JPH0441324B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical scanning device that simultaneously forms a plurality of scanning lines using a plurality of light beams and can vary the pitch of these scanning lines.

FIG. 1a shows an optical scanning device that draws three scanning lines using three light beams, as disclosed in Japanese Patent Application Laid-Open No. 56-104315 by the present applicant, and shows the state within the deflection plane. A plurality of light emitting parts 1a, 1b, 1 shown in FIG. 1b
A plurality of light beams L1, L2, and L3 emitted from the semiconductor array laser 1 having a wavelength of c are incident on the image rotator 3, which is focused by the condensing optical system 2. The light beams L1, L2, L3 whose arrangement has been rotated by the image rotator 3 are reflected by the deflection reflection surface 5 of the rotating polygon mirror 4, and are reflected by the imaging optical system 6.
Spots S1, S2,
The image is formed as S3. As shown in Figure 1c,
The imaged spots S1, S2, and S3 simultaneously form a plurality of scanning lines A1, A2, and A3 on the scanned medium 7 as the rotating polygon mirror 4 rotates. Figure 1d
is the luminous flux L immediately after exiting the image rotator 3
1, L2, L3, and θ is the light flux L1, L2, L rotated by the image rotator 3.
This is the rotation angle between the column No. 3 and the deflection surface. At this time, β is the semiconductor array laser 1 and the scanned medium 7.
Assuming that the composite imaging magnification by the condensing optical system 2 and the imaging optical system 6 between There is the following relationship: p=βd sinθ...(1) As is clear from equation (1), the rotation of the image rotator 3 causes the luminous flux L
Since the rotation angle θ of 1, L2, and L3 changes, the scanning line A
It becomes possible to set the pitch p of comrades 1, A2, and A3 to an arbitrary value.

As described above, by rotating the image rotator 3, the scanning line pitch p can be easily and accurately changed.
Even if the pitch p of 1, A2, and A3 is set to a desired value, multiple scanning lines A formed by the next scan
The pitch between 1, A2, and A3 is the rotational area 4.
Due to the inclination of the deflection reflecting surface 5, unevenness occurs and the value is not necessarily constant.

As a method for removing this pitch unevenness, as shown in FIG.
A means for correcting the influence of the tilting of the deflection/reflection surface 5 using an optical system has been proposed. In FIG. 2, the light beam L emitted from the light source is imaged by the cylindrical lens 8 on the deflection reflection surface 5 of the rotating multi-area 4 in a cross-sectional view orthogonal to the deflection surface, and the light beam reflected by the deflection reflection surface 5 L is imaged as a dot on the scanned medium 7 by an imaging optical system 9 having, for example, a Tori lens. According to such means, the light beam L reflected by the deflection reflection surface 5 is
Regardless of how the deflection/reflection surface 5 is tilted, the image is always formed at the same location on the scanned medium 7.

Figures 3 a to d are explanatory diagrams when the means shown in Figures 1 and 2 are used in combination, Figures 3 a and b show the inside of the deflection plane, and Figures 3 c and d shows the state in a plane perpendicular to the deflection plane. According to the optical scanning device shown in FIG.
Although it is clear that the two functions shown in FIGS.

In equation (1), p is required to be considerably smaller than βd in order to normally make the scanning line pitch p fine. That is, θ becomes a small angle, and the light fluxes L1, L2, L after exiting the image rotator 3
3 travels mostly within the deflection plane, so Figures 3 b and c
As shown in FIG.
2 and B3 are at positions apart from each other. For this reason,
When the rotating multi-surface 4 rotates as shown in FIG. As a result, a defocus occurs as shown in 3d in a plane perpendicular to the deflection plane, and the imaging performance deteriorates particularly in the peripheral area on the scanned medium 7. This phenomenon similarly appears even if the cylindrical lens 8 is placed closer to the semiconductor array laser 1 than the image rotator 3.

