JP2000180780A - Optical scanner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve image-formation performance with respect to oblique incidence of light. SOLUTION: This scanner is equipped with a rotating polygon mirror 28, having plural deflecting surfaces 28A and deflecting incident luminous flux to a main scanning direction, an incident optical system including a cylindrical lens 22, which is a so-cabled an 'overfield optical system' and making the luminous flux incident so that an optical axis is inclined in a subscanning direction by a prescribed angle, and an fθ lens system 26 for focusing the incident luminous flux to scan the surface to be scanned. The bus of the lens 22 included in the incident optical system is curved according to an incident angle on the mirror 28, so that the deterioration of the image-formation performance which changes according to the incident angle on the mirror 28 is decreased.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical scanning apparatus, and more particularly, to an overfilled optical system in which a light beam from a light source is incident so as to straddle a plurality of reflecting surfaces of a rotary polygon mirror. An optical scanning device such as a laser copying machine, a laser printer, or a laser facsimile in which a light beam from a light source is incident on a rotary polygon mirror at a predetermined angle in a sub-scanning cross section, and is scanned and exposed using the light beam to record an image. About.

[0002]

2. Description of the Related Art Optical systems applied to optical scanning devices such as laser printers and digital copiers include an underfilled optical system and an overfilled optical system. The underfilled type optical system defines a width of a light beam incident on a rotary polygon mirror in a direction corresponding to a main scanning direction along a rotation direction of a reflection surface of the rotary polygon mirror (hereinafter, referred to as a surface width). ) Is smaller than that of the optical system (see JP-A-6-18803).

As shown in FIGS. 15 and 16, in an example of an under-filled type optical system, a light beam emitted from a light source 71V is converted into substantially parallel light by a collimator lens 72V and is incident on a rotary polygon mirror 78V, where Mirror 78
The light beam deflected by V is scanned by the fθ lens 76V so as to scan the scanned surface 82V at a substantially constant speed.
Converges on. Here, the width of the light beam incident on the rotating polygon mirror 78V is smaller than the surface width of the rotating polygon mirror 78V.

Focusing on the sub-scanning direction of this optical system, the light beam which has become substantially parallel light by the collimator lens 72V is once converged on the rotary polygon mirror 78V by the cylindrical lens 74V. The light beam deflected by the rotating polygon mirror 78V is fθ
The light is converged again on the surface to be scanned 82V by the lens 76V and the cylindrical mirror 81. The reflection surface of the rotating polygon mirror and the surface to be scanned are f
An optically conjugate relationship is established by the θ lens and the cylindrical mirror 81 to prevent fluctuation (pitch unevenness) of the scanning position in the sub-scanning direction due to the tilt of the rotating polygon mirror 78V.

On the other hand, the overfilled optical system is an optical system in which the width of the light beam incident on the rotary polygon mirror 78W in the main scanning direction is larger than the surface width of the rotary polygon mirror 78W (Japanese Patent Laid-Open No. 6-59209). No., JP-A-8-17
No. 1069). For example, as shown in FIG.
The light beam emitted from the light source 71W becomes substantially parallel light having a width D ₀ by the lens, is incident on the rotating polygon mirror 78W, and the width D _{0 of the} light beam incident on the rotating polygon mirror 78W is determined by the rotating polygon mirror 78W.
It is greater than the surface width D _1.

In the overfilled optical system, the surface width of the rotary polygon mirror 78W can be reduced and the number of surfaces can be increased as compared with the underfilled optical system. There is an advantage that the resolution can be increased and the load on the motor for driving the rotary polygon mirror can be suppressed lower than that of the underfilled type.

[0007] The incidence of the light beam on the rotary polygon mirror is preferably frontal incidence in order to secure a power balance and prevent unevenness of the light beam diameter.

Here, when the front incidence is performed, the direction of light incident on the rotary polygon mirror is a direction inclined from the direction perpendicular to the rotation axis of the rotary polygon mirror to the sub-scanning direction. It is preferable that the inclination angle be as small as possible. However, since it is necessary to avoid interference with the imaging optical system, there is a limit to reducing the tilt angle. Therefore, in order to reduce the angle of inclination of the light incident on the rotating polygonal mirror in the case of front incidence, the light incident on the rotating polygonal mirror and the reflected light from the rotating polygonal mirror are transmitted twice through the imaging optical system. Double pass optical system (DaublePass
Optical systems) have been proposed.

