JP2002287067A - Optical scanner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical scanner which is capable of forming images equally on a surface to be scanned. SOLUTION: An aperture stop 4 having such a rhombic opening at which the directions of two diagonal lines align to the direction corresponding to a horizontal scanning direction and the direction corresponding to a vertical scanning direction, respectively, is disposed on the optical path between a cylindrical lens 3 and a polygon mirror 5, by which the irradiation of the surface 9 to be scanned with a beam is performed equally even in the diagonal line direction of a beam spot array and the quality of the formed images is improved.

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 an image forming apparatus using an optical method, such as a laser beam printer, a digital copying machine, and a laser plate making device.

[0002]

2. Description of the Related Art Conventionally, in an image forming apparatus of this type, a light source for emitting a light beam such as a laser, a rotary polygon mirror, and a scanning image forming lens (fθ lens) are arranged in this order. Is rotated mechanically to deflect the light emitted from the light source, and the deflected light is condensed by a scanning imaging lens to scan the image forming surface (scanned surface) with a beam. Optical systems are often used.

In this type of scanning optical system, an aperture stop is generally arranged to obtain a predetermined beam diameter. Conventionally, as such an aperture stop, an aperture stop having a circular, elliptical, or rectangular aperture, or an aperture configured by combining these apertures has been used.

[0004]

However, in the conventional scanning optical system using the above-described aperture stop,
For the following reasons, the quality of the formed image is not always sufficient.

FIG. 12 shows a rectangular opening 104A, for example.
FIG. 13 is an enlarged view of a cross section of a beam spot S formed by a scanning optical system using the aperture stop 104 on the image forming surface. In this figure, a horizontal direction H is a direction in which light is deflected by the rotating polygon mirror (hereinafter, referred to as a main scanning direction H).
And the vertical direction V indicates a direction orthogonal to the main scanning direction H (hereinafter, referred to as a sub-scanning direction V). In a normal laser printer, for example, the sub-scanning direction V coincides with the sheet feeding direction.

As shown in FIG. 13, the cross-sectional shape of the beam spot S on the image forming plane becomes a shape close to an ellipse or a rhombus due to the influence of diffraction by the rectangular aperture 104A of the aperture stop. That is, the cross-sectional shape of the beam spot S is a rhombus whose diagonal direction coincides with the main scanning direction H and the sub-scanning direction V, or an ellipse close to such a rhombus. The same tendency also occurs when the opening 104A is made elliptical. The “ellipse” here includes a perfect circle, and the “rectangle” includes a square and a rectangle.

As described above, when the cross-sectional shape of the beam spot S becomes a rhombus or an ellipse close thereto, an area between adjacent spots in the diagonal direction D of the beam spot array (hereinafter, referred to as an inter-spot area G). ) Causes a problem such as the occurrence of blanks or the inability to obtain a desired density in the area G between spots. For this reason, conventionally, there was a drawback that an image of sufficient quality could not always be obtained.

[0008] The present invention has been made in view of the above problems, and an object of the present invention is to provide an optical scanning device capable of obtaining better image quality.

[0009]

An optical scanning device according to the present invention comprises:
An optical scanning device for scanning a predetermined surface to be scanned by a light in a first scanning direction and a second scanning direction substantially orthogonal to the first scanning direction, and a light source that emits a light beam; A first optical system including an aperture stop having an aperture of a predetermined shape for narrowing a light beam from the light source, and configured to apply a predetermined optical action to the light beam;
Light deflecting means for deflecting the light beam having passed through the optical system, so that the surface to be scanned is scanned along the first scanning direction, and a light beam deflected by the light deflecting means. A second optical system for forming an image on the surface to be scanned, wherein the aperture of the aperture stop has a direction corresponding to the first scanning direction and a direction corresponding to the second scanning direction in two diagonal directions. And has a rhombus or a shape similar thereto.

[0010] Here, the "rhombus" refers to a quadrangle where two diagonal lines intersect at the respective midpoints, and the "shape similar to the rhombus" refers to a vertex or a straight line or a curve passing through four points regarded as vertices. Wherein the center of the line connecting two adjacent points among the four points is located inside an ellipse circumscribing the opening shape.

