JPH11218702A - Optical scanner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inexpensive and highly reliable optical scanner capable of improving unevenness in the distribution of light quantity on a record medium. SOLUTION: Relating to an optical scanner 10 constituted by overfilled type polygon mirror design, an aperture 17 of an aperture plate 16 arranged between a collimeter lens 14 for converting a laser beam made exit from a semiconductor laser 12 into a parallel beam and a concave lens 18 for enlarging an incident laser beam in a scanning direction by combination with an fθ lens 24 is shaped so that width in a direction vertical to the scanning direction between both the end parts of the aperture 17 in the scanning direction is longer than that of the center part in the scanning direction.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical scanning device, and more particularly, to an optical scanning device having a function of correcting a light quantity distribution in a scanning direction of a light beam on a recording medium to be substantially uniform. .

[0002]

2. Description of the Related Art Conventionally, in an optical scanning apparatus which scans a light beam using a rotary polygon mirror having a plurality of reflecting surfaces on an outer peripheral surface,
As an optical system on the upstream side of the rotary polygon mirror (on the light source side that emits a light beam), an underfill type polygon that irradiates a light beam emitted toward the rotary polygon mirror to only a part of one reflection surface of the rotary polygon mirror Mirror designs (hereinafter referred to as underfill designs) are commonly employed.

FIG. 13 shows an example of an optical scanning device constructed based on an underfill design in a case where the optical axis of a laser beam as a light beam is represented as a straight line. A) is a plan view, and FIG.
Is a side view. In the figure, reference numeral 12 denotes a semiconductor laser,
14 is a collimator lens, 16 is an aperture plate, 20 is a cylindrical lens, 26 is a rotating polygon mirror, and 24 is f
indicates a θ lens, 30 indicates a cylindrical mirror, and 32 indicates a photosensitive member as a drum-shaped recording medium. The opening plate 16 is formed of a plate-like member having a rectangular opening substantially at the center, and the center of the opening 17 of the opening plate 16 is emitted from the semiconductor laser 12 as shown in FIG. The laser beam 13 is disposed so as to substantially coincide with the center (optical axis) of the laser beam 13.

As shown in FIG. 13, in an underfill design, a collimator lens 1 emitted from a semiconductor laser 12 is used.
The laser beam 13 converted into a parallel beam by 4 enters a part of one reflection surface of the rotary polygon mirror 26 via the aperture plate 16 and the cylindrical lens 20.

In contrast to such an underfill design, an overfill type polygon mirror design (hereinafter referred to as an overfill design) in which a light beam is applied to the entire surface in the scanning direction of each reflection surface of the rotary polygon mirror and a part of an adjacent reflection surface. ) Was not so commonly adopted.

[0006] Comparing these two designs, the overfill design has a very small reflective surface required to produce a beam spot of a fixed size on the recording medium, as compared to the underfill design. Since it is possible, it is possible to provide more reflecting surfaces on a rotating polygon mirror having the same diameter. This means that the rotating polygon mirror can be operated at a relatively low rotation speed, and a motor and a driving device with lower power can be used as a drive system for rotating the rotating polygon mirror. I have.

However, in the overfill design having such an effect, the transmission efficiency of the optical system is low, and
This is not generally adopted because there are two negative factors that the light amount distribution on the recording medium is not uniform. In order to compensate for the low transmission efficiency of the optical system, a high-output laser diode or the like is required. Further, the problem of non-uniform light amount distribution will be described more specifically as follows.

A laser beam emitted from a light source such as a semiconductor laser has a Gaussian beam shape. In an overfill design, the beam is expanded by a beam expander or the like so as to irradiate one or more reflecting surfaces of a rotary polygon mirror. You. In this state, when the rotating polygon mirror is rotated so that the beam spot of the laser beam scans the surface of the recording medium, as the rotation proceeds, the amount of the laser beam reflected toward the recording medium changes and the light amount distribution changes. Is non-uniform.
This is due to the fact that the reflecting surface of the rotating polygon mirror cuts out different portions of the Gaussian beam profile, and that the effective reflection width of the reflecting surface changes as the rotating polygon mirror rotates.

Regarding the low transmission efficiency of the optical system, which is one of the two negative factors of the above-mentioned overfill design, a high-power laser diode has been generally used in recent years, and is no longer a major problem. Was. On the other hand, non-uniform light amount distribution is a serious problem because it causes problems such as non-uniform image density and non-uniform line width. Therefore, if the problem of the non-uniformity of the light amount distribution is improved, the overfill design can reduce the load on the motor for rotating the rotating polygon mirror, and can reduce the power consumption and the noise while maintaining high-speed and high-resolution light. It can be widely used as a device that can constitute a scanning device.

Conventionally, as a technique for solving the problem of non-uniform light amount distribution in overfill design, a technique of electrically correcting (Japanese Patent Laid-Open No. 4-255874) and a technique of performing correction using an optical system (particularly, Japanese Unexamined Patent Publication (Kokai) No. 3-80214), a technique for performing correction using a filter has been proposed.

