JP3488432B2 - Multi-beam scanning device, multi-beam scanning method, light source device for multi-beam scanning device and image forming apparatus - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multi-beam scanning device, a multi-beam scanning method, a light source device for the multi-beam scanning device, and an image forming apparatus.

[0002]

2. Description of the Related Art Optical scanning devices are widely known in connection with image forming apparatuses such as digital copying machines and optical printers.
"Multi-beam method" that simultaneously scans multiple scan lines on the surface to be scanned as a method to speed up scanning by the optical scanning device
In this regard, a "multi-beam scanning device" using a semiconductor laser array in which a plurality of light emitting portions are monolithically arranged in one row as a light source is being realized. In the semiconductor laser array, the distance between the light emitting parts does not change, and because the pitch of the light emitting parts is small, the optical system on the optical path from the light source to the surface to be scanned can be used in common for multiple beams, so there is no mechanical fluctuation. On the other hand, a multi-beam optical scanning device with high stability becomes possible. The multi-beam scanning method includes "adjacent scanning" in which adjacent scanning lines are simultaneously scanned and "interlaced scanning" in which one or more scanning lines are separated from each other. The interlaced scanning has some advantages, but has a problem that, as is well known, "scan line pitch unevenness in which the intervals of the scanning lines simultaneously scanned vary with scanning". When the writing density of the optical scanning becomes high as 600 dpi or more, the pitch of the scanning lines also becomes small, so that the scanning line pitch unevenness becomes relatively large with respect to the scanning line pitch.
The influence on the image quality of the image formed by writing becomes large, and the image quality is apt to deteriorate. From this point of view, “adjacent scanning” is suitable as a multi-beam scanning method for high-density image formation.

Optical scanning is performed by a light spot formed on the surface to be scanned. For high-density writing,
Naturally, as the scanning line pitch becomes smaller, the spot diameter in the sub-scanning direction must also become smaller. The light spot is formed by the beam waist of the light beam by design, but the image surface on which the beam waist is formed and the surface to be scanned do not necessarily match due to the influence of the field curvature, etc. The spot diameter is not necessarily equal to the beam waist diameter. Therefore, the field curvature is appropriately corrected in order to suppress the spot diameter variation due to the field curvature as much as possible. Further, regardless of whether it is a multi-beam scanning device or a single-beam scanning device, various errors are inherent in the actual optical scanning device. These errors are errors with respect to the component precision of each optical element that constitutes the optical scanning device and with respect to the assembling precision. If such an error exists, the image plane, which should be matched as much as possible with the scanned surface, is relatively displaced from the actual scanned surface. Such a shift is called "defocus" of the light spot. Considering that defocus is inevitably present in an actually assembled multi-beam scanning device, it is necessary to design the multi-beam scanning device on the premise of the presence of defocus. That is, the design is such that “the variation range of the spot diameter is within the desired range” even in the presence of some defocus.

The permissible range of variation in the spot diameter of the light spot is within a range of ± 10% with respect to the spot diameter W, which is assumed as a standard for optical scanning, that is, within a range of W (1 ± 0.1). It is said that.

For example, when it is assumed that the optical scanning is performed with a light spot having a spot diameter of 40 μm, this “40 μ
“M” is the “spot diameter assumed as a standard for optical scanning”, which is referred to as “target spot diameter” in this specification. In the defocused state, the spot diameter becomes larger than the beam waist diameter. Therefore, when designing the optical system, design the beam spot diameter to be "several% to 10% smaller than the target spot diameter". It is normal to do. The width of defocus so that the variation of the spot diameter of the light spot falls within the above “allowable variation of the spot diameter” is called “depth margin”. The larger the depth margin, the higher the tolerance for the "deviation between the image plane and the scanned surface". It is empirically known that the depth margin needs to be 0.9 mm or more in consideration of the precision of parts of the optical system and the assembling precision. Another problem in multi-beam scanning using a semiconductor laser array as a light source is “divergence of divergence angle”. As is well known, the luminous flux emitted from a semiconductor laser is a divergent luminous flux, the divergence angle is the maximum in the thickness direction of the active layer and the minimum in the direction orthogonal thereto, and the far-field pattern of the luminous flux is It has an elliptical shape whose major axis direction is the thickness direction of the active layer. In the semiconductor laser array, divergent light fluxes are emitted from a plurality of light emitting units, but the divergence angle is not necessarily common to the light emitting units, and there is “variation” among the light emitting units. Therefore, the spot diameter of the optical spot on the surface to be scanned is
The light spots may vary from one light spot to another, and such "variation in spot diameter between light spots" may cause image deterioration.

[0006]

This invention is, for example, 6th invention.
Even for high-density writing of 00 dpi or more, the necessary depth margin is surely secured, the influence of the variation in spot diameter is effectively reduced or prevented, and good multi-beam scanning is realized with a stable spot diameter. This is an issue.

