JPH09222577A - Optical scanning device - Google Patents

Abstract

(57) [Abstract] [Purpose] To prevent deterioration of image quality due to temperature changes, and to reduce size and cost. A laser unit 12 is attached to a vertical portion 11a of a chassis 11, and a cylindrical lens 13, a cover glass 14, a polygon mirror 15, a scanning lens system 16 are arranged in a traveling direction of a laser beam from the laser unit 12.
The folding mirrors 17 are sequentially arranged on the horizontal portion 11b of the chassis 11, and the scanning surface 18 is arranged in the reflection direction of the folding mirrors 17.
Place. Laser unit 12, cover glass 1
4. The folding mirror 17 is fixed via a mounting member having a different coefficient of thermal expansion that cancels the fluctuation of the optical axis of the laser beam due to the temperature change. The cylindrical lens 13 and the scanning lens system 16 are mounted via mounting members 23 and 24 having different coefficients of thermal expansion so as to cancel the fluctuation of the optical axis of the laser light due to the temperature change.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used in laser beam printers, particularly color laser beam printers, full color laser beam printers, etc., in which a laser beam emitted from a laser unit is deflected by a deflecting means and is passed through a scanning lens system to a photosensitive member. The present invention relates to an optical scanning device that forms an image.

[0002]

2. Description of the Related Art A conventional optical scanning device of this type is constructed, for example, as shown in FIG. 9, and a laser beam emitted from a laser unit 1 having a semiconductor laser light source is condensed by a cylindrical lens 2. , Enters the polygon mirror 3 that rotates at a constant speed. The laser light deflected by the polygon mirror 3 passes through the scanning lens system 4 including the spherical lens 4a and the toric lens 4b to correct fθ, and the photosensitive drum rotates at a constant speed in synchronization with the drive signal of the semiconductor laser light source. An image is formed as a spot on the surface 5 to be scanned. Then, the electrostatic latent image formed on the surface to be scanned 5 is printed as an image by an electrophotographic process.

The laser unit 1, the cylindrical lens 2, the polygon mirror 3, and the scanning lens system 4 are installed in an optical box (not shown), and the polygon mirror 3 is rotationally driven by a drive motor (not shown) installed in the optical box. Since the drive motor radiates heat, the optical box is provided with a fan for removing the heat. However, since the heat of the drive motor is thermally conducted to the optical box and the inside thereof, the optical box is gradually thermally deformed, the optical axis of the laser beam is changed, and the spot position on the scanned surface 5 may be changed. Particularly, in a color image device of 400 DPI, which performs multicolor development, the pixel interval is 63.5 μm, but if the spot position fluctuates even by a fraction of this value,
Image misregistration and color change occur.

To solve this problem, when outputting a color image, multicolor development is performed using the same scanning lens system, that is, scanning with the same optical characteristics is repeated to make spot position fluctuations equal. By doing so, deterioration of the image is reduced. Further, when outputting a full-color image with a plurality of laser beams, a "H" -shaped mirror and its moving mechanism are provided, and the flat glass is tilted by the piezoelectric effect to reduce image deterioration.

[0005]

However, in the case of outputting a color image, repeating the scanning with the same optical characteristics requires a lot of time for outputting the image, and in particular, a full-color image is produced by a plurality of laser beams. When outputting, there is a problem that it takes too much time.

[0006] Further, in the case of providing a "C" -shaped mirror and its moving mechanism or inclining the flat glass by the piezoelectric effect or the like, there is a problem that the size becomes large and the cost becomes high.

An object of the present invention is to solve the above-mentioned problems and to provide an optical scanning device which is inexpensive, compact, and capable of obtaining high image quality.