In the optical scanning device of the present invention, the aperture stop is set to 2
You may comprise so that the ratio of the diagonal length of a book may be variable. In this case, the shape and size of the beam spot on the surface to be scanned change, and the shape is mainly adjusted. The configuration in which the ratio of the lengths of the two diagonals is variable can be realized by configuring the aperture stop 4 to be rotatable around at least one of the two diagonals. Alternatively, this can be realized by configuring the aperture of the aperture stop as an intersection of two slits and configuring each of the two slits to be rotatable about the optical axis of the first optical system.

In the optical scanning device of the present invention, the aperture stop may be configured such that the aperture size is variable while keeping the shape of the aperture similar. In this case, the size and shape of the beam spot on the surface to be scanned change, and the size is mainly adjusted. In the configuration in which the aperture size is variable, the aperture of the aperture stop is configured by combining two plate-shaped members having V-shaped notches, and the two plate-shaped members are used for the first or second scanning. This can be realized by making it movable in a direction corresponding to the direction.

In the optical scanning apparatus according to the present invention, the first optical system acts on the light beam from the light source so as to be substantially parallel in the direction corresponding to the first scanning direction, while the second scanning system performs the second scanning. In a direction corresponding to the direction, it is preferable to act so as to become a convergent light beam. in this case,
The first optical system functions to form a light beam from the light source as a linear image near the light deflection unit.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS [First Embodiment] FIG. 1 is a perspective view showing a schematic configuration of an optical scanning device according to a first embodiment of the present invention. The optical scanning apparatus shown in FIG. 1 is used, for example, in a laser printer, and irradiates a light beam onto the surface of a photosensitive material to form a beam spot, and the beam spot is directed in a predetermined direction along the surface of the photosensitive material. (That is, scan). In the following description, the direction of movement of the beam spot is referred to as the main scanning direction H.
The direction orthogonal to the direction is defined as a sub-scanning direction V.
Further, a surface of a photosensitive material (described later) on which a beam spot is formed will be described as a surface 9 to be scanned.

<Structure of Optical Scanning Apparatus>
A light source 1, a collimator lens 2 arranged on the emission side of the light source 1, and a cylindrical lens 3 arranged on the emission side of the collimator lens 2 (ie, the side opposite to the light source 1).
And an aperture optical system including an aperture stop 4 disposed on the exit side of the cylindrical lens 3 (that is, on the side opposite to the collimator lens 2). Collimator lens 2,
Each of the cylindrical lens 3 and the aperture stop 4 has an optical axis (or center axis) whose optical axis Ax of the entire incident optical system.
It is arranged to match.

The light source 1 is composed of, for example, a semiconductor laser element, and emits a light beam having a wavelength of, for example, 780 nm and a substantially circular or elliptical cross section. The light source 1 is driven and controlled by a control unit (not shown), and is turned on and off at a high speed (for example, at several MHz to several tens MHz). Here, the light source 1 corresponds to a specific example of “light source” in the present invention.

The collimator lens 2 is a lens that is rotationally symmetric with respect to the optical axis Ax, and has a function of converting a divergent light beam emitted from the light source 1 into parallel light. Collimator lens 2
Can be constituted by, for example, a single lens having an aspherical surface, and its focal length is, for example, about 5 to 8 mm.
Here, the collimator lens 2 corresponds to a specific example of “first optical system” in the present invention.

The cylindrical lens 3 moves in the sub-scanning direction V
, And has a power only in the direction corresponding to the direction (1), and the light flux which has become parallel light through the collimator lens 2 extends in the direction corresponding to the main scanning direction H near the reflecting surface 6 of the polygon mirror 5 described later. An image is formed as a line image. The focal length of the cylindrical lens 3 is, for example, about 200 to 220 mm. Here, the cylindrical lens 3 corresponds to a specific example of “second optical system” in the present invention.

