JP2002023084A - Multi-light source scanning optical device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the influence of the dispersion of a light beam wavelength at every light source in a multi-light source scanning optical device. SOLUTION: The multi-light source scanning optical device is provided with a light source part 1 having a plurality of light sources LS0 to LS7 arranged in an array shape on a straight line L1 in a plane S1 orthogonal to an optical axis L1, a collimator lens part 12 making light beams LB which are made incident from each of the light sources LS0 to LS7 in the light source part 1 to be almost parallel and a deflection part 6 deflecting the light beams LB which are made incident from the collimator lens part 12 and scanning them in a main scanning direction. The collimator lens part 12 is provided with at least one negative lens 15 for correcting chromatic aberration of magnification.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multi-light source scanning optical device used for writing an image in an image forming apparatus such as a copying machine or a printer.

[0002]

2. Description of the Related Art FIGS. 6 and 7 show an example of a conventional multi-light source scanning optical device. This multi-light source scanning optical device includes a fiber multi-light source 1, a collimator lens 2,
A slit 3, correction lenses 4 and 5, a polygon mirror 6 and a scanning lens 7, which are rotationally driven by a motor (not shown),
8 is provided.

The fiber multi-light source 1 comprises eight light sources LS0, LS1, LS2, LS3, each comprising an optical fiber optically coupled to a laser diode (not shown).
LS4, LS5, LS6 and LS7 are provided. These light sources LS0 to LS7 have an optical axis L1 to reduce a pitch P1 in the sub-scanning direction indicated by a two-dot chain line Y in FIG.
Are arranged on a straight line L2 which is located in a plane S1 perpendicular to the sub-scanning direction and inclined at a predetermined angle with respect to the sub-scanning direction. The pitch P3 of the light sources LS0 to LS7 in the direction of the straight line L2 is 130.
μm, magnification 10 times in the sub-scanning direction, image density 600 dpi
Is assumed, the pitch P1 in the sub-scanning direction is 4.2 μm,
Pitch P2 in the main scanning direction (indicated by arrow X in the figure)
Is 129.9 μm. In addition, the wavelength is 780 nm and 7
Refractive indices N ₇₈₀ and N ₇₉₅ of the collimator lens 2 and the correction lenses 4 and 5 for a light beam of 95 nm, and the respective lens surfaces 2a to 4 of the collimator lens 2 and the correction lenses 4 and 5
The radius of curvature RDY and the core thickness THI of b are as shown in Table 1 below. Also, the light sources LD0 to LD7 and the collimator lens 2
Is 19.81 mm, and the distance between the correction lens 5 and the polygon mirror 6 is 48.58 mm.

[0004]

[Table 1]

The lens surface 2a of the collimator lens 2 is an aspheric surface represented by the following equation (1). In this equation (1), the aspheric coefficient A is -0.2114410 × 10 ^-5 and the aspheric coefficient B is Is −0.765340 × 10 ⁻⁵ , the aspheric coefficient C is −0.953918 × 10 ⁻¹³ , and the aspheric coefficient D is 0.229037 × 10 ⁻¹⁵ . Also, the cone coefficient k
Is 0.

[0006]

[Number 1] ^{Z = c · h 2 / [} 1 + SQRT {1- (1 + k) c 2 · h 2}] + A · h 4 + B · h 6 + C · h 8 + D · h 10 (1) Z: from the vertex C: curvature at surface vertex (= 1 / RDY) k: cone coefficient h: h = √ (X ² + Y ² ) A: fourth-order aspherical coefficient B: sixth-order aspherical coefficient C: 8 Next-order aspherical coefficient D: 10th-order aspherical coefficient

Each light source LS0-L of the multi-fiber light source 1
The light beam LB generated by S7 enters the collimator lens 2 and is converted into substantially parallel light, and further enters the polygon mirror 6 through the slit 3 and the correction lenses 4 and 5. The polygon mirror 6 deflects the light beam LB, and scans the scanning surface S3 such as the surface of the photoconductor in the main scanning direction in the drawing. The correction lenses 4 and 5 have a conjugate relationship between the slit 3 and the reference surface (polygon surface S2) of the polygon mirror 6.

[0008]

However, in the conventional multi-light-source scanning optical device, when the wavelength of the light beam LB generated by each of the light sources LS0 to LS7 changes, the light enters the polygon surface S2 due to chromatic aberration of magnification. Misalignment occurs. For example, when the design wavelength of the light sources LS0 to LS7 is 780 nm, the displacement on the polygon surface S2 when the wavelength changes to 795 nm is as shown in Table 2.

