JP2002148546A - Optical scanner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an optical scanner improving the uniformity of light quantity on a face to be scanned by easily synthesizing/separating a plurality of incident beams and scanning beams. SOLUTION: Beams A, B are made incident on a scanning image forming lens 24 at respective incident angles different from each other in a sub-scanning direction and made incident on the same deflection face of a deflector 18 obliquely to a face orthogonal to a rotational axis to deflect the beams and the deflected beams are emitted from the lens 24 to scan and expose the face to be scanned. The lens 24 is inclined in the sub-scanning direction so that the distortion of spot shapes on the face to be scanned and a difference of beam diameters in a scanning direction which is generated by the oblique incidence of the beams A, B are set in prescribed ranges. In the case of correcting the lens 24 by inclining it, the uniformity of light quantity on the face to be scanned can be improved by inclining the lens 24 in the sub-scanning direction so that the distortion of spot shapes and the difference of the beam diameters in the two beams are set in respective ranges generating no problem on its practical use, instead of trying to obtain an optimum state by noticing only one beam.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical scanning device used in a laser printer, a digital copying machine, and the like, and more particularly, to an optical scanning device that deflects and scans a plurality of beams using the same deflector.

[0002]

2. Description of the Related Art In recent years, multi-color documents have been developed, and an attempt has been made to improve the productivity of color images in an image forming apparatus. Laser printers have been commercialized.

An exposure apparatus used in an image forming apparatus using a plurality of photoconductors employs a method of arranging a plurality of scanning devices corresponding to each photoconductor in parallel. However, the exposure apparatus is reduced in size and the number of parts is reduced. Japanese Patent Laid-Open No. 2000-18075 (hereinafter referred to as Conventional Example 1) proposes a method in which a plurality of beams are deflected by a single deflector to scan a plurality of photoconductors in order to reduce costs.

In the first prior art, as shown in FIG. 11, a plurality of beams are incident on the deflection surface of a single deflector 38 and the plurality of beams are directed to a plane orthogonal to the rotation axis of the deflector 38. By making the light enter the deflection surface at different angles in the sub-scanning direction, separation of a plurality of beams is facilitated.

However, it is easy to separate a plurality of scanning beams simply by making the light incident on the deflector 38 at different angles in the sub-scanning direction. However, the incident beam incident on the deflector 38 and the deflected scanning beam are separated. In order to achieve this, a large incident angle difference must be made in the sub-scanning direction, so that the amount of scanning line curvature increases or the spot shape is remarkably distorted.

One solution to this problem is disclosed in Japanese Patent Laid-Open No. Hei 10-206761 (hereinafter referred to as Conventional Example 2).

The prior art 2 has an optical system for dividing and scanning the surface to be scanned, as shown in FIGS. 12 and 13. The two light sources 40A and 40B are arranged in the main scanning direction with respect to the optical axis of the scanning lens 42. And separates the plurality of beams so that the light is incident on a plane orthogonal to the rotation axis at a different incident angle in the sub-scanning direction. In the case of scanning a plurality of photoconductors, it is possible to divide the incident beam and the scanning beam by using the same arrangement.

In the prior art 2, it is described that it is desirable to reduce the incident angle in the sub-scanning direction. However, since a plurality of beams intersect on the deflection surface, the first scanning beam A and the second In order to separate the scanning beam B, a relatively large incident angle difference is required, which also results in an increase in the amount of scanning line bending or collapse of the Spot shape.

Further, Conventional Example 2 is disclosed in Japanese Unexamined Patent Publication No.
However, when the present invention is applied to a so-called overfilled optical system in which a beam having a width larger than the width in the main scanning direction of the deflecting surface disclosed in Japanese Unexamined Patent Application Publication No. H11-209 (Prior Art 3) is incident on the deflector, the following problems occur.

When two beams are incident on the deflector at different angles in the main scanning direction, rotation and movement of the deflecting surface between the beams for truncating a laser beam having a predetermined intensity distribution represented by a Gaussian distribution Changes in the F number due to the asymmetrical scanning, a light amount difference occurs between the scanning start end and the scanning end end, and a density difference occurs.
Since the change in the number is reversed and the light amount at the scanning start end and the scanning end end is reversed between the beams, even in the case of a small difference in the light amount, in the multicolor image forming apparatus, the color tone is different and the color unevenness occurs. appear.

