JPH0772408A - Scanning optical system - Google Patents

Abstract

PURPOSE:To provide an inexpensive scanning optical system with high accuracy, easy to assemble and unnecessitating the use of an f.theta lens by adopting a curved mirror having a power only in the scanning direction in a scanning optical system used for a laser printer and a laser FAX, etc. CONSTITUTION:A relay optical system introduces a light beam from a light source part 1 to a rotary deflector 3, the rotary deflector 3 scans the light beam from the relay optical system on a scanning surface 5, a curved mirror 4 having a power only in a main scanning direction is arranged between the rotary deflector 3 and the scanning surface 5 and the relay optical system makes the light beam incident on the rotary deflector 3 while keeping a prescribed angle to the scanning surface 5. A lens 6 having a power in the sub- scanning direction is preferably provided in the relay optical system and between the scanning surface 5 and the curved mirror 4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a scanning optical system used for laser printers, laser fax machines, etc.
By adopting a curved mirror that has power only in the scanning direction, it is not necessary to use an f · θ lens,
The present invention relates to an inexpensive and highly accurate scanning optical system that can be easily assembled.

[0002]

2. Description of the Related Art Conventionally, a scanning optical system generally used for a beam scanner of a laser printer or the like is a light source composed of a semiconductor laser or the like and a light source for scanning the light from the light source on a scanning surface at an equal angular velocity. It was composed of a polarizer such as a polygon mirror and an f · θ lens.

The f.theta. Lens is for correcting the difference in scanning speed. If the f.theta. Lens or the like is not used, the light scanned by the polygon mirror 100 at a constant angular velocity does not have the same distance to the scanning surface 200 as shown in FIG. And a difference in distance of (delta z) occurs at both ends. Due to this difference in distance, field curvature occurs from the central portion in the main scanning direction on the image surface to both ends, the size of the spot diameter varies, and a uniform image cannot be obtained. Further, this light spot is scanned at a constant angular velocity around the deflecting and reflecting surface, but the velocity on the image plane has a difference in scanning velocity that increases from the center of the scanning region to both ends.

The f.theta. Lens corrects the curvature of field and the difference in scanning speed and scans the scanning surface with light at a constant speed. However, the f.theta.
In order to correct the field curvature in the main scanning direction and the field curvature in the sub scanning direction, it is necessary to combine a large number of convex lenses and concave lenses, the number of polishing surfaces increases, and it becomes difficult to improve the processing accuracy. There was also the problem of high costs.

Therefore, a scanning optical system that does not use an f.theta. Lens has been proposed. For example, FIG. 8 (a) and FIG. 8 (b)
As shown in FIG. 3, there is a method of preparing two mirrors 300 and 301 and reflecting the scanning light a number of times by these mirrors 300 and 301 to extend the optical path length and reduce (delta z). It was

As shown in FIGS. 9 (a) and 9 (b), some curved mirrors 400 are used to omit the f.theta. Lens.

Further, as shown in FIG. 10, a curved mirror 400
There are those in which the center of curvature in the sub-scanning direction is moved from the scanning plane, and as shown in FIG. 11, the curved mirror 400 is tilted in the sub-scanning direction.

[0008]

However, the above-mentioned FIG.
Two mirrors 300 as shown in FIGS. 8A and 8B,
In the conventional example using 301, the size of the entire optical system becomes large and the mirrors are repeatedly reflected by the two mirrors 300 and 301, so the error tolerance of the mounting angle is small and the assembly work is extremely difficult. was there.

Further, as shown in FIGS. 9A and 9B, in the conventional example in which the curved mirror 400 is adopted, the incident scanning surface and the exit scanning surface of the curved mirror 400 are on the same plane. In order to guide the light onto the scanning surface, it is necessary to split the light with a half mirror or the like. For this reason, there is a problem in that the reduction of the light amount cannot be avoided.

Further, in the conventional example shown in FIGS. 10 and 11, the half mirror can be omitted, but the optical element must be accurately positioned in both the main scanning direction and the sub scanning direction, and the angle and There is a problem that the adjustment of the position is troublesome and the assembling becomes difficult. Particularly, in the method of tilting the curved mirror 400 shown in FIG. 11 in the sub-scanning direction, the scanning line on the image plane is curved in a bow. In order to correct this curvature and scan on the scanning surface, it is necessary to adjust the direction and position of the light incident on the two or more curved mirrors 400 and 401, which makes mounting adjustment more complicated and difficult. There was a serious problem.

