lies in the optical deflection device.

That is, in the embodiment shown in FIG. 4, the “light deflecting device” is the same as the “oscillating mirror 20” as in the example of FIG.
An optical deflector in which A is driven to swing by a driving device "is a combination of two fixed mirrors 20D and 20E.

As shown in FIG.
The surface fixed mirrors 20D and 20E are arranged in the sub-scanning direction (vertical direction in the drawing), and deflect by reflecting an incident light beam three times or more (four times in this example) between the deflecting and reflecting surface as shown in the figure. It is a light beam (claim 3) and has two fixed mirrors 2.
Inclination angles of 0D and 20E in the sub-scan section: θ ₁ , θ ₂
Are opposite to each other, and the “distance between the mirror surface and the deflecting / reflecting surface” of each fixed mirror is equal to the gap 3 between the two in the sub-scan section.
The deflection light flux is set so as to increase toward zero, and exits from the gap 30 between the fixed mirrors 20D and 20E (claim 4).

Further, the light beam first reflected by the deflecting / reflecting surface of the oscillating mirror 20A and incident on one fixed mirror 20D is reflected once by the mirror surface of the one fixed mirror 20D, and then is reflected by the deflecting / reflecting surface. Through the other fixed mirror 20
E is incident on the mirror surface of E (Claim 5), and while the incident light beam is reflected three times or more between the deflecting and reflecting surface, the moving direction of the reflection position on the deflecting and reflecting surface is reversed in the sub-scanning direction. The arrangement of the fixed mirrors 20D and 20E is set (Claim 6), and the deflected light beam is applied to the deflected reflection surface (the incident mirror 18).
The incident light beam is emitted so as to form an angle in the sub-scan section (claim 7).

[0078]

EXAMPLE A specific example of the embodiment shown in FIG. 4 will be shown in the same manner as in the case of the comparative example optical scanning device described above. The “optical arrangement from the semiconductor laser as the light source to the light deflector via the incident mirror” is exactly the same as that of the optical scanning device of the comparative example.

Example 1 Angle of incidence on the deflecting / reflecting surface: 19.4 degrees Effective deflection angle on the deflecting / reflecting surface: 3.71 degrees L (distance between the deflecting / reflecting surface and the upper edge of the fixed mirror 20D): 0 .35 mm Number of reflections on the deflecting reflecting surface: 5 times θ ₁ : 26.022 degrees θ ₂ : 9.7 degrees Data on the optical path from the deflecting reflecting surface to the surface to be scanned Surface number Rm Rs DN 1 ∞ 2.6 12.6 (5 2nd deflective reflection surface) 2 296.55 -11.1 6.417 1.52677 (incident surface of lens 24) 3 -26.86 -35.2 11.74 (exit surface of lens 24) 4 75.84 -12.95 2.56 1.52677 (incident surface of lens 26) 5 151.23 -5.12 29.3 (Emission Surface of Lens 26) Each lens surface of surface numbers 2, 3, 4, and 5 can be represented by the above-described formula (1), and is specified as follows. Incidentally, the surfaces of the surface numbers 2 and 5 are "the generating line connecting the sagittal vertices of the lens surface is curved in the sub-scanning direction".