Further, when the light is made incident at an angle in the sub-scanning direction, the light beam after deflection is curved, so that the beam passing position is different between the central scanning portion and the scanning end portion of the scanning lens, and the spot shape is deformed. Will be.

In order to suppress the deformation of the spot shape, Japanese Patent Application Laid-Open No. 2000-19443 (hereinafter referred to as Conventional Example 4) discloses FIG.
As shown in FIG. 4, the optical axis of the scanning lens 44 is arranged orthogonal to the rotation axis of the deflector and shifted by γ in the sub-scanning direction in parallel with a plane including the deflection reflection position.

However, since the scanning lens 44 having power in the sub-scanning direction is shifted, if the position where the light passes through the scanning lens 44 is different due to a component mounting error or an adjustment error, the effect of suppressing the deformation of the Spot type is reduced.

The use of a plurality of beams is more serious and has power in the sub-scanning direction. Therefore, it is necessary to increase the difference in the incident angle in the sub-scanning direction so as not to interfere with the scanning beam. Then, the curvature difference between the plurality of beams reflected by the deflector becomes large, the difference in the incident position between the scanning center portion and the scanning end portion of the scanning lens becomes larger, and the degree of deformation of the Spot shape becomes larger between the scanning beams.

Further, since the position which can be optimized even if the optical axis of the scanning lens is shifted is limited, the scanning beam which cannot be optimized increases the deformation of the Spot type.

[0016]

SUMMARY OF THE INVENTION The present invention has been made in consideration of the above problems, and has a small size and low cost, facilitates the combined separation of a plurality of incident beams and a scanning beam, and has a uniform light intensity on a surface to be scanned. It is an object of the present invention to provide an optical scanning device in which is improved.

It is another object of the present invention to provide an optical scanning apparatus which minimizes a change in Spot shape that occurs when a plurality of beams are deflected and scanned on the same deflection surface.

[0018]

According to a first aspect of the present invention, a plurality of beams are made to enter a scanning lens at different incident angles in the sub-scanning direction, and the beams of the deflector are brought to the same deflection surface of the deflector. In an optical scanning device that obliquely enters and deflects light onto a surface perpendicular to the rotation axis, emits the scanning lens, and scans and exposes the surface to be scanned, the beam is obliquely incident on the surface to be scanned. The scanning lens is tilted in the sub-scanning direction so that the spot shape distortion and the beam diameter difference in the scanning direction fall within a predetermined range for any beam.

In the above configuration, when correcting the distortion of the spot shape on the surface to be scanned and the beam diameter difference in the scanning direction caused by the oblique incidence of a plurality of beams on the same deflection surface by tilting the scanning lens, 1 Rather than focusing on one beam, the scanning lens should be moved in the sub-scanning direction so that the spot shape distortion and beam diameter difference fall within a range where practically no problem occurs for each beam. By tilting, the uniformity of the light amount on the surface to be scanned can be improved.

According to a second aspect of the present invention, the number of the beams incident on the same deflection surface is two, and the scanning lens has no power in the sub-scanning direction, and the skew of the spot shape of one of the beams. The tilt angle of the scanning lens is set so that insufficient correction results in excessive skew correction of the spot shape of the other beam.

In the above configuration, the spot shape distortion (Spot Rotation) of the beam caused by entering the deflector at an angle in the sub-scanning direction is caused by insufficient correction of the skew of the luminous flux of one beam and the other. By correcting the skew of the beam luminous flux so as to be excessive, the spot shapes of both beams can be improved to the extent that practical use is not hindered, and the beam diameter difference can be reduced.

According to a third aspect of the present invention, the number of the beams incident on the same deflection surface is two, and the scanning lens has no power in the sub-scanning direction, and one of the beams is incident on the scanning lens. The difference between the incident angle of incidence and the exit angle of light reflected from the deflecting surface and exiting from the scanning lens is reversed, and the other beam is incident on the scanning lens and reflected at the deflecting surface and the scanning is performed. The scanning lens is characterized by being inclined in the sub-scanning direction so that the difference from the emission angle of the light emitted from the lens becomes the same.