[0007]

SUMMARY OF THE INVENTION A multi-beam scanning device according to the present invention is capable of detecting a plurality of beams from a semiconductor laser array.
The light is guided to a surface to be scanned through a common optical system including an optical deflector to form a plurality of light spots separated in the sub-scanning direction,
It is a multi-beam scanning device which simultaneously scans a plurality of scanning lines on a surface to be scanned by simultaneously deflecting them by an optical deflector. The multi-beam scanning device according to claim 1 has the following features. The “semiconductor laser array” used as a light source has an inclination angle of φ (90> 90) with respect to the sub-scanning direction with respect to the array direction of the light emitting parts (direction parallel to the active layer).
φ ≧ 0 unit: degrees). Tilt angle: φ includes “φ = 0”. In this case, the arrangement direction of the light emitting units is parallel to the sub scanning direction. When the scanning line pitch (designed interval between adjacent scanning lines) is P and the arrangement pitch of the light emitting portions in the semiconductor laser array is ρ, the emission wavelength of the semiconductor laser array: λ, the target spot in the sub-scanning direction The coefficient: K is defined by the formula: K = 0.82λ / ωz according to the diameter: ωz. The coefficient: K, together with the scanning line pitch: P and the arrangement pitch of the light emitting parts: ρ, condition: (1) 0.01 <K · P / (ρ · cosφ) <0.30 (2) 0.011 <K <0.030 is satisfied. The multi-beam scanning device according to claim 1,
It is possible to have a coupling lens, an aperture, a line image forming optical system, an optical deflector, and a scanning image forming optical system (claim 2). The "coupling lens" is a lens for coupling a plurality of beams from the semiconductor laser array to the optical system thereafter. "Aperture" is
This is for beam-shaping a plurality of beams that have passed through the coupling lens. The "line image forming optical system" focuses each beam-shaped beam in the sub-scanning direction and forms a "long line image in the main scanning direction". A "convex cylindrical lens" or a "concave cylindrical mirror" can be used as this line image forming optical system.

The "optical deflector" has a deflecting / reflecting surface near the image forming position of each line image and deflects each reflected light beam. As a light deflector, a "rotating mirror", that is, a rotating single-sided mirror or a rotating double-sided mirror,
A rotating polygon mirror or the like can be used, and an oscillating mirror such as a galvanometer mirror can also be used. Above all, the rotating polygon mirror is suitable as an optical deflector. The "scan imaging optical system" is an optical system that focuses each beam deflected by the optical deflector toward the surface to be scanned. The scanning imaging optical system
It can be composed of one or more lenses, or can be composed of one or more imaging mirrors (mirrors having an imaging action), and is a combination of one or more lenses and one or more imaging mirrors. It can also be configured with. In the multi-beam scanning device according to claim 2, the inclination angle φ of the semiconductor laser array can be set to “φ = 0” (claim 3) or can be set to “φ> 0” (claim). 4). In the multi-beam scanning device according to claim 2 or 3 or 4, the coupling action of the coupling lens may be a "collimating action" (claim 5) or "a plurality of divergent beams from a semiconductor laser array". Each of them may be a function of forming a divergent beam with weaker divergence ”(claim 6). In the multi-beam scanning device according to claim 2 or 3 or 4, the optical deflector is a rotating mirror such as a rotating polygon mirror, and the scanning image forming optical system has a "function of speeding up scanning by a light spot". (Claim 7). Further, in the multi-beam scanning device according to claim 5, the optical deflector may be a rotating mirror such as a rotating polygon mirror, and the scanning image forming optical system may be an “fθ optical system (optical system having fθ characteristics)”. Yes (claim 8). In the multi-beam scanning device according to any one of claims 2 to 8, the line image forming optical system can be a "cylindrical lens" (claim 9). In the multi-beam scanning device according to claim 4, when the inclination angle φ of the semiconductor laser array is close to 90 degrees, the light beam diameter is set in the main scanning direction on the optical path between the coupling lens and the optical deflector. It is possible to have an expanding "main-scan direction beam expander" (claim 10).

The "light source device" of the present invention is a light source device used in the multi-beam scanning device according to the first aspect, and has a semiconductor laser array, a coupling lens, and an aperture. The “semiconductor laser array” is provided with the arrangement direction of the plurality of light emitting units arranged in one row at the arrangement pitch: ρ inclined with respect to the sub-scanning direction by an inclination angle φ (≧ 0). This "coupling lens" is a lens that couples a plurality of beams from the semiconductor laser array to the optical system thereafter. The “aperture” beam-shapes multiple beams that have passed through the coupling lens. That is, each beam becomes a beam having a predetermined cross-sectional shape because the peripheral portion of the beam is shielded when passing through the aperture of the aperture. The numerical aperture NAz (source) in the sub-scanning direction defined by the aperture satisfies the following condition: (3) 0.01 <NAz (source) <0.30 (claim 11). In the light source device according to claim 11, the inclination angle of the semiconductor laser array: φ is “φ
= 0 ”(Claim 12), and“ φ>
It can be set to "0" (claim 13). Claim 1
In the light source device described in 1 or 12 or 13, the coupling action of the coupling lens may be a "collimation action" (claim 14). In this case, the coupling lens can be composed of "one lens" (claim 15). The coupling action may be an action of "making each of the plurality of divergent beams from the semiconductor laser array a divergent beam with weak divergence" (claim 16). As for the coupling action of the coupling lens, there is another "action of making a plurality of divergent beams from the semiconductor laser array into converging beams".
Is also possible. Also, as shown in the examples, it is of course possible to configure the coupling lens with two or more lenses. In the light source device according to any one of claims 11 to 16, the array pitch of the light emitting portions in the semiconductor laser array: ρ can be 10 μm (claim 17) or “ρ> 10 μm”. You can also Further, in the light source device according to any one of claims 11 to 17, the emission wavelength: λ in the semiconductor laser array is 70.
It can be set to 0 nm or less (claim 18).

