JPH1020230A - Optical scanning device - Google Patents

Abstract

(57) [Summary] [PROBLEMS] In a twice-deflection type optical scanning device, the light beam rotates between the first deflection and the second deflection, and the beam spot shape is destroyed. Provided is a miniaturized twice-deflection type optical scanning device capable of forming an excellent image by using the optical scanning device. SOLUTION: A light beam from a light source 1 is made incident on a first reflecting surface 4 of a scanner 3 having at least two reflecting surfaces, and a light beam b deflected from the first reflecting surface 4 is transmitted to a transmission optical system. 7, 8, 9, 10, and 11, the scanner 3
In the optical scanning device, the light beam c is made incident on a second reflection surface 5 different from the first reflection surface 4 to be deflected, and the deflected light beam c is formed on a surface 14 to be scanned by forming a beam spot for scanning. An optical scanning device configured such that the light beams a and b incident on the first and second reflecting surfaces 4 and 5 of the third light beam are incident at an angle in the sub-scanning direction, and the angles are the same. It is.

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 for a laser beam printer or the like, and more particularly, to deflect by making a light beam twice incident on a scanner as a deflecting means so that the optical path of the light beam does not interfere. The present invention relates to an optical scanning device configured as described above.

[0002]

2. Description of the Related Art Conventionally, an optical scanning device used in a laser beam printer or the like generally applies a light beam emitted from a light source such as a semiconductor laser to a scanning device such as a rotary polygon mirror which is a deflecting means via a shaping optical system. Incident and deflected only once,
The deflected light beam is configured to scan by forming a beam spot on the surface to be scanned by an imaging lens system as an f · θ lens. In such a single deflection by the scanner, the size of the light beam in the main scanning direction is large on the reflecting surface of the scanner, and when the scanner rotates, it is attempted to put the entire light beam on the reflecting surface. The reflection surface must be formed large. For this reason, the size of the scanner is increased, and the number of reflecting surfaces of the scanner cannot be increased so much that the speed of the optical scanning device cannot be increased. Therefore, recently, the light beam deflected by the first reflection surface of the scanner such as a rotary polygon mirror is again guided to the second reflection surface of the scanner via the transmission optical system, and the deflection angle of the light beam deflected for the second time Various proposals have been made from the viewpoint that an optical scanning device configured to scan the surface to be scanned by a scanning optical system can be operated at high speed.

For example, in a self-amplifying deflection scanning optical system described in JP-A-53-97448, the first
The light beam deflected by the reflection surface is provided with an afocal transmission optical system, is incident on a second reflection surface different from the first reflection surface of the scanner, and is incident on the second reflection surface of the scanner. The beam is deflected by irradiating the beam in parallel with the light beam from the first reflection surface, that is, the light beam is deflected twice by different reflection surfaces of the same scanner to perform optical scanning. At this time,
A transmission optical system is provided so that the light beam moves in a direction opposite to the rotation or rotation direction of the scanner.

[0004]

The double-deflection type optical scanning device has the advantage that the scanning angle can be increased and the inclination of the light beam deflected by the first reflecting surface of the scanner due to the tilt of the scanner. The advantage is that the corners can be reduced or offset by the second reflective surface of the scanner. By the way, in the self-amplification deflection scanning optical system, the optical path deflected for the first time and the optical path deflected for the second time are on the same plane, so that the optical scanning device becomes large. Further, the first reflection surface and the second reflection surface of the scanner need to be opposed to each other, and the optical path of the transmission optical system becomes long. Therefore, the degree of freedom in arranging the optical path of the transmission optical system is reduced. In addition, an afocal optic must be used for the transmission optics, which requires at least two lenses,
There is a disadvantage that the structure is complicated, the device becomes large, and the cost is disadvantageous.

In the case where a light beam is incident twice on the same scanner and deflection is performed, the optical path of the first deflection and the second deflection are generally required to make the optical scanning device compact. Must be arranged such that the optical paths for performing the operations do not overlap. That is, each light beam is made incident at an angle to the plane perpendicular to the rotation axis of the scanner so that the light path of the first light beam and the light path of the second light beam do not interfere with each other. It is configured not to do so. For this reason, the optical path for the first deflection and the optical path for the second deflection are separated upward and downward in the direction of the rotation axis of the scanner, and the optical scanning device can be downsized. By the way, with this configuration, the first and second deflections are performed.
When the light beam rotates in the optical path of the transmission optical system provided between the reflection surface and the second reflection surface, and this is scanned by forming a beam spot on the surface to be scanned by the scanning optical system, The shape of the beam spot collapses, making it difficult to obtain a clear image.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a miniaturized double-deflection optical scanning device capable of forming a good image with simple means. . That is, the light beam incident on the first reflecting surface for performing the first deflection and the second reflecting surface for performing the second deflection of the scanner is formed such that the light beam has an angle at each of the reflecting surfaces in the sub-scanning direction. A compact optical scanning device which is configured to be incident so that the respective optical paths do not overlap, and that the incident angles of the light beams incident on the first reflection surface and the second reflection surface of the scanner are the same. Device. Further, the first reflection surface and the second reflection surface of the scanner are parallel to each other, and the optical path from the first reflection surface to the second reflection surface passes through the rotation axis of the scanner.

[0007]

According to the present invention, a light beam from a light source is made incident on a first reflecting surface of a scanner having at least two or more reflecting surfaces, and a light beam deflected from the first reflecting surface is provided. An optical scanning device for re-entering a second reflecting surface different from the first reflecting surface of the scanner by a transmission optical system to form a beam spot on a surface to be scanned with the deflected light beam and scan the light beam. The light beam incident on the first reflection surface and the second reflection surface of the detector is incident at an angle in the sub-scanning direction, and the light beam is configured to be the same angle. Further, an optical scanning device in which the first reflection surface and the second reflection surface of the scanner are parallel, and an optical path from the first reflection surface to the second reflection surface passes through a rotation axis of the scanner. It is.

