JPH08190065A - Optical scanner - Google Patents

Abstract

PURPOSE: To reduce noise and power consumption and to effectively use a mirror face of a rotary polygon mirror. CONSTITUTION: When an angle between a connection surface 24 being on the side opposite to a light source 12 for an optical axis of an image forming optical system 16 when a mirror face 22 is faced perpendicularly to the optical axis of the image forming optical system 16 and the mirror face 22 faced perpendicularly to the optical axis of the image forming optical system 16 is defined as β, and the angle between the connection surface 24 being on the light source 12 side for the optical axis of the image forming system 16 and the mirror face 22 faced perpendicularly to the optical axis of the image forming optical system 16 is defined as γ, the angle γ is made different from the angle β. Since a projecting part is reduced, and its weight is lightened, the noise when the rotary polygon mirror 14 is rotated is reduced, and the power consumption of a driving motor is reduced. Further, the use range of the mirror face 22 is biased by providing a light beam detector 18 on the outside of an image forming surface 20, but the mirror face 22 is biased by the slope of the connection surface 24 also, thus the mirror face 22 is used effectively.

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 for scanning a light beam using a rotating polygon mirror, and more particularly to an optical scanning device for forming an image of a light beam scanned by the rotating polygon mirror on an image forming surface.

[0002]

2. Description of the Related Art As an optical scanning device for scanning a light beam, for example, a rotary polygon mirror as disclosed in JP-A-62-49317 is used. As shown in FIG. 4, the rotary polygon mirror 100 has a connection located between the adjacent mirror surfaces 102 and 102, which is located inward of the extension surfaces of the mirror surfaces 102, for noise reduction and power saving. A surface 104 is provided. Further, in such an optical scanning device, the detector 10 that receives the light beam LB from the light source 106 reflected by the mirror surface 102 in order to set the timing of writing an image.
In many cases, 8 is provided adjacent to the image plane (for example, photosensitive drum) 109.

For example, as shown in FIG. 5A, in an optical scanning device which irradiates a light beam LB toward the center of a rotary polygon mirror mirror surface 110, it is illustrated from a position O where the light beam LB strikes the mirror surface 102 perpendicularly. The distance from the mirror surface 102 to the position Y where the light beam LB impinges when the light beam LB is directed to the end position of the image area of the image plane is A, and when the light beam LB is directed from the position O to a photodetector (not shown)
Assuming that the distance to the position Z where the light beam LB strikes is B, A ≠ B in many cases because the light beam LB is swung to the photodetector.

Therefore, when the angle between the connecting surface 104 and the mirror surface 102 is the same on both sides of the connecting surface 104 (that is, the angle between the connecting surface 104 and the mirror surface 102 is 135 °), the mirror surface 102 should be effectively used. Can not be.

Further, when the angles formed by the connection surface 104 and the mirror surface 102 are the same on both sides of the connection surface 104, if the mirror surface 102 is to be used more effectively, the rotary polygon mirror 110 as shown in FIG. 5B. It is sufficient to offset the position D of the center of rotation of the optical disc with respect to the optical axis M of the imaging lens (not shown) (dimension C), but the amount of entry and exit of the surface increases by Ctan θ, and the characteristic of field curvature deteriorates. Note that in FIG. 5B, C
Is the offset amount, and θ is the rotation angle of the rotary polygon mirror 110. In addition, the amount of entering and leaving the surface here means that the light beam LB irradiated toward the center of the image region is the rotating polygon mirror 110.
, J, the light beam LB irradiated toward the image area start position is the light beam LB incident on the mirror surface 102 of the rotating polygon mirror 110, and the light beam is irradiated toward the image area end position. LB is the mirror surface 1 of the rotating polygon mirror 110.
When the point incident on 02 is L, the distance m from the intersection J to the intersection K (see FIG. 6) and the distance n from the intersection J to the intersection L are larger (for example, m in FIG. 6). ).

Further, in the above-mentioned conventional technique, as shown in FIG. 7, the light beam LB incident on the point e of the image area (2W) on the image plane 112 is diffusely reflected on the image plane 112, The reflected light LBa may be reflected by the connecting surface 104 of the rotary polygon mirror 110 and re-imaged at a point h on the image forming surface 112, appearing as a harmful image in the image quality, and degrading the image quality.

If the prior art attempts to remove harmful images, (1) the focal length of the imaging lens is increased, (2) the number of mirror surfaces of the rotary polygon mirror is reduced, and (3) the imaging optical system There is a method to reduce the angle between the optical axis and the light beam incident on the rotating polygon mirror from the light source.
In (1), the optical path length increases as the focal length increases, which imposes restrictions on downsizing of the device. In (2), the reduction in the number of mirror surfaces limits the speedup of the device. The method (3) has a drawback that the light source or the incident optical system and the imaging optical system may interfere with each other.