In the above configuration, in one of the beams, the sign of the incident angle and the sign of the exit angle of the scanning lens is reversed with the sign of the incident angle of the marginal ray in the sub-scanning direction.
Even if a single scanning lens is used by setting the inclination angle of the scanning lens in the sub-scanning direction so that the incident angle difference of the marginal ray in the sub-scanning direction has the same sign between the incident angle and the emission angle of the scanning lens, It is possible to satisfactorily correct the change in the spot shape of the book beam, and to obtain a good beam diameter over the entire surface to be scanned at low cost.

According to a fourth aspect of the present invention, a plurality of beams emitted from a plurality of light sources enter the deflector with a width larger than the width of the deflecting surface in the main scanning direction, and are deflected by the same deflecting surface.
In an optical scanning device that scans and exposes a plurality of photoconductors with a plurality of beams, a plurality of beams are incident at different angles in a sub-scanning direction with respect to a plane orthogonal to a rotation axis of a deflector, and are incident on the same deflection surface. Intersects forward, and enters the same deflecting surface at a non-zero angle in the main scanning direction with respect to a plane including the rotation axis of the deflector and passing through the center of the surface to be scanned, and intersects after being deflected by the deflecting surface It is characterized by:

In the above configuration, a plurality of beams are made to enter the same deflecting surface at different angles with respect to a plane orthogonal to the rotation axis of the deflector, and the beams intersect in the sub-scanning direction before entering the deflector. By doing so, it is possible to secure a separation space for a plurality of scanning beams and to easily separate the scanning beams.

In addition, the beam incident on the deflector has a predetermined non-zero angle in the main scanning direction with respect to a plane including the rotation axis of the deflector and passing through the center of the surface to be scanned. The combined separation of the beam and the scanning beam can be facilitated.

In a so-called overfilled optical system in which the light beam width of the beam incident on the deflector is larger than the deflecting surface and the deflecting surface substantially has the function of a stop, the plurality of beams cross in the main scanning direction after deflection. Accordingly, the difference in light amount between the scanning start end and the scanning end end due to the asymmetry of the F number is corrected by bringing the center of the laser beam intensity distribution closer to the center of the surface to be scanned, thereby reducing the density difference.

According to a fifth aspect of the present invention, a plane including the non-zero predetermined angle αi, the inscribed radius of the deflector, the rotation axis of the deflector, and passing through the center of the scanned surface passes through the deflection surface. A feature is that a distance δ between the position and the position on the deflection surface at which the maximum light amount of the laser beam intensity distribution is reached is 0 <δ ≦ r × sin (αi / 2).

In the overfilled optical system, since the incident position of the beam incident on the deflector at an angle in the main scanning direction on the deflection surface is configured as described above, the light amount difference caused by the left-right difference of the F number is obtained. And the laser beam intensity distribution center are offset from the surface to be scanned. Color unevenness can be prevented.

According to the invention described in claim 6, the beam is formed by two beams.
As an example, the angles of incidence in the sub-scanning direction on the deflector are β1, β
2, the distance from the deflecting surface to the first turning mirror on the scanning surface side is L, and the interval between the beams on the deflecting surface is t, t / L ≒ tan (β1−β2). And

With the above configuration, the distance between the two scanning beams at the separation position is determined not only by the space between the scanning beams due to the incident angle difference in the sub-scanning direction but also by the distance between the two beams on the deflection surface. Since the scanning beam can be added to the beam separation space, the scanning beam can be easily separated even if there is a scanning line curvature or a scanning line inclination generated after deflection.

In the case of t / Lβtan (β1−β2), the separation margin of the scanning beam becomes 2 × t, and at the same time, the two incident beams intersect at a position shifted from the first mirror in the sub-scanning direction. Therefore, the space between the incident beam and the scanning beam and the space between the scanning beams can be maximized.

[0033]

Embodiments of the present invention will be described below with reference to the drawings. [First Embodiment] As shown in FIGS. 1 and 2, an optical scanning device 10 according to a first embodiment includes four light sources 12A and 12A.
B, 12C, and 12D.
Laser beams A emitted from 2B, 12C, 12D,
By scanning and exposing the photoconductors 32Y, 32M, 32C, and 32K with B, C, and D, a multicolor image of four colors is obtained.

