JPH0619494B2 - Optical scanning device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical scanning device that deflects laser light from a semiconductor laser in a scanning direction by an optical scanning device to scan an exposed body.

[Conventional technology]

Devices such as laser beam printers using the laser beam scanning technology are rapidly developing because both the processing speed and the resolution can be significantly increased. In these devices, in order to obtain high resolution, which is a factor that increases the amount of information handled and improves image quality, the spot of the laser light imaged on the exposure body by the imaging lens is set to an arbitrary size. Need to control.

On the other hand, in recent years, a semiconductor laser has been widely used as a light source of an apparatus using a laser beam scanning technique such as a laser beam printer or a laser disk. The semiconductor laser has the following advantages while being small, highly efficient, fast, stable, and capable of self-modulation.

That is, since the active region (T) of the laser light emitted from the semiconductor laser is extremely narrow with respect to the direction orthogonal to the joint surface, as shown in FIG. 2, the far field pattern is orthogonal to the joint surface. It has a long elliptical shape (Y direction in the figure).

Further, when forming the active region of the semiconductor laser, the accuracy in the direction parallel to the bonding surface can be relatively easily improved by etching technology, while the accuracy in the direction orthogonal to the bonding surface can be improved. Depends on the growth conditions,
Moreover, it is extremely difficult to control this growth condition on the order of submicron. Therefore, the spread angle of the oscillated laser light greatly varies among the individuals, particularly in the direction orthogonal to the joint surface.

Therefore, various proposals have been made in order to optimize the size of a spot obtained by imaging a laser beam from a semiconductor laser having the above-mentioned characteristics on an exposure body.

For example, there is one in which a cylindrical zoom lens is arranged between a laser light source and an optical scanner. With this lens, the cylindrical zoom lens transforms the shape only in the direction orthogonal to the laser beam joining surface to make the spot shape have an appropriate ellipticity ratio. By changing the conversion rate with respect to this direction, the optimum spot shape can always be obtained regardless of variations in this direction among the individual semiconductor lasers (see Japanese Patent Laid-Open No. 57-35824).

[Problems to be solved by the invention]

On the other hand, an apparatus using a laser beam scanning technique such as a laser beam printer has another problem to be solved.
That is, a polygon mirror that rotates at a high speed is often used as an optical scanning path for scanning the imaged laser light on the exposed body. For example, in this polygon mirror, if there is a tilt error with respect to the rotation center of each reflecting surface, scanning unevenness occurs on the exposed body. In order to prevent the scanning unevenness, it is sufficient to improve the processing accuracy of the mirror surface to eliminate the tilt error, but since it tends to increase the cost, it is often corrected by various methods. For example, various methods are already known, such as a method in which a lens group is provided in the optical path of laser light for correction, and a method in which an incident angle is changed by a deflector to perform correction.

That is, in the above-described conventional configuration, it is necessary to perform shape conversion on the laser light by the cylindrical zoom lens and then perform correction on the optical scanner. Therefore, the optical scanning device as a whole is prevented from being made compact, and the cost is increased due to an increase in the number of parts such as lenses.

In view of the above-mentioned circumstances, an object of the present invention is to constantly correct the spot shape on the exposed body by the laser light emitted from the semiconductor laser, and to correct the tilt error of the optical scanner. The purpose of the present invention is to make the entire optical scanning device compact and to reduce the cost.

[Means for solving problems]

In an optical scanning device that deflects a laser beam from a semiconductor laser in a scanning direction by an optical scanner to scan on an exposed body,
In a direction orthogonal to the scanning direction, an anamorphic zoom lens configured to converge the laser light on the deflection surface of the optical scanner and the exposed body, the anamorphic zoom lens, in the propagation direction of the laser light A movable lens unit having a plurality of anamorphic lenses that are movable with respect to each other and have a refractive power in a direction orthogonal to the scanning direction is included.
The anamorphic zoom lens is disposed on the optical path from the semiconductor laser to the optical scanner or on the optical path from the optical scanner to the exposure body, and is orthogonal to the bonding surface of the semiconductor laser. The direction in which the refracting power is large and the direction orthogonal to the scanning direction coincide with each other.

[Action]

According to the optical scanning device of the present invention, the direction orthogonal to the scanning direction affected by the tilt error of the optical scanner and the direction orthogonal to the bonding surface of the semiconductor laser having a large variation in the divergence angle of the laser light are matched, Furthermore, by matching the matched direction with the direction in which the anamorphic zoom lens has a large refractive power, the tilt error of the optical scanner and the divergence of the laser light are corrected at once. That is, the anamorphic zoom lens has a refractive power in the direction orthogonal to the scanning direction and converges the laser light on the deflecting surface of the optical scanner and the exposure body, whereby the tilt error of the optical scanner can be corrected. The movable lens unit includes a plurality of anamorphic lenses that are movable with respect to the propagation direction of the laser light and have a refractive power in a direction orthogonal to the scanning direction. The shape can be corrected.