According to the multi-beam scanning method of the present invention, "a plurality of beams from the semiconductor laser array are guided to a surface to be scanned through a common optical system including an optical deflector, and a plurality of light spots separated in the sub-scanning direction. Is formed and is simultaneously deflected by an optical deflector to simultaneously scan adjacent scanning lines on a surface to be scanned. 1 is used (claim 19). The image forming apparatus of the present invention is an “image forming apparatus that forms a latent image by performing optical scanning on a photosensitive surface of a photosensitive medium by an optical scanning device and visualizes the latent image to obtain an image”. The multi-beam scanning device according to any one of claims 1 to 10 is used as an optical scanning device for optically scanning the photosensitive surface (claim 20). 21. An image forming apparatus according to claim 20, wherein the photosensitive medium is a photoconductive photosensitive member, and the electrostatic latent image formed by uniform charging of the photosensitive surface and optical scanning of the optical scanning device is a "toner image".
Can be visualized as (claim 21). The toner image is fixed on a sheet-shaped recording medium (transfer paper, “OHP sheet (plastic sheet for overhead projector), etc.”.) In the image forming apparatus according to claim 20, for example, “silver salt photographic film” is used as a photosensitive medium. "
Can also be used. In this case, the latent image formed by the optical scanning by the optical scanning device can be visualized by the developing method of the ordinary silver salt photographic process. Such an image forming apparatus can be implemented as, for example, an “optical plate making apparatus” or an “optical drawing apparatus”. The image forming apparatus according to claim 21 can be implemented as a laser printer, a laser plotter, a digital copying machine, a facsimile machine, or the like.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows one embodiment of the multi-beam scanning device of the present invention. The semiconductor laser array 1 as a light source is one in which four light emitting parts ch1 to ch4 are arranged in one row at equal intervals. Although the four light emitting portions are arranged in the sub-scanning direction (tilt angle: φ = 0) in this figure, the semiconductor laser array 1 is tilted with respect to the sub-scanning direction.
The arrangement direction of the light emitting portions is tilted with respect to the sub-scanning direction (tilt angle:
φ> 0). Four light emitting parts ch1 to ch
The four beams radiated from No. 4 are divergent light beams whose major axis direction of the "elliptical far field pattern" is oriented in the main scanning direction as shown in the figure. Is coupled to the subsequent optical system. The form of each coupled beam can be a weakly divergent light beam, a weakly converging light beam, or a parallel light beam, depending on the optical characteristics of the optical system thereafter. The 4 beams that have passed through the coupling lens 2 have an aperture 3
"Beam shaping" by "common line image forming optical system"
By the action of the cylindrical lens 4 which is a rotary polygonal mirror 5 which is a "light deflector", each is focused in the sub-scanning direction.
In the vicinity of the deflecting / reflecting surface, line images that are long in the main scanning direction are formed separately from each other in the sub scanning direction. The four beams deflected at a constant angular velocity by the deflecting / reflecting surface are transmitted through the two lenses 6 and 7 forming the “scanning image forming optical system”, the optical path is bent by the bending mirror 8, and the “scanned surface” is the substance. On the photosensitive medium 9 which forms a light beam, the light beams are condensed as four light spots separated in the sub-scanning direction, and four scanning lines on the surface to be scanned are simultaneously scanned adjacently. One of the beams is incident on the mirror 10 prior to the optical scanning and is focused on the light receiving element 12 by the lens 11. The writing start timing of four beams is determined based on the output of the light receiving element 12. "Scanning and imaging optics"
Is an optical system for converging four beams simultaneously deflected by the optical deflector 5 as four light spots on the surface 9 to be scanned, and is composed of two lenses 6 and 7.