Surface number 2 (incident side surface of lens 24) Km = 1.85E + 02, a4 = 2.08E-06, a6 = -2.905E-09, a8 = -1.15E-1
1, a10 = 2.196E-14 b2 = 3.95E-04, b4 = -9.533E-07, b6 = 1.906E-09, b8 = 1.57E-1
0, b10 = -3.37E-13, b12 = 4.326E-15 d2 = 2.0E-04, d4 = 3.08E-06, d6 = 2.3E-08 ··· Surface number 3 (exit side surface of lens 24) Km = -1.93E-01, a4 = 2.91E-06, a6 = 1.375E-09, a8 = -5.348E-1
2, a10 = 2.535E-14 b2 = -3.253E-04, b4 = 2.14E-07, b6 = 5.939E-09, b8 = 2.108E-
11, b10 = 1.117E-13, b12 = 1.201E-15 d0 = 0, d2 = 0, d4 = 0, ... surface number 4 (incident side surface of lens 26) Km = -1.39E + 01, a4 = -1.102E-06, a6 = -9.881E-10, a8 = 1.072E
-12, a10 = 2.258E-15, a12 = -1.035E-18, a14 = -1.427E-23 b2 = -5.281E-06, b4 = 1.462E-08, b6 = -3.916E-11, b8 = 3.006E
-13, b10 = 5.198E-16, b12 = 4.551E-18 d0 = 0, d2 = 0, d4 = 0, ... Surface number 5 (exit side of lens 26) Km = -6.91E + 01, a4 = -2.188E-06, a6 = 4.3228E-10, a8 = 2.7814
E-12, a10 = -1.214E-15, a12 = 7.686E-19, a14 = 4.073E-22 b2 = 8.18E-05, b4 = -1.48E-07, b6 = 1.26E-10, b8 = 7.0 E-14, b1
2 = 4.5E-18 d2 = -4.0E-05, d4 = -5.0E-09, d6 = 4.38E-11, ... The lenses 24 and 26 are counterclockwise with respect to the luminous flux toward the central image height. The incident side surface of the lens 24 is shifted by 0.3 mm upward (toward the positive direction of the Z axis) with respect to the light beam heading toward the central image height, and the light incident surface of the lens 26 is shifted toward the center image height. Is shifted upward by 1.1 mm (toward the positive direction of the Z axis).

In the case of the first embodiment, the light beam passes through the four corners (shown by black circles) of the light beam cross-sectional shape shown in FIG. 2A during multiple reflection between the deflecting reflection surface and the fixed mirrors 20D and 20E. FIG. 5A and FIG. 5B show the results of ray tracing. FIG. 5A shows a ray tracing result when the deflecting reflecting surface and the fixed mirror are parallel. At this time, the deflected light beam forms a light spot at an image height of 0 on the surface to be scanned.

In FIG. 5A, reference numeral 5-1 denotes a light beam cross-sectional shape on the mirror surface of the fixed mirror 20D when the light is incident on the deflecting / reflecting surface from the incident mirror 18 and reflected, and is incident on the fixed mirror 20D. Show. Hereinafter, reference numerals 5-2, 5-3, and 5-4 in FIG. 5A indicate reflection positions on the fixed mirror 20E in the multiple reflection (2 in the multiple reflection).
The reference numeral 5-5 indicates the cross-sectional shape of the light beam at the reflection position when the light beam is finally reflected by the deflecting reflection surface and becomes a deflecting light beam.

That is, the reflection positions of the fixed mirrors 20D and 20E are shifted upward in the sub-scanning direction from the first to third reflections, and then inverted downward in the sub-scanning direction.

As shown in FIG. 2A, for the image height of the light spot: 0, no "skew" occurs in the deflected light beam.

FIG. 5B shows a change in the light beam cross-sectional shape when the deflected light beam optically scans the peripheral image height. The light beam cross-sectional shapes indicated by reference numerals 5-11, 5-12, 5-13, 5-14, and 2-15 correspond to the light beam cross-sectional shapes 5-1 to 5-5 in FIG.

As is apparent from FIG. 5B, in the first embodiment, the skew is effectively corrected both at the image height of 0 and in the deflecting light flux toward the peripheral image height.

In the optical scanning device of the comparative example, the reflecting surface of the fixed mirror 20C is parallel to the deflecting reflecting surface in the sub-scanning direction. Only the mirror surface of the fixed mirror is shifted to one side, and this causes the skew to increase toward the peripheral image height.

On the other hand, in the first embodiment, since the reflection position on the fixed mirror moves in both directions in the sub-scanning direction, this acts to reduce or correct the skew.

FIGS. 6A and 6B show the “change in spot diameter in the main and sub scanning directions with respect to the defocus amount” of the light spot on the surface to be scanned in the first embodiment. ,
Following (b), the center image height (image height: 0) and the peripheral image height (image height:
25.7 mm).