〔Example〕

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

FIG. 1 shows a schematic configuration of an optical scanning device in a laser beam printer. Laser light (B _O ) is oscillated from the semiconductor laser (1) by pulse modulation according to the input video signal. At this time, the laser beam (B _O ) has a far-field pattern as shown in FIG.
(1) is set so that the direction (Y direction in the drawing) orthogonal to the joining surface coincides with the sub-scanning direction (S direction in FIG. 1) on the photosensitive drum (4). Generated laser light (B _O )
Is collimated by the collimator lens (2) and reflected by one mirror surface of the polygon mirror (3) rotating at high speed. The rotation of the polygon mirror (3), which is an example of an optical scanner, changes the tilt of the mirror surface with respect to the laser light (B _O ), and the reflected laser light (B _R ) is reflected from the exposed body. Scanning is performed in the longitudinal direction of the photosensitive drum (4) which is an example.
The laser beam (B _R) is converged by the fθ lens which is an example of the imaging lens (5), and forms an image on the uniformly charged photosensitive drum (4) reducing the charging potential of the location Let
Then, by repeating the above operation, the photosensitive drum
(4) An electrostatic latent image is formed on it. In the figure (6) is the drum (4)
It is an optical sensor for laser light detection for aligning each scanning start position with respect to the rotation direction of.

After that, although not shown in the figure, toner, which is a color pigment, is selectively adhered to the electrostatic latent image portion and developed, and the output paper is brought into contact with the toner image surface to transfer the toner image onto the paper surface. By heating, the toner is melted and fixed on the paper, and an output image is obtained.

In the optical scanning device according to the present invention, the anamorphic zoom lens (Z) is provided in the optical path of the laser beam described above. As shown in FIG. 1, the anamorphic zoom lens (Z) is an example of an anamorphic lens in which the position of each anamorphic zoom lens (Z) is freely changeable and fixed with respect to the propagation direction of the laser light (B _O ) (P direction in the drawing). First and second cylindrical lens
_{(L 1), (L 2} ) movable lens unit consisting of (U _M), and was fixed in position, the third is an example of the anamorphic lens
It is composed of a fixed lens unit (U _F ) including a cylindrical lens (L ₃ ). Movable lens unit (U
_M ) is interposed between the collimator lens (2) and the polygon mirror (3), and the fixed lens unit (U _F ) is the fθ lens.
It is interposed in the optical path between (5) and the photoconductor drum (4).
Further, each lens (L ₁ ), (L ₂ ), (L ₃ ) has a sub-direction on the photoconductor drum (4) in the direction with a large refracting power (R direction in the figure) as the anamorphic zoom lens (Z). They are arranged so as to coincide with the scanning direction (S direction in the figure).

And with this anamorphic zoom lens (Z),
Shape conversion of laser light and reflection surface (3a) of polygon mirror (3)
The tilt correction of can be done at the same time. That is, as shown in FIGS. 3 (a) and 3 (b), the first and second cylindrical lenses (L ₁ ) and (L ₂ ) are incident laser beams (B _O ), respectively.
While maintaining the positional relationship such that the image is always formed in a straight line parallel to the scanning direction on the reflecting surface (3a) of the polygon mirror (3) according to its diameter (D _O ), that is, both lenses ( The combined focal point of L ₁ ) and (L ₂ ) is moved in the propagation direction of the laser light (P direction in the figure) while maintaining the positional relationship as on the reflecting surface (3a). Laser light reflected by the reflecting surface (3a)
(B _R ) is converged by the fθ lens (5) and the third cylindrical lens (L ₃ ), and the diameter (D _S ) is formed on the photoconductor drum (4).
Is illuminated as a spot with. In other words, this reflective surface
(3a) and the surface of the photoconductor drum (4) are always in a relationship between an object point and an image point, and the reflected laser beam ( _BR ) is always sub-scanned regardless of the inclination of the reflecting surface (3a). It is converged at the same position with respect to the direction (S direction in the figure).

At this time, the incident laser beam diameter (D _O ) and irradiation spot diameter (D
_{What is S} ) Have a relationship. Here, (f ₃ ) is the focal length of the third cylindrical lens, and (f ₁₂ ) is the combined focal length of the first and second cylindrical lenses, and the focal length of each lens is (f ₁ ), (f ₂ ) and the distance between both lenses is (d), It is represented by. That is, by changing the distance between the first and second cylindrical lenses (L ₁ ) and (L ₂ ),
The spot diameter (D _S ) can be changed with respect to the incident laser light diameter (D _O ). For example, even when the incident laser light diameter (D _O ) is (D _O1 ) as shown in FIG. 3 (a), the incident laser light diameter (D _O ) is (( _O ) as shown in FIG. 3 (B). Also in the case of D _O2 ), the spot diameter (D _S ) on the photosensitive drum (4) can be made constant.