Therefore, the optical scanning device thus configured can very well prevent the beam spot from being distorted due to the rotation of the light beam generated between the first deflection and the second deflection by the light beam scanner. Correction can be performed, and the size of the optical scanning device can be reduced.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a perspective view illustrating a configuration of an optical scanning device according to an embodiment. Hereinafter, in the present invention, a rotary polygon mirror is used as a scanner, a direction orthogonal to the rotation axis of the rotary polygon mirror that is the rotation axis of the scanner is defined as a main scanning direction, and a direction parallel to the rotation axis of the rotary polygon mirror is defined as a main scanning direction. Defined as the sub-scanning direction. Further, an optical system provided between the light source 1 and the first reflecting surface of the rotary polygon mirror for performing the first deflection is called a shaping optical system, and the first reflecting surface of the rotary polygon mirror for performing the first deflection and the second reflecting surface are referred to as shaping optical systems. The optical system provided between the second reflecting surface and the second reflecting surface for deflecting the light is referred to as a transmission optical system, and the optical system provided between the second reflecting surface and the surface to be scanned is referred to as a scanning optical system. Deflection by causing a light beam to be incident twice on light is defined as double deflection.

In FIG. 1, a light beam a emitted from a semiconductor laser 1 as a light source passes through a first shaping lens 2 and is shaped, and is applied to a first reflecting surface 4 of a rotary polygon mirror 3 as a scanner in a sub-scanning direction. In this case, the light enters at an angle from below and is deflected for the first time. Light beam b reflected at an angle upward in the sub-scanning direction from the first reflecting surface 4
Is transmitted through the first transmission lens 7, is reflected by the first transmission mirror 8, is transmitted through the second transmission lens 9 and the third transmission lens 10, is reflected by the second transmission mirror 11, and returns to the first position of the polygon mirror 3. The light is incident on the second reflecting surface 5 at an angle from above in the sub-scanning direction, and is deflected a second time. The light beam c deflected at an angle downward in the sub-scanning direction from the second reflection surface 5 is imaged as a beam spot on the surface to be scanned 14 by the first scanning lens 12 and the second scanning lens 13 made of plastic. And configured to scan. The light beam d is for a horizontal synchronization signal, and the light beam c
At the scanning end, and is introduced to a horizontal synchronization sensor 83 via a horizontal synchronization mirror 81 and a horizontal synchronization lens 82.

The shaping lens 2 and the first transmission lens 7 are
The second transmission lens 9 is a cylindrical lens having power only in the sub-scanning direction, and the third transmission lens 10 is a cylindrical lens having power only in the main scanning direction. . The first scanning lens 12 is a spherical lens. The second scanning lens 13 is a plastic lens, and its incident surface has a concave shape with a large radius of curvature in the main scanning direction, and has a convex shape with a small radius of curvature in the sub-scanning direction. Further, this is a surface formed by rotating a cross-sectional curve in the main scanning direction around an axis parallel to the main scanning direction on the surface to be scanned 14 side of the incident surface. Such a surface is usually called a saddle-shaped toric surface. The exit surface is a convex non-circular arc having a large radius of curvature in the main scanning direction (referred to as a non-circular arc because only the main scanning direction is an aspheric surface). The cross section in the sub-scanning direction is a straight line. Such a surface is sometimes called a non-circular cylindrical surface or a non-cylindrical surface.

The first reflecting surface 4 of the rotary polygon mirror 3, which is a scanner.
The light beam a and the light beam b incident on the second reflection surface 5 and the first reflection surface 4 and the second reflection surface 5
, Respectively. In a conventional optical scanning device that deflects only once on the reflecting surface of a rotating polygonal mirror, the size of the light beam incident in the main scanning direction on the reflecting surface of the rotating polygonal mirror is smaller than that of the double-deflection object, which is the object of the present invention. Compared with the optical scanning device, when the rotating polygon mirror is rotated by an angle to obtain a required scanning angle, if the entire light beam is always put on the same reflecting surface, the size of the reflecting surface becomes a certain size. Since the above size is required, the number of reflecting surfaces of the rotary polygon mirror cannot be formed so much. On the other hand, in the twice-deflection type optical scanning device of the present invention, the main scanning light is mainly located near the first reflecting surface 4 where the first deflection is performed.
The light beam is imaged in both the sub-scanning directions, and the size of the light beam a on the first reflecting surface 4 is extremely smaller than that of the once-deflecting optical scanning device. Even if the size in the scanning direction is small, the entire light beam can always enter the first reflecting surface when the rotary polygon mirror 3 is rotated by an angle for obtaining a required scanning angle. Therefore, the reflecting surface of the rotary polygon mirror 3 can be small. In the second deflection, although the light beam b incident on the second reflecting surface 5 of the rotary polygon mirror 3 has a large size in the main scanning direction, the light beam b moves when the rotary polygon mirror 3 rotates. The movement of the second reflecting surface coincides. This is called surface following. For this reason, the size of the second reflection surface 5 in the main scanning direction only needs to be the same as the size of the incident light beam b, and the second reflection surface 5 also needs to be small. Therefore, since the size of the reflecting surface of the rotary polygon mirror 3 can be made smaller than that of a once-deflection type optical scanning device, the number of reflecting surfaces can be increased, and the scanning speed can be increased accordingly.