[0011]

However, in the above-described technique for solving the problem of non-uniform light quantity distribution in the conventional overfill design, the cost of the optical scanning device is increased due to the complicated structure of parts. There has been a problem that the reliability of the optical scanning device is reduced.

In addition, in particular, the above-described correction by the optical system and the correction by the filter affect the phase wavefront of the laser beam, thereby deteriorating the image forming characteristics of the beam spot and possibly deteriorating the image quality. was there.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and provides an inexpensive and highly reliable optical scanning device capable of improving the unevenness of the light amount distribution on a recording medium. It is intended to be.

[0014]

According to a first aspect of the present invention, there is provided an optical scanning device, comprising: a beam emitting means for emitting a light beam; and a plurality of reflecting surfaces. A rotating polygon mirror rotated so that the light beam reflected by the reflecting surface scans over the recording medium; and a light beam applied to the rotating polygon mirror over a wider range in the scanning direction of one reflecting surface of the rotating polygon mirror. A beam expanding means for expanding a light beam emitted from the beam emitting means so that the light is emitted, and a scanning direction arranged in the optical path of the light beam between the beam emitting means and the rotary polygon mirror. And an opening member having an opening whose width in the direction intersecting with the aperture is changed so that the light amount distribution in the scanning direction on the recording medium is substantially uniform.

According to the first aspect of the present invention, the rotating polygon mirror is provided with a plurality of reflecting surfaces so that the rotating polygon mirror is irradiated with the light beam over a wider range than the width of one reflecting surface in the scanning direction. The light beam emitted from the beam emitting means is expanded by the beam expanding means. Therefore, the optical scanning device according to claim 1 is configured based on the overfill design.

The scanning on the recording medium is performed by an aperture member which is arranged in the optical path of the light beam between the beam emitting means and the rotary polygon mirror and has an aperture whose width in a direction intersecting the scanning direction is changed. The light amount distribution in the direction is substantially uniform.

In the optical scanning device configured based on the overfill design, as described above, the light amount distribution in the scanning direction on the recording medium is such that the reflecting surface of the rotating polygon mirror has a Gaussian beam profile according to the scanning position of the light beam. And the effective reflection width of the rotating polygonal mirror changes according to the rotation of the rotating polygonal mirror, thereby changing the value represented by the product of the Gaussian distribution waveform and the cosine waveform. Therefore, in order to make the light amount distribution in the scanning direction on the recording medium substantially uniform,
The width in the direction intersecting the scanning direction may be changed so that the shape of the opening in the opening member is in inverse proportion to the product of the Gaussian distribution waveform and the cosine waveform.

As described above, according to the optical scanning device of the first aspect, since the width of the opening of the opening member in the direction intersecting the scanning direction is changed, the light amount of the beam spot on the recording medium is changed. The distribution can be made substantially uniform.

Further, since such an opening member can be formed by using an opening member conventionally provided in an optical scanning device, there is no need to add a new part, and the optical scanning device can be manufactured at low cost. Further, the configuration can be made without lowering the reliability.

An optical scanning device constructed based on the underfill design is disclosed in Japanese Patent Laid-Open No. 59-69730.
As disclosed in Japanese Patent Application Laid-Open Publication No. H10-209, there is a technique in which a fan-shaped optical path scanned by a rotating polygon mirror is provided with an opening whose width is changed according to a scanning position, and distortion of a beam spot is corrected. This does not have the function of light amount distribution correction.

The above-mentioned opening in the underfill design must be disposed on the recording medium side with respect to the rotary polygon mirror. However, the scanning beam fluctuates at the passing position due to the tilt of the rotary polygon mirror, so that the scanning beam passes through the opening. The light amount of the laser beam fluctuates, and a periodic stripe pattern called banding occurs in the image.

The tilting of the rotary polygon mirror is usually corrected by placing the reflection surface of the rotary polygon mirror and the surface of the recording medium in an optically conjugate relationship, but completely until the laser beam fluctuates along the optical path. It cannot be corrected. Therefore, it can be said that the aperture in the optical scanning device configured based on the underfill design has a serious problem in practical use even if it is limited to the function of correcting the distortion of the beam spot.

According to a second aspect of the present invention, in the optical scanning device according to the first aspect of the present invention, the light beam expanded by the beam expanding means in the optical scanning device according to the first aspect is incident on a rotation center of the rotary polygon mirror. The beam emitting means, the beam expanding means, and the rotating polygon mirror are arranged, and the width of the opening in the direction intersecting the scanning direction is larger at both ends in the scanning direction than in the central part in the scanning direction. An opening is formed.