In the double-pass optical scanning device having the double-pass optical system, as shown in FIGS. 18 and 19, a laser beam B1 modulated according to a recording signal from a laser beam generator 80 (as shown in FIG. Is output obliquely downward, passes through the fθ lens 82, and is incident on the reflection surface of the rotary polygon mirror 84. The incident laser beam B1 is reflected obliquely downward by the rotary polygon mirror 84 as scanning laser beams B2 and B3, and the scanning laser beams B2 and B3 are reflected by fθ
The light again passes through the lens 82 from the opposite side, is reflected by the cylindrical mirror 86, reaches the photosensitive member 88 in the form of a drum, and is recorded on the surface of the photosensitive member 88 as an electrostatic latent image. The angle of inclination (incident angle) to the rotating polygon mirror is minimized as described above. That is, when the inclination angle is excessively large, the distortion of the scanning line on the photoconductor 88 increases, and the light spot diameter on the photoconductor 88 becomes non-uniform.

A multi-beam optical scanning apparatus for forming a color image by irradiating a plurality of light beams with respect to a common scanning optical system has been proposed (Japanese Patent Application Laid-Open No. 63-936).
No. 1). In a multi-beam scanning optical system, in order to independently irradiate a plurality of light beams onto a predetermined surface to be scanned, it is necessary to separate the plurality of light beams after being deflected and reflected by an optical deflector. In the sub-scan section, a light beam is incident from an oblique direction to be separated.

However, when a light beam is incident on the deflecting surface of the optical deflector in an oblique direction in the sub-scanning section, the image forming performance deteriorates as described above if the incident angle of the light beam on the deflecting surface increases (scanning area). (The diameter of the light beam at the end becomes thicker than the diameter of the light beam at the center = uniformity of the light beam diameter at the scanning position is deteriorated).

In order to solve the problem that the imaging performance for oblique incidence deteriorates, the angle between the optical axis of the fθ lens and the deflector reflection surface and the angle between the light incident on the fθ lens and the deflector reflection surface are within a certain range. There is known a technique for preventing the deterioration of the imaging performance by setting to (see JP-A-9-96773). Further, as another technique, the fθ lens includes a rotationally asymmetric lens, and the optical axis of the lens is substantially parallel to the light incident on the lens, and the generatrix connecting the sagittal vertices of the lens is curved in the sub-scanning direction. There is known a technique for preventing deterioration of the imaging performance by causing the image to be deteriorated (Japanese Patent Laid-Open No. 10-73).
778).

[0013]

However, if the angle between the optical axis of the fθ lens and the deflector reflection surface and the angle between the light incident on the fθ lens and the deflector reflection surface are set within a certain range, the scanning line Bending occurs. When the generatrix of the fθ lens is curved in the sub-scanning direction, the bending of the scanning line and the deterioration of the imaging performance are eliminated, but the manufacturing is difficult and the molding process is performed, so that the reliability is deteriorated.

The present invention, in view of the above facts,
It is an object of the present invention to provide an optical scanning device capable of improving imaging performance for oblique incidence.

[0015]

In order to achieve the above object, an optical scanning apparatus according to the present invention has at least one reflecting surface and deflects an incident light beam in a main scanning direction, and at least one deflecting means. An incident optical system for causing a light beam to enter the deflecting means so as to include a region of the reflection surface in the main scanning direction and converging the light beam in a sub-scanning direction intersecting the main scanning direction; and a light spot is scanned. And a scanning optical system for converging the incident light beam on the surface to be scanned, the light beam being incident on the deflecting means so that the optical axis is inclined at a predetermined angle in the sub-scanning direction. The incident optical system is shaped according to the angle of incidence on the deflecting means so that deterioration of the imaging performance caused by deflection in the main scanning direction, which varies according to the angle of incidence on the deflecting means, is reduced. Changed And wherein the Rukoto.