[0011]

SUMMARY OF THE INVENTION The present invention has been devised in view of the above-mentioned problems, and includes a light source section, a relay optical system for guiding light from the light source section to a rotary deflector, and the relay optical system. A rotary deflector for scanning the scanning surface with light at a constant angular velocity, and a curved mirror arranged between the rotary deflector and the scanning surface.
Light is incident on the rotary deflector while forming a predetermined angle with respect to the scanning surface, and the curved mirror is configured to have power only in the main scanning direction.

Further, according to the present invention, a lens having power in the sub-scanning direction may be provided between the relay optical system and the scanning surface and the curved mirror.

Further, in the present invention, the reflecting surface of the curved mirror may be an aspherical surface.

[0014]

In the present invention configured as described above, the relay optical system guides the light from the light source section to the rotary deflector, and the rotary deflector scans the light from the relay optical system on the scanning surface at a constant angular velocity. Then, the curved mirror is arranged between the rotary deflector and the scanning surface, and the relay optical system makes the light incident on the rotary deflector while forming a predetermined angle with respect to the scanning surface, and the curved mirror Have power only in the main scanning direction.

In the present invention, a relay optical system and a lens having power in the sub-scanning direction can be provided between the scanning surface and the curved mirror.

Further, according to the present invention, the reflecting surface of the curved mirror may be an aspherical surface.

[0017]

【Example】

An embodiment of the scanning optical system of the present invention will be described with reference to the drawings.

The scanning optical system of this embodiment is a beam scanner device used for laser printers, laser fax machines, digital copying machines, etc., and all of them are scanning optical systems in which the f.theta. Lens can be omitted.

"First embodiment"

FIG. 1 shows a scanning optical system according to the first embodiment, which comprises a semiconductor laser 1, a condenser lens 2, a polygon mirror 3, a curved mirror 4 and a scanning surface 5. There is.

The semiconductor laser 1 corresponds to a light source section, and is for irradiating laser light. The semiconductor laser 1 is connected to an appropriate driving means, and by irradiating the semiconductor laser 1 with an intensity modulation, a divergent light flux carrying image information and the like can be emitted. The light source section is not limited to the semiconductor laser 1, and other laser generating means, point light source, or the like can be adopted.

The condenser lens 2 corresponds to a relay optical system for guiding the light from the semiconductor laser 1 to the polygon mirror 3, and can convert the divergent light flux from the semiconductor laser 1 into a focused light flux. Then, the condenser lens 2 is configured to make the focused light flux enter the polygon mirror 3 while forming a predetermined angle with respect to the scanning surface.

The polygon mirror 3 corresponds to a rotary deflector, and when combined with the curved mirror 4, the light spot can be scanned at a constant speed on the scanning surface 5. A rotation driving means including an appropriate motor or the like is connected to a support shaft of the polygon mirror 3. The polygon mirror 3 is rotated at a constant angular velocity by this rotation driving means. The rotary deflector is not limited to the polygon mirror 3, and any one can be adopted as long as it can scan a light beam on one plane.

The curved mirror 4 is, as shown in FIGS. 1 and 2,
It is for reflecting the deflected light flux from the polygon mirror 3 and condensing it on the scanning surface 5. The curved mirror 4 is arranged between the polygon mirror 3 and the scanning surface 5, and the reflecting surface 41 is an aspherical surface. The curved mirror 4 has a power only in the main scanning direction and has no power in the sub scanning direction. The main scanning direction is the direction scanned by the polygon mirror 3, and the sub-scanning direction is the direction orthogonal to the main scanning direction. Generally, the sub-scanning direction is the driving direction of the drum when the scanning surface 5 has a drum shape.

The scanning surface 5 is a surface on which the condensed light spot is scanned at a constant speed. When the semiconductor laser 1 emits a light beam modulated by an image signal, an image is formed on the scanning surface 5.