A light beam a and a light beam b incident on the first reflecting surface 4 and the second reflecting surface 5 of the rotary polygon mirror 3
And the light beam b and the light beam c deflected from the first reflection surface 4 and the second reflection surface 5 are three-dimensionally separated from each other. Are made to enter the first reflecting surface 4 and the second reflecting surface 5 of the rotary polygon mirror 3. Thereby, the shaping optical system (first shaping lens 2)
And a transmission optical system (first transmission lens 7, second transmission lens 9 and third transmission lens 10), and a transmission optical system and scanning optical system (first scanning lens 12 and second scanning lens 1).
3) can be arranged upward and downward in the direction of the rotation axis 6 of the rotary polygon mirror 3 so that the light beams a, b, and c can be separated without interfering with each other. The arrangement of the optical system can be freely selected.

Next, Table 1 shows specific examples of numerical values of the optical scanning device having such a configuration. In this table, the radius of curvature of the anamorphic surface in the sub-scanning direction and the main scanning direction is rix and riy, respectively. For the aspherical surface, the radius of curvature indicates a value on the optical axis.

[Table 1]

First shaping lens 2 and first transmission lens 7
Is as shown in the following equation (1), and its aspheric coefficient is shown in Table 2 below.

(Equation 1)

[Table 2]

In the embodiment shown in Table 1, the rotation angle of the rotary polygon mirror 3 from the start of one scan to the end of the scan is 2ω =
24 °. The incident angle α of the light beam a on the rotating polygon mirror 3 in the sub-scanning direction on the first reflecting surface 4 and the incident angle β of the light beam b on the second reflecting surface 5 in the sub-scanning direction are both 6 °. The rotating polygon mirror 3 has 12 surfaces, the radius of the inscribed circle of the rotating polygon mirror 3 is 17 mm, the angle between the first reflecting surface 4 and the second reflecting surface 5 is 90 °, and the light source 1 is a light beam. The wavelength of the laser light is 670 nm.

In this embodiment, the light beam a forms an image in the vicinity of the first reflecting surface 4 of the rotating polygon mirror 3 and in the vicinity of the second reflecting surface 5 of the rotating polygon mirror 3 in the sub-scanning direction. Make up. In other words, the transmission optical system (the first transmission lens 7, the second transmission lens 9, and the third transmission lens 10) makes the first reflecting surface 4 and the second reflecting surface 5 substantially geometrically conjugate with each other. The scanning optical system (the first scanning lens 12 and the second scanning lens 13) configures the second reflecting surface 5 and the surface to be scanned 14 so as to have a substantially conjugate relationship. Therefore, the first reflecting surface 4 and the second reflecting surface 4
The tilt of the reflecting surface 5 is corrected well, and the scanning position in the sub-scanning direction becomes constant. Hereinafter, this point will be described in more detail with reference to the drawings.

FIGS. 2A to 2E are developed views in the sub-scanning direction between the first reflecting surface 4 and the second reflecting surface 5 of the rotary polygon mirror 3. FIG. In the case of the present embodiment, the first
Strictly, the imaging point P near the reflecting surface 4 is slightly deviated from the first reflecting surface 4 as shown in FIG. 2A, and the distance between the first reflecting surface 4 and the first transmission lens 7a is small. Exists. Here, the light beam a from the light source 1 is configured to form an image at the image forming point P in both the main scanning direction and the sub-scanning direction.

If the amount 1 of the displacement of the image point P from the first reflecting surface 4 of the rotary polygon mirror 3 is too large, the displacement of the scanning line on the surface 14 to be scanned due to the inclination of the first reflecting surface 4 becomes large. It becomes a problem. On the other hand, if the displacement 1 is small, the size of the light beam a on the first reflecting surface 4 is too small and the rotating polygon mirror 3
The light beam a is scattered under the influence of the scratches and dust existing on the first reflection surface 4, and a small beam spot cannot be formed on the surface 14 to be scanned. Therefore, an appropriate value exists for the amount of displacement 1 of the imaging point P. In this example, the amount 1 of this shift is 11 mm. Since this value is sufficiently smaller than the optical path length of the transmission optical system from the first reflecting surface 4 to the second reflecting surface 5 of the rotary polygon mirror 3 of 300 mm, the effect of correcting surface tilt can be sufficiently obtained.

Next, a specific calculation example will be described. That is, the displacement l of the image point P from the first reflecting surface 4 of the rotary polygon mirror 3 by the shaping optical system is 11 mm, the optical magnification βd in the sub-scanning direction of the transmission optical system is 1.57, and the scanning optical system has The optical magnification βs in the sub-scanning direction is 0.418. This is a rotating polygon mirror 3.
Of the first reflecting surface 4 of [theta] = 3e-4 [rad] (0.
0172 °), the deviation of the scanning line on the scanned surface 14 is δ = 2 · l · θ · βd · βs = 0.00433 [m
m], and there is no problem at this level. In this embodiment, the diameter of the light beam a incident on the first reflection surface 4 is 0.84 mm in the main scanning direction and 0.13 mm in the sub scanning direction. Therefore, the size of the light beam a on the first reflecting surface 4 is sufficiently large, and the first reflecting surface 4 is not affected by scratches or dust. In general, if the diameter of the light beam in at least one of the main scanning direction and the sub-scanning direction is about 0.5 mm, there is no influence of scratches and dust on the reflecting surface of the rotary polygon mirror 3.

In this embodiment, the imaging point Q near the second reflecting surface 5 is located exactly on the second reflecting surface 5. However, this is effective even if it deviates from the second reflection surface 5.
This will be described in more detail. Although the transmission optical system 7a in FIG. 2A is a temporary existence, the first reflection surface 4 and the second reflection surface 5 have a refractive power that is conjugate. A light beam a which forms an image at a position P shifted by 1 from the first reflecting surface 4 is
The position where the light beam b is imaged again near the second reflecting surface 5 by the temporary transmission optical system 7a is denoted by Q. It is desirable that the actual imaging point near the second reflecting surface 5 exists between the second reflecting surface 5 and the position including the position Q where the image is formed again.