According to the optical scanning device of the second aspect, the light beam expanded by the beam expanding means in the optical scanning device of the first aspect is emitted so that it is incident toward the center of rotation of the rotary polygon mirror. The means, the beam expanding means, and the rotating polygon mirror are arranged, and the opening is formed such that the width of the opening in the direction intersecting the scanning direction is larger at both ends in the scanning direction than at the center in the scanning direction.

In the case where the beam emitting means, the beam expanding means, and the rotary polygon mirror are arranged so that the light beam expanded by the beam expanding means is incident toward the rotation center of the rotary polygon mirror, the rotary polygon mirror is used. The effective reflection width gradually increases with the rotation of the rotary polygon mirror until the reflection surface reaches a position orthogonal to the incident direction of the light beam, and then gradually decreases.

Therefore, an opening member having an opening formed so that both ends in the scanning direction are larger than the width of the opening in the direction intersecting the scanning direction with respect to the central portion in the scanning direction is provided between the beam emitting means and the rotary polygon mirror. By arranging them in the optical path of the light beam between them, the light amount distribution in the scanning direction of the light beam reflected by the rotating polygon mirror can be made substantially uniform.

According to the optical scanning apparatus of the second aspect, the beam expanding means, the beam expanding means, and the light beam expanded by the beam expanding means are incident toward the rotation center of the rotary polygon mirror. In addition, since the aperture is formed so that the width of the opening in the direction intersecting the scanning direction is larger at both ends in the scanning direction as compared with the central portion in the scanning direction, the beam spot on the recording medium is reliably formed. Can be made substantially uniform.

According to a third aspect of the present invention, in the optical scanning device according to the first aspect of the present invention, the effective reflection width of the rotary polygon mirror gradually decreases or increases with the rotation of the rotary polygon mirror. While arranging the beam emitting means, the beam expanding means, and the rotating polygon mirror so that
The opening is formed such that the width of the opening in the direction intersecting the scanning direction gradually increases from one end to the other end in the scanning direction, and a portion where the width of the opening is wide when the effective reflection width is small. The aperture member is arranged such that the light beam that has passed therethrough is reflected by the reflection surface of the rotary polygon mirror.

According to the optical scanning device of the third aspect, the effective reflection width of the rotary polygon mirror in the optical scanning device of the first aspect gradually decreases or increases with the rotation of the rotary polygon mirror. A beam emitting means, a beam expanding means, and a rotating polygon mirror are arranged, and an opening is formed such that the width of the opening in a direction intersecting the scanning direction gradually increases from one end in the scanning direction to the other end, In addition, the aperture member is arranged so that the light beam that has passed through the wide portion of the aperture when the effective reflection width is small is reflected by the reflection surface of the rotary polygon mirror.

When the beam emitting means, the beam expanding means, and the rotary polygon mirror are arranged such that the effective reflection width of the rotary polygon mirror gradually decreases or increases with the rotation of the rotary polygon mirror, The effective reflection width of the rotating polygon mirror is
It gradually decreases or increases with the rotation of the rotating polygon mirror.

Therefore, the opening is formed so that the width of the opening in the direction intersecting the scanning direction gradually increases from one end to the other end in the scanning direction, and the width of the opening is increased when the effective reflection width is small. By disposing the aperture member so that the light beam that has passed through the mirror is reflected by the reflection surface of the rotary polygon mirror, the light amount distribution in the scanning direction of the light beam reflected by the rotary polygon mirror can be made substantially uniform.

Thus, according to the optical scanning device of the third aspect, the beam emitting means and the beam emitting means are such that the effective reflection width of the rotary polygon mirror gradually decreases or increases with the rotation of the rotary polygon mirror. When the enlargement means and the rotating polygon mirror are arranged and the opening is formed so that the width of the opening in the direction intersecting the scanning direction gradually increases from one end to the other end in the scanning direction, and when the effective reflection width is small. Since the aperture member is arranged so that the light beam that has passed through the wide portion of the aperture is reflected by the reflection surface of the rotating polygon mirror, the light quantity distribution of the beam spot on the recording medium can be made substantially uniform. .

According to a fourth aspect of the present invention, in the optical scanning device according to any one of the first to third aspects, the width of the opening member in the opening member in the direction intersecting the scanning direction is stepwise. Or continuously changed.

According to the optical scanning device of the fourth aspect, when the width of the opening in the direction intersecting the scanning direction is changed stepwise, the opening member can be easily designed and manufactured, and when the width is changed continuously. In this case, the light amount distribution on the recording medium can be accurately made uniform.

According to a fifth aspect of the present invention, in the optical scanning device according to any one of the first to fourth aspects, the aperture member in the optical scanning device according to any one of the first to fourth aspects can be finely adjusted in a scanning direction.

The light quantity distribution of the light beam on the recording medium may have a bias due to the alignment of the light beam incident on the rotating polygon mirror. In this case, the opening member can be finely adjusted in the scanning direction, and the deviation can be corrected by adjusting the opening member in accordance with the deviation. For example, since the aperture member can be finely adjusted in the scanning direction, the deviation of the light beam due to the alignment of the light beam incident on the rotary polygon mirror can be easily corrected.

