JPH02250020A - Optical scanner - Google Patents

Abstract

PURPOSE:To make plural pieces of luminous flux which are deflected by a single optical deflector into the luminous flux enabling the scanning wherein the deviation at the time of the superposition of scanning lines is small while maintaining an excellent optical performance in which the curvature of the scanning is small, by a lens system consisting of a 1st lens group which is arrayed along optical axes and a 2nd lens group which is arrayed in a sub- scanning direction. CONSTITUTION:The 1st lens group consists of cylindrical lenses which have refracting power in the scanning direction of an optical scan surface or lenses 4a, 4b, 8, and 9 which are afocal in the subscanning direction and the 2nd lens group consists of anamorphic lenses 10a and 10b which have different refracting powers in the scanning direction and subscanning direction. Therefore, a condenser lens system for scanning is provided with plural optical axes. Consequently, the plural pieces of luminous flux can be made to scan by the relatively simple constitution.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention provides a light beam of 1M, which is suitably used in devices such as color laser beam printers and multicolor laser beam printers having an electrophotographic process, for example. The present invention relates to an optical scanning position sA for optically scanning a surface to be scanned which is each image carrier.

[Prior Art] Conventionally, in an optical scanning device such as a color laser beam printer that uses a plurality of laser beams to optically scan an image carrier and write an image, a plurality of laser beams are used on the deflection surface of one polygon mirror. An f/θ lens is provided for each of the plurality of laser beams reflected by the deflection surface, and the deflection surface and the scanned surface are aligned in a direction perpendicular to the optical scanning direction of the f/θ lens. The surface to be scanned, that is, the image carrier, is optically scanned by correcting the inclination of the deflecting surface so that it is placed in a conjugate relationship. In this case, since one set of scanning optical systems is provided for one laser beam, the apparatus tends to be complicated and the cost tends to be high.

On the other hand, for example, in JP-A-61-92917 and JP-A-58-7 Lens No. 5, two lights with different polarization characteristics or two different wavelengths are used. The two laser beams are mixed into one, and then the laser beam is focused by a lens system with half the number of laser beams and guided near the surface to be scanned, and then polarized beam splitter 1 or a dichroic mirror, etc. The laser beam is separated into two parts, and then the light beam is scanned over the surface of each image carrier.

However, in this method, the two laser beams are mixed and then separated, so the entire device is damaged. υ become sloppy,
Furthermore, when the light scanning angle on the surface to be scanned becomes large, light leakage occurs due to the incident angle characteristics of the polarizing beam splitter or dichroic mirror used to mix or separate light. For this reason, there were problems such as the inability to set the optical scanning angle too wide.
In Publication No. 6 and Publication of Utility Model Application No. 57-160118,
As shown in the figure, a plurality of laser beams are directed to a single deflection surface 50a of a single optical deflector 50 made of a polygon mirror, and the angle of view is set perpendicular to the optical scanning direction of the scanned surface 51,52. Oblique incidence is applied. And a set of f and θ consisting of a spherical system
The light is focused by a lens 53 and divided into a plurality of light beams by an optical device such as a mirror system 54, 55 placed at a position away from the laser beam, and then guided onto the image carrier surface 51, 52 for optical scanning. is being carried out.

In this case, the laser beam obliquely incident on the f/theta lens 53 causes a scanning line to curve on the image carrier surface due to the optical performance of the f/theta lens. For this reason, conventionally, cylindrical lenses 56 and 57 were arranged in front of the image carrier surface to correct the field curvature.

[Problems to be Solved by the Invention] However, in this method, since the light beam enters the cylindrical lens 56, 57 with a scanning angle (angle of view in the scanning direction), the scanning angle is large (I see, the cylindrical lens The apparent refractive power becomes stronger and the laser beam focuses in front of the scanned surface, which means that the curvature of field increases and the spot diameter of the laser beam becomes different between the center and the periphery of the scanning range. There was a problem.

In addition, for example, if three or more laser beams are used, there will be two or more angles of oblique incidence on the f/θ lens made of a spherical lens, and in this case, the angles of oblique incidence will be different.
The f/θ lens characteristics of the scanning line differ depending on the characteristics of the θ lens.

That is, as shown in FIG. 5), since the skew ray is incident on the f/theta lens 53, the f/theta characteristics are disrupted, and the characteristics vary depending on the oblique incidence angle. At this time, the f・θ characteristic is
It can also be said that the correction can be made by arranging an anamorphic lens including a cylindrical lens surface or a toric surface having refractive power in a direction perpendicular to the scanning direction (sub-scanning direction).