The aperture stop 4 has a rhombic opening 4A whose two diagonal directions are the direction corresponding to the main scanning direction H and the direction corresponding to the sub-scanning direction V. The aperture stop 4 corresponds to a specific example of the “aperture stop” of the present invention, and is the most significant feature of the present invention. The shape and size of the opening 4A will be described later.

This optical scanning device also includes a polygon mirror 5 disposed on the exit side of the cylindrical lens 3 (ie, on the side opposite to the collimator lens 2). The polygon mirror 5 is a rotary polygon mirror in which each side surface of a polygonal prism (octagonal prism in the figure) constitutes a reflection surface 6, and is rotated at a speed of, for example, 5000 to 20000 revolutions / minute by a motor (not shown). It has become. The polygon mirror 5 changes the reflection angle of the light beam incident on the reflection surface 6 by its rotation, and thereby deflects and scans the light beam in the main scanning direction H. That is, as shown in FIG.
It can swing in the range of θ. Here, the polygon mirror 5 corresponds to a specific example of “light deflecting unit” in the present invention.

This optical scanning device further includes an fθ lens 7 disposed on the exit side of the polygon mirror 5 (ie, the traveling direction of the light beam reflected on the reflection surface 6), and an exit side of the fθ lens 7 (ie, An imaging optical system including a cylindrical mirror 8 disposed on the opposite side of the polygon mirror 5) is provided.

The fθ lens 7 includes a first imaging lens 7A having a negative refractive power (power and light collecting ability) and a second imaging lens 7B having a positive refractive power. It has a positive refractive power as a whole. The cylindrical mirror 8 is a reflection mirror having a part of a cylindrical surface as a reflection surface, and its axis (cylindrical axis) is oriented in a direction parallel to the main scanning direction H, and a light beam reflected on the reflection surface is used as a reflection surface. 9 are arranged. The light beam reflected by the polygon mirror 5 is incident on the reflection surface of the cylindrical mirror 8 at an incident angle ψ. This incident light flux is condensed only in the sub-scanning direction V by being reflected on the reflection surface of the cylindrical mirror 8. The imaging optical system including the fθ lens 5 and the cylindrical mirror 8 functions to always move the beam spot on the surface 9 to be scanned in the main scanning direction H at a constant linear velocity regardless of the rotation angle of the polygon mirror 5. Things. The scanned surface 9 is formed of a surface of a photosensitive material layer such as selenium formed on the surface of a photosensitive drum, for example, and a latent image is formed at a place where light is irradiated.

Here, the aperture stop 4 shown in FIG. 1 will be described in detail with reference to FIG.

FIG. 2 shows the planar shape of the aperture stop 4. The aperture stop 4 can be manufactured by mechanical plate processing, molding, or the like using a material that is opaque to the light used. As the material, for example, a metal such as iron, aluminum, and brass, a synthetic resin, and ceramic are used.

At the center of the aperture stop 4, a diamond-shaped aperture 4A
Are formed. Two diagonal lines 4X of this opening 4A,
4Y cross each other at their midpoints. Among these, the direction of one diagonal line 4X (in the horizontal direction in the figure) coincides with the direction X corresponding to the main scanning direction H, and the direction of the diagonal line 4Y (in the vertical direction in the figure) corresponds to the sub-scanning direction V. In the direction Y corresponding to. In the present embodiment, the aperture stop 4 is arranged such that a perpendicular passing through the center 4C of the aperture 4A coincides with the optical axis Ax of the incident optical system. That is, the aperture stop 4 is disposed so as to be orthogonal to the optical axis Ax. Regarding the size of the opening 4A, for example, the length of the diagonal line 4X in the direction X is about 5.0 to 5.5 mm, and the length of the diagonal line 4Y in the direction Y is about 3.0 to 3.5 mm. However, it is not limited to these dimensions.

<Operation of Optical Scanning Apparatus> Next, the operation of the optical scanning apparatus configured as described above will be described. First, in response to an instruction to start image formation from an external device such as a computer, the polygon mirror 5 starts rotating. Next, the light source 1 is driven based on the input image information to emit a light beam. Light source 1
Is a divergent light having a substantially circular or elliptical cross-sectional shape, but becomes substantially parallel light by passing through the collimator lens 2. The substantially parallel light flux forms an image near the reflecting surface 6 of the polygon mirror 5 by the power of the cylindrical lens 3 in the sub-scanning direction V. The cross section of the light beam becomes a straight line extending in the direction X corresponding to the main scanning direction H.

