JPH10293260A - Multi-beam scanner - Google Patents

Abstract

(57) [Summary] [Problem] Without changing the spot diameter of a light spot,
A multi-beam scanning device in which pitch deviation is effectively reduced is realized. A plurality of light beams from a plurality of light sources are deflected by a common light deflector, and the plurality of deflected light beams are separated from each other on a surface to be scanned by a common scanning image forming optical system in a sub-scanning direction. In a multi-beam scanning apparatus that collects light beams as a plurality of light spots and simultaneously scans a plurality of scanning lines,
Multiple scanning lines S1 by simultaneous scanning of multiple light spots
The bends in steps S4 to S4 have 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 relation to an image forming apparatus such as an optical printer, is a single beam type in which an image is written by scanning with a single light beam. With the aim of improving the image quality, 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 such that its principal ray coincides with the optical axis of the optical system, and the principal ray of the light beam deflected by the optical deflector is used. 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 from the light source to the surface to be scanned in a sub-scanning direction (from the light source to the surface to be scanned) with respect to the optical axis of the optical system. (A direction parallel to the sub-scanning direction on a virtual optical path obtained by linearly developing an incoming optical path, and a direction parallel to the main scanning direction on the virtual optical path is referred to as a main scanning corresponding direction.) The scanning line scanned by the light spot of the light beam shifted from the optical axis in this manner is not straight but slightly curved.

FIGS. 2A and 2B illustrate a case where four light spots are obtained by 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 indicates “an ideal scanning line when the scanning is performed while the principal ray of the deflected light beam is deflected in a plane including the optical axis of the scanning imaging optical system and parallel to the main scanning corresponding direction. This corresponds to a scanning line in the case of the single beam scanning method and has no bending), and is referred to as a reference line A0.

In the example shown in FIG. 2A, scanning lines S1 and S2
Are symmetric with respect to the reference line A0 in the sub-scanning direction (vertical direction in the figure) with respect to the scanning lines S3 and S4. The scanning lines S1 and S2 are curved “simplely convex” upward in the figure, and the scanning lines S3 and S4 are curved “simplely convex” downward in the figure. FIG. 2A shows the state of the scanning lines when “simultaneous scanning by four light spots” is performed twice successively. Of these two scans, the scan B1 is performed first, and the scan B2 is performed later. Therefore, the optical writing is performed by scanning B1, B
Scanning such as 2 is performed alternately.

Then, due to the curvature of the scanning lines S1 to S4,
In the portion indicated by “A” in FIG.
4 and the scanning line S1 in the scanning B2 (the pitch of the scanning lines) becomes narrower.
The pitch between 2 and S3 becomes wider. 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 four light spots S1 to S
4, a simultaneous scan C1 and a subsequent scan C2 are depicted. The scanning lines S1 and S4 and the scanning lines S2 and S3 are respectively symmetrical in the sub-scanning direction with respect to the reference line A0. The scanning lines S1 and S2 are curved such that there are two “gentle peaks” in the main scanning direction (the left-right direction in the drawing) and “gentle valleys” at the center, and the degree of curvature is the scanning line. S1
Is larger than the scanning line S2. The scanning lines S3 and S4 are
In the main scanning direction, the curve has two “gentle valleys” and a “gentle peak” in the center, and the degree of curvature is greater in the scanning line S4 than in the scanning line S3.

In this case, the scan line S4 in the scan C1
Since the “curvature direction” of the scanning line S1 in the scanning C2 is reversed, the pitch between the scanning lines is large in the portion indicated by “C”, and the pitch is small in the portion indicated by “D”. Therefore, if the image density in the recorded image is “continuous two scans C
1 and C2 at the boundary "in the main scanning direction, 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 disclosed in Japanese Patent Application Laid-Open No. 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 intentional generation of the field curvature, and particularly in a place where the image height is large. The spot diameter tends to be large, which again causes the image quality of the recorded image to deteriorate.