Therefore, the anamorphic zoom lens (Z) having the above configuration and characteristics is provided so that the direction in which the refracting power is large (R direction in the drawing) coincides with the sub-scanning direction (S direction in the drawing). , The direction of the laser beam (B _O ) from the semiconductor laser (1) in which the direction (Y direction in FIG. 2) orthogonal to the bonding surface is matched with the sub-scanning direction (S direction in the drawing) By appropriately moving the first and second cylindrical lenses (L ₁ ) and (L ₂ ) in accordance with the variation in this direction, it is possible to always convert the lens into a constant shape.

FIG. 4 shows another embodiment, in which there is a fixed lens unit (U _F ) between the collimator lens (2) and the polygon mirror (3) and the fθ lens (5) The movable lens unit ( _UM ) is located between the photoconductor drum (4). Anamorphic zoom lens in this case
The action as (Z) is shown in Fig. 5 (a) and (b). That is, the third
Incident laser light (B _O ) by the cylindrical lens (L ₃ )
Are converged on the reflecting surface (3a) of the polygon mirror (3). Then, the laser beam after reflection (B _R), the first and second cylindrical lens (L _1), move the zoom action by always spot diameter (D _S) is a constant (L ₂₎ Such shape conversion is performed. At this time, the first and second cylindrical lenses (L ₁ ) and (L ₂ ) respectively have a combined focal point of both lenses (L ₁ ) and (L ₂ ) as the reflecting surface (3a) of the polygon mirror (3). Move while maintaining the positional relationship as shown above.

Therefore, as shown in FIG. 5 (a), the incident laser beam diameter (D _O ) is
In the case of (D _O3 ), as shown in FIG. 5 (B), when the incident laser beam diameter (D _O ) is (D _O4 ), the spot diameter on the photosensitive drum (4) ( D _S ) can be kept constant.

In other words, the positional relationship between the movable lens unit (U _M ) and the fixed lens unit (U _F ) of the anamorphic zoom lens (Z) with respect to the polygon mirror (3) may be reversed in the front and rear. The optical scanner such as 3) may be located between both lens units (U _M ) and (U _F ).

Number of anamorphic lenses constituting the movable lens unit (U _M) is arbitrary as long as two or more. Further, the shape, type, characteristics, etc. of each lens can be changed as appropriate, and for example, it is possible to reduce the cost by using a plurality of lenses having the same shape. Furthermore, the occupied space can be reduced by using a concave lens instead of the combination of convex lenses. On the other hand, the number of anamorphic lenses forming the fixed lens unit (U _F ) is arbitrary, and the shape type, characteristics, etc. of each lens can be appropriately changed.

[Advantages of the Invention] As is apparent from the above description, according to the optical scanning device of the present invention, the correction of the tilt error of the optical scanner and the correction of the variation of the divergence angle of the laser beam are performed at once by the anamorphic zoom lens. To be executed. As a result, the configuration of the optical system can be simplified, and the entire optical scanning device can be made compact and the cost can be reduced.

[Brief description of drawings]

The drawings show an embodiment of an optical scanning device according to the present invention. FIG. 1 is a schematic view of the optical scanning device, FIG. 2 is a perspective view showing laser light oscillation from a semiconductor laser, and FIGS. (B) is an explanatory diagram showing the operation of the anamorphic zoom lens. Fourth
FIG. 5 is a schematic view corresponding to FIG. 1 showing another embodiment, and FIG.
(A) and (B) are explanatory views corresponding to FIG. 3 (A) and (B) in another embodiment. (1) …… Semiconductor laser, (3) …… Optical scanner, (4) …… Exposure body, (5) …… Imaging lens, (Z) …… Anamorphic zoom lens, (U _M ) …… Movable Lens unit, (U _F ) ... Fixed lens unit, (P) ... Laser beam propagation direction, (R) ... Anamorphic zoom lens with large refracting power, (S)
…… Sub-scanning direction, (Y) …… Direction orthogonal to the bonding surface of the semiconductor laser.

Claims (1)

[Claims] 1. An optical scanning device which deflects laser light from a semiconductor laser in a scanning direction by an optical scanning device to scan on an exposure body, wherein a deflection surface of the optical scanning device and a deflection surface of the optical scanning device are orthogonal to the scanning direction. An anamorphic zoom lens configured to converge the laser light on the exposed body is provided, and the anamorphic zoom lens is movable with respect to the propagation direction of the laser light and has a refractive power in a direction orthogonal to the scanning direction. And a movable lens unit having a plurality of anamorphic lenses, the movable lens unit being arranged on an optical path from the semiconductor laser to the optical scanner or on an optical path from the optical scanner to the exposure body. In addition, the direction orthogonal to the bonding surface of the semiconductor laser and the refractive power of the anamorphic zoom lens With the larger direction of
An optical scanning device, wherein a direction orthogonal to the scanning direction is matched.