As the deflecting means, a rotary polygon mirror such as a polygon mirror having at least one reflecting surface and deflecting the incident light beam in the main scanning direction can be used. A light beam is incident. As the incident optical system, a so-called overfield optical system in which a light beam is incident so as to include at least one reflection surface is employed. 1
In the case of including one reflecting surface, it is sufficient to include a region in the main scanning direction. The incident optical system focuses the light beam in a sub-scanning direction that intersects the main scanning direction. A light beam is incident on the deflecting means so that the optical axis is inclined by a predetermined angle in a sub-scanning direction that intersects the main scanning direction. The light beam deflected by the deflecting means is focused on the surface to be scanned so that the light beam is scanned by the scanning optical system. When a light beam is incident on the deflecting surface of the deflecting means in an oblique direction in the sub-scan section, the imaging performance is degraded as the incident angle of the light beam on the deflecting surface increases. Therefore, the shape of the incident optical system according to the present invention is changed according to the angle of incidence on the deflecting means so that the deterioration of the imaging performance which changes according to the angle of incidence on the deflecting means is reduced. That is, the angle of incidence on the deflecting means is set so that the light beam diameter at the end of the scanning area becomes larger than the light beam diameter in the middle or the uniformity of the light beam diameter at the scanning position is reduced. The shape of the incident optical system is changed accordingly. In this case, it is preferable to change the shape in the sub-scanning direction. By doing this,
The state of the light beam from the incident optical system will change,
When the light beam is obliquely incident, the light beam is multiplied, and a state corresponding to the light beam incident along the optical axis is obtained. As a result, it is possible to prevent deterioration of the imaging performance (deterioration of the uniformity of the light beam diameter at the scanning position) due to the oblique incidence of the light beam. For example, if a light beam is considered as a line image (considering a straight line connecting the light rays at the center and both ends of the light beam),
If the shape is not changed, it can be considered that the line image becomes inclined near both ends of the scanning area by obliquely entering the light beam, but if the shape is changed as in the present invention, it is as if the line image is Can be caught as if it had rotated.
Therefore, it is possible to prevent the deterioration of the imaging performance (the deterioration of the uniformity of the light beam diameter at the scanning position).

The incident optical system includes a single lens having a function of forming a long line image in a direction corresponding to the main scanning direction, and the generatrix of the single lens is curved in the sub scanning direction. The configuration can be changed by forming the curved line.

Although the deflecting means has at least one reflecting surface, it is difficult to manufacture the deflecting means with high accuracy without errors such as surface inclination. Also, when there are a plurality of reflecting surfaces, it is difficult to manufacture each reflecting surface equivalently. For example, the tilt of the reflecting surface occurs within a manufacturing error range. For this reason, the direction may be different for each manufacturing lot or reflecting surface. Therefore, this problem can be solved by providing a function of forming a long line image in a direction corresponding to the main scanning direction. A single lens anamorphic lens such as a cylindrical lens (cylindrical lens) can be used as a function to form a long line image. By forming an incident optical system with such a single lens, the generatrix can be easily formed. Can be curved. For this reason, by forming the generatrix so as to be a curve curved in the sub-scanning direction, the image forming performance is deteriorated when the light beam is obliquely incident (the uniformity of the light beam diameter at the scanning position is deteriorated). Can be easily prevented.

The scanning optical system is arranged so that the curvature of the scanning line is reduced, and the image forming performance is deteriorated by curving the generatrix shape of the incident optical system in the sub-scanning direction according to the arrangement of the scanning optical system. Can be prevented.

That is, the light beam incident on the deflecting means is
When the light is obliquely incident in the sub-scanning direction, the light beam traveling from the deflecting unit to the scanning optical system also becomes oblique. By arranging the scanning optical system so that the degree of curvature of the scanning line curved by the oblique light beam toward the scanning optical system is reduced, the curvature of the scanning line is suppressed. Further, if the generatrix of the single lens is curved in the sub-scanning direction in accordance with the curvature of the scanning line, deterioration of the imaging performance against oblique incidence (deterioration of the uniformity of the luminous flux diameter at the scanning position) is also prevented. can do.

A plurality of light beams can be made incident on the deflecting means, and the plurality of light beams can pass through at least a part of the incident optical system and the scanning optical system to be shared.

When a single scanning exposure is performed, for example, scanning is required for the number of scanning lines required to form an image.
This can be shortened by scanning a plurality of light beams substantially simultaneously to form a plurality of scanning lines. Therefore, a plurality of light beams are made incident on the deflecting means, and the plurality of light beams are passed through at least a part of the incident optical system and the scanning optical system to be common, so that the plurality of light beams are shared by the common scanning optical system and the deflecting device. Because it is scanned by means,
The number of components can be reduced, and cost reduction and miniaturization can be achieved.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. In the first embodiment,
The present invention is applied to an optical scanning device that deflects a light by a rotating polygon mirror and forms a light beam on the deflecting surface as a long and thin line image in a direction along the main scanning direction by one cylindrical lens.