As is clear from the figure, the light spot has a small spot diameter and a large depth margin at the image height of 0 and the peripheral image height in both the main and sub scanning directions. That is, the influence of the skew is extremely effectively reduced as compared with the optical scanning device of the comparative example.

In the optical scanning device of the comparative example, as shown in FIG. 2, since the light beam is inclined due to skew in the light beam passing range on the fixed mirror surface 20C, the light beam is finally reflected by the deflecting reflection surface as a deflected light beam. Although it becomes difficult to process the edge of the fixed mirror 20C so that the light flux is not “eclipsed” by the fixed mirror, in the first embodiment, the incident angle to the deflecting / reflecting surface changes for each reflection, and Since the sign of the incident angle may be different, the "tilt of the light beam due to skew" is finally small, and therefore, the fixed mirrors 20D and 20D
The processing of the edge (slit) of the opening 30 of E is easy.

FIG. 7 shows another embodiment of the present invention, in which only the characteristic portions are shown. The difference from the optical scanning device example (comparative optical scanning device) shown in FIG. 1 lies in the optical deflection device.

That is, in the embodiment shown in FIG. 7, the "light deflecting device" is the same as the "oscillating mirror 20" as in the example of FIG.
The optical deflector in which A is driven to swing by a driving device "is combined with a fixed mirror 20F on one surface.

As shown in FIG.
As shown in the figure, the fixed mirror 20F of the surface reflects the incident light beam three times or more (four times in this example) with the deflecting / reflecting surface to form a deflecting light beam. And the moving direction of the reflection position on the deflecting / reflecting surface is reversed in the sub-scanning direction while the incident light beam is reflected three times or more with the deflecting / reflecting surface (claim 6). The deflected light beam is emitted so as to form an angle in the sub-scan section with respect to the light beam incident on the deflective reflection surface (from the side of the incident mirror 18) (claim 7).

[0095]

EXAMPLE A specific example of the embodiment shown in FIG. 7 will be shown in the same manner as in the case of the comparative example optical scanning device described above. The “optical arrangement from the semiconductor laser as the light source to the light deflector via the incident mirror” is exactly the same as that of the optical scanning device of the comparative example.

Example 2 Angle of incidence on the deflecting and reflecting surface: 19.4 degrees Effective deflection angle on the deflecting and reflecting surface: 3.71 degrees L (distance between the deflecting and reflecting surface and the upper edge of the fixed mirror 20D): 0 .35 mm Number of reflections on the deflecting reflection surface: 5 times θ: 5.55 degrees Data on the optical path from the deflecting reflection surface to the surface to be scanned Surface number Rm Rs DN 1 ∞ ∞ 10.4 (5th reflection deflecting reflection surface) 2 296.55 -11.1 6.417 1.52677 (incident surface of lens 24) 3 -26.86 -35.2 11.74 (exit surface of lens 24) 4 75.84 -12.95 2.56 1.52677 (incident surface of lens 26) 5 151.23 -5.12 29.3 (exit surface of lens 26) Each lens surface of the surface numbers: 2, 3, 4, and 5 can be represented by the above formula (1), and is specified as follows. Incidentally, the surfaces of the surface numbers 2 and 5 are "the generating line connecting the sagittal vertices of the lens surface is curved in the sub-scanning direction".