FIG. 2 schematically illustrates the optical arrangement shown in FIG. 1 as being linearly expanded along the optical path, with the vertical direction as the sub-scanning direction. This figure also shows the “state of image formation in the sub-scanning direction” of the light flux emitted from one light emitting portion of the semiconductor laser array 1. In FIG. 2, the divergent light beam emitted from the light emitting portion is coupled to the subsequent optical system by the coupling lens 2 (in the figure, the coupling action is a collimating action), the beam is shaped by the aperture 3, and the cylindrical shape is formed. The light is condensed in the sub-scanning direction by the lens 4, is imaged as a long line image in the main scanning direction (direction orthogonal to the drawing) in the vicinity of the position of the deflecting reflecting surface of the rotary polygonal mirror 5, and is reflected by the deflecting reflecting surface. While diverging in the scanning direction, it is incident on the scanning and imaging optical system 6A (shown as a combination of the lenses 6 and 7 in FIG. 1), and by the action of the scanning and imaging optical system 6A (on the sub-scanning surface 9 Direction) spot diameter: forms a light spot of ωz. At this time, the spot diameter: ωz is determined by the numerical aperture NAz (img) of the beam incident on the surface 9 to be scanned in the sub-scanning direction and the beam wavelength (emission wavelength of the semiconductor laser): λ, and is a good approximation, 3) It can be expressed as ωz = 0.82λ / NAz (img). Here, in order to make the description general, as shown in FIG. 3A, a state in which the arrangement direction of the light emitting portions ch1 to ch4 in the semiconductor laser array 1 is inclined with respect to the sub-scanning direction at an inclination angle φ Think Then, the “apparent array pitch in the sub-scanning direction” of the light emitting units ch1 to ch4 is given by “ρ · cosφ” using the array pitch: ρ. On the other hand, when the scanning line pitch, which is the interval between the adjacent scanning lines on the surface to be scanned 9, is P, the scanning line pitch: P is “the writing density (dp on the surface to be scanned 9
i) ”. Further, the combined imaging magnification in the sub-scanning direction of the optical system between the semiconductor laser array 1 which is the light source and the surface 9 to be scanned is βz.

Then, under the condition of adjacent scanning,
Since the apparent array pitch of the light emitting parts ch1 to ch4 in the sub-scanning direction: βz times the ρ · cosφ should be equal to the scanning line pitch: P, (4) βz = P / (ρ · cosφ) holds. I have to. On the other hand, when the numerical aperture on the light source side is “NAz (source)” as shown in FIG. 2, (5) NAz (source) = βz · NAz (img). When the equations (3) and (4) are used on the right side of the equation (5), the equation (6) NAz (source) = {P / (ρ · cosφ)} · {0.82λ / ωz} is obtained. Here, when the coefficient: K is defined as K = 0.82λ / ωz, the equation (6) becomes (6A) NAz (source) = K · P / (ρ · cosφ). As is clear from FIG. 2, NAz (sou
rce) is regulated by the opening width of the aperture 3 in the sub scanning direction. If the numerical aperture: NAz (source) is not set appropriately, the following problems will occur. That is, if the aperture width is set too small and the numerical aperture: NAz (source) is too small, the optical energy of optical scanning becomes insufficient, and high-speed scanning cannot be performed. On the other hand, if the numerical aperture is set too large, it is likely to be affected by the above-mentioned “variation of divergence angle for each light spot”, and the spot diameter of the light spot may become uneven on the surface to be scanned. The range of the coefficient: K (= 0.82λ / ωz) is determined by the emission wavelength: λ and the target spot diameter (in the sub-scanning direction): ωz. The value of the coefficient K is the depth margin described above (here, the depth margin in the sub-scanning direction).
is connected with.

When the emission wavelength: λ is 400 to 800 nm and the target spot diameter: ωz is 16 to 60 μm, the coefficient K and the depth margin W are calculated as follows. λ (nm) ωz (μm) K W (mm) 800 22 0.0298 0.90 800 50 0.0131 4.65 800 60 60 0.0109 6.69 780 22 0.0291 0.92 780 30 0.0213 1.72 780 50 0.0128 4.77 400 16 0.0205 0.95 400 30 0.0109 3.35 Depth margin: W is 0 as described above in consideration of optical system component accuracy and assembly accuracy. It is empirically known that "9 mm or more is required." Therefore, as is clear from the first column, the emission wavelength: λ (400 to 800 nm), the target spot system in the sub-scanning direction: ωz (16 ~ 60 nm)
It is understood that the range of the coefficient K should be (2) 0.011 <K <0.030 in the range of. Next, numerical aperture: NAz (sourc
Considering the range of e), its upper limit is determined by the requirement to eliminate the influence of the above-mentioned “variation of divergence angle”. Figure 3
With reference to (b) to (d), these figures show the morphology of the beam at the position of the aperture 3 and the state of the aperture of the aperture. (B) shows the case where the tilt angle: φ is 0, (c) shows the case where φ = 45 degrees, and (d) shows the case where φ = 90 degrees. Full angle at half maximum of the divergence angle of the divergent light beam emitted from the light emitting section in the direction orthogonal to the active layer (angle range having an intensity of 1/2 or more of the peak value of the intensity distribution): θ
Is at least 20 degrees regardless of the light emitting portion. The divergence angle in the sub-scanning direction is the smallest when the tilt angle is φ = 0 as shown in FIG.

