JPH01216313A - Light beam scanner - Google Patents

Abstract

PURPOSE:To reduce the curvature of image in the sub-scanning direction without disturbing the curvature of image in the main scanning direction by constituting a cylindrical optical element which is placed between an optical deflector and the surface to be scanned, of a concave cylindrical mirror and a convex cylindrical mirror. CONSTITUTION:An anamorphic optical system provided between an optical deflector 5 and the surface 11 to be scanned consists of a scanning lens such as an ftheta lens, etc., a convex cylindrical mirror 9 having power in only the direction being orthogonal to the deflecting surface of a light beam, and a concave cylindrical mirror 10 having power in only the direction being orthogonal to the deflecting surface. Accordingly, by bending an optical path of a light beam without providing particularly a reflecting mirror, the device can be miniaturized in the two-dimensional direction. In such a way, the light beam does not pass through a light transmission type optical element except the scanning lens, therefore, the curvature of image in the main scanning direction can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of the Invention) The present invention relates to a light beam scanning device that deflects a light beam to scan a surface to be scanned. The present invention relates to a light beam scanning device capable of scanning.

(Prior Art) In recent years, various systems for reading and/or recording images using light beams have been developed. In such a system, a light beam emitted from a light source is
The light beam is reflected and deflected by an optical deflector such as a rotating polygon mirror, and is sent (sub-scanned) at a constant speed in a direction perpendicular to the direction of deflection to scan the surface to be scanned. However, in conventional scanning devices, axial wobbling easily occurs in the optical deflector that reflects and deflects the light beam to perform main scanning, and as a result, the main scanning line that is deflected and scanned on the scanning surface is moved in the sub-scanning direction. There is a risk that the result will be distorted. In addition, especially when a rotating polygon mirror is used as an optical deflector,
It is technically difficult to make each surface of the rotating polygon mirror completely parallel to the rotation axis, and the problem is that the pitch of the scanning line becomes uneven due to the surface tilt of the rotating polygon mirror. There is.

Therefore, various methods have been proposed for optically correcting the positional deviation of the main scanning line in the sub-scanning direction due to the above-mentioned surface tilt.

For example, by providing an input optical system between the light source and the optical deflector,
The light beam enters the optical deflector as a line image perpendicular to the drive axis of the optical deflector, and an anamorphic optical system is provided between the optical deflector and the surface to be scanned, so that the light beam forms a line image on the optical deflector. A method is known in which a light beam is formed as a point image on a surface to be scanned. As the above-mentioned anamorphic optical system, one is known that consists of a scanning lens such as an fθ lens and a cylindrical optical element such as a cylindrical lens or a cylindrical mirror that has power only in the area intersecting the scanning plane.

Further, Japanese Patent Laid-Open No. 127514/1983 discloses a light beam scanning device comprising a concave cylindrical lens and a concave cylindrical mirror as cylindrical optical elements. In this way, two having opposite powers
Providing two cylindrical optical elements has the advantage that field curvature on the scanned surface can be kept relatively small.

(Problem to be Solved by the Invention) However, in the above device, among the optical elements arranged on the optical path of the light beam deflected by the optical deflector,
Since only a concave cylindrical mirror can change the optical path of a light beam, in order to fold the optical path of the light beam and miniaturize the device two-dimensionally in two directions perpendicular to the deflection direction, the above-mentioned method is required. In addition to the two cylindrical optical elements, it is necessary to provide a reflective mirror, etc.
There is a problem that the structure of the device becomes complicated and the manufacturing cost increases. In addition, since the light beam passes through a concave cylindrical lens made of lens material such as glass, it affects the curvature of field in the main scanning direction, and as a result, the curvature of field in the main scanning direction is reduced once. It is necessary to modify the designed fθ lens to correct the curvature of field in the main scanning direction, and then to correct the curvature of field in the sub-scanning direction again. There is an inconvenience that the one song becomes large.

The present invention has been made in view of the above-mentioned problems, and provides a light beam scanning device that can be miniaturized without complicating the structure of the device and can sufficiently reduce the curvature of field. The purpose is to provide the following.