Surface number 2 (incident side surface of lens 24) Km = 1.85E + 02, a4 = 2.08E-06, a6 = -2.905E-09, a8 = -1.15E-1
1, a10 = 2.196E-14 b2 = 3.95E-04, b4 = -9.533E-07, b6 = 1.906E-09, b8 = 1.57E-1
0, b10 = -3.37E-13, b12 = 4.326E-15 d2 = 2.0E-04, d4 = 3.08E-06, d6 = 2.3E-08 ··· Surface number 3 (exit side surface of lens 24) Km = -1.93E-01, a4 = 2.91E-06, a6 = 1.375E-09, a8 = -5.348E-1
2, a10 = 2.535E-14 b2 = -3.253E-04, b4 = 2.14E-07, b6 = 5.939E-09, b8 = 2.108E-
11, b10 = 1.117E-13, b12 = 1.201E-15 d0 = 0, d2 = 0, d4 = 0, ... Surface number 4 (incident side surface of lens 26) Km = -1.39E + 01, a4 = -1.102E-06, a6 = -9.881E-10, a8 = 1.072E
-12, a10 = 2.258E-15, a12 = -1.035E-18, a14 = -1.427E-23 b2 = -5.281E-06, b4 = 1.462E-08, b6 = -3.916E-11, b8 = 3.006E
-13, b10 = 5.198E-16, b12 = 4.551E-18 d0 = 0, d2 = 0, d4 = 0, ... Surface number 5 (exit side of lens 26) Km = -6.91E + 01, a4 = -2.188E-06, a6 = 4.3228E-10, a8 = 2.7814
E-12, a10 = -1.214E-15, a12 = 7.686E-19, a14 = 4.073E-22 b2 = 8.18E-05, b4 = -1.48E-07, b6 = 1.26E-10, b8 = 7.0 E-14, b1
2 = 4.5E-18 d2 = -4.0E-05, d4 = -5.0E-09, d6 = 4.38E-11, ... The lenses 24 and 26 are counterclockwise with respect to the luminous flux toward the central image height. The incident side of the lens 26 is shifted by 0.3 mm upward (toward the positive direction of the Z axis) with respect to the light beam heading toward the central image height, and the light incident surface of the lens 26 is shifted toward the center image height. Is shifted upward by 1.1 mm (toward the positive direction of the Z axis).

That is, the lenses 24 and 26 are exactly the same as those in the first embodiment except for the distance between the deflecting / reflecting surface and the incident side surface of the lens 24.

FIGS. 8 (a) and 8 (b) show the “change in spot diameter in the main and sub scanning directions with respect to the defocus amount” of the light spot on the surface to be scanned in the second embodiment. ,
Following (b), the center image height (image height: 0) and the peripheral image height (image height:
25.7 mm).

As is clear from the figure, the light spot has a small spot diameter and a large depth margin at the image height of 0 and the peripheral image height in both the main and sub-scanning directions. From this,
It can be seen that the influence of the skew is effectively reduced also in the second embodiment as compared with the optical scanning device of the comparative example.

Since the skew is small, it is easy to process the upper edge of the fixed mirror 20F.

In the first and second embodiments described above, the oscillating mirror having only one deflecting and reflecting surface is used. However, a rotating polygon mirror such as a polygon mirror may be used. Example 1 above,
The oscillating mirror 20A used in Example 2 is a micro oscillating mirror having a small mirror surface width of 4 mm in the main scanning direction and a small effective deflection angle of 3.71 degrees. Therefore, even if the deflection angle is large, the effective scanning width is large. Is as small as 50.4 mm. However, the effective writing width can be increased by arranging a plurality of optical systems in the embodiment in the main scanning direction.

FIG. 9 shows an embodiment of the image forming apparatus. This image forming apparatus is a “laser printer”.

The “laser printer” has a “photoconductive photosensitive member formed in a cylindrical shape” as the photosensitive medium 91. Around the photosensitive medium 91, a charging unit 92 (a contact-type charging roller is illustrated, but a corona charger may be used, of course), a developing unit 94, and a transfer unit 95 (a unit using a corona discharge). Although shown, a contact-type transfer roller may be used), and a cleaning device 97 is provided.

The optical scanning device 9 using the laser beam LB
3 is provided to perform “exposure by optical writing” between the charging roller 92 and the developing device 94.

In FIG. 9, reference numeral 96 denotes a fixing device, and reference numeral S denotes transfer paper as a “sheet-shaped recording medium”.

To form an image, a photosensitive medium 91, which is a photoconductive photosensitive member, is rotated clockwise at a constant speed, and the surface thereof is uniformly charged by a charging means 92.
Is exposed by the optical writing of the laser light beam LB, and an electrostatic latent image is formed. The formed electrostatic latent image is a so-called “negative latent image”
And the image area is exposed.