The polygon mirror 5 reflects the light flux imaged in a straight line on the reflecting surface 6. The reflected light beam is condensed in the main scanning direction H by the fθ lens 7, further reflected by the cylindrical mirror 8, and forms an image on the surface 9 to be scanned as a beam spot. As a result, the surface of the photosensitive drum is exposed, and an electrostatic latent image based on image information is formed. When the main scanning for one row is completed, the main scanning for the next row is performed. During that time, the photosensitive drum is rotated and the surface 9 to be scanned moves in the sub-scanning direction V.

The latent image formed on the surface 9 to be scanned is developed by toner development in a developing section (not shown), and is transferred to a recording paper (not shown) by a transfer section (not shown). The toner image transferred and formed on the recording paper is fixed on the recording paper by heating and pressing in a fixing unit. This allows
An image corresponding to the input image information is obtained.

At this time, the aperture 4A of the aperture stop 4 is
As shown in FIG. 5, since the directions of the two diagonal lines 4X and 4Y match the main scanning direction H and the sub-scanning direction V, respectively, the beam passing through the opening 4A has the shape of the opening 4A. The shape of the beam spot S formed on the surface 9 to be scanned by receiving the corresponding diffraction is, for example, as shown in FIG.
The shape is close to a rectangle in which the paired sides are parallel to the sub-scanning direction V. Therefore, the irradiation intensity (energy density) in the area G between the spots in the diagonal direction of the beam spot array
Is higher than in the conventional case (FIG. 13), and the problem that the formed image does not reach the desired density is eliminated or suppressed.

Further, by forming the opening in a diamond shape, as will be described later, the depth of focus in the main scanning direction H and the sub-scanning direction V becomes larger than in the conventional case where the opening is rectangular or elliptical. Assembly adjustment is easy or unnecessary.

As described above, according to the optical scanning according to the present embodiment, the directions of the two diagonal lines on the optical path respectively correspond to the direction corresponding to the main scanning direction and the direction corresponding to the sub-scanning direction. Aperture stop 4 having such a rhombic aperture
Is provided, the beam is uniformly applied to the surface 9 to be scanned, and the formed image quality is improved.

Note that the shape of the opening 4A does not need to be an accurate rhombus, and some deformation is possible, and it is sufficient if it is "a shape similar to a rhombus". For example, as shown in FIG.
Each side of the diamond may not be straight, but may be slightly curved outward or inward. However, in this case, the degree of curvature is such that the central portion 4P of each side is an ellipse 4 circumscribing the opening 4A.
It is preferable to set the range to be located inside Q.
This is because if the portion of the contour of the aperture in the direction corresponding to the diagonal direction of the beam spot array on the surface 9 to be scanned coincides with the ellipse or expands outward from the ellipse, the direction in this direction is increased. The amount of diffraction is smaller than the amount of diffraction in directions corresponding to the main scanning direction H and the sub-scanning direction V;
As a result, on the surface 9 to be scanned, the beam irradiation intensity in the inter-spot area G (FIG. 13) in the diagonal direction of the beam spot array decreases, and the uniformity of the formed image density becomes insufficient.

Also, for example, as shown in FIG. 4, the four apex corners of the rhombus may be slightly rounded, and, for example, as shown in FIG. May be slightly chamfered. However, even in these cases, as described above, it is preferable that the central portion 4P of each side be located inside the ellipse 4Q circumscribing the opening 4A.

The directions of the two diagonal lines of the aperture 4A of the aperture stop 4 do not have to exactly coincide with the main scanning direction and the sub-scanning direction, respectively.

The position where the aperture stop 4 is arranged is not limited to the position between the cylindrical lens 3 and the polygon mirror 5, but can be arranged at any position between the light source 1 and the polygon mirror 5. .

