JPH0670688B2 - Scanning optics - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a scanning optical device that uses a laser or the like as a light source and records or reproduces information by using a light beam from the light source.

[Conventional technology]

Conventionally, a polygon mirror or a galvanometer mirror has been used as a deflector used in a scanning optical device.

11 to 14 are schematic views showing a general configuration of the scanning optical device. Further, for simplification, it is assumed that an optical system for tilt correction is not necessary.

FIG. 11 shows an example in which a galvanometer mirror is used as the deflector. After the light flux is emitted from the light source 7, it is collimated by the collimator lens 8 and is incident on the mirror surface of the galvanometer mirror 21.
After being reflected by this mirror surface, it forms an image on the surface to be scanned 5 through the arcsin θ lens 10 and the cylindrical lens 18. A photosensitive drum 6 for recording a light source is placed on the surface 5 to be scanned. The light beam incident on the galvanometer mirror 21 is a plane that is perpendicular to the surface to be scanned 5 and that includes the rotation axis 3 of the deflector (hereinafter, assuming that the coordinate system shown in the figure is given for simplicity, this plane is the zx plane. It is incident on the galvanometer mirror 21 inside. The cylindrical lens 18 is inserted for the purpose of correcting the fact that the image surface to be scanned bends in the z-coordinate axis direction as the mirror surface rotates. Also, 11
Is a driving device for the galvanometer mirror 21.

FIG. 12 shows an example in which a polygon mirror is used as the deflector. After the light beam is emitted from the light source 7, it is collimated by the collimator lens 8 and is incident on the mirror surface of the polygon mirror 22.
After being reflected by this mirror surface, it forms an image on the surface to be scanned 5 through the fθ lens 14. The light beam incident on the polygon mirror 22 is incident on the polygon mirror 22 in a plane perpendicular to the scanned surface 5 and the rotation axis 3 of the deflector.

FIG. 13 shows an example in which a polygon mirror is used as the deflector. The light flux emitted from the light source 7 is collimated by the collimator lens 8, enters the mirror surface of the polygon mirror 22, is reflected by this mirror surface, and then passes through the fθ lens 14 and the cylindrical lens 18 to be scanned. An image is formed on the surface 5. The laser light incident on the polygon mirror 22 is incident on the polygon mirror 22 in the zx plane. The cylindrical lens 18 is inserted for the purpose of correcting bending of the scanned image surface in the z-coordinate axis direction as the mirror surface rotates. Also,
Reference numeral 15 is a drive device for the polygon mirror 22.

In the above three examples, the mirror surface is a flat surface, but there is an example in FIG. 14 as an example in which the fθ lens is eliminated by giving the mirror surface a curvature. In this example, the deflector is a polygon mirror 23. The light flux emitted from the light source 7 is collimated by the collimator lens 8 and enters the mirror surface of the polygon mirror 23 as focused light by the imaging lens 16 and is reflected there, and then passes through the cylindrical lens 18. An image is formed on the surface to be scanned 5. Zx after the laser incident on the polygon mirror 23
It is incident on the polygon mirror 23 in a plane. The cylindrical lens 18 is inserted for the purpose of correcting bending of the scanned image surface in the z-coordinate axis direction as the mirror surface rotates. Reference numeral 15 is a polygon mirror driving device.

In the conventional scanning optical device as described above, the curvature of the image plane caused by the scanning of the light beam by the rotation of the mirror surface of the deflector is corrected, and further the scanning of the image on the surface to be scanned by the rotation of the deflector is performed. The speed needs to be constant, which requires several lens systems. In these lens systems, the direction of the light beam reflected by the mirror surface changes depending on the rotation of the mirror surface, so that there is a drawback in that it is generally difficult to design, and the configuration is complicated and expensive. Therefore, it is desired that the directions of the light beams reflected by the mirror surface are symmetrical within one plane.