First, a case where the image point Q of the light beam b near the second reflecting surface 5 is located at both ends of the above range will be described. FIGS. 2B and 2C show a first example of the transmission optical system 7b.
The reflecting surface 4 and the second reflecting surface 5 are completely conjugate with each other, and the image point formed by the transmission optical system 7b coincides with Q, and the second reflecting surface 5 and the surface to be scanned 14 by the scanning optical system 12a that follow. The relationship is slightly deviated from the conjugate, and the light beam c forms an image on the surface 14 to be scanned. In this case, as shown in FIG. 2C, the surface inclination 4 ′ of the first reflecting surface 4 is completely corrected, and the deviation due to the surface inclination 5 ′ of the second reflecting surface 5 occurs as Δ on the scanned surface 14. . FIGS. 2D and 2E show a case where the relationship between the first reflection surface 4 and the second reflection surface 5 by the transmission optical system 7c is slightly deviated from the conjugate, and an image formed by the transmission optical system 7c is formed. The point coincides with the second reflecting surface 5, the second reflecting surface 5 and the surface to be scanned 14 are completely conjugated by the scanning optical system 12b, and the light beam b forms an image on the surface to be scanned 14 as the light beam c. Is the case. In this case, as shown in FIG. 2 (e), on the contrary, the surface inclination 5 'of the second reflecting surface 5 is completely corrected, and the surface inclination 4' of the first reflecting surface 4 is shifted onto the surface 14 to be scanned. It occurs as Δ '. Note that the principal ray is indicated by a broken line. Therefore, if the imaging point near the second reflection surface 5 is between the second reflection surface 5 and the imaging point Q, the surface inclination 4 ′ of the first reflection surface 4 and the second reflection surface 5,
When 5 ′ is in the opposite direction, the displacement due to the surface tilts 4 ′ and 5 ′ is canceled, and the displacement of the scanning line on the surface 14 to be scanned is reduced. Even in the same direction, this shift amount
It is the same or better than the cases shown in (c) and (e), and at least does not worsen.

Next, the configuration of the transmission optical system will be described. In the main scanning direction of the light beam, the function required for the transmission optical system is to convert the light beam a, which forms an image at point P near the first reflecting surface 4, into a parallel beam and guide it to the second reflecting surface 5. The movement of the light beam b moving on the second reflection surface 5 with the rotation of the mirror 3 follows the movement of the second reflection surface 5.

FIG. 3 is a developed cross-sectional view in the main scanning direction showing an example of the transmission optical system, and is not a diagram showing the embodiment of the present invention. However, in view of the function in the main scanning direction of the light beam, FIG. As shown, paraxially, the transmission optical system needs only one lens 201. However, one lens 2
When the transmission optical system is constituted by 01, the aperture of the lens 201 becomes too large and is not practical. Therefore, as shown in a sectional development view in the main scanning direction of FIG.
If the transmission optical system is constituted by 2, 203, the lens aperture can be reduced, which is practical. Therefore, in order for the transmission optical system to have a function in the main scanning direction, it is desirable to configure the lens with two or more lenses having a refractive power in the main scanning direction. On the other hand, the function necessary for the transmission optical system in the sub-scanning direction is to form a light beam a, which forms an image at an imaging point Q near the first reflection surface 4, as a light beam b, near the second reflection surface 5. It is only that. FIG. 5 is a sectional development view of the transmission optical system in the sub-scanning direction. According to the function in the sub-scanning direction,
The number of lenses of the transmission optical system may be one of the lenses 204. From the above, it is preferable that the transmission optical system be configured with three lenses in order to have both the function in the main scanning direction and the function in the sub-scanning direction. In addition, if this transmission optical system combines a lens having a refractive power in the sub-scanning direction and a lens having a refractive power in the main scanning direction into one, the number of lenses in the transmission optical system can be reduced to two. It is possible. In this embodiment, the transmission optical system is constituted by the three lenses of the first transmission lens 7, the second transmission lens 9 and the third transmission lens 10 from the above.

Next, the intersection of the light beam with the optical axis will be described with reference to FIG. FIG. 6 is a cross-sectional development view of the transmission optical system of the embodiment in the main scanning direction, and is a cross-sectional development view of the first transmission mirror 8 and the second transmission mirror 11 (see FIG. 1). That is, the rotating polygon mirror 3 rotates by the angle .theta.1 about the illustrated position during the scanning. Therefore, the light beam a is deflected on the first reflecting surface 4 of the rotary polygon mirror 3 by 2.theta.1, twice the angle .theta.1. The deflected light beam b passes through the first transmission lens 7, the second transmission lens 9 and the third transmission lens 10, which are transmission optical systems, and is deflected by an angle θ2. This light beam b intersects the optical axis O at point R. At the position where the light beam b is incident on the second reflecting surface 5 of the rotating polygon mirror 3 after the intersection, the distance between the deflected light beam b and the optical axis O is determined by the reflection surface when the rotating polygon mirror 3 is rotated by the angle θ1. It becomes equal to the movement amount δ.