In this embodiment, the aperture stop 4 is arranged perpendicular to the optical axis Ax. However, the aperture stop 4 may be slightly inclined from the orthogonal state. In this case, the reflected light from the aperture stop 4 (light that has not passed through the opening 4A) can be prevented from returning to the light source 1, which is rather preferable in that the output of the light source 1 can be stabilized.

[0037]

Next, an example of this embodiment will be described.
In the present embodiment, the cylindrical lens 3, the aperture stop 4,
The surface parameters of the reflecting surface 6, the first imaging lens 7A and the second imaging lens 7B of the polygon mirror 5, and the surface parameters of the cylindrical mirror 8 were set to the values shown in Table 1.

[0038]

[Table 1]

Here, each code indicates the following parameters. Surface No. : Surface number of each optical element rh: Radius of curvature in cross section in main scanning direction rv: Radius of curvature in cross section in sub scanning direction d: Distance on optical axis between each surface (distance to next surface) N: Wavelength 780 nm ：: Incident angle (= reflection angle) in the cross section in the sub-scanning direction of the cylindrical mirror 8

Note that the surface No. Is 1, the number of the surface on the light incident side (the side of the collimator lens 2) of the cylindrical lens 3 is set to 1, and numbers from 2 to 9 are sequentially assigned along the light traveling direction. Therefore, the surface No. 9 is a reflecting surface of the cylindrical mirror 8.

In this embodiment, a light beam emitted from a light source 1 composed of a semiconductor laser at a wavelength of 780 nm and a divergence angle (full width at half maximum) of 33 ° in the main scanning direction and 11 ° in the sub-scanning direction is used. The distance was set to 6.5 mm. The light beam passing through the collimator lens 2 has a 1 / e ² intensity width of 6.28 mm in the direction X corresponding to the main scanning direction H.
Thus, the beam becomes a substantially parallel light beam whose 1 / e ² intensity width in the direction Y corresponding to the sub-scanning direction V is 1.25 mm. In addition, 1
The / e ² intensity width means the beam width when the intensity profile in the light beam cross section is 1 / e ² (e = 2.7182...) Of the peak value.

As the cylindrical lens 3, a lens having a focal length of 207.4 mm having power only in the sub-scanning direction was used, so that a line image was formed near the reflecting surface 6 of the polygon mirror 5. Imaging lenses 7A, 7B
Lens 7 is made of a distance of 220 mm. The fθ lens 7 focuses the light beam deflected by the polygon mirror 5 in the main scanning direction H, and then has a cylindrical mirror 8 having power only in the sub-scanning direction V. As a result, a beam spot was formed on the surface 9 to be scanned.

In this embodiment, the length of the diagonal line 4X in the direction X corresponding to the main scanning direction H is 5.14 mm as the opening 4A of the aperture stop 4, and the direction Y corresponding to the sub-scanning direction V
A diamond-shaped opening having a diagonal line 4Y having a length of 3.34 mm was used. The aperture stop 4 is a cylindrical lens 3
Immediately after, it was arranged almost in close contact.

FIG. 10 is an enlarged view of a beam spot on the surface 9 to be scanned obtained in this embodiment. In this figure, (C) shows the case where the defocus amount (the amount of deviation from the in-focus position) Δf is 0;
(E) shows that the defocus amount Δf is -3 mm,
(B) and (D) show the case of +3 mm, respectively.
This shows a case where the defocus amount Δf is −1.5 mm and +1.5 mm. Note that a minus sign indicates a defocus amount toward the lens, and a plus sign indicates a defocus amount toward the opposite side. In each of the figures (A) to (E), the inner line of the double lines indicates an isointensity line of 13.5% with respect to the peak intensity of the spot, and the outer line indicates the isointensity line with respect to the peak intensity. A 1% isointensity line.

On the other hand, FIG. 11 is an enlarged view of a beam spot on the surface 9 to be scanned obtained in a comparative example of the present embodiment. In this comparative example, a rectangular opening having a width in the main scanning direction of 3.8 mm and a width in the sub-scanning direction of 2.0 mm is used. The other elements were the same as the parameters shown in the above table. The meanings of (A) to (E) in FIG. 11 are the same as those in FIG. 10, and the meaning of the double line is also the same as that in FIG.