In the example of FIG. 12 among the above-mentioned conventional examples, since the light beam is incident on the mirror surface in the plane perpendicular to the surface to be scanned 5 and the rotation axis 3 of the deflector, the reflected light beam also changes its direction in the same plane. There is.
However, the direction of the light beam reflected by the rotation of the polygon mirror 22 becomes asymmetrical, and the curvature of the scanned image surface becomes asymmetrical, and the configuration of the lens system for correcting this becomes complicated. In particular, it is difficult to give a curvature to the mirror surface because the asymmetry becomes remarkable.

On the other hand, as shown in FIG. 11, FIG. 13, and FIG. 14, in the example in which the light flux is incident on the mirror surface from within the zx plane, the symmetry of the reflected light flux is obtained. However, due to the rotation of the mirror surface, the image plane of the scanned light beam is bent in the z-coordinate axis direction, and therefore the cylindrical lens 18 is used to correct this.
Was needed. This cylindrical lens is also used for the purpose of correcting the tilt error of the mirror surface, but since the bending in the z-coordinate axis direction is larger than the influence of the tilt of the mirror surface angle in the above-mentioned conventional example, its design, It was difficult to manufacture and adjust, and it was also difficult to design the fθ lens and the arcsin θ lens other than the cylindrical lens. Further, as shown in FIG. 14, a cylindrical lens is used to correct the curvature of the image plane in the z-coordinate axis direction even if the fθ lens is not used by giving the mirror surface a curvature.
18 was needed.

[Outline of Invention]

An object of the present invention is to solve the above-mentioned drawbacks of the conventional device, and to provide a scanning optical device in which the lens between the reflecting surface of the deflector and the surface to be scanned can be easily designed or the lens can be omitted. Especially.

The above object of the present invention is to provide a light source, a deflector for scanning a light beam generated from the light source on a surface to be scanned, and an imaging lens for forming an image of the light beam generated from the light source on the surface to be scanned. In the scanning optical device having: a light beam generated from the light source, in the plane perpendicular to the surface to be scanned and including the rotation axis of the deflector (orthogonal coordinate axis x, zx plane determined by the z coordinate axis), the deflector Of light incident on the reflecting surface of the deflector at an angle of 2α from the x-coordinate axis and entering the reflecting surface of the deflector and exiting from the reflecting surface of the deflector are on the same plane (orthogonal coordinate axes x, zx axes). Plane), the axis of rotation of the deflector and the reflecting surface of the deflector make a non-zero β, and the reflecting surface of the deflector is the z-axis.
This is achieved by satisfying the condition of 0.5 × 2α <β <1.2 × 2α, where the light flux which forms an angle α with the coordinate axis and is emitted from the reflecting surface of the deflector is guided parallel to the x-coordinate axis direction.

〔Example〕

According to the present invention, the reflected light of the light beam is made symmetrical by making the light beam incident on the deflector from within the zx plane (the plane including the rotation axis of the deflector and perpendicular to the surface to be scanned), and further, the z coordinate axis of the image plane of the light beam. By setting the deflector rotation axis and the mirror surface to be tilted so that the bending of the direction is within the allowable range from the plane, and also by setting the deflector rotation axis to be tilted in the zx plane, The curvature of the image plane in the z-coordinate axis direction is set to fall within the allowable range from the plane. Further, here, the surface to be scanned is parallel to the z-coordinate axis direction.

Hereinafter, detailed description will be made with reference to the drawings.