At this time, the deflected light beam b is deflected to the side where the incident angle increases by the angle θ 2 with respect to the second reflecting surface 5 of the rotary polygon mirror 3, and is reflected by the second reflecting surface 5. The light beam c is deflected by 2 · θ1 + θ2. That is, the deflection angle of the light beam is set to θ as compared with an ordinary optical scanning device of the type in which the light beam is made incident on a one-time rotating polygon mirror and deflected.
Can be increased by two. Therefore, when the light beam b scanning the scanning end of the scanning area by the transmission optical system intersects the optical axis O, the deflection angle of the light beam c deflected by the second reflection surface 5 can be increased by 2.multidot..theta.1 + .theta.2. .

Next, the relationship between the number of mirrors of the transmission optical system and the number of intersections between the light beam and the optical axis will be described with reference to FIGS. The number obtained by subtracting the number of times the light beam at the scanning end intersects the optical axis from the number of mirrors of the transmission optical system is an odd number. That is, in the case shown in FIG. 7A, the number of mirrors and the number of intersections are the same as those in this embodiment. The number of mirrors used in the transmission optical system is the first transmission mirror 8 and the second transmission mirror 1
1 two. As shown in the developed view of FIG. 8A, in this case, the number of intersections with the optical axis O is one, as indicated by the dashed principal ray. In the example shown in FIG. 7B, the number of mirrors is three, that is, the first transmission mirror 8, the second transmission mirror 11, and the third transmission mirror 15. FIG.
As can be seen from the developed view shown in (b), the number of intersections with the optical axis O in this case is two. Therefore, FIG.
In the present embodiment, the moving direction δ of the light beam b on the second reflecting surface 5 when the rotating polygon mirror 3 is rotated by the second deflection is the same as the moving direction of the second reflecting surface 5. And the light beam b incident on the second reflecting surface 5 is
Surface can be reliably followed.

Next, the correction of the rotation of the light beam generated in the transmission optical system, which is a feature of the present invention, will be described in detail with reference to FIGS. Light source 1 via shaping optics
Is incident on the first reflecting surface 4 of the rotary polygon mirror 3 from below at an angle in the sub-scanning direction, and the first deflection is performed. Since the optical path between the first deflection and the second deflection as the light beam b has an angle in the sub-scanning direction, the coordinate system of the light beam b on the second reflection surface 5 is rotated. That is, a light beam a having a coordinate system in which the main scanning direction is y, the sub-scanning direction is x, and the optical axis direction is z is reflected by the first reflecting surface 4 at an angle in the sub-scanning direction, and further transmitted in the first direction. When reflected by the mirror 8, the coordinate system of the reflected light beam b rotates as shown in FIG. This light beam b is further reflected by the second transmission mirror 11 and, when it is incident on the second reflection surface 5 of the rotary polygon mirror 3, when the light beam b in FIG.
, The coordinate system of the light beam b rotates. That is, the y direction of the light beam b and the main scanning direction, and the x direction of the light beam b and the sub scanning direction are shifted by a predetermined angle θ.

As described above, when the light beam b is deflected by the rotary polygon mirror 5 for the second time and becomes the light beam c, the light beam b shown in FIG.
As shown in FIG. 1, the coordinate system of the deflected light beam c is always inclined at an angle θ. Even if the light beam c inclined by the angle θ is imaged on the surface 14 to be scanned by the anamorphic scanning optical system, it is not imaged at one point, and the shape of the beam spot is broken. In such a case, as shown in FIG. 12, if the cylindrical lens 211 having a refractive power in the sub-scanning direction is arranged so as to be inclined along the inclination θ of the light beam c, the light beam that forms an image on the surface 14 to be scanned Although the imaging characteristic of c is good, it is necessary to increase the effective diameter of the cylindrical lens 211 in the sub-scanning direction. In addition, there is a problem that a scanning line on the scanned surface 14 is inclined according to the inclination of the cylindrical lens 211.

FIG. 13 is a diagram in which the optical path of the transmission optical system is projected in the main scanning direction. The angle between the optical axis O ₁ after the first deflection by the first reflecting surface 4 of the rotary polygon mirror 3 and the optical axis O ₂ before the second deflection by the second reflecting surface 5 of the rotary polygon mirror 3 is γ. I do. Light beam a to first reflection surface 4 and second reflection surface 5
And the incident angle of the light beam b in the sub-scanning direction is α,
β. FIG. 14 shows the result of calculating the rotation angle of the light beam b. The rotation angle θ is positive in the counterclockwise direction. However, it is based on the following conditions. The optical path length from the first reflecting surface 4 to the second reflecting surface 5 is sufficiently large with respect to the size of the rotating polygon mirror 3. The optical path from the first reflecting surface 4 to the second reflecting surface 5 is symmetric with respect to the bisector of the optical axis O ₁ after the _first deflection and the optical axis O ₂ before the second deflection. As shown in FIG.
When the incident angle α and the incident angle β to the first reflecting surface 4 and the second reflecting surface 5 in the sub-scanning direction are the same, when γ is 180 °
In this case, the rotation angle θ becomes zero. The above conditions,
Unlike the above, when the size of the rotary polygon mirror 3 cannot be ignored with respect to the optical path length, if the incident angles α and β to the first reflecting surface 4 and the second reflecting surface 5 are different, the rotation angle θ
Is slightly dependent on the size of the rotary polygon mirror 3. In addition, even when the optical path is not symmetric, the value of the rotation angle θ slightly changes if the incident angle α and the incident angle β are different. Where incident angle α =
If the incident angle is β, the rotation angle θ is always 0.

In this embodiment, the incident angle α of the light beam a on the first reflecting surface 4 and the second reflecting surface 5 and the light beam b
If only the incident angle α of the light beam a on the first reflecting surface 4 is changed to 3 ° and the incident angle β of the light beam b on the second reflecting surface is changed to 6 °, the scanning end of the scanning end is changed. The beam spot shape by the light beam c becomes a collapsed shape as shown in FIG. This figure is an isointensity diagram of the beam spot. Note that the shape of the beam spot depends on the size of the beam spot. If a smaller beam spot is to be formed, the shape of the beam spot becomes worse.