As can be seen from FIG. 11, in the comparative example, the focal plane (Δf = 0) and the defocus amount Δf = ± 1.
Each of the beam spots at the position of 5 mm and the position of the defocus amount Δf = ± 3 mm has a substantially elliptical shape at a high intensity (for example, 13.5%). However, the shape at the low intensity (for example, 1%) extends in the main scanning direction and the sub-scanning direction, but does not extend in the diagonal direction of the arrangement of the beam spots (the direction D in FIG. 2). In the arrangement of the beam spots having such a shape, the gap between the beam spots in the diagonal direction of the array is large, and it is not possible to obtain a uniform density over the entire image.

On the other hand, as can be seen from FIG. 10, in this embodiment, at any position, the beam spot has a shape such that the intensity distribution spreads in the diagonal direction of the array, and as a result, The occurrence of uneven image density in the diagonal direction of the array is effectively suppressed. That is, the focal plane (Δf = 0), the defocus amount Δf = ± 1.5 mm
And the position of the defocus amount Δf = ± 3 mm, the beam spot shape at a high intensity (eg, 13.5%) does not change much, but a low intensity (eg, 1
%), The spot shape does not spread so much in the main scanning direction and the sub-scanning direction, but extends in the diagonal direction of the arrangement of the beam spots. For this reason, even in the diagonal direction of the arrangement of the beam spots, the gap between the beam spots is filled (the region where the beam irradiation intensity is zero or extremely weak is eliminated), and it is possible to obtain an image with a uniform density distribution.

In this embodiment, on the surface 9 to be scanned,
The beam spot size is about 65 μm in the main scanning direction H.
m (1 / e^TwoIntensity width), and about 75 μm (1
/ E ^TwoStrength range). In this example, compared to the comparative example
And the side lobes (secondary
Image due to the above-described diffracted light)
There was little change in the image shape when scumming occurred. this
As a result, the depth of focus increases, and the image
Deterioration is small and good quality images can be obtained stably
I understood.

[Second Embodiment] Next, a second embodiment will be described.

In this embodiment, as shown in FIG. 6, the aperture stop 4 is inclined from a position perpendicular to the optical axis. Specifically, the aperture stop 4 is rotated and inclined by a predetermined angle around a straight line 4XX along a diagonal line 4X in a direction corresponding to the main scanning direction H. Thereby, the same effect as changing the length of the diagonal line 4Y of the opening 4A can be obtained. Similarly, the length of the diagonal line 4X of the aperture 4A is changed by rotating the aperture stop 4 by a predetermined angle and tilting the straight line 4YY along the diagonal line 4Y in the direction corresponding to the sub-scanning direction V as the central axis. It is possible to obtain the same effect as described above. Accordingly, while observing the shape and size of the beam spot on the surface 9 to be scanned, the shape (the ratio of the two diagonal lines 4X and 4Y) and the size (the two diagonal lines 4X and 4Y) of the opening 4A are optimized so as to optimize the shape.
4Y) can be adjusted.

Also, instead of rotating the aperture stop 4 only in one direction with only one of the straight lines 4XX and 4YY as the central axis, the aperture stop 4 is rotated in both directions about the central axis and tilted. Is also good. In this case, by setting the inclination angle to be equal in both directions, it is possible to change the opening size while maintaining a shape similar to the original planar shape of the opening 4A.

The configuration other than the aperture stop 4 is the same as that of the first embodiment, and a description thereof will be omitted.

In this embodiment, since the aperture stop 4 is inclined from a position orthogonal to the improvement, the first stop is used.
As described in the first embodiment, the reflected light from the aperture stop 4 can be prevented from returning to the light source 1. Therefore, in addition to the variable aperture size, there is an advantage that the output of the light source 1 can be stabilized.