(Means for Solving the Problems) In the light beam scanning device of the present invention, an anamorphic optical system provided between an optical deflector and a surface to be scanned has a scanning lens such as an fθ lens, a light beam deflection surface, and a scanning lens such as an fθ lens. It is characterized by comprising a convex cylindrical mirror that has power only in a direction perpendicular to the deflection surface, and a concave cylindrical mirror that has power only in a direction perpendicular to the deflection surface.

Note that the above-mentioned deflection plane means a plane formed by a light beam that moves due to the deflection of the optical deflector.

(Function) Since the above-mentioned light beam scanning device is equipped with two cylindrical mirrors in the anamorphic optical system, the optical path of the light beam can be bent without providing any other reflecting mirror, and the device can be moved in two-dimensional directions. It can be downsized to

Furthermore, in the above device, since the light beam does not pass through any light-transmissive optical element other than the scanning lens, the curvature of field in the main scanning direction can be reduced.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings.

FIG. 1 is a plan view of a light beam scanning device according to an embodiment of the present invention, and FIG. 2 is a side view thereof.

First, the main scanning of the light beam will be explained with reference to FIG.

A light beam 2 emitted from a light source 1 is expanded to a desired beam diameter by a beam expander 3, passes through a cylindrical lens 4, and enters a rotating polygon mirror 5, which is an optical deflector. In this device, the beam expander 3
and the cylindrical lens 4 constitute an optical system for incidence. The cylindrical lens 4 allows the light beam 2 to enter the rotating polygon mirror 5 as a line image perpendicular to the rotation axis of the rotating polygon mirror 5, and in FIG. 1 only allows the light beam to pass therethrough. The rotating polygon mirror 5 rotates in the direction of arrow A to reflect and deflect the light beam 2, and the deflected light beam becomes the first
The light enters an fθ lens 8 which is a scanning lens consisting of two lenses, a lens 6 and a second lens 7. The light beam 2 that has passed through the fθ lens 8 is incident on the convex cylindrical mirror 9 and the concave cylindrical mirror 10 and is reflected, and then main scans the surface to be scanned 11 in the direction of arrow B.

The above two cylindrical mirrors9. IO has refractive power only in a plane that intersects the deflection plane of the light beam, and in FIG. 1, these cylindrical mirrors 9. IO functions only as a reflective mirror. The fθ lens 8 focuses the light beam 2 reflected and deflected at a constant angular velocity by the rotating polygon mirror 5 on the scanned surface II and scans it at a constant velocity, as shown in FIG. In the plane, the light beam 2 is focused and bundled on the scanned surface 11 only by the fθ lens 8, and main scans the scanned surface at a constant speed.

Next, with reference to FIG. 2, correction of surface tilt etc. in this apparatus will be explained.

In the plane shown in FIG. 2, the light beam 2 is once focused by the cylindrical lens 4 on the reflecting surface 5a of the rotating polygon mirror, and then deflected by the rotating polygon mirror 5.
The light becomes diverging light and enters the fθ lens 8. This light beam is focused on the scanned surface 11 by an fθ lens 8 having a focusing effect, a convex cylindrical mirror 9 having a diverging effect, and a convex cylindrical mirror IO having a focusing effect. If the rotating polygon mirror 1!5 is driven without surface tilt or axis wobbling, the light beam 2 will pass through the optical path shown by the solid line in the figure, but if the rotary polygon mirror 5 has a surface tilt or the like, the reflecting surface 5a will become 5a. If it shifts to the position ', the optical path of the light beam will move to the position indicated by the dashed line in the figure. However, since both the light beam along the optical path shown by the solid line and the light beam along the optical path shown by the dashed-dotted line are emitted from the same point on the reflecting surface 5a, the above-mentioned fθ lens 8. Convex cylindrical mirror9. The anamorphic optical system including the concave cylindrical mirror 10 focuses the light beams taking any optical path onto the same position on the surface to be scanned 11 . Therefore, even if the rotating polygon mirror is tilted, highly accurate scanning can be performed without positional deviation of the scanning line in the sub-scanning direction. The light beam 2 from which effects such as surface tilt have been removed is repeatedly scanned in the direction of arrow B (see FIG. 1) over the scanned surface 11, which is sub-scanned in the direction of arrow C. is scanned two-dimensionally by the light beam 2.