Therefore, the aperture width of the aperture of the aperture in the sub-scanning direction is as follows: NA: NAz (source) is (7) NAz (source) ≤sin [tan ^-1 {√ [(2 / ln2) tan ( θ / 2)]}], the divergence angle θ should be set to 20 degrees, that is, (7A) NAz (source) ≦ 0.03. Numerical aperture: NAz
The lower limit of (source) is determined by "imaging magnification in the sub-scanning direction in the optical system: βz". Imaging magnification in sub-scanning direction: β
z is the lateral magnification of the optical system (coupling lens and cylindrical lens) between the light source and the deflecting / reflecting surface of the optical deflector in the sub-scanning direction: | β ₁ |, and the sub-scanning direction of the scanning imaging optical system. Lateral magnification of: | β ₂ | product: | β ₁ | × | β ₂ | ”. The lower limit of the magnification: | β ₁ | is 1.8 in the light of experience. That is, | β ₁ | ≧ 1.8. magnification:
When | β ₁ | becomes 1.8 or less, the position of the cylindrical lens 3 is close to the optical deflector, so that the layout interference between the cylindrical lens 3 and the optical deflector 5 occurs.
In this case, if the cylindrical lens 3 is separated from the light deflector 5 in order to avoid interference, it is necessary to separate the coupling lens 2 from the light source in order to secure the magnification. In this case, the coupling lens 2 Since the amount of light that can be coupled is absolutely small, the amount of light for optical scanning may become insufficient. In the example shown in FIG. 2, the coupling action of the coupling lens 2 is a collimating action. In this case, the combined imaging magnification of the coupling lens 2 and the cylindrical lens 4 is | β ₁ | Ratio of focal length 2 of fcp: fcp and focal length of cylindrical lens 4 in the sub-scanning direction: fcy: fcy / f
given in cp. The practically usable focal length of the coupling lens: fcp is about 30 mm at maximum.
When fcp is 30 mm or more, the problem of insufficient light amount occurs. Focal length of cylindrical lens: f
cy is 54 mm considering the avoidance of interference with the optical deflector.
The degree is the minimum value. Therefore, also in this case, the minimum value of | β ₁ | is 1.8.

On the other hand, the practical usable range of the magnification in the sub-scanning direction of the scanning imaging optical system: | β ₂ | is 0.5 ≦ | β _2.
| ≦ 2.0. In the magnification range of | β ₂ | ≦ 0.5,
It is necessary to dispose the lens on the surface to be scanned close to the surface to be scanned, and the length of the lens in the main scanning direction becomes large, making processing difficult and increasing the cost. Conversely, | β ₂ |
In the magnification range of ≧ 2.0, the image plane position variation is likely to be large due to the environmental variation and the mounting error of the scanning optical system, and it is difficult to reduce the diameter of the light spot, and it is difficult to perform high-density optical scanning. Taking the above into consideration, "imaging magnification in the sub-scanning direction: βz
(= | Β ₁ | × | β ₂ |) ”has a lower limit of about 1.8 × 0.5 = 0.9. Here, using equations (4) and (6A), “NAz (source) = βz · K”, and the coefficient: K
Since the lower limit value of is 0.011, the numerical aperture is NAz.
(source) becomes (8) NAz (source) ≧ 0.01. Therefore, by combining the equations (7A) and (8), (9) 0.01 ≦ NAz (source) ≦ 0.30, and “NAz (source) = K · P / (ρ · cosφ)”
Taking into account (1), 0.01 <K · P / (ρ · cosφ) <0.30 is obtained. Here, the emission wavelength: λ is 400 to 800 n
Target spot diameter: ωz is 30 μm
An example of the coefficient K and the depth margin is as follows. λ (nm) ωz (μm) K W (mm) 800 30 0.022 1.67 780 30 0.021 1.72 700 30 0.019 1.91 600 30 0.016 2.23 550 30 0.015 2.43 500 30 0.014 2.68 450 30 30 0.012 2.97 400 30 0.011 3.35 As is apparent from these results, the target spot diameter:
When ωz is the same, the shorter the emission wavelength: λ, the larger the depth margin: W. Therefore, the accuracy condition imposed on the optical system becomes lenient and the cost can be reduced. Also, as the emission wavelength: λ becomes shorter, the numerical aperture:
Since NAz (source) is also small, it is "more difficult to be affected" by the variation in divergence angle. From this point of view, the semiconductor laser array used preferably has an emission wavelength: λ of 700 nm or less (claim 18).