[0012]

SUMMARY OF THE INVENTION It is an object of the present invention to realize a multi-beam scanning apparatus capable of effectively reducing a pitch deviation 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 scanned by a common scanning image forming optical system. A multi-beam scanning device that converges as a plurality of light spots separated from each other in the sub-scanning direction on the surface to be scanned and simultaneously scans a plurality of scanning lines, wherein the scanning imaging optical system includes a reflection type imaging element. Have. `` Reflective imaging element ''
Has an image forming function, and a plurality of deflected light beams deflected by a common optical deflector are incident on the reflection type imaging element and reflected. The reflective imaging element is arranged so that the optical path of the reflected light beam does not overlap with the optical path of the incident light beam, and the bending of a plurality of scanning lines due to simultaneous scanning of a plurality of light spots has the same direction. It is determined (claim 1).

"A plurality of scanning lines bend in the same direction" means, for example, "scanning lines S1 and S2 in FIG. 2A and scanning lines S1 and S2 in FIG. 2B." In the portion where the image height of each light spot is the same, 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 curvatures of the scanning lines S1 and S2 are the same, and the curvatures of the scanning lines S3 and S4 are the same. 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 set to "all have 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 at one time" is performed. By aligning the bending directions of the n scanning lines, the pitch deviation of the scanning lines can be effectively reduced.

Further, 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. .

As described above, the "deployment position" of the reflection type imaging element is such that the light path of the reflected light beam does not overlap with the light path of the incident light beam, and that a plurality of scanning lines are bent by simultaneous scanning of a plurality of light spots. Are arranged in the same direction, but such an arrangement is such that the reflection type imaging element is rotated around an axis parallel to the main scanning corresponding direction, and the reflection surface is rotated with respect to the incident direction of the incident light beam. To tilt in the sub-scanning direction or the main scanning direction.
(So-called "tilt"), or to translate the reflective imaging element in the sub-scanning corresponding direction (so-called "shift").
By arranging the reflection type imaging element with tilt and shift in this manner, the scanning of the plurality of scanning lines is simultaneously adjusted in the “same direction”, and the tilt and shift are adjusted. Pitch deviation between lines can be effectively reduced.

In the multi-beam scanning device according to the first aspect, it is possible to have “an optical element having power at least in the sub-scanning corresponding direction between the reflection type imaging element and the surface to be scanned”. 2). 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 toroidal lens or a deformation thereof (a deformed toroidal lens having a barrel-shaped surface).

In the multi-beam scanning device according to the first or second aspect, the plurality of light spots condensed on the surface to be scanned by the scanning image forming optical system scan the adjacent scanning lines simultaneously. be able to.

[0021]

FIG. 1A shows a first embodiment of the present invention. As shown in FIG. 1A, the four light beams emitted from the light source unit 100 are converted into parallel light beams by a common coupling lens 200, and are focused in the sub-scanning corresponding direction by a cylinder lens 250, respectively. A reflection type having an image forming function of forming a long line image in the main scanning corresponding direction near the deflecting reflection surface of the polygon mirror 30 serving as a deflector and being simultaneously deflected by the polygon mirror 30 to form a “scanning image forming optical system”. The concave mirror 41 serving as an imaging element (has a function of making the main scanning speed uniform, so that f
(referred to as the θ mirror 41) and collected as “four light spots separated from each other in the sub-scanning direction” on the photoconductive photoreceptor 500 whose peripheral surface matches the surface to be scanned by the action of the fθ mirror 41. Illuminate the four scanning lines S1, S2, S3
Scan S4 simultaneously.

FIG. 1B 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 reflection-type imaging element, adjusts the tilt angle: β and the shift amount: ΔZ in the sub-scanning corresponding direction so that the optical path of the reflected light beam CF does not overlap the optical path of the incident light beam BF. With this arrangement, the curvatures of the four scanning lines S1 to S4 are aligned in the same direction, and the pitch deviation is effectively reduced.