FIG. 1 is an overall view for explaining the principle of the present invention,
As shown in the figure, it has Cartesian coordinate axes x, y, and z coordinate axes. Second
The drawing is a cross-sectional view taken along the zx plane of FIG. 1 and shows the case where the scanning angle of the mirror is zero. That is, this is a case where the light flux that enters the mirror and the light flux that exits the mirror are in the same plane. In FIG. 1, a light beam emitted from a light source passes through a collimator lens (not shown) and is incident on a mirror surface 2 of a deflector as incident light 1, and is reflected by this mirror surface to be reflected light 4. And forms an image on the surface to be scanned. The light flux may pass through a lens system, which is not shown in the drawing, which is used as necessary, before reaching the surface to be scanned from the light source. The mirror surface 2 of the deflector is fixed to the rotary shaft 3 of the deflector, and rotates about this rotary shaft, whereby the reflected light 4 scans the surface to be scanned. A photosensitive drum 6 for recording is placed on the surface 5 to be scanned. Next, the angle between the rotation axis and the mirror surface will be described with reference to FIG. First, the incident light is x
It is incident at an angle of 2α from the coordinate axis. On the other hand, the mirror surface is fixed at an angle of β that is not 0 with respect to the rotation axis, and when the scanning angle is 0, the mirror surface is set so as to make an angle of α with respect to the z coordinate axis. It becomes parallel light. Since β is 0 in the conventional example, as the mirror rotates, the relationship between the direction vector of the incident light and the normal vector of the mirror surface changes, and a z-coordinate axis direction component is generated in the direction vector of the reflected light. Further, when the rotation center of the mirror and the position of the mirror surface of the incident light are different, the incident position is displaced in the z coordinate axis direction, and the image forming position is changed.

In the present invention, since the mirror surface and the rotation axis are set to an angle of β which is not 0, the bending of the image forming surface in the z coordinate axis direction, which occurs when the mirror rotates, is within the allowable range. Therefore, the light rays reflected by the mirror surface up to the surface to be scanned fall within the range that can be regarded as a plane.

The value of β depends on the angle of the incident light, the position of the incident light, the curvature of the mirror surface, and the radius of gyration of the mirror surface (the distance between the incident position of the light ray on the mirror surface and the axis of rotation when the scanning angle is 0 °). It turns out that it takes a different value.

As a result of studying these conditions variously, it was found that β in which the curvature of the image plane in the z-coordinate axis direction is within an allowable amount has a relationship with 2α of 0.5 × 2α <β <1.2 × 2α.

Tables 1 to 22 below show values of β according to the present invention for several incident light directions, the position of the image plane in the z coordinate axis direction at several scanning angles at that β, and the image plane according to the conventional example. The position in the z coordinate axis direction is shown.

In each table, 2α means the angle that incident light makes with the x coordinate axis, β means the angle between the rotation axis of the deflector according to the present invention and the mirror surface, and θ.
Is the rotation angle of the mirror, and here represents the angle of rotation of the mirror surface around the rotation axis of the deflector, and θ = 0 °
At this time, the laser light is reflected in the zx plane.
The image positions are all 200 mm from the rotation center of the mirror, and the position in the z coordinate axis direction is shown in mm. No lens system is included between the mirror surface and the image plane.

Tables 1 to 4 show the case where the mirror surface is flat and the turning radius of the mirror is zero.

Tables 5 to 8 show the case where the mirror surface is a plane mirror and the turning radius a of the mirror is changed.

Tables 9 to 22 show cases where the mirror surface has a curvature r and is a spherical mirror or a cylindrical surface mirror, and the rotation radius a of the mirror is changed.

FIG. 3 shows a first embodiment of the present invention, which uses a galvanometer mirror as a deflector. FIG. 4 is a view showing only the galvanometer mirror shown in FIG. In FIG. 4, the Galvano mirror 9 is fixed to the rotary shaft 3 by a fork-type support 12 as shown in the figure in order to tilt it at an angle according to the present invention with respect to the rotary shaft 3. The mirror 9 makes a sine vibration around the rotation axis 3 by a mirror driving device 12.

After the light flux is emitted from the light source 7, it is collimated by the collimator lens 8 and then incident on the mirror 9 of the galvano mirror. After being reflected by this mirror surface, it passes through the arcsin θ lens 10 and
An image is formed on the surface to be scanned.

Unlike the conventional example (FIG. 11), since the curvature of the image plane in the z-coordinate axis direction is small in this embodiment, a cylindrical lens for correcting this is not necessary.