[0009]

[Table 2]

As shown in Table 2, the polygon surface S2
Is -1.38 mm at the maximum, and the optical axis L1
The light beam LB generated by the light sources LS0 to LS7 farther from the light source LS7 has a larger displacement due to a change in wavelength. Therefore, each light source L
If there is a variation in the wavelength of the light beam LB generated by S0 to LS7, the light beam LB may not be incident accurately if the effective diameter of the polygon mirror 6 is insufficient. Even if this blurring does not occur, if there is a misalignment on the polygon surface S2, the polygon mirror 6 moves the scanning lens 7,
8 is shifted, and finally the scanning surface S3
The above-described scanning performance changes for each of the light sources LS0 to LS7, and problems such as inclination of the image plane on the scanned surface S3 occur. When each of the light sources LS0 to LS7 performs multi-oscillation due to multi-mode oscillation, a so-called thick beam diameter is generated due to a positional shift due to the chromatic aberration of magnification.

SUMMARY OF THE INVENTION It is an object of the present invention to reduce the variation in wavelength of each light source and the effect of multiple oscillations of each light source in a multiple light source scanning optical device.

[0012]

According to the present invention, there is provided a light source unit having a plurality of light sources arranged in an array on a straight line in a plane orthogonal to an optical axis. A multi-light source scanning optical device including a collimator lens unit that converts light beams incident from the respective light sources of the light source unit into substantially parallel light, and a deflection unit that deflects the light beam incident from the collimator lens unit and scans in the main scanning direction. The collimator lens section is provided with at least one negative lens for correcting chromatic aberration of magnification.

The light source unit having the plurality of light sources includes:
For example, there are a fiber multi light source and a laser diode array light source. In the multi-light source scanning optical device of the present invention,
Since the collimator men's section includes at least one negative lens that corrects the chromatic aberration of magnification, even if the wavelength of the light beam of each light source varies, the displacement of the light beam in the deflecting unit is reduced and the scanning performance of each light source is improved. It is possible to prevent the inclination of the image plane on the surface to be scanned and the blurring in the deflection unit due to the variation. Further, even when the light source section is a fiber multi-light source and multi-mode oscillation occurs, it is possible to prevent the beam diameter from increasing.

[0014] The collimator lens section preferably includes a lens formed by laminating a negative lens and a positive lens.

Further, the multi-light source scanning optical device of the present invention is provided with a light beam regulating surface on which a light beam enters from the collimator lens unit, and interposed between the light beam regulating surface and the deflecting unit. It is preferable to include a correction lens unit including at least two lenses that make the light beam regulating surface and the deflecting unit conjugate.

If the light beam regulating surface and the deflecting portion have a conjugate relationship by the correction lens portion, the position of incidence on the deflecting portion (polygon mirror) is corrected, and a good image surface on the surface to be scanned can be obtained.

It is preferable that at least one of the lenses constituting the collimator lens portion and the correction lens portion has an aspherical surface.

In this case, good image surface performance can be obtained for all the light rays incident from the plurality of light sources of the light source section.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention shown in the drawings will be described in detail. (First Embodiment) FIGS. 1 and 2 show a multi-light-source scanning optical device according to a first embodiment of the present invention. The multi-light-source scanning optical device includes a fiber multi-light source 1, a collimator lens unit 12, a slit 3, correction lenses 4 and 5, a polygon mirror 6, and scanning lenses 7 and 8.

The fiber multi-light source 1 has the same structure as the multi-light source scanning optical device shown in FIGS. 6 and 7, and includes eight light sources LS0 to LS7 each comprising an optical fiber optically coupled to a laser diode (not shown). It has. These light sources LS0 to LS7 are located in a plane S1 orthogonal to the optical axis L1, and are arranged on a straight line L2 inclined at a predetermined angle with respect to the sub-scanning direction. Light source LS0
~ LS7, the pitch P3 in the direction of the straight line L2 is 130 m, assuming a magnification of 10 in the sub-scanning direction and an image density of 600 dpi, the pitch P1 in the sub-scanning direction is 4.2 m, and the pitch P2 in the main scanning direction is 129.9 m. (See FIG. 7). As shown in FIG. 3, the light source LS0 of the eight light sources LS0 to LS7 is arranged on the optical axis L1, and the light sources LS1,
LS5, light sources LS2 and LS6, and light sources LS3 and LS7 are arranged symmetrically with respect to the optical axis L1.

The collimator lens section 12 is constituted by bonding a lens 15 as a positive lens and a lens 16 as a negative lens. These lenses 15, 16
Refractive indices N ₇₈₀ , N ₇₉₅ and lens surfaces 15a, 15b, 1
The radius of curvature RDY and the core thickness THI of 6a and 16b are as shown in Table 3 below.