The electrostatic latent image is reversely developed by the developing device 94 to form a toner image on the photosensitive medium 91.
The transfer paper S is sent to the transfer unit at the same time as the toner image on the photosensitive medium 91 moves to the transfer position, and is superposed on the toner image at the transfer unit. Electrotransferred.

The transfer paper S on which the toner image has been transferred is sent to the fixing device 96, where the toner image is fixed in the fixing device 96 and discharged outside. The surface of the photosensitive medium 91 after the transfer of the toner image is cleaned by the cleaning device 97 to remove residual toner, paper dust, and the like.
The above-described OHP sheet can be used instead of the transfer paper, and the transfer of the toner image can be performed via an “intermediate transfer medium” such as an intermediate transfer belt.

As the optical scanning device 93, the optical scanning device according to the first or second embodiment described above (a plurality of sets as necessary,
When used (arranged in a direction perpendicular to the drawing), good image formation can be performed.

The optical deflecting device according to the embodiment described above with reference to FIGS. 4 and 7 rotates or swings the deflecting reflection surface around an axis to move the deflecting reflection surface with respect to a surface orthogonal to the axis. An optical deflector 20A for reflecting and deflecting a light beam incident from an inclined direction, and one or more fixed mirrors 20C arranged opposite to the deflecting and reflecting surface of the optical deflector and reflecting a plurality of times between the deflecting and reflecting surface; 20D (or 20F), and the inclination angles of the one or more fixed mirrors with respect to the axis in the sub-scanning section: θ ₁ , θ ₂ (or θ) indicate the skew of the deflected light beam for optically scanning the surface to be scanned. Is a light deflecting device (claim 1) determined so as to effectively reduce.

In the optical deflecting device shown in FIG. 7, the fixed mirror 20F has one surface (claim 2).

In the light deflecting device shown in FIG.
D and 20E are arranged in the sub-scanning direction on two surfaces, and
The light is reflected at least three times between the deflecting and reflecting surfaces to form a deflecting light flux
(Claim 3) Sub-mirrors of the two fixed mirrors 20D and 29E
Angle of inclination in scanning section: θ₁, Θ ₂Are opposite to each other
The distance between the mirror surface of the constant mirror and the deflective reflection surface is
Inside, so as to increase toward the gap 30 between the two.
And the deflected light beam exits from the gap 30.
4). In addition, the light is first reflected by the
The light beam incident on the fixed mirror 20D is
Is reflected once by the mirror surface of
And make it incident on the mirror surface of the other fixed mirror 20E
(Claim 5).

In both the optical deflectors shown in FIGS. 4 and 7, the moving direction of the reflection position on the deflection / reflection surface is reversed in the sub-scanning direction while the incident light beam is reflected three times or more between the deflection / reflection surface. , Each fixed mirror 20D, 20E (or 2
0F) is set (claim 6), and the deflected light beam is emitted so as to form an angle in the sub-scan section with respect to the light beam incident on the deflecting reflection surface 20A (claim 7).

In each of the optical deflectors of the first and second embodiments, the optical deflector is a "micro oscillating mirror which oscillates at a high speed".

Therefore, when the light deflectors of FIGS. 4 and 7 and the first and second embodiments are used, the light beam from the light source 10 is deflected by the light deflector, and the deflected light beams are scanned and imaged by the optical systems 24 and 26.
2. An optical scanning method in which a light spot is formed by guiding light to a surface to be scanned 28 by means of a light spot, and optical scanning of the surface to be scanned is performed by the light spot. Claim 9) is implemented.

When the optical deflector of FIG. 7 or the second embodiment is used,
The light beam from the light source 10 is deflected by the light deflector, and the deflected light beam is scanned by the scanning / imaging optical systems 24 and 26 onto the surface 28 to be scanned.
An optical scanning method using a light deflecting device according to claim 2 as an optical deflecting device.
0) is performed.

Further, when the light deflecting device of FIG. 4 or Embodiment 1 is used, the light beam from the light source 10 is deflected by the light deflecting device, and the deflected light beam is scanned by the scanning / imaging optical systems 24 and 26 onto the surface 28 to be scanned. 7. An optical scanning method in which a light spot is formed by guiding light, and an optical scanning of a surface to be scanned is performed by the light spot, wherein the optical deflection device according to any one of claims 3 to 6 is used as an optical deflection device. (Claim 11) is implemented.