In the apparatus of this embodiment, the cylindrical optical element in the anamorphic optical system consists of two cylindrical mirrors, so the optical path of the light beam 2 changes each time it is incident on these cylindrical mirrors. Therefore, by arranging these cylindrical mirrors as shown in the figure, this device bends the optical path of the light beam and moves the device in two-dimensional directions (up and down in FIG. 2) without using any reflecting mirrors other than these cylindrical mirrors.

It can be made more compact in the left and right direction.

Furthermore, since this device does not include any light-transmitting optical elements other than the fθ lens in the anamorphic optical system, it also has the advantage that surface tilt correction can be performed without disturbing the field curvature in the main scanning direction. An example of a specific configuration of an anamorphic optical system will be shown below, and the state of field curvature in such an apparatus is shown in FIG. 1 to 4 below are the radius of curvature of the lens surface of each lens of the fθ lens 8 shown in FIG. 2 and the mirror surface of the two cylindrical mirrors, dl,
d2 is the axial thickness of the first lens 6 and the second lens 7, do is the distance from the deflection point to the lens surface 1, and d2 is the distance from the first lens 6 to the second lens 7. , d4 is the distance from the lens surface r4 to the mirror surface r5, d5 is the distance from the mirror surface 2 to the mirror surface rs, dB is the distance from the mirror surface rs to the scanned surface, nl
, n2 are the refractive indices of the first lens 6 and the second lens 7, respectively (vehicle position is #ll1). The wavelength of the light beam is 832.8ns, the deflection angle of the rotating polygon mirror is ±15'', and the focal length of the entire fθ lens is 690III.
11. The angle between the light beam incident on the convex cylindrical mirror and the reflected light beam and the angle between the light beam incident on the concave cylindrical mirror and the reflected light beam are each 7°.

do = 30.000 rs --143,396dB -7,000
nt -1,51509r2-1131.879
62-21.000r3-”ds
-10,00012-1,77882r4--tsg
, eae da -182,441rs -94,0
8065-221,077r6 = 312.223
ds・H2,788 As shown in FIG. 3, the curvature of field can be made extremely small in an apparatus equipped with the above-mentioned anamorphic optical system.

(Effects of the Invention) As explained above, according to the light beam scanning device of the present invention, the cylindrical optical element disposed between the optical deflector and the surface to be scanned is composed of a concave cylindrical mirror and a convex cylindrical mirror. As a result, the optical path of the light beam can be folded without providing any other reflecting mirror, and the device can be made smaller without complicating its configuration. At the same time, in this device, the deflected light beam does not pass through any light-transmissive optical element other than the fθ lens, so the curvature of field in the sub-scanning direction can be reduced without disturbing the curvature of field in the main scanning direction. It becomes possible to do so.

[Brief explanation of the drawing]

FIG. 1 is a plan view of a light beam scanning device according to an embodiment of the present invention, FIG. 2 is a side view of the device, and FIG. 3 is a graph showing the state of field curvature in the device. 2... Light beam 5... Rotating polygon mirror 8...
・fθ lens 9...Convex cylindrical mirror lO...Concave cylindrical mirror 11...Scanned surface Fig. 3 Deviation % (θ) (mm)

Claims (1)

[Scope of Claims] A light beam scanning device that scans a light beam reflected and deflected by an optical deflector in the main scanning direction on a surface to be scanned that is relatively sent in the sub-scanning direction at a constant speed, comprising: an input optical system that makes the light beam incident on the optical deflector as a line image perpendicular to the drive axis of the optical deflector, and an analyzer that focuses the light beam deflected by the optical deflector on the scanned surface as a point image. Equipped with a morphic optical system,
The anamorphic optical system is characterized by comprising a scanning lens, a convex cylindrical mirror having power only in a direction perpendicular to the deflection plane of the light beam, and a concave cylindrical mirror having power only in the direction perpendicular to the deflection plane. A light beam scanning device.