In addition, in the scanning direction, by arranging a second condensing lens, changing the magnification in the scanning direction, and arranging a dedicated curved surface shape, one scanning line can be overlapped to some extent with the other scanning line with a different oblique incidence angle. You can also match them.

However, f・ in the scanning direction of the scanning line due to the oblique incidence angle
The θ characteristics do not change linearly.

For example, the oblique incidence angle Φ. When , the coordinate of the scanning direction of the scanning light beam with respect to the scanning angle θ on the optical deflector side is X (Φ = Φ.) (θ)
, when the focal length of the f·θ lens is f and the angle of incidence of the skew ray is α.

For this reason, it is not possible to match the scanning lines incident on the f/theta lens at different incident angles.Due to this drawback, different color development is required, especially in color LBP etc. that require precision in multicolor registration. When trying to overlap the corresponding scan lines, color shift occurs. For example, if you try to superimpose scanning lines with grazing incidence angles of 2.5 degrees and 7.5 degrees using the same second condensing lens (anamorphic lens), you can use an f-theta lens with a focal length tJt of 313.55 mm at a scanning angle of 30 degrees (scanning angle of 30 degrees). ~0 at position 160 mm);
If a correction is made using the magnification in the scanning direction so that the scanning points coincide with each other at a scanning angle of about 30 degrees, this time the scanning points will deviate by about 60 μm at a scanning angle of about 16 degrees.

Moreover, even if the balance is taken in the upward direction, the 1121st group is composed of a cylindrical lens having refractive power in the scanning direction of the optical scanning surface or an afocal lens in the sub-scanning direction, and the 2nd The lens group is composed of anamorphic lenses having different refractive powers in the scanning direction and the sub-scanning direction. This makes it possible to provide multiple optical axes in the scanning condensing lens system, and by setting the multiple optical axes to symmetrical scanning planes, f
- The θ characteristics are unified for each scanning beam, and the curvature of the scanning line can be basically eliminated.

Furthermore, compared to a configuration in which a scanning condensing lens is provided for each of a plurality of light beams, the configuration is simpler, and the optical deflector and scanning condensing lens system can be arranged in a small space.

[Example] Fig. 1 is a diagram showing the state of the first embodiment of the present invention in the scanning plane and the sub-scanning plane, and Fig. 2 is a perspective view of the optical deflector and the scanning condensing lens portion. .

Since a shift of 0 μm occurs, for example, in a printer with a resolution of 400 DPI, the shift will be half a pixel.

Therefore, an object of the present invention is to solve the above problems.
The f and θ characteristics are unified for multiple scanning lines formed by multiple scanning light beams, and optical scanning is performed with good optical performance with less curvature of the scanning lines and less deviation when overlapping the scanning lines. It is an object of the present invention to provide an optical scanning device which is capable of achieving high performance and has a compact and simple configuration.

[Means for Solving the Problems] In an optical scanning device according to the present invention for achieving the above object, a plurality of light beams deflected by a single optical deflector,
A scanning lens consisting of a 1121st lens group arranged along the optical axis that refracts these light beams by the same single lens, and a second lens group arranged in the sub-scanning direction that exerts a refracting action on each light beam. The configuration is such that the light is focused onto the surface to be scanned by a condensing lens system.

This embodiment shows a case in which two laser beams are used to optically scan the surfaces to be scanned, each having different optical information. In FIGS. 1 and 2, the light beams divergently emitted from two semiconductor laser oscillators 1a and lb are converted into parallel light beams by collimator lenses 2a and 2b, respectively, and are passed through a cylindrical lens 4a through a light beam diaphragm 3a and 3b. , 4b. The cylindrical lenses 4a and 4b have refractive power in the sub-scanning direction (direction perpendicular to the scanning plane formed by the scanning light flux over time), and condense the light fluxes from the laser oscillators 1a and lb, respectively, in the sub-scanning direction. ing. Here, the cylindrical lens 4b
The light flux from the cylindrical lens 4a is reflected by the mirror 5 and guided to the rotating polygon mirror 7 as an optical deflector through the cover glass 6, and the light flux from the cylindrical lens 4a is guided to the polygon mirror 7 through the cover glass 6. The rotating polygon mirror 7 rotates at a constant speed in the direction of the arrow, and the two light beams incident thereon are reflected and deflected by the reflecting surface 7a to form a scanning condenser lens system 8.9.10
a, 10b, lens system 8.9. lOa, lob
has f/θ characteristics in the scanning direction, and in the sub-scanning direction, two optical axes 0. ．． 0. and a rotating polygon mirror 7
In this system, conjugate points are set between the reflective surface 7a and the scanned surfaces 13a and 13b to correct the tilt of the deflection reflective surface 7a. Among these, the lens 8.9 is a cylindrical lens that has refractive power only in the scanning direction, and the two laser beams enter the lens 8.9 almost perpendicularly with their tip axes parallel, and pass through the lens 8.9 while remaining parallel. The light enters lenses 10a and 10b, respectively. Since the lenses 10a and LOb are anamorphic lenses having different refractive powers in the scanning direction and the sub-scanning direction, the light flux is thereby scanned in the direction of the arrow on the scanned surfaces 13a and 13b via the cover glass 11. .