[0037]

Embodiments of the present invention will be described below in detail with reference to the drawings.

[First Embodiment] First, referring to FIG.
The configuration of the optical scanning device 10 according to the first embodiment will be described.

As shown in FIG. 1, the optical scanning device 10 according to the first embodiment includes a semiconductor laser 12 that generates a laser beam. A collimator lens 14 for converting a laser beam into a parallel beam, and an aperture plate 1 composed of a plate-like member having an aperture 17 provided at a substantially central portion.
6. A concave lens 1 for expanding an incident laser beam in the scanning direction by combining with an fθ lens 24 described later.
8. Cylindrical lens 20 and folding mirror 2
2 are arranged in order.

The opening 17 provided in the opening plate 16
The opening 17 has a shape in which the opening width in the vertical direction (direction perpendicular to the scanning direction) at both ends of the opening 17 in the left-right direction (scanning direction) is larger than that at the center in the left-right direction.
The shape can be any of (A), (B) and (C). Further, as shown in FIGS. 2A to 2C, the aperture plate 16 has a center of the aperture 17 substantially coincident with a center (optical axis) of a laser beam 13 to be described later emitted from the semiconductor laser 12. It is arranged.

On the other hand, in the direction of reflection of the laser beam from the bending mirror 22, an fθ lens 24 and a rotary polygon mirror 26 having a plurality of (12 in this embodiment) reflecting surfaces 28 on its outer peripheral surface are sequentially arranged. And the reflecting surface 2 of the rotating polygon mirror 26
8, the fθ lens 24 and the cylindrical mirror 30 for correcting the tilt of the rotary polygon mirror 26 are arranged in order in the reflection direction of the laser beam. Of the photoconductor 32 is disposed.

As described above, in the optical scanning device 10 according to the first embodiment, both the laser beam reflected by the folding mirror 22 and the laser beam reflected by the reflecting surface 28 of the rotary polygon mirror 26 are used. Are the same fθ
The laser beam passing through the fθ lens 24 is obliquely incident on the reflection surface 28 of the rotary polygon mirror 26 from above, so as to pass through the lens 24, and the incident laser beam is obliquely downwardly reflected by the reflection surface 28 of the rotary polygon mirror 26. The components are arranged such that the light is reflected to the fθ lens 24 again.

The semiconductor laser 12 is used as the beam emitting means of the present invention by the concave lens 18 and the fθ lens 24.
Is the beam expanding means of the present invention, the aperture plate 16 is the aperture member of the present invention, the photoconductor 32 is the recording medium of the present invention,
Each corresponds.

Next, the operation of the optical scanning device 10 configured as described above will be described with reference to FIG. In addition, FIG.
FIG. 3 is a diagram showing the operation of the optical scanning device 10 shown in FIG. 1 when the optical axis of the laser beam 13 is represented by a straight line,
3A is a plan view, and FIG. 3B is a side view.

As shown in FIGS. 3A and 3B,
After the laser beam 13 emitted from the semiconductor laser 12 is converted into a parallel beam by the collimator lens 14,
It passes through the opening 17 of the opening plate 16. After the laser beam 13 that has passed through the opening 17 is expanded in the scanning direction by the concave lens 18 and the fθ lens 24, a part of the expanded laser beam 13 is reflected by one reflection surface 28 of the rotary polygon mirror 26, and again fθ A beam spot 34 is formed on the photoconductor 32 by passing through the lens 24. Note that f
The θ lens 24 has a rotating polygon mirror 26 in addition to the roles described above.
Of the beam spot 34 on the photoreceptor 32.

Here, the intensity distribution of the laser beam incident on the rotary polygon mirror 26 will be considered. Semiconductor laser 1
2, the beam divergence angle (full width at half maximum) is 30 ° in the scanning direction,
Assuming that the angle is 9 ° in the direction perpendicular to the scanning direction and the focal length of the collimator lens 14 is 12.5 mm, the intensity of the laser beam is 1 / e ² of the intensity at the beam center (e is the natural logarithm base). each beam radius omega _x and omega _y scanning direction and the scanning direction and vertical direction of the collimated light (laser beam emitted from the collimator lens 14) is as follows at the point where the.

Ω _x = sin (30 ° / 2) × 12.5 ×
1.69 = 5.47 mm ω _y = sin (9 ° / 2) × 12.5 × 1.69 = 1.
However, vignetting due to the opening of the collimator lens 14 is not considered. In addition, the constant 1.69 in each of the above equations is a half width and 1 / e ² of the intensity of the laser beam at the center of the beam.
Is the correction value between the width between the two points.