[0008]

SUMMARY OF THE INVENTION In consideration of the above facts, the present invention achieves low noise and power saving in an optical scanning device which scans a light beam with a rotating polygon mirror and effectively uses the mirror surface of the rotating polygon mirror. In addition, the quality of the image formed on the image forming surface is prevented.

[0009]

According to a first aspect of the present invention, there is provided a rotary polygonal mirror for scanning a beam of light from a light source, and an image forming for forming an image of the beam of light scanned by the rotary polygonal mirror. An optical scanning device including an optical system, wherein a flat connecting surface is provided between the mirror surfaces of the rotary polygon mirror, and when the mirror surface of the rotary polygon mirror is oriented perpendicular to the optical axis of the imaging optical system, When the angle formed by the mirror surface and the connection surface on the side opposite to the light source with respect to the optical axis is β, the angle formed by the connection surface and the mirror surface on the light source side with respect to the optical axis is γ, The feature is that β ≠ γ.

The invention described in claim 2 is the same as claim 1.
In the optical scanning device described in (1), the focal length of the imaging optical system is f, the angle between the light beam incident on the rotary polygon mirror from the light source and the optical axis of the imaging optical system is α (rad), and The distance from the optical axis of the imaging optical system to the end of the effective scanning width is W,
Then β (rad) <(2fπ−αf−W) / 2
The feature is that it is f.

Where β (rad) <(2fπ−αf−
How to derive W) / 2f will be described below.

In a scanning optical device as shown in FIG. 8,
Assuming that the angle formed by the light beam 12A from the light source 12 and the normal line of the mirror surface 22 of the rotary polygon mirror 14 is a (rad), the light beam 20A returning from the imaging surface (scanned surface) 20 is connected. It reflects at (π-β) -a with respect to the normal line of the surface 24. That is, since 22A reflected by the mirror surface 22 and the light beam 20A are parallel to each other due to the characteristics of the imaging optical system (f-θ lens), the light beam 20A forms an angle δ− with respect to the normal line of the connection surface 24. It reflects at a (rad) and the angle δ is the angle π−β.

Therefore, the angle formed by the light beam 12A emitted from the light source 12 and the light beam 24A reflected by the connection surface 24 is 2a + 2 (π-β-a) = 2 (π-β) = constant.

Next, the distance X from the optical axis 16A of the image forming optical system 16 to the position V where the light beam 24A forms an image on the image forming surface 20 is X = {2 (π−β) −α} f. Can be represented (f is the focal length of the imaging optical system 16) If the position V is outside the end of the effective scanning width (position at a distance W from the optical axis of the imaging optical system), image formation The surface is not irradiated with an unnecessary light beam, and W <X, that is, W <
It suffices to satisfy the relationship of {2 (π-β) -α} f.

Transforming the above equation,

[0016]

In the optical scanning device according to the first aspect of the present invention, since the flat connecting surface is provided between the mirror surfaces of the rotary polygon mirror, the protruding portion is reduced, and the noise (wind noise) during rotation of the rotary polygon mirror is reduced. can do. Furthermore, since the air resistance during rotation is reduced and the weight is reduced, the power consumption of the drive motor can be saved.

Further, when the mirror surface of the rotary polygon mirror is oriented perpendicular to the optical axis of the imaging optical system, the angle β formed by the connection surface on the side opposite to the light source with respect to the optical axis and the mirror surface, Since the angle γ between the connection surface on the light source side and the mirror surface with respect to the optical axis is different, the mirror surface can be used by providing a light beam detector outside the image formation surface for timing the image writing. Since the range is biased, as a result, the mirror surface can be effectively used.

Further, the light beam incident on the image forming surface is reflected by the image forming surface, the reflected light beam returns to the connecting surface via the image forming optical system, and is further reflected by the connecting surface to form an image again. If a light beam traveling in the direction of the image plane through the optical system is applied to the inside of the effective scanning width of the image plane (image forming surface), the image quality will deteriorate. However, in the optical scanning device according to the second aspect, the focal length of the imaging optical system is f, and the angle between the light beam incident on the rotating polygon mirror from the light source and the optical axis of the imaging optical system is α (rad). , Β (rad) <(2fπ−αf−W) / 2f is satisfied, where W is the distance from the optical axis of the image forming optical system to the end of the effective scanning width on the image forming surface. The light beam reflected by the image forming surface and returning to the image forming surface is irradiated to the outside of the effective scanning width of the image forming surface, and it is possible to prevent deterioration of image quality due to unnecessary light beams. it can.