FIG. 3 shows a first embodiment of the present invention.
It is a figure showing a form. As shown in FIG.
The four light beams radiated from the light source 00 are converted into parallel light beams by the common coupling lens 200,
0, the light is condensed in the sub-scanning corresponding direction, forms an image as a long linear image in the main scanning corresponding direction at a position near the deflecting reflection surface of the polygon mirror 30 which is a common optical deflector, and
The light is simultaneously deflected by 0 and enters the fθ mirror 42.
Each of the light beams reflected by the fθ mirror 42 passes through a long toroidal lens 45 (“at least an optical element having power in the sub-scanning corresponding direction” in the invention described in claim 2).
The light is focused on the photoconductor 500. The condensing action is the fθ mirror 42
And a long toroidal lens 45. The condensed four light beams form “four light spots separated from each other in the sub-scanning direction” on the photoconductor 500, and the four scanning lines S
1, S2, S3, and S4 are simultaneously scanned.

As shown in FIG. 3 (b) following FIG. 1 (b),
fθ mirror 42 is such that the optical path of reflected light beam CF ′ is incident light beam B
A tilt angle: β and a shift amount: ΔZ in the sub-scanning corresponding direction are given so as not to overlap with the optical path of F ′. With this arrangement, the bending of the four scanning lines S1 to S4 is changed in the same direction. Alignment and pitch deviation are effectively reduced.

In the embodiment shown in FIG. 1, the scanning line S1
3C is "a simple curve that is convex in one of the sub-scanning directions" as shown in FIG. 3C, but in the embodiment shown in FIG. 3A, the long toroidal lens 45 is used. As a result, the scanning lines S1 to S4 bend in a “valley shape in the center of the main scanning” as shown in FIG.
bending amount of (c-1): bending amount from W ₁ (c-2): it is reduced to W _2.

In the embodiment shown in FIGS. 1 and 3, the function of the coupling lens 200 is changed to a collimating function, and the four light beams from the light source unit 100 are respectively referred to as "weakly divergent light beams" and "weakly convergent light beams". You can also

In the embodiment described with reference to FIGS. 1 and 3, the scanning lines S1 to S4 which are simultaneously scanned are "scanning lines adjacent to each other in a recorded image". 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, in FIGS. 1 and 3, between the scanning lines S1 and S2,
The interval between the scanning lines S2 and S3 and the interval between the scanning lines S3 and S4 may be an integral multiple of the scanning line pitch for forming a recording image. However, if the intervals between the scanning lines are too wide, the imaging effect of the reflection type imaging element on each polarized light beam is considerably different, and even if the scanning lines have the same bending direction, the degree of bending is different for each scanning line. In this case, the pitch deviation between the scanning lines becomes large. Therefore, a small value of about 10 or less is appropriate as an integer in the integral multiple.

[0028]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, two specific examples similar to the embodiment described with reference to FIG. 3 will be described. FIG. 4 is a diagram for explaining the “optical arrangement according to the embodiment” described below. In order to avoid complication, the same reference numerals as those in FIG. 3 are used for those which do not seem to be confused.

FIG. 4 is a diagram showing a state in which the light source section 100 scans the surface 500 to be scanned.
The optical path leading to the (peripheral surface of the photoreceptor) is linearly developed, and this is folded at the reflection position of the fθ mirror 42. The actual arrangement of the optical system is as shown in FIG. In the embodiment of FIG. 3, the light source unit 100 having four light sources has been described. However, in the first embodiment described below, three light sources (light emitting units) are provided, and in the second embodiment, two light sources are provided. It is. In the following description, the unit of “amount having a dimension of length” is “mm” unless otherwise specified.

In FIG. 4, a coupling lens 200 is shown.
The light source side is a radius of curvature in the plane of r _cp1 = ∞, the surface of the aperture-side curvature radius sphere of r _cp2 = -10.2987, thickness: d _cp = 3, the refractive index of the material n _cp = 1 .712
At 205, a “plano-convex lens” with a focal length: f _cp = 14.46 turns the light beam from the light source unit 100 into a weak divergent light beam close to a parallel light beam.

In the cylinder lens 250, the surface on the aperture side is a cylindrical surface with a radius of curvature: r _cy1 = 29.5, the surface on the polygon mirror side is a plane with a radius of curvature: r _cp2 = ∞, and the thickness is d _cy = 3. , Material refractive index: n _cy = 1.51
1176 is a “plano-convex lens”. The part from the light source 100 to the cylinder lens 250 is a light source side optical system unit A
It is unitized as 1.