As shown in FIG. 2, the optical scanning device of the present embodiment comprises a rotary polygon mirror 2 as a deflecting means for deflecting a light beam.
8, a photosensitive drum 30 coated with an image-recording photosensitive member irradiated with a light beam reflected and deflected by the rotating polygon mirror 28, and a laser light source device 20 for emitting one or more light beams. Have been. The rotating polygon mirror 28 is formed in a regular polygonal prism shape, and its side surface portion is formed of a plane reflecting surface that functions as a deflecting surface 28A. The rotary polygon mirror 28 is installed so that it is rotated in the direction of arrow P at a predetermined angular velocity by a driving means such as a motor (not shown) around a substantially vertical rotation axis O, and the light beam from the light source is deflected at a constant angular velocity. ing.

In the following description, the surface formed by the trajectory of the light beam reflected and deflected by the rotary polygon mirror 28 will be referred to as the main scanning surface, and the direction in which the main scanning surface and the photosensitive drum 30 intersect will be described. A main scanning direction, and a direction intersecting (particularly orthogonal to) the main scanning plane is defined as a sub-scanning direction.

The photosensitive drum 30 is formed in a slender, substantially cylindrical shape having a surface coated with a photosensitive material sensitive to a light beam. The photoconductor drum 30 is arranged so that the longitudinal direction of the photoconductor drum 30 substantially coincides with the direction (the arrow Q direction in FIG. 2) along the main scanning direction of the light beam scanned by the rotary polygon mirror 28. The photosensitive drum 30 is configured to rotate in a direction indicated by an arrow S at a predetermined rotation speed about a rotation axis by a driving unit (not shown).

The laser light source device 20 includes a semiconductor laser 14 that emits a divergent light beam that is a diffused light beam having a divergence angle in a direction corresponding to the main scanning direction larger than a divergence angle in a direction corresponding to the sub-scanning direction. It is composed of a collimator lens 16 for shaping a light beam emitted from 14 and an aperture stop 18 for beam forming. The semiconductor laser 14 is controlled to be turned on / off by a modulation means (not shown) in accordance with an image signal.

On the exit side of the aperture stop 18, a cylindrical lens 22 as a single lens of the incident optical system of the present invention is provided. The cylindrical lens 22 is provided so as to converge the transmitted light beam only in the sub-scanning direction.
8 is a lens system for forming a light beam as an elongated linear image in the direction along the main scanning direction by converging the light at or near the deflection surface 28A.

On the axis of the light beam emitted from the laser light source device 20 and on the exit side of the cylindrical lens 22, a plane mirror 24 for causing the light beam to enter the rotary polygon mirror 28 from the front.
Is arranged.

Between the plane mirror 24 and the rotary polygon mirror 28,
The light beam reflected and deflected by the rotary polygon mirror 28 is focused on the photosensitive drum 30 as a light spot to form an image, and the formed light spot is moved at a constant speed on the surface of the photosensitive drum 30 by deflection scanning. F for
The θ lens system 26 is arranged. This fθ lens system 2
6 is a part of the scanning optical system of the present invention,
Thus, the light beam incident on the rotary polygon mirror 28 from the front and the light beam reflected and deflected by the rotary polygon mirror 28 are both incident.

That is, the light beam passes through the fθ lens system 26 twice before and after the reflection and deflection by the rotary polygon mirror 28. The optical system as a whole forms a so-called front incidence / double-pass optical system. ing. In order to prevent the light incident on the rotating polygon mirror 28 and the reflected light from the rotating polygon mirror 28 from overlapping, the direction of the incident light on the rotating polygon mirror 28 is orthogonal to the rotation axis of the rotating polygon mirror 28. The direction is inclined in the sub-scanning direction from the moving direction.

Next, the operation around the cylindrical lens 22 will be described in detail. As described in the above section, the light beam obliquely incident on the rotating polygon mirror 28 has a curved scanning line due to the deflection scanning of the rotating polygon mirror 28.