Here, the deflecting surface of one deflector 18 has
Although the laser beams A, B, C, and D are incident thereon, laser beams A and B deflected on the right side of the deflector 18 shown in FIG.

The laser beams A and B emitted from the light sources 12A and 12B are condensed by the coupling lenses 14A and 14B and are diverged as loose divergent light.
A, 14 °.

The laser beams A and B are applied to shaping optical systems 16A and 16B provided after the coupling lenses 14A and 14B.
16B, the laser beam A is focused in the sub-scanning direction.
Is turned directly toward the deflector 18 by the first mirror 20, and the laser beam B returns to the reflection mirror 22 and
It is turned back by the mirror 20 and faces the deflector 18.

The laser beams A and B turned back by the first mirror 20 are applied to the scanning image forming lens 2 serving also as a scanning lens.
4, the light is converted into substantially parallel light, and is formed on the deflection surface 18A as a linear image long in the main scanning direction.

The laser beams A and B deflected by the deflecting surface 18A of the deflector 18 pass through the scanning imaging lens 24 again and are scanned at substantially constant speed while being focused in the main scanning direction. Mirrors 26A and 26 for separating
The light is returned by B and enters the cylindrical mirrors 28A and 28B which are the sub-scanning focusing optical elements.

The laser beams A and B incident on the cylindrical mirrors 28A and 28B converge in the sub-scanning direction, are turned by the final turning mirrors 30A and 30B, pass through the cover glass, and scan the photoconductors 32Y and 32M.

When the photosensitive members 32Y and 32M are scanned and exposed, a latent image is formed, developed and visualized according to the latent image, and is transferred to the intermediate transfer member 40. Intermediate transfer member 40
Above, the developed images on the photoconductors 32Y and 32M are superimposed to form a multicolor image, and this image is transferred and fixed to paper P as a medium to obtain a color print.

As described above, in this embodiment, 4
Needless to say, by scanning and exposing four photoconductors with one laser beam, a multicolor image of four colors can be obtained.

As shown in FIG. 3, in the optical scanning device 10, the incident angle with respect to a plane L perpendicular to the rotation axis 18B of the deflector 18 is such that the laser beam A is obliquely below 2.4.
°, the laser beam B is 1.5 ° from obliquely below,
This constitutes a so-called sagittal offset incidence optical system.

As described above, the laser beams A and B obliquely incident in the sub-scanning direction are deflected and scanned by the deflector 18 and enter the scanning image forming lens 24. Scanning imaging lens 2
4 has Power only in the main scanning direction and P in the sub-scanning direction.
This is a so-called cylinder lens having no power.

The reason for using a cylinder lens is that, if it has power in the sub-scanning direction, it will be refracted in the sub-scanning direction, so that the incident beam and the scanning beam will approach each other. This is because it is possible to produce a large number of cylinder lenses by a single polishing step and cutting-out step, so that it can be produced at low cost.

Further, in this embodiment, the optical axis of the scanning image forming lens 24 is disposed at an angle of 6.8 ° in the sub-scanning direction with respect to a plane L orthogonal to the rotation axis 18B of the deflector 18, so that the laser beam The beam diameters of the photoconductors 32Y and 32M of A and B on the surface to be scanned are made uniform at the center of scanning and at the scanning end.

This is because, when a laser beam is obliquely incident on the deflecting surface 18A in the sub-scanning direction, the deflecting surface of the scanning beam is not flat but conical. Optical scanning imaging lens 2
A difference occurs in the angle of incidence on the light beam 4 and the spot shape changes, so that the beam diameter differs between the central scanning portion and the scanning end portion.

In addition, when the laser beams A and B are incident on the deflector 18 at different angles in the sub-scanning direction as in the present embodiment, the degree of skew of the scanning beam is different, and either of the laser beams A and B is different. With such a scanning beam, the beam diameter at the scanning center and the beam diameter at the scanning end greatly differ.