For example, the focal length f of the image forming optical system is 143.
mm, the angle α between the light beam entering the rotating polygon mirror from the light source and the optical axis of the imaging optical system is 1 (rad), from the optical axis of the imaging optical system on the imaging surface to the end of the effective scanning width. When the distance W of is set to 108 mm and these values are substituted into the equation (1), Expression (1) is as follows.

[0020] Here, as in the prior art, the angles formed by the connection surface and the mirror surfaces adjacent to both sides are the same (angle β is 135 deg ≈ 2.356).
rad), the number of mirror surfaces of the rotary polygon mirror is 4, the distance W and the angle α are fixed, and the harmful image is directed to the outside of the end of the effective scanning width of the image forming surface. That is, the focal length f> 189.2 mm must be set,
This leads to an increase in the size of the device.

If the focal length f and the distance W are fixed and the harmful image is directed toward the outside of the end of the effective scanning width of the image plane, That is, α <46.73 deg must be set, and the light source and the imaging optical system may approach each other and interfere with each other.

On the other hand, in the present invention, the size of the device is increased,
It is possible to prevent the generation of harmful images without the light source and the imaging optical system interfering with each other.

[0023]

【Example】

[First Embodiment] A first embodiment of the present invention will be described with reference to FIG.

FIG. 1 shows a main part of an optical scanning device 10 to which the present invention is applied. As shown in FIG. 1, the optical scanning device 10 of the present embodiment includes a light source (laser or the like) 12, a rotary polygon mirror 14, an imaging optical system 16, a photodetector 18, and an imaging surface 20.

Four flat mirror surfaces 22 are formed on the outer circumference of the rotary polygon mirror 14, and a flat connecting surface 24 is formed at the boundary between the adjacent mirror surfaces 22. The angle between the adjacent mirror surfaces 22 is 90 °.

When the mirror surface 22 is oriented perpendicularly to the optical axis of the image forming optical system 16, the connecting surface 24 and the image forming optical system 16 on the side opposite to the light source 12 with respect to the optical axis of the image forming optical system 16. Is β, and the connection surface 2 on the light source 12 side with respect to the optical axis of the imaging optical system 16 is β.
4 and a mirror surface 2 oriented perpendicular to the optical axis of the imaging optical system 16.
When the angle formed with 2 is γ, this rotating polygon mirror 14
Is different from the angle β and the angle γ. In this embodiment, the angle β is 133.2 ° (≈2.32 rad) and the angle γ is 13
It is set to 6.8 ° (≈2.39 rad).

The image forming optical system 16 is arranged laterally of the rotary polygon mirror 14 at a predetermined interval, and the light source 12 is arranged in a direction different from that of the image forming optical system 16. The imaging optical system 16 of this embodiment is an f-θ lens, and its optical axis is orthogonal to the rotation axis of the rotary polygon mirror 14. Also, the light source 1
The optical axis of 2 is also orthogonal to the rotation axis of the rotary polygon mirror 14.

In this optical scanning device 10, the angle α formed by the optical axis 16A of the imaging optical system 16 and the light beam 12A from the light source 12 toward the rotary polygon mirror 14 is 65 ° (≈1.1).
3rad), a circle 23 inscribed in the mirror surface 22 of the rotary polygon mirror 14
Has a radius R of 11 mm, an offset amount C between the rotation center D of the rotary polygon mirror 14 and the light beam 12A emitted from the light source 12.
Is 0.53 mm.

On the mirror surface 22, the light beam 12
When the position where A is perpendicular to the mirror surface 22 is O, the position where the light beam 12A toward the image region end position i is Y is Y, and the position where the light beam 12A toward the photodetector 18 is Z is Z, the position Y is defined as the position Y. Is A is 4.35 mm, and the distance B from the position O to the position Z is 4.75 mm.

As described above, in the rotary polygon mirror 14 of this embodiment, since the connection surface 24, that is, the chamfered portion is formed at the boundary between the mirror surfaces 22 and 22, the weight is reduced and the amount of material used is reduced. And the noise during rotation is reduced.

The usable area of the mirror surface 22 irradiates the photodetector 18 located outside the image plane 20 with the light beam, so that the center of the width of the rotary polygon mirror 14 (the mirror surface 22 passing through the center D of rotation). Although the dimensions are different on both sides in the rotation direction with respect to the (normal line), the mirror surface 22 is effectively used because the connection surface 24 is inclined accordingly.