FIG. 3 is a perspective view of the '2nd embodiment. In the figure, the light source, collimator lens, cylindrical lens, and surface to be scanned are omitted for simplicity.

In FIG. 3, two sets of scanning condensing lens systems 18a, L9
a, 20a, 20b; 18b.

19b, 20c, and 20d are arranged at symmetrical positions with respect to the rotating polygon mirror 7, so as to scan the four laser beams. The optical path of the light beam is bent by mirrors 21, 22, 23, and 24, and the scanning of c, , c, , c, and c4 is performed, respectively.The second embodiment essentially has the configuration of the first embodiment. Two sets of mirrors are arranged symmetrically around the polygon mirror 7, and the operation and effect are basically the same as in the first embodiment. In the second embodiment, full-color image information can be recorded by developing the respective scanning lines C1 to C4 into Y (yellow), M (magenta), C (cyan), B, and (black) and overlapping them. can.

FIG. 4 is a perspective view of the 3' embodiment, and the collimator lens, cylindrical lens, scanned surface, etc. are also omitted for simplicity. However, four laser beams were converted into one set of scanning condensing lens system 28.29°30a, 3
0b, 30c, 30d, mirror 31.3
2.33.34 respectively, D, ,D, ,D, ,D
, to perform scanning. The functions and effects are also basically the same as in the first embodiment. Since four laser beams are scanned, full-color image information can be recorded as in the second embodiment.

[Effect] According to the present invention having the above configuration, a single optical deflector is used, and a condensing lens system for scanning is combined with a lens group that refracts a plurality of light beams by the same single lens, and for each light beam. In this way, the condensing lens system has a plurality of parallel optical axes in the sub-scanning direction, so multiple light beams can be scanned simultaneously with a relatively simple configuration. , an optical scanning device is realized in which basically the f/θ characteristics of each scanning line are unified, and scanning line curvature does not occur.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the state of the first embodiment of the present invention in the scanning plane and the sub-scanning plane, FIG. 2 is a perspective view of the main part of the first embodiment, and FIG. 3 is a diagram showing the second embodiment. FIG. 4 is a perspective view for explaining the third embodiment, and FIG. 5 is a perspective view for explaining the conventional example. la, 1b...Laser oscillator, 2a, 2b...
... Collimator lens, 4a, 4b ... Cylindrical lens, 7 ... Rotating polygon mirror, 8.9.1
8a, 18b, 19a, 19b, 28.29----
Cylindrical lens, 10a% lOb, 20a, 2
0b, 20c, 20d, 30a, 30b, 30c, 30
d...Anamorphic lens, 13a, 13b.
...Scanned surface

Claims (1)

[Claims] 1. A plurality of light beams from a light source are deflected through a single optical deflector, and each light beam is guided onto a corresponding scanned surface through a scanning condenser lens system. In an optical scanning device that performs optical scanning,
The scanning condensing lens system includes a first lens group that refracts these light beams by the same single lens, and a sub-scanning direction (out of two directions perpendicular to the optical axis) that refracts each light beam. An optical scanning device including a second lens group arranged in a direction perpendicular to the scanning direction. 2. The first lens group is configured by arranging cylindrical lenses having refractive power only in the scanning plane or afocal lenses in the sub-scanning direction along the optical axis, and parallel to the scanning condensing lens system. The optical scanning device according to claim 1, wherein a plurality of optical axes are provided. 3. The optical scanning device according to claim 1, wherein the second lens group is configured by arranging anamorphic lenses having different refractive powers in the scanning direction and the sub-scanning direction, respectively, along the sub-scanning direction.