<Modification> As shown in FIG. 7, in this modification, a plate-shaped first aperture member having a slit-shaped opening 4S1 and a plate-shaped second diaphragm having a slit-shaped opening 4S2 are provided. The aperture stop 4 is configured by superimposing and combining an aperture member. In particular,
An opening 4A is formed by an overlapping portion of the slit-shaped openings 4S1 and 4S2, and a perpendicular line 4C passing through the center of the opening 4A is arranged so as to coincide with the optical axis Ax.
In this case, by adopting a mechanism that allows each of the first aperture member and the second aperture member to rotate by the same angle in directions opposite to each other about the perpendicular line 4C, the shape of the opening 4A, that is, two The ratio of the lengths of the diagonal lines 4X and 4Y can be changed. Thereby, the scanned surface 9
The upper beam spot shape can be easily adjusted. The other configuration is the same as that of the first embodiment.

[Third Embodiment] Next, a third embodiment will be described.

In the present embodiment, as shown in FIG.
The aperture is formed by combining a plate-shaped first aperture member having a “V” -shaped notch 4N1 and a plate-shaped second aperture member having a “V” -shaped notch 4N2 in an overlapping manner. The diaphragm 4 is configured. Specifically, the first and second aperture members are arranged such that the notch 4N1 and the notch 4N2 face each other along the X direction corresponding to the main scanning direction H, and these two notches 4N1, An aperture 4A is formed by the overlapping portion of the aperture 4N2, and the aperture stop 4 is connected to a perpendicular line 4C passing through the center of the aperture 4A.
Are arranged to coincide with the optical axis Ax. In this case, furthermore, by adopting a mechanism that allows each of the first aperture member and the second aperture member to move by the same distance in opposite directions along the X direction, two diagonal lines 4 are formed.
The length of X, 4Y can be adjusted. That is, the size of the opening 4A can be changed while maintaining a similar shape. Thereby, the shape and size of the beam spot on the scanned surface 9 can be easily adjusted. In addition,
Other configurations are the same as those in the first embodiment.

In the present embodiment, the first and second
Are arranged such that the notches 4N1 and 4N2 face each other along the X direction. For example, as shown in FIG. 9, the notches 4N1 and 4N2 correspond to the Y direction corresponding to the sub-scanning direction V. The aperture stop 4 may be arranged so as to face each other along the direction. Also in this case, furthermore, by adopting a mechanism that allows each of the first aperture member and the second aperture member to move by the same distance in the opposite direction along the Y direction, 2
The length of one diagonal line 4X, 4Y can be adjusted.

As described above, the present invention has been described with reference to some embodiments. However, the present invention is not limited to these embodiments, and various modifications are possible. For example, FIGS.
It is also possible to combine two or more of the embodiments shown in (or FIG. 9).

In each of the above embodiments, the case where the optical scanning is applied to a recording apparatus for recording on a paper medium such as a laser printer or a laser copying machine has been described as an example. The present invention can be widely applied to a display device such as a beam scanning type data projector and other devices.

[0060]

As described above, according to the optical scanning device according to any one of the first to eighth aspects, the shape of the aperture of the aperture stop corresponds to the direction corresponding to the first scanning direction. And the shape corresponding to the rhombus or two diagonal lines is the direction corresponding to the second scanning direction, so that the beam irradiation in the area between the spots in the arrangement direction of the beam spots on the surface to be scanned is performed. A decrease in strength can be effectively prevented, and image formation and image display with less density unevenness can be performed.

In particular, according to the optical scanning device of the second aspect, since the ratio of the lengths of the two diagonal lines of the diamond-shaped opening is variable, the beam spot is adjusted according to the specifications of the optical system. Mainly to adjust the shape to the optimum state.

According to the optical scanning device of the third aspect, the size of the beam spot itself is adjusted since the size of the rhombic opening is variable while maintaining the similar shape. Is possible.

[Brief description of the drawings]

FIG. 1 is a perspective view illustrating a schematic configuration of an optical scanning device according to an embodiment of the present invention.

FIG. 2 is a plan view illustrating a configuration of the aperture stop illustrated in FIG.

FIG. 3 is a plan view illustrating a configuration of an aperture stop according to a modification of the first embodiment.

