JPH1068898A - Multibeam scanner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to lessen pitch deviation by setting the bends of plural scanning lines by the simultaneously scanning of plural light spots at the same direction. SOLUTION: Four luminous fluxes which are made into parallel luminous fluxes and are radiated from a light source device 10 are converted only in the direction corresponding to the sub-scanning by a cylinder lens 20 which is a line image forming optical system and are formed as the line image long in the direction corresponding to the main-scanning near the polarizing reflection surface of a polygon mirror 30. The four luminous fluxes are polarized and are made incident on an fθ lens 40 and are condensed as the four light spots separated from each other in the sub-scanning direction onto a surface 50 to be scanned to simultaneously scan the four scanning lines. A photoconductive photoreceptor is disposed in the position of the surface 50 to be scanned and the four spots simultaneously scan the photoreceptor in actuality. The main rays of the four luminous fluxes exist always on the same side with respect to the optical axis in the optical path from the light source device 10 to the surface 50 to be scanned and the four scanning lines S1 to S4 to be simultaneously scanned by the four light spots have the bends of the scanning lines in the same direction.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a multi-beam scanning device.

[0002]

2. Description of the Related Art An optical scanning device, which has been widely known in connection with an image forming apparatus such as an optical printer, is a single beam type in which an image is written by optical scanning by deflecting a single light beam. In order to improve the image writing speed, it is intended to realize a “multi-beam scanning device” that scans a plurality of scanning lines at a time with a plurality of light beams.

In the single beam scanning system, a light beam emitted from a light source is guided to an optical deflector so that its principal ray coincides with the optical axis of the optical system, and the main beam of the light beam deflected by the optical deflector is changed. The light beam is deflected in a plane including the optical axis of a scanning imaging optical system such as an fθ lens. In such a single-beam scanning method, “bending” hardly occurs on a scanning line that is a movement locus of a light spot.

However, in the multi-beam scanning device, a part of a plurality of light beams from the light source is transmitted in a sub-scanning direction (from the light source to the scanning direction) with respect to the optical axis of the optical system. The main scanning direction corresponds to the direction corresponding to the sub-scanning direction on the virtual optical path obtained by linearly expanding the optical path reaching the scanning surface, and the direction corresponding to the main scanning direction on the virtual optical path. The scanning line for scanning the light spot by the light beam shifted from the optical axis is not straight but slightly curved.

FIGS. 2A and 2B illustrate a case where four light spots are obtained by four light beams from four light sources and four scanning lines are simultaneously scanned. S1 to S4 indicate scanning lines, respectively. A line A indicated by a broken line is an ideal scanning line (single line in the case where scanning is performed while the principal ray of the deflected light beam is deflected in a plane parallel to the main scanning corresponding direction, including the optical axis of the scanning imaging optical system. (This corresponds to a scanning line in the case of the beam scanning method and has no bending.) ", And is referred to as a reference line A.

In the example shown in FIG. 2A, scanning lines S1, S
2 are symmetrical with respect to the reference line A with respect to the scanning lines S3 and S4 in the sub-scanning direction (vertical direction in the drawing). The scanning lines S1 and S2 are simply convexly curved upward in the figure, and the scanning lines S3 and S4 are simply convexly curved downward in the figure. FIG. 2A shows a state where “simultaneous scanning by four light spots” is performed twice consecutively. Of these two scans, the scan B1 is performed earlier, and the scan B2 is performed later. Therefore, optical writing is performed by alternately repeating the scans such as the scans B1 and B2.

[0007] Then, due to the curvature of the scanning lines S1 to S4, the interval (scanning line pitch) between the scanning line S4 in the scanning B1 and the scanning line S1 in the scanning B2 in the portion indicated by "A" in the figure. The pitch between the scanning lines S2 and S3 becomes wider at the portion indicated by "b". In other words, the image density of the recorded image written by scanning in the vicinity of the central portion in the main scanning direction periodically fluctuates in the sub-scanning direction, causing deterioration in the image quality of the recorded image.

FIG. 2B shows a simultaneous scan C1 by four light spots and a subsequent scan C2.
The scanning lines S1 and S4 and the scanning lines S2 and S3 are respectively symmetrical with respect to the reference line A in the sub-scanning direction. Scanning line S1,
S2 is a curve having two gentle peaks and a gentle valley in the center in the main scanning direction (the left-right direction in the figure), and the degree of curvature is higher for the scanning line S1 than for the scanning line S2.
Greater than. The scanning lines S3 and S4 have two gentle valleys in the main scanning direction and a curved shape with a gentle peak at the center, and the degree of the curvature is larger in the scanning line S4 than in the scanning line S3.