For this reason, in this embodiment, the beam generated when the laser beams A and B enter the deflector 18 at angles different from 1.5 ° and 2.4 ° in the sub-scanning direction.
Spot Rotation (Spot Rotation)
One laser beam A is over-corrected, that is, the angle difference between the light beams on both sides of the peripheral light in the sub-scanning direction is inverted between incidence and emission to the scanning imaging lens 24, and the other laser beam B is under-corrected, that is, The angle of inclination of the scanning imaging lens 24 in the sub-scanning direction was set to 6.8 ° so that the angle difference between the light rays on both sides of the light was the same sign for the incidence and the emission. Simply put, unless the scanning imaging lens 24 is tilted in the sub-scanning direction,
The difference between the angle of incidence and the angle of emission to the scanning imaging lens 24 is the same, but the difference is reversed depending on the tilt angle.

Thus, even if the scanning imaging lens 24 (two lenses in this embodiment) is single, the laser beams A and B
Of the spot shape can be satisfactorily corrected, and a good beam diameter can be obtained over the entire scanned surface of the photoreceptor at low cost.

FIG. 4 shows the difference between the beam diameters of the laser beams A and B on the surface to be scanned at the scanning center portion and the scanning end portion in this embodiment, and FIG. 5 shows the change in the spot shape of the laser beam. Is shown.

In the graph shown in FIG. 4, the laser beam A having the sub-scanning angle of 2.4 ° has the lower limit of the inclination angle of the scanning imaging lens 24 of 8 °, and when the inclination angle becomes smaller, the scanning center portion and the scanning end portion become smaller. Increases the beam diameter difference. The laser beam B having a sub-scanning angle of 1.5 ° has an inclination angle of 5.
When the inclination angle increases with the lower limit of 6 °, the beam diameter difference between the scanning center portion and the scanning end portion increases.

From this, it is desirable that the inclination angle of the scanning imaging lens 24 for reducing the beam diameter difference between the laser beams A and B is about 6.8 ° where the beam diameter difference curves intersect.

FIG. 5 shows a change in the spot shape of the laser beams A and B corresponding to the graph of FIG.
It is. The incident angle of the laser beam B in the sub scanning direction is 1.5 °
In this case, the Spot shape at both ends of the scanning is
When the inclination angle of 4 is 5.6 ° (a), the collapse is the least, and up to the inclination angle of 6.8 ° (b), the change of the shape is small.

However, when the inclination angle of the scanning imaging lens 24 is 8 ° (c), the Spot shape rapidly deteriorates. This is because, as the tilt angle of the scanning imaging lens 24 is increased with respect to the skew of the peripheral light beam generated when the sub-scanning incident angle is 1.5 °, the amount by which the skew of the Spot shape is corrected increases,
Overcorrection starts at 5.6 °, and S exceeds 8 °
This indicates that the pot shape is deteriorated.

On the other hand, in the case of the laser beam A whose incident angle in the sub-scanning direction is 2.4 °, the inclination angle of the scanning image forming lens 24 is 8 °.
(F) In the vicinity, the skew correction of the peripheral luminous flux becomes good, and the change in the Spot shape at both ends of the scanning is small, but below that, the skew correction of the peripheral luminous flux is insufficient, and the tilt angle is 5.6 °.
In (d), it can be seen that insufficient correction is large and the Spot shape is disturbed.

As described above, with respect to the two laser beams A and B having different sub-scanning incident angles, one laser beam A
Is that the skew of the peripheral light beam is excessively corrected, and the other laser beam B is formed by setting the inclination angle of the scanning imaging lens 24 so that the skew of the peripheral light beam is insufficiently corrected. Can be improved so as not to hinder actual use, and an optical scanning device having a small beam diameter difference can be provided.

The light sources 12A, 12A in this embodiment
As described above, the laser beams A and B emitted from B enter the plane orthogonal to the rotation axis of the deflector 18 at different angles in the sub-scanning direction and intersect near the first mirror 20. In addition, as shown in FIG. 6, in addition, in the main scanning direction, the laser beams A and B are reciprocal with respect to a plane including the rotation axis of the deflector 18 and passing through the center of the scanned surface of the photosensitive member. Α1 = α2 = 4 °
And enters the deflector 18 at an angle with an angle of.

Further, the laser beams A and B are made incident on the deflecting surface 18A so as to be shifted by δ = 0.32 mm with respect to a plane including the rotation axis of the deflector 18 and passing through the center of the surface to be scanned of the photosensitive member. At the same rotation angle of the device 18, the laser beams A and B cross the main scanning direction after deflection.