An object of the present invention is to improve the above-mentioned drawbacks, and to provide an optical scanning medium in which the scanning line pitch can be changed by rotating an image rotator, and in which pitch unevenness caused by the tilting of the deflection reflection surface of a rotating polygon mirror is eliminated. The gist of this is to scan a medium to be scanned with a light beam, a light source section having a plurality of light emitting sections arranged in a row, and to form images of the plurality of light beams emitted from the light source section in a linear manner. a deflector having a deflection reflecting surface near a line image formed by the first optical system; and a second optical system that forms images of the light beams deflected by the deflector on the scanned medium. The first optical system includes a first condensing optical system, an image rotator, and a second condensing optical system in order from the light source side, and each of the plurality of light beams emitted from the light source section The image rotator is arranged near a point where the central ray of light intersects after passing through the first condensing optical system, and the second condensing optical system is placed in the vicinity of the point where the central ray intersects with the deflection reflection surface of the deflector. The image rotator is arranged so as to be optically conjugate within the scanning medium, and by rotating the image rotator, the intervals between the plurality of light beams focused on the scanning medium are changed.

The present invention will be explained in detail below based on the embodiments shown in FIG. 4 and below. However, the same reference numerals as in FIGS. 1 to 3 indicate the same members.

In FIG. 4, a plurality of light beams L1, L2, L3 emitted from the semiconductor array laser 1 are sequentially
The light enters the scanning medium 7 via the second focusing optical system 11 , the rotating polygon mirror 4 , and the imaging optical system 9 . The light beams L1, L2, and L3 are collimated by the first optical condenser system 10 and then enter the image rotator 3. At this time, the image rotator 3 is disposed at the intersection T of the central rays of the plurality of light beams L1, L2, and L3, that is, near the center of the exit pupil of the first converging optical system 10. In the case of a light source capable of emitting a plurality of mutually parallel light beams, such as the semiconductor array laser 1, this intersection point T coincides with the focal point of the first focusing optical system 10. The light flux L1 that passed through the image rotator 3,
The arrangement of L2 and L3 is rotated as shown in FIG. These light beams L1, L2, and L3 are imaged near the deflection reflection surface of the rotating polygon mirror in a cross section orthogonal to the deflection surface by the second converging optical system 11, and are formed into a plurality of line images B.
1, B2, and B3, and the deflection reflection surface 5 is arranged so as to be conjugate with the exit pupil of the first condensing optical system 10 within the deflection plane. Therefore, these line images B1, B2, and B3 are formed at the same location within the deflection plane, and even when the rotating polygon mirror 4 rotates, no defocus occurs in the mirror images B1', B2', and B3'. Line images B1, B2, formed in this way,
B3 will be imaged onto the scanned medium 7 via the imaging optical system 9.

FIG. 5 shows a preferred embodiment of the second condensing optical system 11, where a shows the inside of the deflection plane and b shows the inside of the plane orthogonal to the deflection plane. This second condensing optical system 11
consists of a cylindrical lens 12 and a spherical lens 13. The cylindrical lens 12 has power in the deflection plane, and its object side focal point coincides with the intersection T of the light beams L1, L2, and L3 in the image rotator 3. The spherical lens 13 has positive power,
It is arranged on the image side of the cylindrical lens 12, and its object side focus is on the cylindrical lens 12.
This image-side focus is located on the deflection-reflection surface 5.

Such a second condensing optical system 11 forms line images B1, B2, and B3, and the first condensing optical system 1
It becomes possible to simultaneously form the exit pupil of the optical system including the optical system 0 and the second condensing optical system 11 on the deflection/reflection surface 5. Alternatively, a cylindrical lens having positive power in a cross section perpendicular to the deflection surface may be inserted into an afocal lens system including two positive spherical lenses to form the second condensing afocal system 11. Furthermore, contrary to FIG. 4, it is also possible to provide the first converging optical system 10 with a function of forming line images B1, B2, and B3.