In this case, the scan line S in the scan C1
4 and the "curvature direction" of the scanning line S1 in the scanning C2 are opposite, so that the pitch between the scanning lines is large in the portion indicated by "c" and small in the portion indicated by "d".
Therefore, the image density of the recorded image fluctuates in the main scanning direction at the boundary between the two continuous scans C1 and C2, which causes deterioration in image quality.

[0010] As described above, in the multi-beam scanning apparatus, the fluctuation of the pitch between the scanning lines caused by the curvature of the scanning lines is called "pitch deviation". As described above, the pitch deviation causes the image quality of a recorded image to deteriorate.

As a method of reducing the "pitch deviation" as described above, there is known a "method of intentionally generating a field curvature" by a scanning image forming optical system, as described in JP-A-7-199109. Have been. Although the pitch deviation itself is reduced by this method, the spot diameter of the light spot on the surface to be scanned fluctuates greatly with the image height due to the generation of the field curvature. This tends to increase the size of the recorded image, which again deteriorates the image quality of the recorded image.

[0012]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a multi-beam scanning apparatus in which a pitch deviation is effectively reduced without a large change in the spot diameter of a light spot.

[0013]

According to the multi-beam scanning apparatus of the present invention, "a plurality of light beams from a plurality of light sources are deflected by a common optical deflector, and a plurality of deflected light beams are received by a common scanning image forming optical system. A multi-beam scanning device that converges on a scanning surface as a plurality of light spots separated from each other in the sub-scanning direction and simultaneously scans a plurality of scanning lines. Are made to have the same direction "(claim 1). "A plurality of scanning lines are bent in the same direction" means, for example, the scanning lines S1 and S2 in FIG.
As in the scanning lines S1 and S2 in (b), in a portion where the image height of each light spot is the same, it means that the scanning line is bent in the same direction. In this sense, for example, FIG.
The scanning lines S2 and S3 in (a) have the scanning lines bent in opposite directions. That is, in the example of FIG. 2A, among the four scanning lines S1 to S4, the scanning lines S1 and S2 have the same curvature and the scanning lines S3 and S4 have the same curvature. The directions of the bends in the lines S1 and S2 are opposite to the directions of the bends in the scanning lines S3 and S4.

In the present invention, assuming that the number of scanning lines scanned simultaneously is n (> 1), the curvatures of these n scanning lines are made to be "all in the same direction". .

As described with reference to FIG. 2, since the pitch deviation of the scanning line is caused by "the direction of the bend in the adjacent scanning line is reversed", as described in the present invention, "the scanning is performed at one time." By aligning the bending directions of the n scanning lines, the pitch deviation of the scanning lines can be effectively reduced.

In the present invention, since the curvature of field is not intentionally generated in order to reduce the pitch deviation of the scanning line, the spot diameter of the light spot does not greatly vary with the image height. .

The "scanning optical system" can be constituted by a lens system such as an fθ lens. In such a case, to make the bends of a plurality of scanning lines scanned simultaneously by a plurality of light spots have the same direction,
It is sufficient that the principal rays of all the light beams emitted from the light source are always on the same side with respect to the optical axis on the optical path from the light source to the surface to be scanned.

The scanning imaging optics can also be configured to "have a reflective imaging element with an imaging function", where the reflective imaging element is "a plurality of reflective imaging elements deflected by a common optical deflector. The arrangement is determined such that the deflected light beam enters and is reflected by the reflective imaging element, and that the optical path of the reflected light beam from the reflective imaging element does not overlap the optical path of the incident light beam. 3).

Such a deployed configuration is achieved, for example, by rotating the reflection type imaging element around an axis parallel to the main scanning corresponding direction, and setting the reflecting surface in the sub-scanning corresponding direction with respect to the incident direction of the incident light beam. Tilting (so-called “tilt”) or moving the reflective imaging element in the sub-scanning corresponding direction (so-called “shift”)
In this manner, by arranging the reflection type imaging element with a tilt and a shift, it is possible to simultaneously align the curvatures of a plurality of scanning lines in the “same direction”.

In the multi-beam scanning device according to the third aspect, it is possible to have "an optical element having power at least in the sub-scanning direction" between the reflection type imaging element and the surface to be scanned. 4). The “optical element having power at least in the sub-scanning corresponding direction” is, for example, a cylinder lens having power in the sub-scanning corresponding direction, or a toric lens or a deformation thereof (a deformed toric lens having a barrel-shaped surface).

In the multi-beam scanning apparatus according to claim 1, the plurality of light spots converged on the surface to be scanned by the scanning image forming optical system simultaneously scan adjacent scanning lines. (Claim 5).