[0008]

An optical scanning device according to the present invention for achieving the above object is provided with a mounting member which is thermally deformed in an optical scanning device which scans a laser beam onto a surface to be scanned by an optical member. It is characterized in that the optical member is attached to the base via the optical member, and a change in the optical axis of the laser beam due to the thermal deformation of the base is offset by the thermal deformation of the attaching member.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail with reference to the embodiments shown in FIGS. FIG. 1 is a development view along the optical path of the first embodiment in which the optical path is shown by a straight line, FIG. 2 is a schematic plan view, and FIG. 3 is a schematic side view. For example, in a vertical portion 11a of a chassis 11 made of a metal plate. Is a semiconductor laser light source 1
A laser unit 12 equipped with 2a and a collimator lens 12b is attached. This laser unit 1
A cylindrical lens 13, a dustproof cover glass 14, and a polygon mirror 15 for deflecting the laser light are sequentially arranged on the horizontal portion 11 b of the chassis 11 in the traveling direction of the laser light emitted from the laser light source 2. Further, in the traveling direction of the laser light deflected by the polygon mirror 15, the cover glass 14, the scanning lens system 16 having the fθ characteristic, and the folding mirror 17 for folding the laser light to the outside are provided on the horizontal portion 11b of the chassis 11. The scanning surface 18 such as the photosensitive drum is disposed in the folding direction of the folding mirror 17.

Here, the scanning lens system 16 is a spherical lens 16a and a toric lens 16 of an anamorphic lens system.
The deflective reflection surface 15 of the polygon mirror 15
The laser light deflected by a is focused on the surface to be scanned 18 via the folding mirror 17 to form a spot. In addition, the deflective reflection surface 15a and the scanned surface 1
8 is provided so as to be conjugate with the scanning lens system 16, and the tilt of the deflective reflection surface 15a is corrected.

Further, as shown in the enlarged sectional view of FIG. 4, in the laser unit 12, a semiconductor laser light source 12a and a collimator lens 12b are housed in a housing 12c.
It is attached to the vertical portion 11 a of the chassis 11 via the first and the second parts 22. Further, as shown in FIG. 1, the cylindrical lens 13 and the scanning lens system 16 are respectively attached to the mounting member 2
It is fixed to the horizontal portion 11 b of the chassis 11 via 3, 24.

Further, as shown in FIG. 5, the cover glass 14
Is a vertical plate 2 erected on the bottom plate 11b of the chassis 11.
5 is attached to the bracket 5 via a bracket 26 and mounting members 27 and 28. Then, as shown in FIG. 6, the polygon mirror 15 is fixed to the rotary shaft 29 a of the drive motor 29, and the drive motor 29 is mounted on the chassis 1 via the mounting member 30.
It is attached to the first mounting hole 11c. In addition, as shown in FIG. 7, the folding mirror 17 includes a tilt plate 31 provided on the chassis 11, a bracket 32 and mounting members 33, 3 and 3.
It is fixed through 4. A fan (not shown) for dissipating heat generated by the drive motor 29 is provided in the chassis 11.

The heat generated by the drive motor 29 is transferred to the chassis 11 via the mounting member 30, and the temperature of the chassis 11 increases in the vicinity of the drive motor 29 due to the thermal resistance of the chassis 11, and the air is blown by the fan. Then it will be lower. Due to such a temperature difference, the chassis 11 is deformed as shown by the dotted line in FIG. 6, the optical axis of the laser light emitted from the laser unit 12 is changed in the sub-scanning direction, and the spot position on the scanned surface 18 is changed to the sub-direction. It may fluctuate in the scanning direction.

In order to suppress the fluctuation of the spot position, the mounting members 21, 22, 23, 24, 27, 2 are used in the embodiment.
The coefficient of thermal expansion of each of 8, 33 and 34 is optimally selected. That is, in the laser unit 12 shown in FIG. 4, the mounting members 21 and 22 are composed of different members. Here, the thermal expansion coefficients of the mounting members 21 and 22 are respectively k1, k2,
When these thicknesses are a and their intervals are b, the optical axis variation angle θ of the collimator lens 12b when the temperature change is T degrees is θ = (k1−k2) · a · T / b.

As a result, the fluctuation amount of the spot position on the surface to be scanned 18 is changed to the fluctuation angle θ by the cylindrical lens 13.
It is a value obtained by multiplying the focal length of by the lateral magnification in the sub-scanning direction. Therefore, in order to cancel the fluctuation amount of the spot position when the mounting members 21 and 22 are members having the same thermal expansion coefficient,
The thermal expansion coefficients k1 and k2 of the mounting members 21 and 22 are determined to suppress the fluctuation of the spot position due to the temperature change.