That is, the multi-beam scanning device described above with reference to FIGS. 1 and 2 uses a common optical system 2 including a light deflector 5 for a plurality of beams from the semiconductor laser array 1.
The plurality of scanning spots on the surface 9 to be scanned are formed by forming a plurality of light spots separated in the sub-scanning direction by being guided to the surface 9 to be scanned via 4, 6, 7 and deflecting them simultaneously by the optical deflector 5. In a multi-beam scanning device that performs adjacent scanning at the same time,
In the semiconductor laser array 1, the arrangement direction of its light emitting portions is tilted with respect to the sub-scanning direction: φ (90> φ ≧ 0 Unit: degree)
Are arranged with. When the scanning line pitch is P and the array pitch of the light emitting portions in the semiconductor laser array is ρ, the emission wavelength of the semiconductor laser array is λ,
According to the target spot diameter: ωz in the sub-scanning direction, K defined by K = 0.82λ / ωz, and P and ρ satisfy the condition: (1) 0.01 <K · P / (ρ · cosφ) <0.30 (2) By satisfying 0.011 <K <0.030, a depth margin of 0.9 mm or more is realized and the spot diameter variation in the sub-scanning direction is effectively suppressed within the allowable range. In addition, good multi-beam scanning can be realized without problems such as insufficient light quantity and “uneven spot diameter due to dispersion of divergence angle”. Also,
The multi-beam scanning device described in the above embodiments includes a coupling lens 2 for coupling a plurality of beams from the semiconductor laser array 1 to a subsequent optical system, and an aperture for beam-shaping the plurality of beams transmitted through the coupling lens. 3, a line image imaging optical system 4 for converging each of the beam-shaped beams in the sub-scanning direction to form a long line image in the main scanning direction, and a deflection reflection near the image forming position of each line image. It has an optical deflector 5 having a surface, and scanning and imaging optical systems 6 and 7 for converging each beam deflected by the optical deflector toward a surface to be scanned (claim 2). Further, in the light source device in the multi-beam scanning device described in the above embodiment, the arrangement direction of the plurality of light emitting portions arranged in one row at the arrangement pitch: ρ is inclined with respect to the sub-scanning direction: φ (≧ 0) The semiconductor laser array 1 inclined and provided, the coupling lens 2 for coupling the plural beams from the semiconductor laser array to the optical system thereafter, and the plural beams transmitted through the coupling lens are beam-shaped. The numerical aperture NAz (source) in the sub-scanning direction defined by the aperture 3 satisfies the condition: (3) 0.01 <NAz (source) <0.30 (claim 11). ).

[0018]

[Examples] Six specific examples will be given below.

The optical system configuration of each example described below is the same as that of the embodiment shown in FIG. In some of the following examples, a surface shape that is not a spherical surface is used as an optical surface, and therefore, the description of such an aspherical surface shape will be first described below. However, the content of this invention is
It is not limited to the following expression. First, the main scanning section (virtual plane section including the optical axis and parallel to the main scanning direction)
The non-circular arc shape inside is expressed as follows. The depth in the optical axis direction is X, the coordinate in the main scanning direction is Y, the paraxial radius of curvature in the main scanning section is R _m , the constants are K _m , and A _i (i = 1, 2,
3 ,. ． ． ) Is represented by the following formula. X = (Y ² / R _m ) / [1 + √ {(1 + K _m ) (Y / R _m ) ² }] + ΣA _i Y ⁱ (10) Sub-scan section (virtual plane section orthogonal to the main scanning direction) The internal curvature is the position in the main scanning direction (coordinates:
Y) ”, the curvature: C _S (Y) is represented by C _S (Y) = {1 / R _S (0)} + ΣB _i Y ⁱ (11). R _S (0) is the paraxial radius of curvature in the sub-scan section at Y = 0. "I" in the sum of the second term on the right side
Are 1, 2, 3 ,. ． ． Is. Next, in the case where the shape in the main scanning cross section is a non-arc shape, the shape in the sub-scanning section is also a non-arc shape, and the non-circular shape in the sub-scanning section changes with the coordinate Y. , Z is the coordinate in the sub-scanning direction, and is represented by the following equation. X = (Y ² / R _m ) / [1 + √ {(1 + K _m ) (Y / R _m ) ² }] + ΣA _i Y ⁱ + C _S (Y) · Z ² / [1 + √ {(1 + K _S ) (C _S (Y) ・ Z) ² }] + (F ₀ + F ₁・ Y + F ₂・ Y ² + F ₃・ Y ³ + F ₄・ Y ⁴ + ・ ・) ・ Z + (G ₀ + G ₁・ Y + G ₂・ Y ² + G ₃・ Y ³ + G ₄・ Y ⁴ + ・ ・) ・ Z ² + (H ₀ + H ₁・ Y + H ₂・ Y ² + H ₃・ Y ³ + H ₄・ Y ⁴ + ・ ・) ・ Z ³ + (I ₀ + I ₁・ Y + I ₂・ Y ² + I ₃・ Y ³ + I ₄・ Y ⁴ + ・) ・ Z ⁴ + (J ₀ + _{J 1 · Y + J 2 ·} Y 2 + J 3 · Y 3 + J 4 · Y 4 + ··) · Z 5 + (K 0 + K 1 · Y + K 2 · Y 2 + K 3 · Y 3 + K ₄・ Y ⁴ + ・ ・) ・ Z ⁶ + (L ₀ + L ₁・ Y + L ₂・ Y ² + L ₃・ Y ³ + L ₄・ Y ⁴ + ・ ・) ・ Z ⁷ + (M ₀ + M ₁・ Y + M ₂・ Y ² + M ₃・ Y ³ + M ₄・ Y ⁴ + ・ ・) ・ Z ⁸ + (N ₀ + N ₁・ Y + N ₂・ Y ² + N ₃・Y ³ + N ₄ · Y ⁴ + ··) · Z ⁹ +. ． ． (12) The third term “K _m ” on the right side is given by the following equation. It is represented by K _S (Y) = K _S (0) + ΣC _i Y ⁱ (13). K _S (0) is a conic constant in the sub-scan section at Y = 0. "I" in the sum of the second term on the right side is
1, 2, 3 ,. ． ． Is.