Further, in this embodiment, since the amount of entering and leaving the surface is minimized, the deterioration of the characteristic of the image curvature is suppressed.

[Second Embodiment] Next, a second embodiment of the present invention will be described.

The scanning optical device 10 of the present embodiment has the same structure as that of the first embodiment, but the specifications of each part are different.

In the present embodiment, the angle β is the angle (2fπ-α
f-W) / 2f.

Specifically, the distance W from the optical axis 16A of the imaging optical system 16 to the end of the effective scanning width on the imaging plane 20.
108 mm, the focal length f of the imaging optical system 16 is 140 mm,
The angle α formed by the optical axis of the imaging optical system 16 and the light beam LB emitted from the light source 12 is 1 rad (= 57.3 °), and the connecting surface 24 and the rotating polygon mirror rotation direction side of the connecting surface 24. An angle β formed by the mirror surface 22 adjacent to the side opposite to is 2.23 rad (= 128 °), for example.

Since the above values satisfy the equation (1) as follows, in the scanning optical device 10 of this embodiment, the image plane 2
At 0, harmful images can be prevented.

[0038] Note that the values of the focal length f, the angle α, the angle β, the distance W, and the like are merely examples, and may be values that satisfy the expression (1).

Further, in FIG. 2, the distance W is constant (108 m
It is a graph showing the relationship between the angle α and the angle β when the focal length f is changed in three steps by setting m), and harmful images are prevented by using in the region below the line of the graph. be able to.

Further, in FIG. 3, the distance W is fixed (108
(mm) is a graph showing the relationship between the focal length f and the angle β when the angle α is changed in three steps, and a harmful image is prevented by using the region below the line of the graph. be able to.

[0041]

As described above, in the optical scanning device according to the first aspect, a flat connecting surface is provided between the mirror surfaces of the rotary polygon mirror, and the mirror surface of the rotary polygon mirror is set as the optical axis of the imaging optical system. The angle β formed by the mirror surface and the connection surface on the side opposite to the light source with respect to the optical axis and the angle γ formed by the mirror surface and the connection surface on the light source side with respect to the optical axis Since the change is made, there is an excellent effect that the noise reduction and the power saving can be achieved and the mirror surface of the rotary polygon mirror can be effectively used.

Further, in the optical scanning device according to claim 2,
Since the unnecessary light beam is irradiated to the outside of the effective scanning width of the image plane, there is an excellent effect that the quality of the image formed on the image plane can be prevented from being deteriorated. Further, since the interference between the light source and the imaging optical system and the focal length do not become long, the device does not become large.

[Brief description of drawings]

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

FIG. 2 is a graph showing a specific example of an angle α and an angle β in the second example.

FIG. 3 is a graph showing a specific example of the focal length f and the angle β in the second embodiment.

FIG. 4 is a perspective view of a conventional optical scanning device.

5 (A) and 5 (B) are plan views of the rotary polygon mirror seen from the direction of the rotation axis for explaining that the conventional mirror surface is not effectively used.

FIG. 6 is a plan view of the rotary polygon mirror viewed from the direction of the rotation axis for explaining the entering / exiting amount.

FIG. 7 is a configuration diagram of a conventional optical scanning device for explaining deterioration of image quality.

[Figure 8]

[Explanation of symbols]

 10 Optical Scanning Device 12 Light Source 14 Rotating Polyhedral Mirror 16 Imaging Optical System 20 Imaging Surface 22 Mirror Surface 24 Connection Surface

Claims (2)

[Claims] 1. An optical scanning device comprising: a rotary polygon mirror that scans a light beam from a light source; and an imaging optical system that forms an image of the beam light scanned by the rotary polygon mirror on an imaging surface. , A flat connecting surface is provided between the mirror surfaces of the rotary polygon mirror, and when the mirror surface of the rotary polygon mirror is oriented perpendicular to the optical axis of the imaging optical system, the connection is on the opposite side of the optical axis from the optical axis. The optical scanning device is characterized in that β ≠ γ, where β is an angle formed by a surface and the mirror surface and γ is an angle formed by the connection surface on the light source side with respect to the optical axis and the mirror surface. . 2. The focal length of the imaging optical system is f, and the angle formed by the light beam incident on the rotary polygon mirror from the light source and the optical axis of the imaging optical system is α (rad). 2. The light according to claim 1, wherein β (rad) <(2fπ−αf−W) / 2f when the distance from the optical axis of the system to the end of the effective scanning width is W. Scanning device.