If the incident angle α is equal to the incident angle β,
As shown in FIG. 14, the rotation angle θ = 0, and the beam angle
The shape of the pot becomes good. In this embodiment, the incident angle α = input
Launch angle β = 6 °, light beam c at the scanning end 1, c According to 2
The beam spot shape is good as shown in FIG.
is there. Even when γ = 180 °, the rotation angle θ = 0
In this case, the beam spot shape is good.
You.

Next, γ = 180 °, that is, the first reflecting surface 4
The case where the and the second reflection surface 5 are parallel will be described. FIG.
In, the angle between the optical axis O ₁ and the optical axis O ₂ is γ, and this angle is equal to the angle between the first reflection surface 4 and the second reflection surface 5. In the case of the present embodiment, γ = 90 °, but separately from the present embodiment, when the first reflecting surface 4 and the second reflecting surface 5 are parallel, γ = 180 °, and the graph of FIG. From this, the rotation angle θ of the light beam becomes zero. An optical path diagram in this case is shown in FIG. That is, the light beam b deflected upward by the first reflecting surface 4 of the rotating polygon mirror 3 is reflected by the first transmission mirror 8, passes right above the rotating polygon mirror 3, intersects with the rotation axis 6,
The light is reflected by the second transmission mirror 11 and is incident on the second reflection surface 5 of the rotary polygon mirror 3 from above, where it is deflected downward to become a light beam c.

Next, rotation correction of a light beam generated by deflection will be described with reference to FIGS. In an optical scanning device of the type in which light is incident on the reflecting surface of the scanner at an angle in the sub-scanning direction, a coordinate system in the main scanning direction y, the sub-scanning direction x, and the optical axis direction z as shown in FIG. Light beam b having an angle in the sub-scanning direction
Is incident on the second reflection surface 5, the light beam c deflected here is curved, and the coordinate system of the light beam c is rotated.
At this time, the light beam c _{0 at} the scanning center does not rotate, but the beams c ₁ and c ₂ at the scanning end are rotated in different directions at both scanning ends as shown in FIG. Even if the light beams c ₁ and c ₂ whose scanning ends are inclined are imaged on the surface to be scanned 14 by an anamorphic scanning optical system, they are not imaged at one point, and the beam spot shape is distorted. Scanning surface 14
The scanning lines above do not provide good imaging.

In this embodiment, the second scanning lens 13
Are arranged eccentrically. For example, if the eccentricity of the second scanning lens 13 is changed to zero and arranged so as not to be eccentric, the beam spot shape by the light beams c ₁ and c ₂ at the scanning end becomes It has a collapsed shape as shown in FIG.
As described above, the shape of the beam spot depends on the size of the light beam. If a smaller beam spot is to be formed, the shape becomes worse. In this embodiment, since the first shaping lens 2 of the shaping optical system is a lens which is rotationally symmetric about the optical axis, the image of the light beam a incident on the first reflecting surface 4 of the rotary polygon mirror 3 is formed by main scanning. Direction and sub-scanning direction. Therefore, the rotation of the light beam b deflected by the first reflecting surface 4 does not matter.

As described above, in this embodiment, the second
The correction is performed by disposing the scanning lens 13 eccentrically in the sub-scanning direction. Here, the incident surface of the second scanning lens 13 is convex in the sub-scanning direction, and the radius of curvature in the main scanning direction is extremely large, so that it is regarded as a cylindrical surface and is shown in FIG. As shown in FIG. 20, the light beam c that scans the scanning end is incident obliquely with respect to the optical axis of the second scanning lens 13. Since the second scanning lens 13 is eccentrically arranged, the light beam c enters obliquely even in the sub-scanning direction.

Light beam c incident on second scanning lens 13
Out of all directions perpendicular to the principal ray of light, the direction receiving the strongest refracting power by the incident surface is not the circumferential direction L of the incident surface,
The direction M has an angle φ with respect to the circumferential direction L. FIG.
In the case shown in (1), the rotation direction in the direction M with respect to the circumferential direction L is clockwise as viewed in the traveling direction of the light beam c.
When the eccentric direction of the second scanning lens 13 in the sub-scanning direction is opposite, or when the incident position in the main scanning direction is on the opposite side with respect to the optical axis O, or when the incident surface is concave in the sub-scanning direction, The direction of the rotation direction M with respect to the circumferential direction L is shown in FIG.
Counter-clockwise, opposite to 0.

The magnitude of the angle φ with respect to the circumferential direction L depends on the amount of eccentricity in the sub-scanning direction, the incident angle in the main scanning direction, and the radius of curvature of the incident surface. At each deflection angle, FIG.
The rotation direction of the deflected light beam c shown in FIG.
If the rotation direction of the direction M with respect to the circumferential direction L shown in FIG. 0 coincides, the beam spot shape becomes good. Therefore, FIG.
The second scanning lens 13 may be disposed eccentrically in the direction indicated by the arrow B in FIG. The second scanning lens 13 of the present embodiment is arranged eccentrically by 2.67 mm toward the side where the transmission optical system exists in the sub-scanning direction. Although the second scanning lens 13 has a refracting power at the entrance surface, the same effect can be obtained by decentering in the same direction even if the exit surface is a lens having a positive refracting power. Further, if the lens has a negative refractive power in the sub-scanning direction, the same effect can be obtained by decentering in the opposite direction. Since the rotation of the coordinate system due to deflection does not occur in the light beam c _{0 at} the scanning center, the problem that the beam spot shape originally collapses does not occur, and the direction coincides with the circumferential direction L even if the second scanning lens 13 is decentered. Therefore, the beam spot shape is not affected. Therefore, the beam spot shape is still good. Further, although a slight spherical aberration occurs due to the eccentricity, this does not substantially cause a problem.