Example 1 The optical arrangement of Example 1 is shown in FIG. Reference numeral 111 is a semiconductor laser array, reference numeral 121 is a coupling lens, reference numeral 131 is an aperture, reference numeral 141 is a cylindrical lens, reference numeral 151 is a rotary polygon mirror, reference numerals 161, 171.
Reference numeral 181 denotes a lens forming the scanning and imaging optical system, and reference numeral 19 denotes a surface to be scanned. Of course, depending on the layout of the multi-beam scanning device, a plane mirror for bending the optical path can be arranged on the optical path from the light source to the surface to be scanned to bend the optical path appropriately. This point is the same in the other examples. "Semiconductor laser array as light source" Number of light emitting parts: 4 Arrangement pitch of light emitting parts: ρ = 14 µm Emission wavelength: 780 nm Maximum output: 15 mW Tilt angle: φ = 0 degree "Coupling lens" Lens configuration: 1 group 2 elements Focus Distance: 30 mm Coupling function: Collimating function "Cylindrical lens" Focal length in sub-scanning direction: 70.62 mm "Aperture" Aperture width in main scanning direction: 5.2 mm Aperture width in sub-scanning direction: 1.04 mm "Rotating polygon mirror" Number of deflecting / reflecting surfaces: 6 Radius of inscribed circle: 25 mm Incident angle (angle formed by beam incident direction from light source side and optical axis of scanning imaging optical system): 60 degrees Writing density: 1200 dpi Target sub-scanning direction Spot diameter: 50 μm “Data of optical element between rotating polygon mirror and scanned surface” Main scanning of i-th surface counted from the rotating polygon mirror side Curvature in a plane radial: R _mi, the curvature in the sub-scan section radius: R _Si,
It is assumed that the surface spacing is X and the surface shift amount in the main scanning direction (upward shift in FIG. 4) is Y. The refractive index is n. In addition,
In each of the following examples, the radii of curvature: R _mi , R _Si are “paraxial radii of curvature” other than spherical surfaces.

Surface number: i R _mi R _Si X Y n Deflection reflection surface 0 ∞ ∞ 51.38 1.627 Lens 161 1 -96.76 Spherical surface 15.07 0 1.78571 2 -93.27 Spherical surface 9.76 0 Lens 171 3 -2450.2 Spherical surface 19.90 0 1.60909 4 -161.76 Spherical surface 127.00 0 Lens 181 5 -630.00 -55.53 3.00 0 1.57211 6 -700.00 -24.42 101.72 0 Surface number 5 That is, the incident side surface of the lens 181 is "the shape in the main scanning cross section is expressed by a non-arcuate shape (expressed by the formula (10) above. It is). Table 1 shows each constant of the above equation (10).

[0022]

[Table 1]

In Example 1, the coefficient of conditional expression (2):
K is K = 0.82 × 780 × 10 ⁻³ /50=0.01279, which satisfies the expression (2). K · P / in conditional expression (1)
(ρ · cos φ) is K · P / (ρ · cos φ) = 0.01279 × 21.16
7/14 = 0.01934, which satisfies the expression (1). Light emitting unit ch1 in Example 1 (21 μm from the optical axis of the coupling lens 121)
The distance from the spot diameter in the sub-scanning direction of the light spot formed by the light flux from
The fluctuation due to defocus at each image height position obtained by dividing m into 9 parts is shown in FIG. 5A for the main scanning direction and in FIG. 5B for the sub scanning direction. The "depth margin" is 3.10 mm in the main scanning direction and 2.25 mm in the sub-scanning direction, which is much larger than 0.9 mm. "Adjacent scanning" can be performed. Numerical aperture: NAz (source)
Since the value of is as small as 0.01934, the influence of the dispersion of the divergence angle among the light emitting units is effectively avoided. The exposure energy is 4.4 mJ as the substance of the surface to be scanned.
Scanning speed: 3 when using a photoconductive photoconductor of / m ²
Exposure threshold energy is 11.44 at 80.8 m / sec.
Since the output power is mW and the maximum output of the semiconductor laser array used is 15 mW or less, there is no shortage of light amount in multi-beam scanning.

