JPS5915216A - Optical scanner - Google Patents

Abstract

PURPOSE:To eliminate the uneven pitch occuring in the inclination of the deflecting reflection surface of a rotary polyhedral mirror by disposing the point where the central rays of the luminuous fluxes emitted from a light source part intersect after the rays pass the 1st condenser optical system and the deflecting reflection surface so as to be optically conjugate within the plane of deflectuion. CONSTITUTION:An image rotator 3 is disposed near the point T where the central rays of luminous fluxes L1, L2, L3 intersect, that is, the center of the exit pupil of the 1st condenser optical system 10. The fluxes L1-L3 are rotated in the disposition and are made incident to the 2nd condenser optical system 11, by which the images thereof are formed near the deflecting reflection surface 5 of a rotary polyhedral mirror 4 and line images B1-B3 are formed. The surface 5 is so disposed as to be conjugate with the exit pupil of the system 10 within the plane of deflection. The images B1-B3 are formed in the same place within the plane of deflection and the defocusing in the mirror image is obviated even if the mirror 4 rotates.

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 makes the pitch of these scanning lines variable.

Figure 1(a) is Japanese Patent Application Laid-Open No. 56-10431 by the present applicant.
This figure shows an optical scanning device that draws three scanning lines using three light beams in Publication No. 5, and shows the state within the deflection plane. 1st
A plurality of light beams L1.
L2 and L3 are focused by the optical focusing system 2 and input into the image raw data 3. This image raw data 3
The luminous fluxes L1, L2, and L3 whose arrangement has been rotated by
St, S2, S are reflected by the deflection reflecting surface 5 of the rotating polygon mirror 4, and are reflected onto the scanned medium 7 via the imaging optical system 6.
It is imaged as 3. As shown in FIG. 1(c), the imaged spots S1, S2, S3 are formed on a plurality of scanning lines A1, A2, A on the scanning medium 7 as the rotating polygon mirror 4 rotates.
3 at the same time. FIG. 1(d) is a cross-sectional view of the light beams L1, A2, and A3 after the image raw data 3 has been emitted, and O is the column of the light beams L1, A2, and A3 rotated by the image raw data 3. This is the rotation angle formed with the deflection surface. At this time, if β is the combined imaging magnification of the condensing optical system 2 and the imaging optical system 6 between the semiconductor array laser 1 and the scanned medium 7, then the pitch p of the scanning lines A1, A2, and A3 is The relationship □p=βd 5irl .=(1) exists between the light emitting section], a, b, and the interval d between the ICs. As is clear from equation (1), the rotation angle θ of the light beams L1, A2, and A3 changes due to the rotation of the image raw data 3, so the pitch p of the scanning lines AI, A2, and A3 is
can be set to any value.

By rotating the image raw data 3 in this way, the scanning line pitch p can be easily and accurately changed. However, the pitch between the plurality of scanning lines A1, A2, and A3 formed by the next scan becomes uneven due to the tilting of the deflection reflection surface 5 of the rotating polygon mirror 4, and if it becomes a constant value. is not limited.

As a method for eliminating this pitch unevenness, a method has been proposed that uses an optical system to correct the influence of the tilting of the deflection/reflection surface 5, as shown in the invention of Japanese Patent Laid-Open No. 56-36622 shown in FIG. In FIG. 2, a beam of light emitted from a light source is imaged by a cylindrical lens 8 on a deflection reflection surface 5'' of a rotating polygon mirror 4 in a cross section perpendicular to the deflection surface, and is reflected by this deflection reflection surface 5. The light beam is imaged as a dot on the scanning medium 7 by an imaging optical system 9 having, for example, a ]-rick lens. According to such a means, the light beam reflected by the deflection reflection surface 5 is always imaged at the same location on the scanned medium 7, regardless of whether or not the deflection reflection surface 5 is tilted.

FIGS. 3(a) to 3(d) are explanatory views when the means shown in FIGS. 1 and 2 are used together, and FIG. 3(a)
, (b) shows the state in the deflection plane, and Fig. 3 (c),
(d) shows the state in a plane perpendicular to the deflection plane.

Although it is clear that the optical scanning device shown in FIG. 3 can simultaneously provide the two functions shown in FIGS. 1 and 2 described above, it also has the following drawbacks. There is.