FIG. 5 shows a second embodiment of the present invention, in which a polygon mirror is used as a deflector. FIG. 6 is an enlarged view of the polygon mirror 13 of FIG. 5, and the mirror surface of the polygon mirror 13 is not parallel to the rotation axis 3 as shown in this figure. Therefore, as shown in FIG. 5, the rotation axis 3 of the polygon mirror is set at an angle different from that of the conventional example.

The light flux shown in FIG. 5 is emitted from the light source 7, collimated by the collimator lens 8 and then incident on the mirror surface of the polygon mirror 13, and after being reflected by this mirror surface, the fθ lens. An image is formed on the surface to be scanned through 14.

FIG. 7 shows a third embodiment of the present invention, which is an example in which an arcsin θ lens is not used because the galvano mirror of the first embodiment uses a convex spherical mirror instead of a plane mirror.

The light flux emitted from the light source 7 is collimated by the collimator lens 8 and then enters the galvanometer mirror 17 as focused light by the imaging lens 16 and is reflected by the collimator lens 8 and is then reflected on the scan surface 5. Form an image.

FIG. 8 shows a fourth embodiment of the present invention, which is an example of correcting the tilt error of the mirror surface by adding a cylindrical lens to the third embodiment.

Although a cylindrical lens is used in this example, the cylindrical lens is designed, manufactured, and adjusted conventionally because the image surface is less bent in the z-coordinate axis direction than the conventional example in which the image surface is strongly bent in the z-coordinate axis direction. It's easier than usual.

FIG. 9 shows a fifth embodiment of the present invention, which is an example in which the fθ lens is not used because the mirror of the polygon mirror of the second embodiment is changed from a flat surface to a convex spherical surface.

After the light flux is emitted from the light source 7, it is collimated by the collimator lens 8 and then is incident on the mirror surface of the polygon mirror 19 as converged light by the imaging lens 16 and is reflected there, after which it is scanned 5 Image on.

FIG. 10 shows a sixth embodiment of the present invention. By adding a single spherical lens to the fifth embodiment,
In this example, the deterioration of the fθ characteristic is corrected.

〔The invention's effect〕

As described above, according to the present invention, the reflected light from the deflector can be regarded as symmetrical in one plane, which facilitates the design of the lens between the mirror surface and the surface to be scanned, or It can be omitted.

[Brief description of drawings]

1 is an overall view showing the principle of the present invention, FIG. 2 is a sectional view showing the principle of the present invention, FIGS. 3 to 10 are views showing an embodiment of the present invention, and FIG. 11 to FIG. FIG. 14 is a diagram showing a conventional example. 1 ... Incident light, 2 ... Mirror surface of deflector 3 ... Rotation axis, 4 ... Reflected light 5 ... Scanning surface, 6 ... Photosensitive drum

Claims (1)

[Claims] 1. A light source, a deflector for scanning a light beam generated from the light source on a surface to be scanned, and an imaging lens for forming an image of the light beam generated from the light source on the surface to be scanned. In the scanning optical device, the light beam generated from the light source is reflected by the deflector in a plane that is perpendicular to the surface to be scanned and includes the rotation axis of the deflector (orthogonal coordinate axis x, zx plane determined by the z coordinate axis). A light beam incident on the surface at an angle of 2α from the x coordinate axis, and a light beam incident on the reflecting surface of the deflector and a light beam emitted from the reflecting surface of the deflector are on the same plane (zx plane determined by the orthogonal coordinate axes x and z coordinate axes). , The angle of rotation of the deflector and the reflecting surface of the deflector form a non-zero β, and the reflecting surface of the deflector is the z-axis.
A scanning optical device characterized in that a light beam which forms an angle α with respect to the coordinate axis and is emitted from the reflecting surface of the deflector is guided in parallel with the x-coordinate axis direction and satisfies the condition of 0.5 × 2α <β <1.2 × 2α. .