When the light deflectors of FIGS. 4 and 7 and the first and second embodiments are used, the light beam from the light source 10 is deflected by the light deflector, and the deflected light beam is scanned by the scanning / imaging optical systems 24 and 26. An optical scanning method using a light deflecting device according to claim 7 as an optical deflecting device in an optical scanning method in which a light spot is formed by guiding light to a surface and light scanning of a surface to be scanned is performed by the light spot. ), And an optical scanning method using the optical deflecting device according to claim 8 (claim 13).

When the light deflectors of FIGS. 4 and 7 and the first and second embodiments are used, the light beam from the light source 10 is coupled, and the coupled light beam is sub-scanned by the line image forming optical system 16. And the deflecting surface 20A of the optical deflector.
In the vicinity of the position where the light beam is finally reflected, an optical scanning method for forming a long line image in the main scanning direction (claim 14) is performed.

In each of the first and second embodiments, in order to correct the bending of the scanning line, at least one lens whose line connecting the vertices of the sagittal line of the lens surface curves in the sub-scanning direction is used in the scanning imaging optical system. (Claim 15).

In the optical scanning devices of FIGS. 4 and 7 and the first and second embodiments, the light beam from the light source 10 is deflected by the light deflector, and the deflected light beam is scanned by the scanning / imaging optical systems 24 and 26 onto the surface 28 to be scanned. An optical scanning device that forms a light spot by guiding light to the surface and performs optical scanning of a surface to be scanned by the light spot is an optical scanning device that uses the optical deflecting device according to claim 1 as an optical deflecting device. The optical scanning device according to the second embodiment shown in FIG. 7 is an optical scanning device using the optical deflection device according to the second aspect as an optical deflection device (claim 17).

FIG. 4 shows an optical scanning device according to the first embodiment,
A light beam from the side is deflected by a light deflector, and the deflected light beam is guided to a surface to be scanned 28 by scanning and imaging optical systems 24 and 26 to form a light spot, and the light spot performs light scanning on the surface to be scanned. The optical scanning device is an optical scanning device using the optical deflection device according to any one of claims 3 to 6 as an optical deflection device (claim 18).

4 and 7, the optical scanning device according to the first and second embodiments is an optical scanning device using the optical deflecting device according to claim 7 as an optical deflecting device (claim 19). An optical scanning device using the optical deflection device according to claim 8 (claim 20).
But also.

4 and 7, and the optical scanning devices of the first and second embodiments, the coupling lens 12 for coupling the light beam from the light source 10 and the light beam coupled by the coupling lens in the sub-scanning direction. A line image forming optical system 1 that focuses and forms a long line image in the main scanning direction in the vicinity of the position where the light is finally reflected by the deflecting reflection surface of the optical deflector.
In any of the optical scanning devices according to the first and second embodiments, the scanning image forming optical system includes a series of sagittal vertices of the lens surface in order to correct the bending of the scanning line. There is at least one lens whose line is curved in the sub-scanning direction.

The image forming apparatus shown in FIG. 9 is an image forming apparatus which forms an image by optically scanning a photosensitive medium 91.
The optical scanning device 93 according to any one of claims 16 to 21 is used for optical scanning of the photosensitive medium 91 (claim 23), and a latent image is formed on the photosensitive medium by optical scanning of the photosensitive medium 91. The latent image is visualized (claim 24), the photosensitive medium 91 is a photoconductive photoconductor, the latent image is formed as an electrostatic latent image, visualized as a toner image, and the toner image is The sheet is finally carried on the sheet-shaped recording medium S (claim 25).

[0127]

As described above, according to the present invention, a novel optical deflector, optical scanning method, optical scanning device, and image forming apparatus can be realized. The light deflecting device of the present invention enables high-speed optical scanning and effectively reduces the skew of the deflecting light beam, so that the diameter of the light spot is reduced and the fluctuation due to the image height of the light spot is effectively reduced. Reduction in light enables good optical scanning.