In the first embodiment constructed as described above, when a divergent light beam is emitted from the semiconductor laser 1, it is converted into a convergent light beam by the condenser lens 2, and the converged light beam is guided to the polygon mirror 3. Has become. As shown in FIG. 3, the focused light flux is made to enter the polygon mirror 3 while forming a predetermined angle with respect to the scanning surface.

Then, the light beam is scanned toward the curved mirror 4 by the polygon mirror 3 rotated at a constant angular velocity. On the curved mirror 4, a scanning speed difference occurs in the scanned light beam. However, since the curved mirror 4 has power in the main scanning direction, the light beam can be reflected on the scanning surface 5 so as to correct the difference in scanning speed and the curvature of field.

As a result, the light beam scanned by the polygon mirror 3 is reflected by the curved mirror 4, the scanning speed difference is corrected, and the scanning surface 5 is scanned at a constant speed.

As described above, the first embodiment has an effect that constant-speed scanning can be performed on the scanning surface 5 by using the curved mirror 4 without using the f.theta. Lens. Since the field curvature (delta z) as seen in FIGS. 7 and 8 is also corrected, a high-definition image can be formed. At the same time, the curve of the scanning line in the sub-scanning plane caused by the fact that the rotation axis of the rotary deflector and the optical axis of the incident light from the relay optical system are not perpendicular is also corrected by the curved mirror 4 having no power in the sub-scanning direction. Therefore, there is an effect that position adjustment in the sub-scanning direction becomes unnecessary. Also curved mirror 4
Is configured to have power only in the main scanning direction, the shape of the reflecting surface is simplified. From these, there is an effect that the labor of assembling is small and the processing cost of each optical component can be made low.

"Second embodiment"

FIG. 4 shows the scanning optical system of the second embodiment, which includes a semiconductor laser 1, a condenser lens 2, and a first lens.
The cylindrical lens 21, the polygon mirror 3, the curved mirror 4, the scanning surface 5, and the second cylindrical lens 6.

The condenser lens 2 and the first cylindrical lens 21 correspond to a relay optical system for guiding the light from the semiconductor laser 1 to the polygon mirror 3. The first cylindrical lens 21 is a lens for forming a long line image in the main scanning direction. The second cylindrical lens 6 is inserted between the curved mirror 4 and the scanning surface 5. The second cylindrical lens 6 is for making the polygon mirror 3 and the scanning surface 5 substantially conjugate. With the first cylindrical lens 21 and the second cylindrical lens 6, it is possible to correct surface tilt. The first cylindrical lens 21 and the second cylindrical lens 6
And correspond to a lens having power in the sub-scanning direction.

The second embodiment constructed as described above is the second embodiment.
In the embodiment, by using the curved mirror 4 without using the f.theta. Lens, it is possible to perform the uniform velocity scanning on the scanning surface 5 and to perform the surface tilt correction. There is. The rest of the configuration / operation is the same as that of the first embodiment, so the explanation is omitted.

"About curved mirror 4"

The reflecting surface 41 of the curved mirror 4 may be an aspherical surface, and in this case, it may be a curved surface satisfying the following formula.

[0037]

[Equation 1]

Further, the reflecting surface 41 of the curved mirror 4 can be a quadratic curved surface, and in this case, a curved surface satisfying the following equation can be used.

[0039]

[Equation 2]

Here, k is a conic coefficient, and k ≧ −
It is designed to satisfy 1.

"Specific Example of First Embodiment"

Next, a specific example of the first embodiment is shown in Table 1, and its characteristic data are shown in FIGS. 5 (a), 5 (b), 5 (c),
It will be shown in FIG.

[0043]

[Table 1]

FIG. 5A shows the distortion aberration, in which the horizontal axis represents the scanning position in the main scanning direction and the vertical axis represents the distortion degree. FIG. 5B shows the scanning position in the sub-scanning direction, and shows the bending of the scanning line, which is the positional deviation of the scanning line. The horizontal axis is the scanning position in the main scanning direction,
The vertical axis represents the light collecting position in the sub-scanning direction. FIG. 5 (c)
Represents the field curvature in the main scanning direction, the horizontal axis represents the scanning position in the main scanning direction, and the vertical axis represents the degree of curvature. Figure 5
(D) shows the field curvature in the sub-scanning direction, the horizontal axis represents the scanning position in the main scanning direction, and the vertical axis represents the degree of curvature.