[0022]

[Table 3]

The lens surface 15a of the lens 15 is an aspheric surface represented by the above formula (1), the conic coefficient k is 0, the aspheric coefficient A is -0.835372 × 10 ^-5 , and the aspheric coefficient B
Is 0.210699 × 10 ^-6 and the aspheric coefficient C is 0.32
0158 × 10 ⁻⁶ , aspheric coefficient D is −0.302636
× 10 ^-7 . The lens surface 15b of the lens 15 and the lens surface 16a of the lens 16 have the same shape, and these lens surfaces 15b and 16a are bonded to each other.

[0024] The correction lens 4 and 5 are identical to those shown in FIGS. 6 and 7, the refractive index N _{78 0,} N ₇₉₅ and the radius of curvature RDY and core thickness THI of each lens surface 4a~5b the above table As shown in FIG. The refractive indices N ₇₈₀ and N ₇₉₅ , the radius of curvature RDY and the core thickness THI of the correction lenses 4 and 5 are shown in FIG.
, The slit 3 and the polygon surface S2 are set to have a conjugate relationship. The slit 3 has the same structure as that shown in FIGS. 6 and 7, and the distance between the correction lens 5 and the polygon mirror 6 is 48.58 mm.

In the first embodiment, each of the light sources LS0 to LS
7, the light beam L on the polygonal surface S2 when the wavelength of the light beam generated from 7 changes from the design wavelength of 780 nm to 795 nm.
When the displacement of B was calculated, it was as shown in Table 4 below.

[0026]

[Table 4]

As shown in Table 4, in the first embodiment, the displacement of the light beam is 0.03 mm at the maximum, and in the multi-light-source scanning optical device shown in FIGS.
Compared with 1.38 mm, the displacement on the polygon surface S2 is greatly reduced. Therefore, in the multi-light source scanning optical device according to the first embodiment, even when the wavelength of the light beam LB generated by each of the light sources LS0 to LS7 varies, the surface to be scanned due to the variation in the scanning performance among the light sources LS0 to LS7 can be used. Can be prevented from being tilted by the polygon mirror 5. Further, even when multi-mode oscillation occurs, it is possible to prevent so-called increase in beam diameter.

Furthermore, since the slits 3 and the polygonal surface S2 are in a conjugate relationship by providing the correction lenses 4 and 5 as described above, the incident position on the polygon mirror 6 is corrected, and a good image is obtained on the surface S3 to be scanned. An image plane can be obtained. Furthermore, since the lens surface 15a of the lens 15 forming the collimator unit 12 is aspheric, a plurality of light sources LS0 to
The chromatic aberration of magnification and the like can be corrected for all the rays generated by the LS7.

(Second Embodiment) FIG. 5 shows a multi-light source scanning optical device according to a second embodiment of the present invention. In the second embodiment, the lens 25, which is a positive lens, and the lens 26, which is a negative lens, forming the collimator unit 12 are not bonded and are separated from each other. Refractive index N _780, N _{7 95} lenses 25, 26 and correction lens 4 and 5 of the collimator 12, the radius of curvature RDY and core thickness THI are shown in Table 5 below.

[0030]

[Table 5]

One lens surface 25a of the lens 25 constituting the collimator section 12 is an aspherical surface represented by the above equation (1). The conical coefficient k is 0, and the aspherical coefficient A is -0.0.
226370 × 10 ⁻³ , coefficient B is −0.691425 ×
10 ⁻⁵ , the aspheric coefficient C is −0.235630 × 10 ⁻⁶ ,
The aspheric coefficient D is 0.286144 × 10 ^-9 . The correction lenses 4 and 5 are the same as those in the first embodiment. The slit 2 is the same as that of the first embodiment, and the distance between the correction lens 5 and the polygon mirror 6 is 48.58 mm.

The light beam LB generated by each of the light sources LS0 to LS7
Is calculated from the design wavelength of 780 nm to 795 nm as shown in Table 6 below.

[0033]

[Table 6]

As shown in Table 6, in the second embodiment, the polygonal surface S of the light beam LB generated by the light sources LS0 to LS7
2 is 0.15 mm at the maximum, which is significantly reduced as compared with the multi-light-source scanning optical device shown in FIGS. Therefore, in the multi-light-source scanning optical device according to the second embodiment, the light rays L generated by each of the light sources LS0 to LS7.
Even when the wavelength of B varies, the inclination of the image plane on the scanned surface S3 and the blurring of the polygon mirror 5 can be prevented. Further, even when multi-mode oscillation occurs, it is possible to prevent so-called increase in beam diameter.