In this case, the intensity distribution U of the collimated light
_{(x, y) is, U (x, y) =} [exp (-x 2 / ω x 2) × exp (-y
² / ω _y ² )] ² , and the light amount distribution I _{(x) in} the scanning direction when the aperture width of the aperture plate 16 in the direction perpendicular to the scanning direction is infinite is: I _(x) = I _O [exp ( −x ² / ω _x ² )] ² where

[0049]

(Equation 1)

When the aperture width of the aperture plate 16 in the direction perpendicular to the scanning direction is 2a, the light amount distribution I _{(x) in} the scanning direction is as follows: I _(x) = Q · I _O [exp (−x ² / ω _x ² )] ² where

[0051]

(Equation 2)

Since I _O and Q are constants, the light amount distribution in the scanning direction when the aperture widths are different is represented by a Gaussian distribution having different peaks.

Accordingly, the opening 17 of the opening plate 16 is
The light amount distribution in the scanning direction when the shape shown in FIG.
As shown by the solid line in the upper graph of FIG. 4, the state is a combination of Gaussian distributions with different peaks.

The light quantity distribution on the reflecting surface 28 of the rotary polygon mirror 26 is determined by the beam expansion rate of the concave lens 18 and the fθ lens 24. If this beam expansion rate is set high, only the central part of the Gaussian beam is used, and the uniformity of the light amount distribution is improved, but the transmittance of the optical system is reduced.

Here, in the first embodiment, since the laser beam 13 is incident on the rotary polygon mirror 26 from the front, FIG.
As shown in FIGS. 5A to 5C, the rotary polygon mirror 2
When 6 rotates in the direction of arrow A in FIG. 5, the effective reflection width ratio (the ratio of the effective reflection width to the maximum effective reflection width) of the rotating polygon mirror 26 changes between cos−15 ° and cos15 °.

Laser beam 13 that forms an image on photoconductor 32
Is obtained from the light amount distribution of the laser beam incident on the rotary polygon mirror 26 shown by the solid line in the upper graph of FIG.
It becomes an integral value of a portion cut out by the effective reflection surface of the rotary polygon mirror 26. Accordingly, the light amount distribution on the photoreceptor 32 has a light amount decrease of cos15 ° = cos−15 ° ≒ 0.97 at both ends in the scanning direction with respect to the light amount distribution of the laser beam incident on the rotating polygon mirror 26, and is smooth. Turned polygon mirror 2
The discontinuous portion of the light intensity distribution of the laser beam incident on the laser beam 6 disappears and changes to a smooth change.

In the first embodiment, the collimated light is made to pass through the openings in which the opening widths at both ends in the scanning direction are gradually increased from the center, and then expanded three times in the scanning direction by the concave lens 18 and the fθ lens 24. When the light enters the rotary polygon mirror 26 having a width of 7 mm in the scanning direction of the reflecting surface 28, by appropriately setting the change position of the width of the opening, as shown in FIG. The non-uniform light amount, which was 5% or more, could be suppressed to 1% or less. In addition,
In FIG. 6, the light amount at the center in the scanning direction is represented as 100%.

When the aperture shape is as shown in FIG. 2A, the light amount distribution of the laser beam incident on the rotary polygon mirror 26 has a sharp change point, but the aperture shape is changed as shown in FIG.
By obliquely cutting the portion where the opening width changes as shown in (B), the distribution of the light amount of the laser beam incident on the rotating polygon mirror 26 can be changed with a smooth curve.

As described above in detail, in the optical scanning device 10 according to the first embodiment, the optical scanning device 10 formed on the basis of the overfill design is perpendicular to the scanning direction of the aperture 17 in the aperture plate 16 of the aperture plate 16. Since the width in the direction is changed along the scanning direction, the light amount distribution of the laser beam on the photoconductor 32 can be made substantially uniform.

The aperture plate 16 used at this time is
Since it is possible to use a conventionally provided optical scanning device configured based on the overfill design, there is no need to add new parts, and the optical scanning device can be configured at low cost, There is no decrease in the reliability of the optical scanning device.

[Second Embodiment] Next, a second embodiment of the present invention will be described. First, referring to FIG.
The configuration of the optical scanning device 10B according to the embodiment will be described. In FIG. 7, portions denoted by the same reference numerals as those in FIG. 1 have the same functions.

As shown in the figure, the optical scanning device 10B according to the second embodiment includes a semiconductor laser 12 that generates a laser beam. A collimator lens 14 for converting a laser beam into a parallel beam, and an aperture plate 1 composed of a plate-like member having an aperture 17 provided at a substantially central portion.
6. A beam expander lens 19 for expanding an incident laser beam and a bending mirror 22 are arranged in this order.

On the other hand, in the reflection direction of the laser beam from the folding mirror 22, a cylindrical lens 20 and a rotary polygon mirror 26 having a plurality of (12 in this embodiment) reflecting surfaces 28 on its outer peripheral surface are arranged in this order. And a rotating polygon mirror 26
Lens 2 that forms a beam spot 34 on the photoconductor 32 in the direction of reflection of the laser beam by the reflection surface 28
4. A cylindrical mirror 30 for correcting the tilting of the rotary polygon mirror 26 is arranged in order, and a drum type photoconductor 32 is arranged in the direction of reflection of the laser beam from the cylindrical mirror 30.