The mirror surface of the fθ mirror 42 is X in the optical axis direction.
When taking the Y axis in the direction orthogonal to the axis and the optical axis, R is the paraxial radius of curvature, K, A, B, C, D,. . X = Y ² / [R + R√ {1- (1 + K _i ) (Y / R) ² }] + A
.Y ⁴ + B · Y ⁶ + C · Y ⁸ + D · Y ¹⁰ +. . . Is a coaxial aspherical surface obtained by rotating the “non-circular shape” represented by the following formula around the axis of symmetry, and the non-circular shape is as follows: R = −405.046, K = −1.46661 ^{, A = 3.12269 × 10 ~ 10} , B = -9.1975
6 × 10 to ¹⁵ , C = −1.14331 × 10 to ¹⁸ , D = −1.3909
It is specified by 5 × 10 to ²³ .

The long toroidal lens 45 has a “barrel-shaped toroidal surface” on the fθ mirror 42 side and a “normal toroidal surface” on the surface to be scanned. The “barrel toroidal surface” is defined as “the optical axis and the longitudinal direction (the longitudinal direction perpendicular to the optical axis).
When the shape in the plane including “x” takes the x-axis in the optical axis direction and the y-axis in the longitudinal direction, r _M1 is the paraxial radius of curvature in the plane, k, a, b, c, d,. . X = y ² / [r _M1 + r _M1 √ {1- (1 + k) (Y / r _M1 ) ² }]
+ A · y ⁴ + by · y ⁶ + c · y ⁸ + d · y ¹⁰ +. . . In the “non-arc shape” represented by the following formula, the non-arc shape is separated from the non-arc shape on the optical axis by “r _S1 ” toward the fθ mirror side around the “axis parallel to the longitudinal direction”. This is the shape obtained by rotation.

The "normal toroidal surface" has a radius of curvature "r _M2 " in a plane including the optical axis and the longitudinal direction, and has a radius of curvature "r _S2 " in a plane including the optical axis and orthogonal to the longitudinal direction. Is a toroidal surface.

The elongated toroidal lens 45 each quantity and a wall thickness: d _TR, the material of the refractive index: n _TR is as follows.

[0036] _{r M1 = 692.522, k = -1.7171} , a = -8.45792 × 10 ~ 10, b = 1.09879 × 10 ~ 14, c = 1.47422 × 10 ~ 18, d = 2.92312 × 10 to ²³ r _S1 = 69.2, r _M2 = 667.087, r _S2 = 30.8, d _TR = 3.254, n _TR = 1.5721.

Intervals shown in FIG. 4: d _{1 to} d ₅ , L ₀ , L, f
The tilt angle of the θ mirror 42 in the main scanning corresponding direction: α ₄₁ , the shift amount in the sub scanning corresponding direction: Z ₄₁ , the long toroidal lens 45 shift amount in the sub scanning corresponding direction: Z _45, and the tilt angles: α ₄₅ , β ₄₅ is the following value. _{d 1 = 12.569, d 2 =} 14.46, d 3 = 20, d 4
_{= 57.8, d 5 = 122.27,} L 0 = 124.17
9, L = 105.53, α ₄₁ = 0.2 degrees, Z ₄₁ = 14,
Z ₄₅ = 7.6, α ₄₅ = 0.05 degrees, β ₄₅ = 1.28 degrees.

In the first embodiment shown in FIG. 4, the light source unit 100 includes three light sources LD1 and LD1 having an emission wavelength of 780 nm.
An interval between LD2 and LD3 in the sub-scanning corresponding direction: P ₀ = 14
A monolithic semiconductor laser array arranged in μm, and the light emitting part of the light source LD2 in the middle is a coupling lens 2
It is located on the optical axis of 00.

At this time, three scanning lines S1 to S3 which are simultaneously scanned are subjected to two successive scans D1 and D2, as shown in FIG. As shown in the figure, the three scanning lines are bent in the same direction with the same image height. For a scan width of 297 mm, the amount of curvature of the scan line (“w ₂ ” in FIG. 2) is 25.
The pitch deviation between adjacent scanning lines is as small as 1.3 to 1.6 μm. Further, when the scanning is repeated, the pitch deviation between the scanning line S3 of the preceding scanning: D1 and the scanning line S1 of the subsequent scanning: D2 is small on the order of 2 μm.