FIG. 4 is a plan view illustrating a configuration of an aperture stop according to another modification of the first embodiment.

FIG. 5 is a plan view illustrating a configuration of an aperture stop according to still another modified example of the first embodiment.

FIG. 6 is a plan view illustrating a configuration of an aperture stop according to a second embodiment of the present invention.

FIG. 7 is a plan view illustrating a configuration of an aperture stop according to a modification of the second embodiment.

FIG. 8 is a plan view illustrating a configuration of an aperture stop according to a third embodiment of the present invention.

FIG. 9 is a plan view illustrating a configuration of an aperture stop according to a modification of the third embodiment.

FIG. 10 is an enlarged cross-sectional view illustrating a shape of a beam spot on a scanned surface obtained in one embodiment.

FIG. 11 is an enlarged sectional view illustrating a shape of a beam spot on a scanned surface obtained in a comparative example.

FIG. 12 is a plan view illustrating a configuration of an aperture stop used in a conventional optical scanning device.

FIG. 13 is a diagram illustrating an arrangement of beam spots on a surface to be scanned in a conventional optical scanning device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Light source, 2 ... Collimator lens, 3 ... Cylindrical lens, 4 ... Aperture stop, 4A ... Aperture, 4X, 4Y ... Diagonal line, 5 ... Polygon mirror, 6 ... Reflection surface, 7 ... f [theta] lens, 7A ... First connection Image lens, 7B: second imaging lens, 8: cylindrical mirror, 9: scanned surface, Ax
Optical axis (of the incident optical system), H: main scanning direction, V: sub-scanning direction.

 ────────────────────────────────────────────────── ─── Continued on front page F term (reference) 2C362 AA34 AA36 AA40 AA43 AA48 DA03 2H042 AA13 AA19 AA24 2H045 AA01 BA41 CA04 CB24 DA22 5C051 AA02 CA07 DA01 DB02 DB21 DB22 DB24 DB30 DC04 DC07 FA01 5C072 AA03 DA HA13 HB10 XA01 XA05

Claims (8)

[Claims] An optical scanning device for scanning a predetermined surface to be scanned with light in a first scanning direction and a second scanning direction substantially orthogonal to the first scanning direction, comprising: A light source that emits light, and a first optical system that includes an aperture stop having an aperture of a predetermined shape for narrowing a light beam from the light source, and that is configured to apply a predetermined optical action to the light beam; Light deflecting means for deflecting a light beam having passed through the first optical system so that the surface to be scanned is scanned along a first scanning direction; A second optical system that forms the focused light beam on the surface to be scanned, wherein the aperture of the aperture stop has two directions corresponding to the first scanning direction and the second scanning direction. The diagonal direction of the book, rhombus or similar That the optical scanning apparatus characterized by having a shape. 2. The optical scanning device according to claim 1, wherein the aperture stop is configured such that a ratio of lengths of the two diagonal lines is variable. 3. The optical scanning device according to claim 2, wherein the aperture stop is configured to be rotatable around at least one of the two diagonal lines. 4. The aperture of the aperture stop is formed as an intersection of two slits, and each of the two slits is rotatable about an optical axis of the first optical system. The optical scanning device according to claim 2, wherein: 5. The optical scanning device according to claim 1, wherein the aperture stop is configured such that the size of the aperture is variable while keeping the shape of the aperture similar. 6. The aperture of the aperture stop is formed by combining two plate members having a V-shaped notch, and the two plate members correspond to the first scanning direction. The optical scanning device according to claim 5, wherein the optical scanning device is configured to be movable in a moving direction. 7. The aperture of the aperture stop is formed by combining two plate members having a V-shaped notch, and the two plate members correspond to the second scanning direction. The optical scanning device according to claim 5, wherein the optical scanning device is configured to be movable in a moving direction. 8. The first optical system acts on a light beam from the light source so that the light beam becomes a substantially parallel light beam in a direction corresponding to the first scanning direction, while acting on the second scanning direction. 8. The light-emitting device according to claim 1, wherein said light-emitting device acts to form a convergent light beam in a corresponding direction.
The optical scanning device according to claim 1.