[0022]

FIG. 1A shows a first embodiment of the present invention. The light source device 10 emits four parallel light beams. These four
The luminous flux of the book is transferred to a cylinder lens 20 which is a line image forming optical system.
Thus, the light is focused only in the sub-scanning corresponding direction, and is formed as a line image long in the main scanning corresponding direction near the deflecting reflection surface of the polygon mirror 30 which is a “common optical deflector”.

The four light beams are deflected by the polygon mirror 30 and are incident on the fθ lens 40 which is a “common scanning image forming optical system”. The light is condensed as a “light spot” and four scanning lines are simultaneously scanned. Since a photoconductive photoconductor is provided at the position of the surface to be scanned 50, the four light spots actually scan the photoconductor at the same time.

In the optical path from the light source device 10 to the surface 50 to be scanned, the principal rays of the four light beams are always on the same side with respect to the optical axis, so that four light spots scan simultaneously. Of the scanning lines S1 to S4 are “the scanning lines have the same bending direction”.

FIG. 1B shows a simultaneous scanning A1 by these four light spots and a subsequent simultaneous scanning A2.
In the above, since the scanning lines S1 to S4 have the same bending direction, the pitch deviation of the scanning lines is effectively reduced. Therefore, in a recorded image formed by alternately repeating the simultaneous scans A1 and A2, image quality deterioration due to pitch deviation is effectively prevented.

The multi-beam scanning device shown in FIG. 1A has a function of correcting so-called "face tilt".
Further, the light beam emitted from the light source device 10 can be a weakly divergent light beam or a weakly convergent light beam depending on the design of the scanning imaging optical system.

FIG. 3 shows the first embodiment of the present invention.
It is a figure showing a form. As shown in FIG. 3A, the four light beams emitted from the light source unit 100 are converted into parallel light beams by a common collimating lens 200, and are simultaneously deflected by a polygon mirror 30 which is a common light deflector. The concave mirror 41 which is a reflection type imaging element having an imaging function that forms an “imaging optical system” (at least has a function of making the main scanning at a constant speed, and is hereinafter referred to as an fθ mirror 41. (This is an anamorphic imaging system in which the imaging power is different in the scanning corresponding direction.) The “sub-scanning” is performed on the photoconductive photoconductor 500 whose peripheral surface matches the surface to be scanned by the action of the fθ mirror 41. As four light spots separated from one another in four directions, and the four scanning lines S1, S2, S3,
Scan S4 simultaneously.

FIG. 3B shows the state of the optical path from the polygon mirror 30 to the photosensitive member 500 as viewed from the main scanning corresponding direction. As shown in this figure, the fθ mirror 41, which is a reflective imaging element, is given a tilt angle: β and a shift amount: ΔZ so that the optical path of the reflected light flux C does not overlap with the optical path of the incident light flux B. , With this deployment
The curvatures of the scanning lines S1 to S4 are aligned in the same direction to effectively reduce the pitch deviation.

FIG. 4 shows a first embodiment of the present invention.
It is a figure showing a form. As shown in FIG. 4A, the four light beams emitted from the light source unit 100 are converted into parallel light beams by a common collimating lens 200, and are simultaneously deflected by a polygon mirror 30, which is a common light deflector. The light is reflected by 41, and is condensed on the photoconductor 500 via a long toroidal lens 45 for correcting surface tilt ("an optical element having power at least in the direction corresponding to the sub-scanning" in the fourth aspect of the present invention). The light condensing action is performed by the fθ mirror 41 and the long toroidal lens 45. Focused 4
The light beam forms “four light spots separated from each other in the sub-scanning direction” on the photoconductor 500, and the four scanning lines S1, S
2, S3 and S4 are simultaneously scanned.

As shown in FIG. 4B, as in FIG. 3B, the fθ mirror 41 is configured such that the optical path of the reflected light beam C is
The tilt angle: β and the shift amount: ΔZ are given so as not to overlap with the optical paths of the four scan lines S1, S2, S3, and S4. Reduced.

In the embodiment shown in FIG. 3, the scanning line S1
The bends of S4 to S4 are “simple curves that are convex in one of the sub-scanning directions” as shown in FIG.
In the embodiment shown in FIG. 4, the shape of the scanning lines S1 to S4 is changed by the action of the long toroidal lens 45 in FIG.
As shown in (c-2), “the central portion in the main scanning direction becomes a valley shape”
Bending amount also, (c-1) of the bending amount: reduced to W _2: bending amount from W ₁ (c-2).