The semiconductor laser 12 serves as the beam emitting means of the present invention, the beam expander lens 19 serves as the beam expanding means of the present invention, the aperture plate 16 serves as the aperture member of the present invention, and the photosensitive member 32 serves as the aperture member of the present invention. Each corresponds to the recording medium of the present invention.

Next, the operation of the optical scanning device 10B configured as described above will be described with reference to FIG. FIG.
FIG. 9 is a diagram showing the operation of the optical scanning device 10B shown in FIG. 7 when the optical axis of the laser beam 13 is represented by a straight line,
FIG. 8A is a plan view, and FIG. 8B is a side view.

As shown in FIGS. 8A and 8B,
After the laser beam 13 emitted from the semiconductor laser 12 is converted into a parallel beam by the collimator lens 14,
It passes through the opening 17 of the opening plate 16. After the laser beam 13 that has passed through the opening 17 is expanded by the beam expander lens 19, a part of the expanded laser beam 13 is reflected by one reflecting surface 28 of the rotary polygon mirror 26,
A beam spot 34 is formed on the photoconductor 32 by passing through the fθ lens 24. Note that the fθ lens 24 is
In addition to the above-mentioned role, it also has a role of converting the constant angular velocity movement of the rotary polygon mirror 26 into the constant linear velocity movement of the beam spot 34 on the photoconductor 32.

The optical scanning device 1 according to the second embodiment
9B, the laser beam 13 is tilted 6 degrees with respect to the rotating polygon mirror 26 as shown in FIGS. 9A to 9C in order.
The light is incident from the direction of 0 °, and therefore the rotating polygon mirror 2
When the mirror 6 rotates in the direction of arrow A in FIG. 9, the effective reflection width ratio of the rotary polygon mirror 26 changes between cos 15 ° and cos 45 °.

As shown in FIG. 10, the opening 17 of the opening plate 16 has a shape in which the opening width in the direction perpendicular to the scanning direction in the right half of FIG. And In this case, the light quantity distribution of the laser beam incident on the rotary polygon mirror 26 is a state in which three Gaussian distributions having different peaks are combined as shown by the solid line in the upper graph of FIG.

The laser beam 13 which forms an image on the photosensitive member 32
Is the integral value of the portion of the effective reflection surface of the rotary polygon mirror 26 cut out from the light intensity distribution of the laser beam incident on the rotary polygon mirror 26 shown by the solid line in the upper graph of FIG. Therefore, the light amount distribution on the photoconductor 32 is different from the light amount distribution of the laser beam incident on the rotary polygon mirror 26 at both ends in the scanning direction at cos 15 ° ≒ 0.97 and cos 4.
When the light amount is reduced by 5 ° ≒ 0.71, a discontinuous portion of the light amount distribution of the laser beam which is smoothed and is incident on the rotary polygon mirror 26 is eliminated and changes to a smooth change.

In the second embodiment, the collimated light is passed through an opening in which the opening width at one end is gradually increased from the opening width at the other end. As shown in FIG. 11, by appropriately setting the changing position of the opening width and the number of changing steps when the light is incident on the rotating polygon mirror 26 in which the width of the reflecting surface 28 in the scanning direction is 7 mm is enlarged. , 3 in the uncorrected state
The non-uniform light amount, which was 0% or more, could be suppressed to 2% or less. In FIG. 11, the light amount at the center in the scanning direction is 100%.
It is expressed as

As described above in detail, in the optical scanning device 10B according to the second embodiment, the optical scanning device 10B, which is configured based on the overfill design, is perpendicular to the scanning direction of the opening 17 in the aperture plate 16 of the aperture plate 16. Since the width in the direction is changed along the scanning direction, the light amount distribution of the laser beam on the photoconductor 32 can be made substantially uniform.

The aperture plate 16 used at this time is
Since it is possible to use a conventionally provided optical scanning device configured based on the overfill design, there is no need to add new parts, and the optical scanning device can be configured at low cost, There is no decrease in the reliability of the optical scanning device.

In order to completely correct the light quantity distribution of the laser beam on the photosensitive member 32, the aperture plate 16 must have a shape inversely proportional to the product of the Gaussian distribution and the cosine waveform (the above first shape).
In the aperture plate 16 of the optical scanning device 10 according to the embodiment, FIG.
It is sufficient to provide an opening having the shape shown in FIG. 1C), but in this case, difficulty arises in manufacturing, particularly when performing an inspection.

On the other hand, even when the width of the opening is changed stepwise, a sufficient light amount correction effect can be obtained as described in the first and second embodiments. In this way, by making the width of the opening gradually change, the design and manufacture of the opening plate can be facilitated.