With this configuration, the light sources 12A and 12B and the coupling lenses 14A and 14A shown in FIG.
4B and the shaping optical systems 16A and 16B can be arranged without causing interference, and at the same time, the separation space between the incident beam and the scanning beam to the deflector 18 in the sub-scanning direction in the sub-scanning direction while having the minimum sub-scanning incident angle difference. , And separation of a plurality of scanning beams can be easily performed.

Next, the effect of offsetting the laser beams A and B so as to intersect the main scanning direction after deflection when the rotation angle of the deflector 18 is the same will be described with reference to FIG.
This will be described with reference to FIG.

FIG. 6 is a view of the laser beams A and B incident on the deflector 18 as viewed from the main scanning cross-sectional direction. The laser beam A has an angle α1 from the optical axis of the scanning imaging lens 24 above the plane of the drawing. The laser beam B enters the deflector 18 from below the optical axis at an angle of α2.

At this time, when the deflector 18 has the same rotation angle, the laser beam A and the laser beam B intersect after deflecting and reflecting, so that a plane including the rotation axis of the deflector 18 and the center of the surface to be scanned of the photosensitive member, That is, the light is incident on the plane including the optical axis of the scanning imaging lens 24 offset by δ.

As shown in FIG. 7, in a so-called overfilled optical system in which the light beam width of the laser beam incident on the deflector 18 is larger than the deflecting surface 18A and the deflecting surface 18A substantially has the function of a stop, Is dependent on the projected width of the deflection surface 18A in the main scanning direction viewed from the scanning beam direction corresponding to the substantial F number and the laser beam intensity distribution represented by the Gaussian distribution.

When the laser beam A is made to enter the deflector 18 obliquely in the main scanning direction with respect to the plane M including the optical axis of the scanning image forming lens 24, the laser beam A becomes −θ when the maximum scanning field angle is θ. When scanned angularly, the deflector 18
Since the normal A1 of the deflecting surface 18A is rotated by-([theta]-[alpha] 1) / 2 [deg.] From a position parallel to the optical axis of the scanning imaging lens 24, the width of the deflecting surface 18A in the main scanning direction is viewed from the scanning beam direction. The width of the deflection surface 18A in the main scanning direction is 1 × cos ((θ
−α1) / 2).

Conversely, when scanning is performed at the angle of + θ, the normal A2 rotates by (θ + α1) / 2 °, and the width of the deflection surface 18A in the main scanning direction as viewed from the traveling direction of the scanning beam is 1 × cos ((θ
+ Α1) / 2).

The width of the deflection surface in the main scanning direction as viewed from the scanning beam traveling direction when the scanning field angle is -θ is d (-θ), and the width in the main scanning direction when the scanning field angle is + θ is d (+ θ). Then
Since θ and α are positive numbers, d (−θ)> d (+ θ). For this reason, the F-number on the side obliquely incident in the main scanning direction becomes smaller, and if the intensity distribution of the light beam is uniform, the amount of light on the obliquely incident side increases.

On the other hand, the laser beam has an intensity distribution represented by a Gaussian distribution. In the case of an overfilled optical system, the laser beam A having a certain intensity distribution is reflected and deflected in accordance with the rotation and movement of the deflecting surface, so that the surface to be scanned depends on which part of the laser beam A is reflected. The upper light quantity changes.

Therefore, when the laser beam is obliquely incident in the main scanning direction, as shown in FIG. 8, when the center of the laser beam intensity distribution is made coincident with the plane including the optical axis of the scanning image forming lens 24, the surface to be scanned is The maximum amount of light is on the opposite side of the incident side and the opposite side only at the position obtained by multiplying the angle formed between the incident beam and the plane including the optical axis of the scanning lens by the focal length of the scanning image forming lens 24. Will be different.

In order to correct the non-uniform light amount due to the above, the position where the maximum light amount of the laser beam intensity distribution reaches the distance δ [0 <δ, with respect to a plane including the rotation axis of the deflector 18 and passing through the center of the surface to be scanned. .Ltoreq.r.times.sin (.alpha.1 / 2)] so that the laser beam A is obliquely incident.