As shown in FIG. 4D, in the simultaneous scanning D1 by the four light spots and the subsequent simultaneous scanning D2, the curvatures of the scanning lines S1 to S4 are aligned in the same direction. The "pitch deviation" of the scanning line is effectively reduced, and in a recorded image formed by alternately repeating the simultaneous scans D1 and D2, image quality deterioration due to the pitch deviation is effectively prevented.

In the embodiment shown in FIGS. 3 and 4,
By using a coupling lens instead of the collimating lens 200, the four light beams from the light source device 100 can be respectively coupled to a weakly divergent light beam or a weakly convergent light beam.

In the embodiment described with reference to FIGS. 1, 3 and 4, the scanning lines S1 to S4 which are simultaneously scanned
Are "scan lines adjacent to each other in a recorded image" (claim 5). However, a plurality of scanning lines that are simultaneously scanned by the multi-beam need not necessarily be adjacent on the recorded image. For example, between the scanning lines S1 and S2, between the scanning lines S2 and S3, between the scanning lines S3 and S4,
It may be an integral multiple of the scanning line pitch for forming a recorded image. However, when the interval between the scanning lines that are simultaneously scanned becomes large, the problem of deteriorating the image quality of the recorded image occurs even if the bending directions of the plurality of scanning lines are aligned in the same direction.

FIG. 5 shows a scanning line S1 among four scanning lines S1 to S4 which are simultaneously scanned by four light spots.
And between S2 and S2, between S2 and S3, and between S3 and S4 are set to three pitches of "scanning line pitch for forming a recorded image". Therefore, the interval between the scanning lines S1 and S4 is nine pitches apart from the scanning line pitch, and the scanning lines have the same direction with respect to the scanning lines S1 to S4. The light beam gradually increases from the scanning line S4 of the light beam passing near the optical axis of the scanning image forming optical system to the scanning line S1 of the light beam scanning the position farthest from the optical axis.

Considering the case where scanning is performed by "3 pitch steps" of the recording pitch by using such scanning lines S1 to S4, the scanning of the light spot for scanning the scanning line S1 is a solid line in the first scanning. , The next scan scans the dashed scan line S1 ′, and scans the next scan scans the dashed scan line S1 ″. In this case, for example, between the scanning line S1 ″ and the scanning line S4 that is adjacent to the scanning line S1 ″, the above-mentioned “pitch deviation” appears significantly.

Considering such a phenomenon, it is understood that a plurality of light spots simultaneously scan adjacent scanning lines on a recorded image (claim 5), thereby effectively suppressing the pitch deviation. Will be.

[0038]

As described above, according to the present invention, a novel multi-beam scanning device can be realized. In the present invention, as described above, since the curvatures of the scanning lines scanned simultaneously by a plurality of light spots are aligned in the same direction, the pitch deviation is effectively reduced to form a “good-looking” recorded image. It is possible to

[Brief description of the drawings]

FIG. 1 is a diagram for describing one embodiment of the present invention.

FIG. 2 is a diagram for explaining pitch deviation peculiar to multi-beam scanning, which is a problem to be solved by the present invention.

FIG. 3 is a diagram for explaining another embodiment of the present invention.

FIG. 4 is a diagram for explaining another embodiment of the present invention.

FIG. 5 is a diagram for explaining an effect of the invention described in claim 5;

[Explanation of symbols]

S1, S2, S3, S4 Scan lines scanned simultaneously by four light spots 50 Scanned surface

Claims (5)

[Claims] A plurality of light beams from a plurality of light sources are deflected by a common optical deflector, and the plurality of deflected light beams are separated from each other in a sub-scanning direction on a surface to be scanned by a common scanning image forming optical system. In a multi-beam scanning apparatus that converges as a light spot and simultaneously scans a plurality of scanning lines, the bending of a plurality of scanning lines due to the simultaneous scanning of a plurality of light spots is directed in the same direction. Multi-beam scanning device. 2. The multi-beam scanning device according to claim 1, wherein the scanning image forming optical system is a lens system. 3. The multi-beam scanning apparatus according to claim 1, wherein the scanning image forming optical system has a reflection type image forming element having an image forming function, and a plurality of deflected light beams deflected by a common optical deflector. However, the incident light is incident on the reflection type imaging element and is reflected, and the reflection type imaging element is characterized in that the arrangement is determined so that the optical path of the reflected light flux does not overlap with the optical path of the incident light flux. Multi-beam scanning device. 4. A multi-beam scanning apparatus according to claim 3, further comprising an optical element having power at least in a sub-scanning corresponding direction between the reflection type imaging element and the surface to be scanned. Scanning device. 5. The multi-beam scanning apparatus according to claim 1, wherein the plurality of light spots converged on the surface to be scanned by the scanning image forming optical system simultaneously scan adjacent scanning lines. A multi-beam scanning device for scanning.