In FIG. 6, the first focusing optical system 10 is composed of a spherical lens 14 having a positive power in a plane orthogonal to the deflection plane and a cylindrical lens 15 having a positive power. The positive spherical lenses 12 and 13 of the optical system 11 are the first
The exit pupil of the converging optical system 10 is imaged onto the deflection reflection surface 5. FIG. 6a, which shows the inside of the deflection plane, shows the same effect as FIG. 5a, and FIG. By focusing the light beams L1, L2, and L3 on the exit pupil in the plane using the cylindrical lens 15 in a plane perpendicular to the deflection plane, line images 1, B2, and B3 can be formed on the deflection reflection plane. . Incidentally, here, the light flux emitted from the first condensing collinear system 10 or the second collimating optical system 11 does not necessarily need to be collimated.

Placing the image rotator 3 near the exit pupil of the first condensing optical system 10 not only makes the image rotator 3 smaller, but also enables the following applications. That is, FIG. 7a is a perspective view of the image rotator 3, and the bottom surface 17 has a seventh
As shown in Figure b, by bonding a density filter 18 that has a high absorption rate in the center, the intensity distribution of the laser beam having a Gaussian distribution is made uniform, and the resolution on the scanned medium 7 is improved. can be increased. Further, as shown in FIG. 8, a one-dimensional Fresnel lens 19 is attached to the bottom surface 1 of the image rotator
It can also be used as a line image forming means if it is bonded to 7 and has a cylindrical lens effect.

As described above, according to the optical scanning device according to the present invention,
By rotating the image rotator, it is possible to easily change the pitch of the scanning line consisting of multiple light beams, and it is also possible to eliminate pitch irregularities caused by tilting of the deflection reflection surface caused by processing errors of the rotating polygon mirror, resulting in good optical scanning. It becomes possible.

[Brief explanation of drawings]

FIGS. 1a to d are explanatory diagrams of a conventional device that makes the pitch of scanning lines variable. FIG. 2 is a block diagram of a conventional device that removes uneven pitch of scanning lines caused by tilting of the deflection-reflection surface. FIGS. d is an explanatory diagram of an optical scanning device combining FIG. 1 and FIG. 2, FIG. 4 and the following show embodiments of the optical scanning device according to the invention, FIG. , b and FIGS. 6a and b are explanatory diagrams of the embodiment, FIG. 7a is a perspective view of an image rotator with a density filter on the side, b is a plan view of the density filter, and FIG. 8 is a Fresnel on the bottom. FIG. 2 is a perspective view of an image rotator provided with a lens. Symbol 1 is a semiconductor array laser, 1a, 1b,
1c is a light emitting unit, 2 is a condensing optical system, 3 is an image rotator, 4 is a rotating polygon mirror, 5 is a deflection reflection surface, 7
1 is a scanned medium, 9 is an imaging optical system, 10 is a first condensing optical system, 11 is a second condensing optical system, 18 is a density filter, 19 is a Fresnel lens, L1, L2,
L3 is the luminous flux, S1, S2, S3 are spots, A
1, A2, and A3 are scanning lines, B1, B2, and B3 are line images, and B1', B2', and B3' are mirror images.

Claims (1)

[Claims] 1. A scanned medium to be scanned with a light beam, a light source section having a plurality of light emitting sections arranged in a row, and a first light source section that forms linear images of the plurality of light beams emitted from the light source section.
comprising an optical system, a deflector having a deflection reflecting surface in the vicinity of a line image formed by the first optical system, and a second optical system that images the light beam deflected by the deflector on the scanned medium, The first optical system includes a first focusing optical system, an image rotator, and a second focusing optical system in order from the light source side, and the center ray of each of the plurality of light beams emitted from the light source. The image rotator is placed near a point where the images intersect after passing through the first condensing optical system, and the second condensing optical system is optically connected to the intersection point and the deflection reflecting surface of the deflector within the deflection plane. An optical scanning device characterized in that the plurality of light beams are arranged so as to be conjugate with each other, and by rotating the image rotator, the intervals between the plurality of light beams that are imaged on the scanned medium are changed.