In equation (1), p is required to be considerably smaller than βd in order to make the scanning line pinch p finer. That is, θ is a small angle, and the light beams Ll, 2, and A3 after emitting image raw data 3 mostly travel within the deflection plane, so as shown in FIGS. 3(b) and 3(c),
A plurality of line images B1, 82 and B3 formed on the deflection reflection surface 5 by the cylindrical lens 8 are located at positions apart from each other. Therefore, when the rotating polygon mirror 4 rotates as shown in FIG. 3(b), the line image 81. B
2. The mirror images Bl', B2', and B3' of B3 move in the optical axis direction of the imaging optical system 9, and the third
As shown in FIG. 3(d), defocus occurs, and the imaging performance deteriorates particularly in the periphery of the scanned medium 7.

This phenomenon appears similarly even if the cylindrical lens 8 is placed closer to the semiconductor array laser 1 than the image raw data 3.

An object of the present invention is to improve the above-mentioned drawbacks, to provide an optical scanning medium that allows the scanning line pitch to be changed by rotating image raw data, and that eliminates the pitch unevenness caused by the tilting of the deflection reflection surface of the rotating polygon mirror. The gist thereof is to provide a scanning 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 method of linearly connecting the plurality of light beams emitted from the light source section. a first optical system for imaging, a deflector having a deflection reflecting surface near the line image formed by the first optical system, and a second optical system for respectively forming an image of the light beam deflected by the deflector on the scanned medium. The first optical system includes a first condensing optical system, an image raw data, and a second condensing optical system in order from the light/i section side, and the light emitted from the light source section. The image raw data is arranged near a point where the center rays of each of the plurality of light beams intersect after passing through the first focusing optical system, and the second focusing optical system is connected to the intersection point and the deflection reflection of the deflector. The image raw data is arranged so as to be optically conjugate with the surface in the deflection plane, and the image raw data is rotated S to change the intervals of the plurality of light beams that are imaged on the scanned medium. That is.

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 postage.

In FIG. 4, a plurality of light beams L1, L2, L3 emitted from the semiconductor array laser 1 are sequentially transferred to the first condensing optical system 1.
0, the image raw data 3, the second condensing optical system 11, the rotating polygon mirror 4, and the imaging optical system 9 to enter the scanned medium 7.

The light beams L1, L2, and L3 are collimated by the first optical condenser system 1° and then enter the image raw data 3. At this time, the image raw data 3 is arranged near the intersection T of the center 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 io. This intersection point T coincides with the focal point of the first focusing optical system 10 in the case of a light source capable of emitting a plurality of mutually parallel light beams, such as a semiconductor array laser l. The light fluxes L1, l+2, and L3 that have passed through the image raw data 3 are the first
The arrangement is rotated as shown in Figure (d), and the light enters the second optical focusing system IJ. This luminous flux L1. L2 and B3 are imaged near the deflection reflection surface 5 of the rotating polygon mirror 4 in a cross section perpendicular to the deflection surface by the second converging optical system 11, and a plurality of line images B2 and B3 are formed. The deflection reflection surface 5 is arranged so as to be conjugate with the exit pupil of the first condensing optical system 1o in the deflection plane. Therefore, these line image days 1
, B2, and B3 are formed at the same location in the deflection plane, and even when the rotating polygon mirror 4 rotates, the mirror images Bl', 82'
, 83' will not be defocused. The line images B1, B2, and B3 thus formed are 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, in which (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 a positive power in the deflection plane, and its object-side focal point is the light beam L1. L2
, L3 coincides with the intersection T. The spherical lens 13 has positive power and is arranged on the image side of the cylindrical lens 12, and its object side focal point is on the cylindrical lens 1.
This image-side focus coincides with the image-side focus of No. 2 and is located on the deflection/reflection surface 5.

With such a second condensing optical system 11, the line image old, B2
, B3 and the exit pupil of the optical system combining the first condensing collinear system 10 and the second condensing collinear system 11 can be simultaneously formed on the deflection/reflection surface 5. Alternatively, the second condensing optical system 11 may be formed by inserting a cylindrical lens having positive power in a cross section orthogonal to the deflection surface into an afocal lens system including two positive spherical lenses. Furthermore,
Contrary to FIG. 4, the line image old, B2,
It is also possible to provide the function of forming B3.