That is, as shown in FIG. 3A, the curvature of the scanning line is such that the light beam 25 obliquely incident on the rotary polygon mirror 28 with respect to the deflecting surface 28A has a trajectory of the light beam due to the deflection scanning of the rotary polygon mirror 28. A scanning line formed in a sub-scanning section (a plane parallel to the XY plane) caused by drawing a surface is curved (for example, a displacement of a distance e in FIG. 3). A curved scanning line is incident on the fθ lens system 26 disposed on the center of the obliquely incident light flux 25, and the photosensitive drum 3 as a surface to be scanned is scanned.
The curvature of the scanning line appears as it is at zero. This is the curvature of the scanning line due to oblique incidence.

Next, the deterioration of the imaging performance will be described with reference to FIG.
This will be described with reference to (B), (C), and (D). FIG.
(B) is an explanatory diagram for explaining a light beam incident on the deflection surface 28A of the rotary polygon mirror 28 and a light beam deflected. In the overfilled type optical system, a light beam 27 of a predetermined size (including at least a deflecting surface) is directed toward the rotating polygon mirror.
Is incident, and a part of the incident light beam 27 (light beam reflected by the deflecting surface) is deflected. FIG. 3B is a view as viewed from above the rotary polygon mirror 28. In FIG. 3B, a central ray of the light beam 27 is a principal ray P, and both side edges of the principal ray P (near the boundary of reflection of the deflecting surface). Of light U and light L.
FIG. 3C is an image diagram when the vicinity of one deflection surface (FIG. 3B) is viewed as a sub-scanning cross section.

As shown in FIG. 3C, light rays L, P, U
Are reflected on the deflecting surface 28A as light beams having different heights in the sub-scanning direction in the order of the light beams L, P, and U. The light beam, which is a light beam, becomes a focal line formed in the sub-scanning direction by the incident-side tilt correction cylindrical lens. Therefore, as shown in FIG. 3D, the light beams L, P, and U become a line image rotated by the rotation angle φ on the XY plane on the deflection surface of the rotary polygon mirror 28.
The rotation angle φ changes in proportion to the rotation angle of the rotary polygon mirror 28.

FIG. 4A is an image diagram showing the trajectory of the principal ray P after being deflected and scanned by the rotary polygon mirror 28 and the states of the rays U and L around the principal ray P.
(B) is a diagram showing the main part. As shown in FIGS. 4A and 4B, as the angle of view in the main scanning section increases (the absolute value of the Y coordinate increases),
The rotation angles φ of P and U increase. Thereafter, at the stage where the light beam is transmitted and reflected by the fθ lens system 26 and the cylindrical mirror 81, the light beams L and U around the principal ray P receive an asymmetric refracting power from the fθ lens system 26 and the cylindrical mirror 81. As a result, rays L,
U rotates around the principal ray P in the YZ plane, and the imaging performance deteriorates.

FIG. 7 is an image diagram showing contour lines of the power of the light spot in order to show how the imaging performance deteriorates. FIG. 7A shows an image having an image height of 100%.
(B) shows the image height of 70%, FIG. 7 (C) shows the image height of 70%, FIG. 7 (D) shows the image height of -70%,
FIG. 7E shows the case where the image height is -100%. Since the angle of rotation φ of the light beam increases the main scanning angle of view, as shown in FIG. 7, the shape of the light spot is disturbed as the angle of main scanning increases.

As described above, the shape of the light spot is disturbed as the angle of view in the main scanning direction increases. However, the present inventor has proposed that the shape of the cylindrical lens 22 be curved in the sub-scanning direction with respect to its generating line. It has been found that disturbance of the spot shape can be reduced. That is, the light beam incident at an angle of view in the main scanning direction is
The light fluxes (light rays L, P, and U) are provided by the cylindrical lens 22 having the generatrix 2 curved so that the light flux does not rotate after passing through the fθ lens system 26 or the cylindrical mirror 81 when passing through the fθ lens system 26 and the cylindrical mirror 81. ) Is incident on the fθ lens system 26, which can prevent the imaging performance from deteriorating.

FIG. 5 shows the trajectory of the principal ray P after the generatrix of the cylindrical lens 22 is curved in the sub-scanning direction and deflected and scanned by the rotary polygon mirror 28, and the ray U around the principal ray P of the principal part. And the relationship between light rays L.