Further, the cylindrical lens 1 shown in FIG.
In 3 and the scanning lens system 16, the mounting members 23 and 24 are composed of members having different coefficients of thermal expansion. Here, assuming that the thermal expansion coefficients of the mounting members 23 and 24 are k3 and k4, the thicknesses thereof are c and d, and the lateral magnification in the sub-scanning direction is m, the spot position when the temperature change is T degrees. The variation amount D1 in the sub-scanning direction is D1 = k3.c.T + (k4.d-k3.c) .T.m.

Therefore, the thermal expansion coefficients k3 and k4 of the mounting members 23 and 24 are determined so as to cancel the fluctuation amount D1 when the mounting members 23 and 24 are members having the same thermal expansion coefficient, and the spots due to the temperature change are determined. The fluctuation of the position is suppressed.

Further, in the cover glass 14 shown in FIG.
The mounting members 27 and 28 are composed of members having different thermal expansion coefficients. Here, when the thickness of the cover glass 14 is d and the refractive index is n, the fluctuation amount D2 of the laser light when the cover glass 14 is inclined by θ with respect to the laser light is D2 = d · (n−1)・ Sine θ / n. If the thermal expansion coefficients of the mounting members 26 and 27 are K5 and K6, their thickness is e, and their interval is f, the spot position variation amount D3 when the temperature change is T degrees is D3. = D ・ (n-1) ・ sin {(k5-k6) ・ e ・ T / f} /
n.

Therefore, the coefficient of thermal expansion k5, k6 of each of the mounting members 26, 27 is determined by multiplying the magnification by the insertion position based on the variation D3, and the variation D3 of the spot position in the sub-scanning direction due to the temperature change is determined. Hold down.

In the folding mirror 17 shown in FIG. 7, the mounting members 33 and 34 are composed of members having different coefficients of thermal expansion. Assuming that the thermal expansion coefficients of the mounting members 33 and 34 are k7 and k8, their thickness is g, their distance is h, and the distance between the folding mirror 17 and the surface 18 to be scanned is L, the temperature change is T degrees. Variation of spot position in the sub-scanning direction of
D4 is D4 = 2 · L · g · (k7−k8) · T / h.

Therefore, the thermal expansion coefficients k7 and k8, the thickness g and the interval h of the mounting members 33 and 34 are set so as to cancel out the fluctuation amount D4 when the mounting members 33 and 34 are members having the same thermal expansion coefficient. The change amount D4 of the spot position in the sub-scanning direction due to the temperature change is suppressed.

With such a configuration, the laser light emitted from the laser unit 12 is condensed by the cylindrical lens 13 and is incident on the deflective reflection surface 15a of the polygon mirror 15. The laser light deflected by the polygon mirror 15 passes through the scanning lens system 16 and is reflected by the reflection mirror 17, and scans in the direction of the arrow while forming a spot image on the surface 18 to be scanned.

At this time, even if the chassis 11 is deformed by the heat generated by the drive motor 29, each mounting member 21, 2
2, 23, 24, 27, 28, 33, 34 can be thermally deformed to cancel the fluctuation of the optical axis. This allows
It is possible to prevent the color shift and the change of the color appearance due to the temperature change, and it is possible to improve the image quality. Further, it is possible to eliminate the need for the repetition of the conventional optical scanning and the "C" -shaped mirror and its moving mechanism, which makes it possible to shorten the image forming time and realize the downsizing and cost reduction.

FIG. 8 is a schematic block diagram of a second embodiment in which the above-described embodiment is applied to a full-color image forming apparatus.
Four cylindrical lenses 13a to 13d, two cover glasses 14a and 14b, in the traveling direction of the laser light emitted from each of the laser units 12a to 12d,
One polygon mirror 15 is sequentially arranged, and four laser beams are deflected in the traveling direction of the laser beam deflected by the polygon mirror 15.
A set of scanning lens systems 16a to 16d and four folding mirrors 17a to 17d are arranged. Further, further four folding mirrors 19a to 19d and four folding mirrors 20a to 20d are arranged between the folding mirrors 17a to 17d and the photosensitive drums 18a to 18d.