In FIG. 6, the first condensing 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 lens 12.13 of the second condensing optical system 11 is
As in FIG. 5(a), the exit pupil of the first condensing optical system 10 is imaged onto the deflection/reflection surface 5. FIG. 6(a) showing the inside of the deflection plane shows the same effect as FIG. 5(a), and FIG. 6(b) showing the inside of the plane perpendicular to the deflection plane shows
By focusing the light beams L1, L2, and L3 on the exit pupil in the deflection plane of the condensing optical system 11 using the cylindrical lens 15 in a plane orthogonal to the deflection plane, a line image B1 is formed on the deflection reflection plane. , B2, and B3 can be formed. 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 raw data 3 near the exit pupil of the first condensing optical system 10 not only makes the image raw data 3 smaller, but also enables the following applications. That is, FIG. 7(a) is a perspective view of the image raw data 3, and as shown in FIG. 7(b), a density filter 18 is glued to the bottom surface 17 so that the absorption rate is high in the center. By doing so, the intensity distribution of the laser beam having a Gaussian distribution can be made uniform, and the resolution of the scanned medium 7'' can be improved. Further, as shown in FIG. 8, if a one-dimensional Fresnel lens 19 is bonded to the bottom surface 17 of the image rotary lens 3 to have a cylindrical triple lens function, it can also be used as a line image forming means.

As described above, according to the optical scanning device according to the present invention, it is possible to easily change the scanning line pitch consisting of a plurality of light beams by rotating the image low-take, and it is also possible to easily change the pitch of the scanning line made up of a plurality of light beams, and also to prevent the tilting of the deflecting reflection surface due to processing errors of the rotating polygon mirror. It is also possible to remove pitch unevenness due to the above, and it is possible to perform good optical scanning.

[Brief explanation of drawings]

Figures 1 (a) to (d) are explanatory diagrams of a conventional device that makes the pitch of scanning lines variable; Figure 3 (
a) to (d) are explanatory diagrams of an optical scanning device combining FIG. 1 and FIG. 2, and FIG. 4 and the following show embodiments of the optical scanning device according to the present invention, and FIG. , Figure 5(a'),
(b) and FIGS. 6(a) and (b) are explanatory diagrams of the embodiment, respectively. FIG. 7(a) is a perspective view of an image raw data unit with a density filter provided on the bottom surface, and (b) is a perspective view of an image loader with a density filter installed on the bottom. The plan view and FIG. 8 are perspective views of an image low-take in which a Fresnel lens is provided on the bottom surface. Symbol l is a semiconductor array laser, 1a, lb, and 1c are light emitting parts, 2 is a condensing optical system, 3 is an image low take, 4 is a rotating polygon mirror, 5 is a deflection reflection surface, 7 is a scanned medium, and 9 is a Imaging optical system, 10 is a first condensing optical system, 11 is a second condensing optical system, 18 is a concentration filter, 19 is a Fresnel lens,
Ll, L2. 'L3 is the luminous flux, Sl, B2, B3 are spots, A1, A2, A3 are scanning lines, B1.82, B3
is a line image, and Bl', B2', and 83' are mirror images. Patent applicant Canon Co., Ltd.

Claims (1)

[Claims] 1. A scanned medium to be scanned with a light beam, a light source 81) having a plurality of light emitting sections arranged in a row, and a first optical system that forms linear images of the plurality of light beams emitted from the light source sections. , a deflector having a deflection reflecting surface near the line image formed by the first optical system, and a second optical system that focuses the light beam deflected by the deflector on the scanning medium, respectively (#N, Said first
The optical system includes a first focusing optical system, an image raw data system, and a second focusing optical system sequentially from the light source side, and the center ray of each of the plurality of light beams emitted from the light source section is The image raw data is arranged near a point where the image data intersects after passing through the first focusing optical system, and the second focusing optical system is optically positioned between the intersection point and the deflection reflection 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 to each other, and by rotating the image raw data, the intervals between the plurality of light beams that are imaged on the scanned medium are changed.