In the overfilled optical system, the rotary polygon mirror 2
Since the width of the light beam incident on the mirror 8 in the main scanning direction is larger than the surface width of the rotary polygon mirror 28, as shown in FIG.
The area of use of the light beam when scanning the central portion and the end portion of the photosensitive drum 30 (scanned surface) is different from each other. As a result, as shown in FIG. 6, the light beam incident on the cylindrical lens 22 has a different area in which the light beam used to scan the central portion and the end of the photosensitive drum 30 (scanned surface) is different. When the light beam is directed toward the central portion and the end portion of the photosensitive drum 30 (scanned surface) by being curved, the light beam is reflected by the rotating polygon mirror 28 and enters the fθ lens system 26 when the photosensitive drum 30 (scanned surface). ), The rotation of each of the light beams L, P, and U at the center portion and the end portion can be reduced, and the deterioration of the imaging performance can be prevented.

Therefore, in this embodiment, the cylindrical lens 2
2 is curved about its generatrix. As shown in FIG. 1, the shape is a shape in which the generating line is curved in one direction (sub-scanning direction), and when the X-axis, the Y-axis, and the Z-axis are taken, it can be expressed by the following equation.

[0042]

(Equation 1)

However, the sign of “±” is “−” when Ry> 0 and “+” when Ry <0.

In the cylindrical lens of the present embodiment, the curvature Ry
Is 350 mm, and the radius Rx having power in the sub-scanning direction is 154,807 mm. Note that, in the present embodiment, the curvature of the generating line is formed on an arc in consideration of simplicity of manufacture.

As described above, since the cylindrical lens 22 is curved, each light beam traveling toward the center and the end of the photosensitive drum 30 in the main scanning direction is reflected by the rotary polygon mirror 28 and enters the fθ lens system 26. In this case, the rotation of the light beams L, P, and U at the central portion and the end portion of the photosensitive drum 30 can be reduced, thereby preventing the imaging performance from deteriorating.

Table 1 below shows the overall optical data of the optical scanning device (FIG. 2) of the present embodiment.

[0047]

[Table 1] Incident angle to rotating polygon mirror 1.2 degrees

FIG. 9 shows a comparison result of comparing changes in the light beam diameter of the cylindrical lens of the present embodiment with those of the conventional cylindrical lens. FIG. 9A shows the light beam diameter in the sub-scanning direction, and FIG. 9B shows the light beam diameter in the main scanning direction. FIG. 10 shows the shape change of the changing light beam diameter in FIG. That is, FIG. 10 is an image diagram showing the contour of the power of the light spot with respect to the imaging performance. FIG.
(A) shows an image height of 100%, and FIG. 9 (B) shows an image height of 70%.
FIG. 9 (C) shows an image height of 0%,
FIG. 9D shows an image with an image height of −70%, and FIG. 9E shows an image with an image height of −100%. Since the rotation angle φ of the light beam has a large main scanning angle of view, as shown in FIG. 9, the shape of the light spot is substantially maintained without change irrespective of the main scanning angle of view. As shown in FIGS. 9 and 10, it can be understood that the light beam is well imaged and the light beam diameter is substantially uniform.

Next, a second embodiment will be described. In addition,
This embodiment has substantially the same configuration as the above embodiment,
The same portions are denoted by the same reference numerals, and detailed description is omitted.

As shown in FIG. 11, the optical scanning device of this embodiment has a plurality of light source devices 50 each having a cylindrical lens.
52, and photosensitive drums 54 and 56 corresponding to the light source devices 50 and 52, respectively. The light source device 5
Optical members are also provided to separate and guide the light beams 51 and 53 emitted from the light beams 0 and 52 to the photosensitive drums 54 and 56, respectively.

In the present embodiment, the optical system is configured to scan the light beams 51 and 53 emitted from the light source devices 50 and 52 through the common rotary polygon mirror 28 and the fθ lens system 26. I have. The first light source 50 is used to easily separate the light beam irradiated to each of the photosensitive drums 54 and 56.
The angle at which the light beam emitted from the second light source enters the rotary polygon mirror 28 is 2.4 degrees, and the angle at which the light beam emitted from the second light source 52 enters the rotary polygon mirror 28 is 1.2 degrees. In this case, the radius R of the cylindrical lens in the bending direction is 12
0 and 350 mm.