Therefore, good optical scanning can be realized by the optical scanning device using the optical deflection device, and good image formation can be realized by the image forming apparatus using the optical scanning device.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining a comparative example optical scanning device.

FIG. 2 is a diagram for explaining a skew of a deflection light beam in the optical scanning device of the comparative example.

FIG. 3 is a diagram for explaining a change in spot diameter caused by a skew of a deflection light beam.

FIG. 4 is a diagram showing only a characteristic portion of the first embodiment of the present invention.

FIG. 5 is a diagram for explaining a skew reduction effect in the first embodiment.

FIG. 6 is a diagram for describing improvement in spot diameter variation in the first embodiment.

FIG. 7 is a diagram showing another embodiment of the present invention, showing only characteristic portions.

FIG. 8 is a diagram for describing improvement in spot diameter variation in the second embodiment.

FIG. 9 is a diagram illustrating one embodiment of an image forming apparatus.

[Explanation of symbols]

 18 Incident mirror 20A Swing mirror (deflection / reflection surface) 20D, 20E Fixed mirror

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Claims (25)

[Claims] 1. An optical deflector for rotating or swinging a deflecting / reflecting surface about an axis to reflect and deflect a light beam incident from a direction inclined with respect to a plane perpendicular to the axis. 1 that is arranged to face the deflecting / reflecting surface and reflects a light beam multiple times with the deflecting / reflecting surface
A tilt angle of the one or more fixed mirrors with respect to the axis in the sub-scanning section is determined so as to effectively reduce a skew of a deflected light beam that optically scans the surface to be scanned. A light deflecting device. 2. The optical deflecting device according to claim 1, wherein the fixed mirror has one surface. 3. A light deflecting device according to claim 1, wherein the fixed mirror is disposed on the two surfaces in the sub-scanning direction, and the incident light beam is reflected at least three times between the deflecting and reflecting surface to form a deflected light beam. Characteristic light deflecting device. 4. The optical deflector according to claim 3, wherein the inclination angles of the two fixed mirrors in the sub-scanning cross section are opposite to each other, and the distance between the mirror surface of each fixed mirror and the deflecting reflection surface is: An optical deflecting device, which is set so as to increase toward the gap between the two in the sub-scanning cross section, and emits a deflected light beam from the gap. 5. The light deflecting device according to claim 4, wherein the light flux first reflected by the deflecting reflection surface and incident on one of the fixed mirrors is reflected by one of the mirror surfaces of the one fixed mirror.
An optical deflecting device, wherein the light is reflected once and then enters the mirror surface of the other fixed mirror via the deflecting / reflecting surface. 6. An optical deflecting device according to claim 2, wherein the incident light beam is reflected three times or more between the deflecting reflection surface and the deflecting reflection surface.
An optical deflecting device, wherein the arrangement of each fixed mirror is set such that the moving direction of the reflection position on the deflecting reflection surface is reversed in the sub-scanning direction. 7. The light deflecting device according to claim 1, wherein the deflecting light beam is emitted so as to form an angle in the sub-scan section with respect to the light beam incident on the deflecting reflection surface. Light deflecting device. 8. An optical deflecting device according to claim 1, wherein said optical deflector is a micro oscillating mirror which oscillates at a high speed. 9. A light beam from a light source side is deflected by an optical deflector, and the deflected light beam is guided to a surface to be scanned by a scanning image forming optical system to form a light spot. An optical scanning method for performing optical scanning, wherein the optical deflecting device according to claim 1 is used as an optical deflecting device. 10. A light beam from a light source side is deflected by a light deflector, and the deflected light beam is guided to a surface to be scanned by a scanning image forming optical system to form a light spot. An optical scanning method for performing optical scanning, wherein the optical deflecting device according to claim 2 is used as an optical deflecting device. 11. A light beam from a light source side is deflected by a light deflector, and the deflected light beam is guided to a surface to be scanned by a scanning image forming optical system to form a light spot. An optical scanning method for performing optical scanning, wherein the optical deflection device according to any one of claims 3 to 6 is used as the optical deflection device. 