In this embodiment, since the second scanning lens 13 is eccentrically arranged as described above, the beam spot shape by the light beams c ₁ and c ₂ at the scanning end is good as shown in FIG. . This correction is performed by the second scanning lens 13.
May be arranged so as to be inclined about an axis parallel to the main scanning direction. That is, as shown in FIG. 21, if the second scanning lens 13a is arranged to be inclined about an axis parallel to the main scanning direction, the light beam is obliquely oblique in the sub-scanning direction as in the case of eccentricity in the sub-scanning direction. Since c is incident, a similar effect can be obtained. Further, as another solution, the second scanning lens 13 may be formed and arranged so as to be curved in the sub-scanning direction. That is, as shown in FIG. 22, the second scanning lens 13b is curved in the sub-scanning direction, and the curved center line N
If the light beam c is arranged so as to be incident along this curve, the coordinate system of the rotated light beam c at each deflection angle and the coordinate system of the principal axis direction and the sub-axis direction at the local position of the lens And the shape of the beam spot becomes good.

Next, the correction of the curvature of the scanning line will be described.
You. As shown in FIG. 26, the second reflecting surface 5 of the rotary polygon mirror 3
When the light beam b enters at an angle in the sub-scanning direction,
The reflected and deflected light beam c is curved, and at the scanning center,
Light beam c like a solid line 0, but scanning end So the broken line
Light beam c 1, c It becomes 2. However, the sub-scanning method
Direction, the second reflecting surface 5 of the rotary polygon mirror 3 and the surface to be scanned 1
4 is geometrically optically conjugate, the light beam at the scanning center
C 0 is also the light beam c at the scanning end 1, c 2 also on the scanned surface 14
At the same position in the sub-scanning direction,
The scanning line on 4 is a straight line.

In this embodiment, the first transmission lens 7
In addition, a lens having a shape in which the length in the sub-scanning direction is shorter than the length in the main scanning direction is used for the first scanning lens 12.
These lenses have an extremely short length in the sub-scanning direction, and have a minimum length necessary for transmitting a light beam. Therefore, the light beam a incident on the rotary polygon mirror 3 is the first
The light beam b does not interfere with the first scanning lens 12 without interfering with the conduction lens 7. Also, since the light beam and the lens do not interfere, the light beam a and the light beam b
Can be reduced in the sub-scanning direction, the curvature of the light beam b and the light beam c deflected by the respective reflecting surfaces decreases, and the second transmission lens 9, the third transmission lens 10, the second scanning It is possible to reduce the diameter of the lens 13 in the sub-scanning direction. Further, in the present embodiment, the diameters of the entrance surfaces of the first transmission lens 7 and the first scanning lens 12 in the sub-scanning direction are such that the light beam a and the light beam b incident on the rotary polygon mirror 3 at the positions of the respective reflection surfaces. And the distances between the deflected light beam b and the light beam c match.
In FIG. 23, the solid lines are the light beams b ₀ and c ₀ at the scanning center without deviation, and the light beams b ₁ , c ₁ and b ₂ at the scanning end where the deviation in the sub-scanning direction indicated by the broken line is the largest. , C ₂
If the lens aperture is larger than this, the incident light beam b and the light beam c will interfere with the lens. Conversely, if the lens diameter is smaller than this, the reflected light beam b and the light beam c pass outside the lens. Therefore, with the above configuration, the allowable value of the deviation of the light beam b and the light beam c in the sub-scanning direction is maximized.

Next, the shift of the scanning area will be described with reference to FIG. In the conventional optical scanning device, the scanning start position and the scanning end position are symmetrical with respect to the optical axis of the scanning optical system, and the horizontal synchronization signal detection position is provided outside. With such a configuration, it is necessary to increase the use area of the scanning lens system only on the horizontal synchronization signal detection side,
In general, it is desirable that the lens be symmetrical with respect to the optical axis in manufacturing. In such a case, the lens diameter must be increased. In particular, in the case of a positive lens such as a scanning lens, when the aperture becomes large, the thickness of the lens in the optical axis direction must be increased accordingly in order to secure the thickness of the outer periphery of the lens. In the present invention, the horizontal synchronization signal detection position and the scanning end position are arranged so as to be symmetric with respect to the optical axis of the scanning optical system. Therefore, the aperture of the first scanning lens 12 in the main scanning direction can be reduced.

Next, tilting of the horizontal synchronous lens will be described. As described in the rotation correction of the light beam generated by the above-described deflection, in the optical scanning device in which the light beam is incident at an angle in the sub-scanning direction, the coordinate system in the main scanning direction y, the sub-scanning direction x, and the optical axis direction z is used. Is incident on the second reflecting surface 5 of the rotary polygon mirror 3 at an angle in the sub-scanning direction, and the deflected light beam c is bent and deflected, so that the coordinate system of the light beam c is rotated. (See FIG. 17). When the light beam d rotates due to the deflection of the second reflecting surface 5 of the rotary polygon mirror 3, the beam spot by the horizontal synchronization signal light beam d is not formed at one point, the beam spot shape is broken, and the detection accuracy is deteriorated. Therefore, in this embodiment, as shown in FIG. 1, the horizontal synchronizing lens 82 is disposed at an angle of 2.4 ° clockwise with the optical axis as the axis of rotation as viewed in the direction of the beam as shown in FIG. doing. Therefore, the coordinate system of the rotated light beam d and the horizontal synchronization lens 8
2 and the coordinate system in the generatrix direction and the circumferential direction coincide with each other, the shape of the beam spot becomes good, and the beam spot is introduced into the horizontal synchronization sensor 83, and the detection accuracy is improved.