FIG. 12 shows a change in the diameter of each light beam (on the surface to be scanned) when a plurality of light beams enter the rotary polygon mirror at different incident angles in the present embodiment. FIG. 12A shows the light beam diameter in the sub-scanning direction.
(B) shows the beam diameter in the main scanning direction. As can be understood from FIG. 12, the light beams emitted from each of the light source devices 50 and 52 maintain the uniformity of the light beams.

As described above, in the present embodiment, when a light beam is incident on the rotary polygon mirror at different incident angles, the generatrix of each corresponding cylindrical lens is curved. For this reason, even when a plurality of light beams are emitted using a plurality of light source devices, the performance is not easily degraded by using a common optical system (fθ lens system or rotating polygon mirror), and each light beam can be easily emitted. The light beam can be separated, and a compact and low-cost optical scanning device can be provided.

In this embodiment, a case has been described in which light beams are emitted from a plurality of light source devices. However, the present invention is not limited to this, and a plurality of light beams are emitted from a single light source device. The present invention is also applicable to such a case. Further, in the present embodiment, two light beams are described as a plurality of light beams, but the present invention is not limited to this, and can be applied to three or more light beams.

Next, a third embodiment will be described. In this embodiment, since the configuration is substantially the same as that of the above-described embodiment, the same portions are denoted by the same reference numerals and detailed description thereof will be omitted.

In the present embodiment, the fθ lens system is tilted (t
The present invention is applied to a case where the curvature of the scanning line due to the oblique incidence on the rotary polygon mirror is corrected by performing (ilt). In the present embodiment, the deterioration of the imaging performance due to oblique incidence and the inclination of the fθ lens system is corrected by bending the cylindrical lens. That is, the optical scanning device according to the present embodiment achieves both linearity of scanning lines and uniformity of light flux. Note that, in the optical scanning device shown in FIG.
μm.

As shown in FIG. 13, in the present embodiment,
The f1 lens system is composed of the L1 lens 60 and the L2 lenses 62 and 64. That is, the fθ lens system responsible for the light beam emitted from the first light source 50 is
0 and an L2 lens 62, and a second light source 52
The fθ lens system that is responsible for the light flux emitted from the lens is composed of an L1 lens 60 and an L2 lens 64. L2 lens 6
Reference numerals 2 and 64 denote lenses having the same shape in order to eliminate the curvature of the scanning line, and set the inclination angles of the L2 lens 62 and the L2 lens 64 to 1.7 degrees and 1.5 degrees, respectively.

In this embodiment, the radius R, which is the degree of curvature of the cylindrical lens to be curved, is 1 in the light source device 50.
25 mm and 400 mm in the light source device 52.

By setting as described above, the curvature of the scanning line can be suppressed. FIG. 14 shows a change in the diameter of each light beam (on the surface to be scanned) when a plurality of light beams are incident on the rotating polygon mirror at different incident angles and the L2 lens is inclined in the present embodiment. . FIG.
FIG. 14A shows the light beam diameter in the sub-scanning direction, and FIG. 14B shows the light beam diameter in the main scanning direction. As can be understood from FIG. 14, the light beams emitted from each of the light source devices 50 and 52 maintain the uniformity of the light beams. Further, the linearity of the scanning line can be improved.

In the present embodiment, the curvature of the scanning line due to the oblique incidence has been described. However, when assembling and adjusting the optical scanning device in manufacturing, the curvature of the scanning line is caused by the dispersion of parts and the like. The amount of curvature may be different. In that case, it is possible to adjust the inclination of the fθ lens system in order to equalize the difference in the curvature of the scanning line for each light beam. In that case, the uniformity of the light beam diameter may be deteriorated as described above. In order to compensate for the uniformity of the light beam diameter, the cylindrical lens is formed of plastic (resin), and the cylindrical lens is mechanically curved with the inclination angle of the fθ lens system or the deterioration of the light beam diameter to compensate for the light beam diameter deterioration. You can also. Further, several kinds of lenses having different curvatures may be prepared and exchanged.

In the above embodiment, the case where the curvature of the cylindrical lens is set to be an arc has been described. However, the present invention is not limited to this, and another curve may be used. For example, it is possible to compensate more strictly by forming a shape represented by a higher-order polynomial.