12. A light beam from a light source side is deflected by a light deflector, and the deflected light beam is guided to a surface to be scanned by a scanning image forming optical system to form a light spot, and the light spot forms a light spot on the surface to be scanned. An optical scanning method for performing optical scanning, wherein the optical deflecting device according to claim 7 is used as an optical deflecting device. 13. A light beam from a light source is deflected by an optical deflector, and the deflected light beam is guided to a surface to be scanned by a scanning image forming optical system to form a light spot. An optical scanning method for performing optical scanning, wherein the optical deflecting device according to claim 8 is used as an optical deflecting device. 14. The optical scanning method according to claim 9, wherein a light beam from a light source is coupled, and the coupled light beam is focused in a sub-scanning direction by a line image forming optical system. An optical scanning method characterized by forming an image as a long linear image in the main scanning direction in the vicinity of a position where the light is finally reflected by the deflection reflecting surface of the optical deflector. 15. The optical scanning method according to claim 9, wherein a line connecting the sagittal vertices of the lens surface is curved in the sub-scanning direction in order to correct the bending of the scanning line. One or more,
An optical scanning method for use in a scanning imaging optical system. 16. A light beam from a light source is deflected by a light deflector, and the deflected light beam is guided to a surface to be scanned by a scanning image forming optical system to form a light spot. An optical scanning device for performing optical scanning, wherein the optical deflection device according to claim 1 is used as the optical deflection device. 17. A light beam from a light source side is deflected by an optical deflector, and the deflected light beam is guided to a surface to be scanned by a scanning image forming optical system to form a light spot, and the light spot forms a light spot on the surface to be scanned. An optical scanning device that performs optical scanning, wherein the optical deflection device according to claim 2 is used as the optical deflection device. 18. A light beam from a light source side is deflected by an optical deflector, and the deflected light beam is guided to a surface to be scanned by a scanning image forming optical system to form a light spot. An optical scanning device for performing optical scanning, wherein the optical deflection device according to any one of claims 3 to 6 is used as the optical deflection device. 19. A light beam from a light source side is deflected by a light deflector, and the deflected light beam is guided to a surface to be scanned by a scanning image forming optical system to form a light spot, and the light spot forms a light spot on the surface to be scanned. An optical scanning device for performing optical scanning, wherein the optical deflection device according to claim 7 is used as the optical deflection device. 20. A light beam from a light source side is deflected by an optical deflector, and the deflected light beam is guided to a surface to be scanned by a scanning image forming optical system to form a light spot, and the light spot forms a light spot on the surface to be scanned. An optical scanning device for performing optical scanning, wherein the optical deflection device according to claim 8 is used as the optical deflection device. 21. An optical scanning device according to any one of claims 16 to 20, wherein: a coupling lens for coupling a light beam from a light source; and a light beam coupled by the coupling lens in a sub-scanning direction. An optical scanning device, comprising: a line image forming optical system that forms a long line image in a main scanning direction in the vicinity of a position where the light is converged and finally reflected by a deflection reflecting surface of an optical deflector. 22. The optical scanning device according to claim 16, wherein the scanning image forming optical system corrects a curvature of the scanning line by:
An optical scanning device comprising: at least one lens in which a line connecting the sagittal vertices of a lens surface curves in the sub-scanning direction. 23. An image forming apparatus for forming an image by optically scanning a photosensitive medium, wherein the optical scanning apparatus according to any one of claims 16 to 22 is used for optically scanning the photosensitive medium. Image forming device. 24. The image forming apparatus according to claim 23, wherein a latent image is formed on the photosensitive medium by optical scanning of the photosensitive medium, and the latent image is visualized. 25. The image forming apparatus according to claim 24, wherein the photosensitive medium is a photoconductive photoreceptor, the latent image is formed as an electrostatic latent image, visualized as a toner image, and the toner image is formed in a sheet shape. An image forming apparatus, which is finally carried on a recording medium according to (1).