These laser units 12a-12
d, cylindrical lenses 13a to 13d, cover glasses 14a to 14d, folding mirrors 17a to 17d, 19
a to 19d and 20a to 20d are attached to the chassis 11 (not shown) via the attachment members (not shown) similar to the attachment members 21, 22, 23, 24, 27, 28, 33, 34 of the first embodiment. Has been.

The laser beams emitted from the laser units 12a to 12d are cylindrical lenses 13a to 13d.
The laser unit 12a is focused linearly by 3d,
The laser light from 12b is common to the cover glass 14a.
The common deflective reflection surface 15 of the polygon mirror 15
The laser light from the laser units 12c and 12d is incident on a, passes through the common cover glass 14b, and is incident on the deflection reflection surface 15b. The polygon mirror 15 is the center P
By rotating around the axis, the deflective reflection surfaces 15a, 15b
The laser light deflected by is condensed by the scanning lens systems 16a to 16d having the f.theta.
The spots a to 17d, 19a to 19d, and 20a to 20d are sequentially folded, and the photosensitive drums 18a to 18d are scanned with spots, respectively.

In this embodiment, the laser units 12a ...
12d, cylindrical lenses 13a to 13d, scanning lens systems 16a to 16d, folding mirrors 17a to 17d,
19a to 19d and 20a to 20d are attached to the mounting members 21, 22, 23, 24, 27, 28, 33, 3 of the first embodiment.
Since the same mounting member as that of No. 4 is used, the same effect as that of the first embodiment can be obtained, the pixels forming an image can be superposed with high accuracy, and color misregistration and color change can be prevented. It is possible to obtain a few high-quality full-color images.

[0028]

As described above, in the optical scanning device according to the present invention, the fluctuation of the optical axis due to the thermal deformation of the base is offset by the thermal deformation of the mounting member. It is possible to prevent this, and it is possible to obtain a high image quality with little color shift and color change. In addition, since it is possible to eliminate the repetition of scanning which is conventionally required, it is possible to shorten the time for outputting an image. Furthermore, the “H” -shaped mirror and its moving mechanism, which are conventionally required, can be omitted, and the mechanism for inclining the flat glass by the piezoelectric effect or the like can be eliminated, so that downsizing and cost reduction can be realized. .

[Brief description of drawings]

FIG. 1 is a development view along an optical path of a first embodiment.

FIG. 2 is a schematic plan view.

FIG. 3 is a schematic side view.

FIG. 4 is a partial cross-sectional view of a mounting portion of a laser unit.

FIG. 5 is a partial cross-sectional view of a mounting portion of a cover glass.

FIG. 6 is a partial cross-sectional view of a mounting portion of a drive motor.

FIG. 7 is a side view of a mounting portion of a folding mirror.

FIG. 8 is a schematic configuration diagram of a full-color image device according to a second embodiment.

FIG. 9 is a schematic configuration diagram of a conventional example.

[Explanation of symbols]

 11 Chassis 12 Laser Unit 13 Cylindrical Lens 14 Flat Glass 15 Polygon Mirror 16 Scanning Lens System 17 Folding Mirror 18 Scanned Surface

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical display location H04N 1/113 H04N 1/04 104A

Claims (6)

[Claims] 1. An optical scanning device for scanning a laser beam onto a surface to be scanned by an optical member, wherein the optical member is attached to a base via a heat-deformable attaching member, and the light of the laser light is produced by thermal deformation of the base. An optical scanning device, characterized in that axial fluctuations are canceled by thermal deformation of the mounting member. 2. The optical scanning device according to claim 1, wherein the optical member is a folding mirror, and the mounting member changes a reflection angle of the folding mirror by thermal deformation. 3. The optical scanning device according to claim 1, wherein the optical member is flat glass, and the mounting member changes an angle of the flat glass with respect to the optical axis by thermal deformation. 4. The optical member is a laser unit,
The optical scanning device according to claim 1, wherein the mounting member changes an emission angle of the laser unit by thermal deformation. 5. The optical scanning device according to claim 2, wherein the mounting member is composed of two members having different coefficients of thermal expansion. 6. The optical scanning device according to claim 1, wherein the optical member is a cylindrical lens and a scanning lens system, and the mounting member of the cylindrical lens and the mounting member of the scanning lens system are members having different coefficients of thermal expansion. .