FIG. 6 shows only the characteristic portions of the "second embodiment". In the second embodiment, the light source side optical system unit A1 in the first embodiment shown in FIG.
The arrangement of the optical system on the optical path from the cylinder lens 250 to the surface to be scanned is exactly the same as that of the first embodiment.

The light source section has independent semiconductor lasers LD1 'and LD2' as light sources. These semiconductor lasers L
The light beams from D1 'and LD2' are "weakly divergent light beams" by the corresponding coupling lenses 15-1 and 15-2.
And the light around the light flux is blocked by the apertures 20-1 and 20-2, respectively. The light beam from the semiconductor laser LD1 is in a P-polarized state, passes through the aperture 20-1, and then passes through the polarization reflection film 62 of the beam combining prism PL. The luminous flux from the semiconductor laser LD2 'is initially in the P-polarized state, but after passing through the aperture 20-2, it is halved.
The light passes through the wave plate 60 to be in the S-polarized state, is internally reflected by the prism surface 61 of the beam combining prism PL, is reflected by the polarization reflection film 62, and emerges from the beam combining prism PL.

The optical axes of the coupling lenses 15-1 and 15-2 are parallel to each other, and these optical axes coincide with the optical axis Ax of the optical system below the cylinder lens 250. The semiconductor laser LD1 ′ has a light-emitting portion on the optical axis of the coupling lens 15-1 in the sub-scanning corresponding direction (the vertical direction in FIG. 7), but the light-emitting portion of the semiconductor laser LD2 ′ is in the sub-scanning corresponding direction. It is shifted from the optical axis of the coupling lens 15-2 by a minute distance: δZ. Therefore, when the light beam from the semiconductor laser LD2 'is emitted from the beam combining prism PL, the light beam from the semiconductor laser LD1' is slightly inclined with respect to the sub-scanning corresponding direction with respect to the light beam from the semiconductor laser LD1 '. Light spots are separated on the surface in the sub-scanning direction.

The distances shown in FIG. 6 are d ₁ , d ₂ (common to the light beams from the semiconductor lasers LD 1 ′, LD 2 ′), d.
₃ (= d ₃₁ + d ₃₂ + d ₃₃ ) and δZ are respectively
d ₁ = 12.569, d ₂ = 6.0, d ₃ = 29, δZ =
0.0141.

In the second embodiment, 2
Two scanning lines: two scanning lines following the states of S1 and S2:
FIG. 6 shows E1 and E2. As shown in the figure, the two scanning lines: S1 and S2 are bent in “the same image height and the same direction”. For an optical scanning width of 297 mm, the amount of curvature of the scanning line (“w ₂ ” in FIG. 2) is as small as 25 to 27 μm, and the pitch deviation between adjacent scanning lines is as small as 1.2 μm. Further, when the scanning is repeated, the pitch deviation between the scanning line: S2 of the preceding scanning: E1 and the scanning line: S1 of the subsequent optical scanning: E2 is as small as 1 μm.

[0045]

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 an embodiment of the present invention.

FIG. 5 is a diagram illustrating a state of a scanning line according to the embodiment of FIG. 4;

FIG. 6 is a view for explaining only a characteristic portion of another embodiment of the present invention.

FIG. 7 is a diagram showing a state of a scanning line according to the embodiment of FIG. 6;

[Explanation of symbols]

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

Claims (2)

[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 on a surface to be scanned in a sub-scanning direction by a common scanning image forming optical system. In a multi-beam scanning device that converges as a plurality of light spots and scans a plurality of scanning lines simultaneously, the scanning imaging optical system has a reflective imaging element with an imaging function and is deflected by a common optical deflector. The plurality of deflected luminous fluxes are incident on and reflected by the reflective imaging element, and the reflective imaging element has a configuration in which the optical path of the reflected luminous flux does not overlap with the optical path of the incident luminous flux, and A multi-beam scanning apparatus characterized in that the arrangement is determined so that the bending of a plurality of scanning lines by simultaneous scanning is in the same direction. 2. The multi-beam scanning apparatus according to claim 1, 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.