[0062]

As described above, according to the present invention, the light beam obliquely incident on the deflecting means having a plurality of reflecting surfaces is changed by the incident optical system according to the angle of incidence on the deflecting means. Since the shape is changed in accordance with the degree of the curvature so as to reduce the curvature of the scanning line formed by the deflection in the main scanning direction, the deterioration of the imaging performance with respect to the oblique incidence of the light beam (scanning position) (Deterioration of the uniformity of the luminous flux diameter) can be prevented.

[Brief description of the drawings]

FIG. 1 is an image diagram showing a cylindrical lens used in an optical scanning device according to an embodiment of the present invention, (A) showing a perspective view of the cylindrical lens, (B) showing a left side view,
(C) shows a front view.

FIG. 2 is a perspective view schematically showing an optical scanning device according to the embodiment of the present invention.

FIG. 3 is an explanatory diagram for explaining a problem caused by conventional oblique incidence.

FIG. 4 is an image diagram showing a chief ray trajectory after incidence of a rotating polygon mirror by oblique incidence in the related art and a state of light rays around the trajectory.

FIG. 5 is an image diagram showing a trajectory of a principal ray after incidence on a rotary polygon mirror due to oblique incidence according to the embodiment of the present invention and a state of a light beam around the trajectory.

FIG. 6 is an image diagram showing a state of a light beam incident on a rotary polygon mirror after a cylindrical lens and a use area.

FIG. 7 is an explanatory view showing a state in which imaging performance on a photosensitive member is deteriorated due to oblique incidence in the related art.

FIG. 8 is an explanatory diagram for explaining that a light beam incident on a rotary polygon mirror in an overfilled optical system uses different areas at a central portion and an end portion on a photoconductor.

FIG. 9 is a diagram showing a change in a light beam diameter on a photoconductor by a cylindrical lens according to the first embodiment and a change in a light beam diameter on a photoconductor by a conventional cylindrical lens.

FIG. 10 is an image diagram showing an image forming performance state on the photoconductor of the first embodiment.

FIG. 11 is a configuration diagram schematically illustrating an optical scanning device according to a second embodiment.

FIG. 12 is a diagram illustrating a change in a light flux diameter on a photoconductor in a second embodiment.

FIG. 13 is a configuration diagram schematically illustrating an optical scanning device according to a third embodiment.

FIG. 14 is a diagram illustrating a change in light beam diameter on a photoconductor in a third embodiment.

FIG. 15 is a front view for explaining an underfield optical system.

FIG. 16 is a side view of the underfield optical system.

FIG. 17 is an explanatory diagram for explaining an overfield optical system.

FIG. 18 is a side view of a front incidence / double pass optical system.

FIG. 19 is a front view of a front incidence / double pass optical system.

[Explanation of symbols]

 Reference Signs List 14 semiconductor laser 16 collimator lens 18 aperture 20 laser light source device 22 cylindrical lens 24 plane mirror 26 fθ lens system 28 rotating polygon mirror 28A deflection surface 30 photosensitive drum 81 cylindrical mirror

Claims (4)

[Claims] 1. A deflecting device having at least one reflecting surface and deflecting an incident light beam in the main scanning direction, and a light beam applied to the deflecting device so as to include at least one region of the reflecting surface in the main scanning direction. And an incident optical system that focuses a light beam in a sub-scanning direction that intersects the main scanning direction, and a scanning optical system that focuses a light beam incident so that a light spot is scanned on a surface to be scanned. In the optical scanning device, a light beam is incident on the deflecting means so that an optical axis is inclined by a predetermined angle in the sub-scanning direction, and the incident optical system changes according to an incident angle on the deflecting means. An optical scanning device, wherein the shape is changed in accordance with the angle of incidence on the deflecting means so that the deterioration of the imaging performance caused by the deflection in the main scanning direction is reduced. 2. The incident optical system includes a single lens having a function of forming a long line image in a direction corresponding to the main scanning direction, wherein a generating line of the single lens is curved in a sub-scanning direction. The optical scanning device according to claim 1, wherein the shape is changed by forming a curved line. 3. The method according to claim 1, wherein the scanning optical system is arranged so that the curvature of the scanning line is reduced, and the generatrix of the incident optical system is curved in the sub-scanning direction according to the arrangement of the scanning optical system. The optical scanning device according to claim 2. 4. The deflecting means receives a plurality of light beams, and passes the plurality of light beams through at least a part of the incident optical system and the scanning optical system to be common. The optical scanning device according to claim 3.