Next, tilting of the horizontal synchronization sensor 83 will be described. In this embodiment, at the same time as the horizontal synchronization lens 82 is tilted, the horizontal synchronization sensor 83 is also tilted in the direction of arrow D by the same angle of 2.4 ° as the horizontal synchronization lens 82. Therefore, when the horizontal synchronization lens 82 is inclined, the direction in which the beam spot scans on the horizontal synchronization sensor 83 is also inclined by the same angle. Therefore, the horizontal synchronizing signal light beam d
Scans vertically, so that the detection sensitivity is further improved.

In the above-described embodiment, a rotary polygon mirror is used as a scanner. However, the scanner is not limited to a rotary polygon mirror, but may have at least two or more reflecting surfaces. Alternatively, an optical scanning device using both front and back surfaces of a rotating two-sided mirror and galvano mirrors that perform sinusoidal vibration about a rotation axis may be used. It is particularly effective when used for laser printers, but it is also effective for other image forming devices such as digital copying machines, facsimile machines, laser scanning displays, image input devices such as scanners, laser devices for reading optical marks, and lasers for surface inspection. Of course, the present invention can be applied to a scanning device and the like.

[0046]

As described above, according to the optical scanning device of the present invention, the incident angles of the light beams incident on the first and second reflection surfaces of the scanner in the sub-scanning direction are the same. Or by configuring the scanner so that the first reflection surface and the second reflection surface are parallel to each other, it is possible to prevent the beam spot from being deformed due to the rotation of the light beam. Optical system to deflect the light
The arrangement of the transmission optical system and the scanning optical system is relatively free, the size can be reduced, and it is possible to provide a small-sized optical scanning device having a high scanning speed and good images.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a configuration of an optical scanning device according to an embodiment;

FIG. 2 (a), (b), (c), (d), (e)
Exploded view for explaining that the tilt in the sub-scanning direction and the scanning position are constant,

FIG. 3 is a development view of a transmission optical system in a main scanning direction,

FIG. 4 is a development view of a transmission optical system in a sub-scanning direction,

FIG. 5 is a development view of a transmission optical system in a sub-scanning direction,

FIG. 6 is a development view of a transmission optical system in a main scanning direction for explaining intersection of light beams,

FIGS. 7A and 7B are plan views for explaining the intersection of the number of mirrors of a transmission optical system and a light beam;

8A and 8B are development views of the transmission optical system in FIG. 7 in the main scanning direction.

FIG. 9 is a side view for explaining rotation of a light beam generated in the transmission optical system;

FIG. 10 is a side view of a rotating polygon mirror for explaining rotation of a light beam;

FIG. 11 is a side view of a rotating polygon mirror for explaining rotation of a light beam;

FIG. 12 is a front view of a cylindrical lens for explaining decentering of the scanning optical system;

FIG. 13 is an optical path diagram in which the optical path of the transmission optical system is projected in the main scanning direction.

FIG. 14 is a graph showing a relationship between a rotation angle and an angle between optical axes of a first reflection surface and a second reflection surface;

FIG. 15 is an intensity diagram of a beam spot,

FIG. 16 is an intensity diagram of a beam spot,

FIGS. 17A and 17B are perspective views for explaining rotation of a light beam on a second reflection surface, and explanatory diagrams showing a coordinate system;

FIG. 18 is an intensity diagram of a beam spot,

FIG. 19 is a front view of a second scanning lens for explaining the eccentricity of the scanning lens;

FIG. 20 is a perspective view of a part of a second scanning lens for explaining decentering of the scanning lens;

FIG. 21 is a side view of the second scanning lens for explaining the eccentricity of the scanning lens;

FIG. 22 is a front view of a second scanning lens for explaining the eccentricity of the scanning lens;

FIG. 23 is an explanatory diagram for explaining scanning line curvature correction;

FIG. 24 is an explanatory diagram for explaining a shift of a scanning region;

FIG. 25 is a side view of an optical scanning device showing an optical path according to a modification;

FIG. 26 is an explanatory diagram for explaining scanning line curvature correction;

[Explanation of symbols]

 Reference Signs List 1 light source (semiconductor laser) 2 shaping lens 3 rotating polygon mirror 4 first reflecting surface 5 second reflecting surface 6 rotation axis 7 first transmission lens 8 first transmission mirror 9 second transmission lens 10 third transmission lens 11 second transmission Mirror 12 first scanning lens 13 second scanning lens 14 scanned surface 81 horizontal synchronization mirror 82 horizontal synchronization lens 83 horizontal synchronization sensor

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Yujiro Nomura 3-3-5 Yamato, Suwa-shi, Nagano Pref. Seiko Epson Corporation

Claims (2)

[Claims] 1. A light beam from a light source is made incident on a first reflection surface of a scanner having at least two reflection surfaces, and a light beam deflected from the first reflection surface is transmitted by the transmission optical system to the scanner. An optical scanning device that re-enters a second reflecting surface different from the first reflecting surface to form a beam spot on the surface to be scanned and scans the deflected light beam, wherein the first reflecting surface and the second 2. An optical scanning device, wherein light beams incident on the two reflection surfaces are incident at angles in the sub-scanning direction, and the angles are the same. 2. The scanner according to claim 1, wherein the first reflection surface and the second reflection surface of the scanner are parallel to each other, and an optical path from the first reflection surface to the second reflection surface passes through a rotation axis of the scanner. An optical scanning device characterized by the above-mentioned.