The center of the laser beam intensity distribution can be shifted by making the center of the laser beam intensity coincide with the center of the deflecting surface at the time of rotation of the deflector 18 for scanning the center of the surface to be scanned. α1 / 2 °, and the center of the deflection surface is δ = r ×
Since the laser beam A moves in the oblique incident direction by sin (α / 2), the laser beam A may be incident beforehand shifted by that amount.

However, the F-number change is small at the obliquely incident side at both scanning ends and large at the opposite side, so that the non-uniform light amount due to the F-number change is opposite to the non-uniform light amount due to the laser beam intensity distribution. sin
If (α1 / 2) is shifted, the amount of light on the oblique incidence side increases by the amount of non-uniformity due to the F number. Therefore, δ is 0 <δ ≦ r × s
It is desirable to set it in the range of in (α1 / 2).

In this embodiment, the deflector inscribed radius r
Is 12.5 mm and α1 = 4 °, so r × sin
(Α1 / 2) is 0.436, and δ = 0.32 mm is within the scope of the present invention. FIG. 9 shows the light amount difference at both ends of scanning when δ is changed in the present embodiment. In the present embodiment, the difference in light amount at both ends can be corrected by setting δ to around 0.32.

As described above, even when one laser beam A is obliquely incident on the plane including the optical axis of the scanning image forming lens 24 in the main scanning direction by the overfilled optical system, the light amount difference between both ends of the scanning is small. Although there is an effect that the laser beam can be corrected, in this embodiment, two laser beams A and B are used, each of which is incident from a different side, so that the deflection surfaces are shifted by 0.32 mm in opposite directions. 18 to correct individual light quantity differences and
It is possible to correct non-uniform light quantity between colors and obtain a good multicolor image without color unevenness.

[Second Embodiment] As shown in FIG. 10, the basic structure is almost the same as that of the first embodiment. However, in the second embodiment, laser beams A and B The scanning direction incident angles β1 and β2 are 2.5 ° and 1.2 °, respectively.
The distance L from the deflecting surface 18 to the first mirror 36 is 135 m
m, and the laser beams A and B are turned back to the deflector 18 by the same first mirror 36.

At this time, the laser beam A and the laser beam B intersect on the surface of the first mirror 36, the interval t between the incident positions of the laser beam A and the laser beam B on the deflection surface 18 is 3 mm, and tan (β1 −β2) Δt / L.

As in this embodiment, laser beams A and B
Crossing at a position separating the scanning beam and the incident beam, it is possible to prevent a decrease in margin due to a difference in the sub-scanning incident angle of a plurality of beams generated on the incident side. Accordingly, a margin between the maximum incident beam and the inner scanning beam can be secured, and the arrangement of the first mirror 36 can be facilitated.

Further, with the above configuration, the margin between a plurality of scanning beams is obtained by multiplying the cosine of the sub-scanning angle difference between the scanning beams by the distance from the deflector 18 to the second mirror.
This is the sum of the beam intervals t on the deflecting surface, and the margin between the largest scanning beams can be secured with the smallest difference in the sub-scanning incidence angle. It is easy to separate a plurality of scanning beams even if the scanning line is tilted due to the above.

[0078]

As described above, according to the first to third aspects, the scanning lens is tilted and the spot shape skew of the plurality of beams obliquely incident in the sub-scanning direction is corrected, so that the spot shape change of the plurality of beams can be improved. The beam diameter can be corrected and a uniform beam diameter can be obtained over the entire surface to be scanned.

According to the fourth aspect, a plurality of beams intersect in the sub-scanning direction before entering the deflector and intersect in the main scanning direction after deflecting and reflecting, so that a separation space for the plurality of incident beams and the scanning beam can be secured. In addition to facilitating the synthesis separation, it is possible to prevent non-uniform light intensity on the surface to be scanned.

According to a fifth aspect of the present invention, the laser beam is made incident at a position where the non-uniformity of the F-number and the non-uniform light amount due to the laser beam intensity distribution cancel each other, thereby eliminating the light amount difference between the scanning start end and the scanning end. The occurrence of a print density difference can be prevented.

According to the sixth aspect, a margin between the largest scanning beams can be secured with the smallest difference in the sub-scanning incident angle.
It becomes easy to separate a plurality of scanning beams even if the scanning line is curved due to the sub-scanning oblique incidence or the scanning line is inclined due to component accuracy.