When the width of the opening is changed stepwise, the maximum opening width at which the same light amount correction effect can be obtained can be reduced as compared with the case where the width is changed continuously. Since the amount of change in the scanning direction (the difference between the maximum aperture width and the minimum aperture width) can be reduced, the influence on the beam spot size can be minimized.

That is, the beam spot size to be focused is:
It has a finite size due to the diffraction of light, is proportional to the wavelength of the light, and has the property of being inversely proportional to the aperture angle at the time of focusing (焦点 aperture width / focal length), and varies according to the aperture width. The smaller the amount of change in the aperture width in the scanning direction, the smaller the effect on the beam spot size.

The beam spot size in the direction perpendicular to the scanning direction on the photosensitive member 32 is determined by the aperture width of the aperture plate 16 in the direction perpendicular to the scanning direction. That is, as described above, the focused beam spot size has the property of being inversely proportional to the aperture angle (≒ opening width / focal length). Therefore, as the opening width increases, the beam spot size in the direction perpendicular to the scanning direction decreases. . If the beam spot size is larger than the design value, it may cause poor image quality such as poor resolution. However, the smaller the beam spot size, the greater the tolerance. In the first embodiment, the beam spot size in the direction perpendicular to the scanning direction at both scanning ends is reduced by about 10% as compared with the scanning center, but there is no problem in image quality. In the second embodiment, the difference is larger than that in the first embodiment, but there is no practical problem if it is noted that the beam spot size becomes smaller and the depth of focus becomes shallower.

Further, as a characteristic of the optical system, there is a characteristic that the beam spot size at both ends of the scanning becomes large. In this case, by applying the present invention, the beam spot size can be made uniform. .

The light quantity distribution of the laser beam on the photoreceptor 32 may have a bias due to the alignment of the laser beam incident on the rotary polygon mirror 26. In this case, the bias can be corrected by making the aperture plate 16 finely adjustable in the scanning direction. FIG.
FIG. 12A shows a configuration in which the aperture plate 16 can be finely adjusted in the scanning direction. FIG.
(B) is a side view as seen from the direction in which the laser beam is incident.

As shown in the figure, the opening plate 16 is
6 is finely moved in the scanning direction using an adjustment tool such as an eccentric shaft 42 with the holding member 40 for holding the laser beam 6 substantially perpendicular to the optical axis of the laser beam, and then the light amount balance is adjusted. .

In each of the above embodiments, the case where the aperture plate 16 is disposed at a position adjacent to the collimator lens 14 has been described. However, the present invention is not limited to this. 12 and rotating polygon mirror 26
May be arranged at any position on the optical path of the laser beam. However, in this case, it is necessary to appropriately change the size of the opening of the opening plate 16 according to the arrangement position.

[0082]

According to the first aspect of the present invention, since the width of the opening of the opening member in the direction intersecting the scanning direction is changed, the light amount distribution of the beam spot on the recording medium is changed. Can be made substantially uniform, and the aperture member can be configured using the aperture member conventionally provided in the optical scanning device, so that there is no need to add new parts, and the optical scanning device can be used. The effect that it can be comprised at low cost and without reducing reliability is obtained.

According to the optical scanning device of the second aspect, the beam emitting means, the beam expanding means, and the beam expanding means are provided so that the light beam expanded by the beam expanding means is incident toward the center of rotation of the rotary polygon mirror. Since the rotating polygon mirror is arranged and the opening is formed so that the width of the opening in the direction intersecting the scanning direction is larger at both ends in the scanning direction than at the center in the scanning direction, the beam spot on the recording medium is surely formed. The effect that the light quantity distribution can be made substantially uniform can be obtained.

Further, according to the optical scanning device of the third aspect, the beam emitting means and the beam expanding means such that the effective reflection width of the rotary polygon mirror gradually decreases or increases with the rotation of the rotary polygon mirror. Means, and a rotating polygon mirror, and an opening is formed so that the width of the opening in a direction intersecting the scanning direction is gradually increased from one end to the other end in the scanning direction, and the opening is formed when the effective reflection width is small. Since the aperture member is arranged so that the light beam that has passed through the wide portion is reflected by the reflection surface of the rotary polygon mirror, the light quantity distribution of the beam spot on the recording medium can be reliably made substantially uniform.
The effect is obtained.

According to the optical scanning device of the fourth aspect, when the width of the opening in the direction intersecting the scanning direction is changed stepwise, the opening member can be easily designed and manufactured, and the opening member can be continuously changed. In this case, the effect that the light amount distribution on the recording medium can be accurately made uniform can be obtained.

Further, according to the optical scanning device of the present invention, since the aperture member can be finely adjusted in the scanning direction, the deviation of the light beam due to the alignment of the light beam incident on the rotary polygon mirror can be easily corrected. Can be obtained.