Further, since the slits 2 and the polygon surface S2 are in a conjugate relationship by providing the correction lenses 4 and 5 as described above, the incident position on the polygon mirror 6 can be corrected, and the collimator section 12 is constituted. Since the lens surface 25a of the lens 25 is aspherical, a plurality of light sources LS
The chromatic aberration of magnification and the like can be corrected for all the light beams LB that generate 0 to LS7.

The present invention is not limited to the above embodiment, and various modifications are possible. For example, the light source unit including a plurality of light sources is not limited to the multi-fiber light source, and may be a laser diode array light source. Further, in the above-described embodiment, the collimator unit 12 is configured by the lenses 15 and 25 that are the positive lenses and the lenses 16 and 26 that are the negative lenses. However, the configuration of the collimator unit 12 is not limited to this. It is sufficient that at least one negative lens for correction is provided. Further, in the above embodiment, the lens surfaces 15a, 2 of the lenses 15, 25 of the collimator lens unit 12 are arranged.
Although 5a is an aspheric surface, the lens surface of another lens may be an aspheric surface.

[0037]

As is apparent from the above description, in the multi-light-source scanning optical apparatus of the present invention, since the collimator men's section has at least one negative lens for correcting the chromatic aberration of magnification, the light beam of each light source Even if there is a variation in the wavelengths, it is possible to reduce the positional deviation of the light beam in the deflecting unit and to prevent the variation in the scanning performance of each light source on the surface to be scanned and the so-called shading in the deflecting unit. Further, even when the light source section is a fiber multi-light source and multi-mode oscillation occurs, it is possible to prevent so-called increase in beam diameter. Therefore, in the multi-light-source scanning optical device according to the present invention, it is possible to reduce the influence of wavelength variation and multi-mode oscillation for each light source, and obtain a good image surface on the surface to be scanned for all light sources.

[Brief description of the drawings]

FIG. 1 is a schematic plan view showing a multi-light-source scanning optical device according to a first embodiment of the present invention.

FIG. 2 is an enlarged view of a main part of FIG.

FIG. 3 is a schematic plan view showing the relationship among a light source, a collimator, and a slit.

FIG. 4 is a schematic plan view for explaining a relationship between a slit and a polygon surface.

FIG. 5 is a main part enlarged plan view showing a multi-light-source scanning optical device according to a second embodiment of the present invention.

FIG. 6 is a schematic plan view showing a conventional multi-light-source scanning optical device.

FIG. 7 is a schematic perspective view for explaining the arrangement of a light source.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Fiber multi light source (light source part) 2 Collimator lens 3 Slit (light flux regulating surface) 4,5 Correction lens 6 Polygon mirror 7,8 Scanning lens 12 Collimator lens part 15,16,25,26 Lens P1, P2, P3 Pitch S1 Plane S2 Polygon surface S3 Scanned surface X Main scanning direction Y Sub scanning direction

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (Reference) H04N 1/113 H04N 1/04 104A F-term (Reference) 2C362 AA13 BA58 BA84 BA86 2H045 BA23 CB22 CB24 2H087 KA19 LA25 PA03 PA04 PA17 PA18 PB04 QA02 QA06 QA14 QA22 QA25 QA37 QA41 QA46 RA05 RA12 RA32 RA45 5C072 AA03 BA19 DA02 HA02 HA06 HA08 HA13 XA01

Claims (4)

[Claims] 1. A light source unit having a plurality of light sources arranged in an array on a straight line in a plane orthogonal to an optical axis, and a light beam incident from each light source of the light source unit is made substantially parallel light. A multi-light source scanning optical device comprising: a collimator lens unit; and a deflecting unit that deflects a light beam incident from the collimator lens unit and scans the light beam in the main scanning direction. The collimator lens unit includes a negative lens for correcting chromatic aberration of magnification. A multi-light-source scanning optical device, comprising at least one sheet. 2. The optical scanning device according to claim 1, wherein the collimator lens unit includes a lens obtained by bonding a negative lens and a positive lens. 3. A light beam regulating surface on which light rays are incident from the collimator lens portion, and a light beam regulating surface interposed between the light beam regulating surface and the deflecting portion, and the light beam regulating surface and the deflecting portion are conjugated in a main scanning section. The multi-light-source scanning optical device according to claim 1, further comprising a correction lens unit including at least two lenses in a relationship. 4. The multi-light-source scanning optical device according to claim 3, wherein at least one surface of at least one of the lenses constituting the collimator lens unit and the correction lens unit is aspherical.