[Brief description of the drawings]

FIG. 1 is a plan configuration diagram of an optical scanning device according to a first embodiment.

FIG. 2 is a side view of the optical scanning device according to the first embodiment.

FIG. 3 is a sub-scan sectional view of an optical system of the optical scanning device according to the first embodiment.

FIG. 4 is a graph showing a beam diameter difference on a surface to be scanned between a scanning center portion and a scanning end portion.

FIG. 5 is a diagram showing spot shapes on a surface to be scanned at a scanning center portion and a scanning end portion.

FIG. 6 is a main scanning cross-sectional view of the optical system of the optical scanning device according to the first embodiment.

FIG. 7 is a diagram illustrating a relationship between a light beam width and an intensity distribution in an overfilled optical system.

FIG. 8 is a graph showing non-uniform light amount in the main scanning direction in the overfilled optical system.

FIG. 9 is a graph showing a relationship between an offset amount and a light amount difference in an overfilled optical system.

FIG. 10 is a sub-scan sectional view of an optical system of an optical scanning device according to a second embodiment.

FIG. 11 is a side view of the optical scanning device of Conventional Example 1.

FIG. 12 is a sub-scanning cross-sectional view of an optical system of an optical scanning device of Conventional Example 2.

FIG. 13 is a main scanning cross-sectional view of the optical system of the optical scanning device of Conventional Example 2.

FIG. 14 is a sub-scanning sectional view of the optical system of the optical scanning device of Conventional Example 4.

[Description of Signs] 18 Deflector 24 Scanning imaging lens (scanning lens) 36 First mirror (first folding mirror)

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Claims (6)

[Claims] 1. A plurality of beams are made to enter a scanning lens at different incident angles in a sub-scanning direction, and obliquely enter the same deflecting surface of a deflector obliquely with respect to a plane orthogonal to a rotation axis of the deflector. In an optical scanning device that deflects and emits the scanning lens to scan and expose a surface to be scanned, distortion of a spot shape on the surface to be scanned caused by oblique incidence of the beam, and a difference in beam diameter in the scanning direction are reduced. , So that each beam falls within a predetermined range,
An optical scanning device, wherein the scanning lens is tilted in a sub-scanning direction. 2. The method according to claim 1, wherein the number of the beams incident on the same deflection surface is two, and the scanning lens has no power in the sub-scanning direction. 2. The optical scanning device according to claim 1, wherein the inclination angle of the scanning lens is set so that the skew of the spot shape is excessive. 3. The method according to claim 2, wherein the number of the beams incident on the same deflection surface is two, and the scanning lens has no power in a sub-scanning direction. The difference between the emission angle reflected from the surface and the emission angle emitted from the scanning lens is reversed, and the incidence angle of the other beam incident on the scanning lens and the emission angle reflected from the deflecting surface and emitted from the scanning lens. The optical scanning device according to claim 1, wherein the scanning lens is tilted in the sub-scanning direction so that a difference between the scanning lenses is the same. 4. A plurality of beams emitted from a plurality of light sources are incident on a deflector with a width larger than the width of the deflecting surface in the main scanning direction, are deflected by the same deflecting surface, and a plurality of photosensitive members are deflected by the plurality of beams. In an optical scanning apparatus for performing scanning exposure, a plurality of beams are incident at different angles in a sub-scanning direction with respect to a plane orthogonal to a rotation axis of a deflector and intersect before being incident on the same deflection surface; An optical scanning device which enters the same deflecting surface at an angle other than 0 in the main scanning direction with respect to a plane including the rotation axis and passing through the center of the surface to be scanned, crosses after being deflected by the deflecting surface. 5. A position where a plane which includes the non-zero predetermined angle αi, an inscribed radius of the deflector r, a rotation axis of the deflector and passes through the center of the surface to be scanned passes through the deflection surface, and a laser beam intensity distribution. The distance δ from the position on the deflection surface at which the maximum light amount is
The optical scanning device according to claim 4, wherein <δ ≦ r × sin (αi / 2). 6. The two beams, the angles of incidence on the deflector in the sub-scanning direction are β1, β2, the distance from the deflecting surface to the first turning mirror on the scanning surface side is L, and T / L @ tan
The optical scanning device according to claim 4, wherein (β1−β2).