[Brief description of the drawings]

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

FIG. 2 is a schematic view showing three examples of an opening shape of an aperture plate in the optical scanning device according to the first embodiment.

3A and 3B are diagrams illustrating an operation of the optical scanning device when the optical axis of the laser beam is indicated by a straight line in the optical scanning device according to the first embodiment, where FIG. 3A is a plan view and FIG. It is.

FIG. 4 is a graph showing a light amount distribution in a scanning direction and a direction perpendicular to the scanning direction of the laser beam incident on the rotary polygon mirror of the optical scanning device according to the first embodiment.

FIGS. 5A to 5C are diagrams used to describe an effective reflection width ratio of the rotating polygon mirror in the optical scanning device according to the first embodiment, and FIGS. FIG. 9 is a plan view showing a change in the effective reflection width of the rotating polygon mirror accompanying the above.

FIG. 6 is a graph showing the effect of correcting the light amount distribution by the optical scanning device according to the first embodiment.

FIG. 7 is a configuration diagram illustrating a schematic configuration of an optical scanning device according to a second embodiment.

8A and 8B are diagrams illustrating an operation of the optical scanning device when the optical axis of a laser beam is indicated by a straight line in the optical scanning device according to the second embodiment, where FIG. 8A is a plan view and FIG. It is.

FIGS. 9A to 9C are diagrams used for describing an effective reflection width ratio of a rotary polygon mirror in the optical scanning device according to the second embodiment, and FIGS. 9A to 9C each illustrate a lapse of time when the rotary polygon mirror rotates; FIG. 9 is a plan view showing a change in the effective reflection width of the rotating polygon mirror accompanying the above.

FIG. 10 is a graph showing a light amount distribution in a scanning direction and a direction perpendicular to the scanning direction of a laser beam incident on a rotary polygon mirror of the optical scanning device according to the second embodiment.

FIG. 11 is a graph showing the effect of correcting the light amount distribution by the optical scanning device according to the second embodiment.

FIGS. 12A and 12B are configuration diagrams showing a schematic configuration that enables fine adjustment of the aperture plate in the scanning direction in the optical scanning device according to each embodiment, where FIG. 12A is a plan view and FIG. 12B is a side view.

13A and 13B are diagrams showing a schematic configuration of an optical scanning device according to a conventional underfill type polygon mirror design, in which FIG.
(B) is a side view.

FIG. 14 is a schematic diagram showing a conventional opening shape and a positional relationship between the opening and a laser beam.

DESCRIPTION OF SYMBOLS 10, 10B optical scanning device 12 Semiconductor laser (beam emitting means) 14 Collimator lens 16 Opening plate (opening member) 18 Concave lens (beam expanding means) 19 Beam expander lens (beam expanding means) 20 Cylindrical lens 22 Folding mirror 24 fθ lens (beam expanding means) 26 rotating polygon mirror 28 reflecting surface 30 cylindrical mirror 32 photoconductor (recording medium) 34 beam spot 40 holding member 42 eccentric shaft 44 fixing screw

Claims (5)

[Claims] 1. A beam emitting means for emitting a light beam, and a rotation comprising a plurality of reflecting surfaces, wherein the light beam emitted from the beam emitting means and reflected by the reflecting surface is rotated so as to scan a recording medium. A polygonal mirror; and a beam expander for expanding a light beam emitted from the beam emitting means such that the light beam is irradiated to the rotary polygonal mirror over a wider range than a width of one reflecting surface of the rotary polygonal mirror in a scanning direction. Means, arranged in an optical path of the light beam between the beam emitting means and the rotary polygon mirror, and having a width in a direction intersecting a scanning direction and a light amount distribution in a scanning direction on the recording medium being substantially uniform. An opening member having an opening changed so as to form an optical scanning device. 2. The apparatus according to claim 1, wherein said beam emitting means, said beam expanding means, and said rotary polygon mirror are arranged such that the light beam expanded by said beam expanding means is incident toward a rotation center of said rotary polygon mirror. 2. The optical scanning device according to claim 1, wherein the opening is formed such that the width of the opening in the direction intersecting the scanning direction is larger at both ends in the scanning direction than at the center in the scanning direction. 3. The beam emitting means, the beam expanding means, and the effective reflection width of the rotary polygon mirror gradually decrease or increase with the rotation of the rotary polygon mirror.
And the rotating polygon mirror is arranged, and the opening is formed so that the width of the opening in the direction intersecting the scanning direction gradually increases from one end to the other end in the scanning direction, and the effective reflection width is small. 2. The optical scanning device according to claim 1, wherein the aperture member is arranged such that a light beam that has passed through a portion where the width of the aperture is wide is reflected by a reflection surface of the rotary polygon mirror. 4. The optical scanning device according to claim 1, wherein the width of the opening in the opening member in a direction intersecting the scanning direction is changed stepwise or continuously. 5. The optical scanning device according to claim 1, wherein the aperture member is finely adjustable in a scanning direction.