"Specific Example of Second Embodiment"

Next, a concrete example of the second embodiment is shown in Table 2, and characteristic data are shown in FIGS. 6 (a), 6 (b), 6 (c) and 6
It will be shown in (d). The display method of the figure is
It is similar to (a) to FIG. 5 (d).

[0047]

[Table 2]

[0048]

According to the present invention configured as described above, the light source section, the relay optical system for guiding the light from the light source section to the rotary deflector, and the light from the relay optical system at the scanning surface at a constant angular velocity. And a curved mirror arranged between the rotary deflector and the scanning surface.
The relay optical system allows light to enter the rotary deflector while forming a predetermined angle with respect to the scanning surface, and the curved mirror is configured to have power only in the main scanning direction. By using the curved mirror 4 without using the f.theta. lens, it is possible to perform constant velocity scanning on the scanning surface 5. Since the curved mirror has a power only in the main scanning direction and no power in the sub-scanning direction, it is easy to process and assemble, and cost reduction can be realized. Therefore, there is an effect that a high-definition scanning optical unit can be provided.

Further, according to the present invention, the field curvature (delta z) as shown in FIGS. 7 and 8 is also corrected, so that a high definition image can be formed. At the same time, since the curved mirror corrects the curvature of the scanning line caused by the fact that the rotation axis of the rotary deflector and the optical axis of the incident light from the relay optical system are not perpendicular, the position adjustment in the sub-scanning direction becomes unnecessary. effective. Further, since the curved mirror is configured to have power only in the main scanning direction, the shape of the reflecting surface is simplified. From these things, there is an outstanding effect that the labor of assembling is small and the processing cost of each optical component can be made high-definition and inexpensive.

Further, since the relay optical system of the present invention and a lens having a power in the sub-scanning direction can be provided between the scanning surface and the curved mirror, surface tilt correction can be performed. .

[0051]

[Brief description of drawings]

FIG. 1 is a perspective view showing a configuration of a first embodiment of the present invention.

FIG. 2 is a diagram showing the configuration of the first embodiment.

FIG. 3 is a diagram showing the configuration of the first embodiment.

FIG. 4 is a perspective view showing a configuration of a second exemplary embodiment of the present invention.

FIG. 5A is a diagram showing characteristic data of the first embodiment.

FIG. 5B is a diagram showing characteristic data of the first embodiment.

FIG. 5C is a diagram showing characteristic data of the first embodiment.

FIG. 5 (d) is a diagram showing characteristic data of the first embodiment.

FIG. 6 (a) is a diagram showing characteristic data of the second embodiment.

FIG. 6 (b) is a diagram showing characteristic data of the second embodiment.

FIG. 6C is a diagram showing characteristic data of the second embodiment.

FIG. 6 (d) is a diagram showing characteristic data of the second embodiment.

FIG. 7 is a diagram illustrating a conventional technique.

FIG. 8A is a diagram illustrating a conventional technique.

FIG. 8B is a diagram illustrating a conventional technique.

FIG. 9A is a diagram illustrating a conventional technique.

FIG. 9B is a diagram illustrating a conventional technique.

FIG. 10 is a diagram illustrating a conventional technique.

FIG. 11 is a diagram illustrating a conventional technique.

[Explanation of symbols]

 1 Semiconductor Laser 2 Condensing Lens 21 First Cylindrical Lens 3 Polygon Mirror 4 Curved Mirror 41 Reflecting Surface 5 Scanning Surface 6 Second Cylindrical Lens

Claims (3)

[Claims] 1. A light source unit, a relay optical system for guiding light from the light source unit to a rotary deflector, and a rotary deflector for scanning light from the relay optical system at a constant angular velocity on a scanning surface. , The rotary optical deflector and a curved mirror arranged between the scanning planes, and the relay optical system allows light to enter the rotary deflector while forming a predetermined angle with respect to the scanning plane. The curved optical mirror is configured to have power only in the main scanning direction. 2. The scanning optical system according to claim 1, wherein a lens having power in the sub-scanning direction is provided between the relay optical system and the scanning surface and the curved mirror. 3. The scanning optical system according to claim 1, wherein the reflecting surface of the curved mirror is an aspherical surface.