Example 2 The optical arrangement of Example 2 is shown in FIG. Reference numeral 112 is a semiconductor laser array, reference numeral 122 is a coupling lens, reference numeral 132 is an aperture, reference numeral 142 is a cylindrical lens, reference numeral 152 is a rotary polygon mirror, reference numerals 162 and 172 are lenses forming a scanning imaging optical system, and reference numeral 19 is The surface to be scanned is shown. "Semiconductor laser array as light source" Number of light emitting parts: 4 Arrangement pitch of light emitting parts: ρ = 20 µm Emission wavelength: 670 nm Maximum output: 8 mW Tilt angle: φ = 29.45 degrees "Coupling lens" Lens configuration: 1 element per group Configuration Focal length: 30mm Coupling action: Collimating action "Cylindrical lens" Focal length in sub-scanning direction: 51.88mm "Aperture" Aperture width in main scanning direction: 7.9mm Aperture width in sub-scanning direction: 1.2mm "Rotation" Polygonal mirror ”Deflection / reflection surface number: 5 Inscribed circle radius: 18 mm Incidence angle (angle formed by the beam incident direction from the light source side and the optical axis of the scanning imaging optical system): 60 degrees Writing density: 1200 dpi scanning direction of the spot diameter: 30 [mu] m "data of optical elements located between the rotary polygon mirror and the scan surface" surface _{number: i R mi R Si X Y} n deflecting reflection surface ∞ ∞ 72.49 0.206 Lens 162 1 1617.54 -52.00 35.00 0 1.52657 2 -146.53 -195.27 62.91 0.204 Lens 172 3 413.68 -71.31 13.94 0 1.52657 4 824.88 -27.70 160.22 0 Surface numbers 1 to 3 are (10) and (11). ), The surface number 4 is specified by equations (11) to (13). Tables 2 to 6 show the constants of the expressions (10) to (13).

[0025]

[Table 2]

[Table 3]

[0026]

[Table 4]

[Table 5]

[0027]

[Table 6]

In Example 2, the coefficient of conditional expression (2):
K satisfies the equation (2) with K = 0.82 × 670 × 10 ⁻³ /30=0.01831. K · P / (ρ · of conditional expression (1)
cos φ) is K · P / (ρ · cos φ) = 0.01831 × 21.167 / 20 · cos (29.45 degrees) = 0.02225, which satisfies the expression (1). The light emitting unit ch1 in Example 2 (28.4 from the optical axis of the coupling lens 122).
(3 μm apart in the sub-scanning direction), the spot diameter in the sub-scanning direction of the light spot formed by the light beam from “± 15
The fluctuation due to defocus at each image height position obtained by dividing 0 mm into 21 equal parts is shown in FIG. 7A for the main scanning direction and in FIG. 7B for the sub scanning direction. "Depth margin" is 1.57 mm in the main scanning direction and 2.00 m in the sub scanning direction
Since m is much larger than 0.9 mm, "adjacent scanning by multi-beam" can be performed with a stable spot diameter in both main and sub scanning directions. Numerical aperture: NAz (source)
Since the value of is as small as 0.02225, the influence of the dispersion of the divergence angle among the light emitting units is effectively avoided. The exposure energy is 6.3 mJ as a substance of the scanned surface.
Scanning speed: 3 when using a photoconductive photoconductor of / m ²
Exposure threshold energy is 7.22 m at 80.8 m / sec.
The maximum output of the semiconductor laser array used is W:
Since it is 8 mW or less, there is no shortage of light amount in multi-beam scanning.

Example 3 The optical arrangement of Example 3 is shown in FIG. Reference numeral 113 is a semiconductor laser array, reference numeral 123 is a coupling lens, reference numeral 133 is an aperture, reference numeral 143 is a cylindrical lens, reference numeral 153 is a rotary polygon mirror, reference numerals 163, 173.
Reference numeral 182 denotes a lens forming the scanning image forming optical system, and reference numeral 19 denotes a surface to be scanned. "Semiconductor laser array as light source" Number of light emitting parts: 4 Arrangement pitch of light emitting parts: ρ = 14 µm Emission wavelength: 780 nm Maximum output: 10 mW Tilt angle: φ = 0 degree "Coupling lens" Lens configuration: 1 group 1 element focus Distance: 15 mm Coupling function: Collimating function "Cylindrical lens" Focal length in sub-scanning direction: 70.62 mm "Aperture" Aperture width in main scanning direction: 5.5 mm Aperture width in sub-scanning direction: 0.88 mm "Rotating polygon mirror" Number of deflecting / reflecting surfaces: 6 Radius of inscribed circle: 25 mm Incident angle (angle between beam incident direction from light source side and optical axis of scanning imaging optical system): 60 degrees Writing density: 600 dpi Target sub-scanning direction spot diameter: 60 [mu] m "data of optical elements located between the rotary polygon mirror and the scan surface" surface _{number: i R mi R Si X Y} n deflecting reflection surface 0 ∞ 51.38 1.627 Lens 163 1 -96.76 Spherical 15.07 0 1.78571 2 -93.27 Spherical 9.76 0 Lens 173 3 -2450.2 Spherical 19.90 0 1.60909 4 -161.76 Spherical 127.00 0 Lens 182 5 -630.00 -55.53 3.00 0 1.57211 6 -700.00 -24.42 101.72 0 Surface No. 5, that is, the incident side surface of the lens 182 is “a shape in the main scanning cross section is a non-arc shape (represented by formula (10))”. Table 7 shows each coefficient of the above equation (10).

[0030]

[Table 7]

In the third embodiment, the "scan imaging optical system" is the same as that in the first embodiment. In Example 3, the coefficient K of the conditional expression (2) is K = 0.82 × 780 × 10 ⁻³ /60=0.01066, which satisfies the expression (2). K · P / in conditional expression (1)
(ρ · cos φ) is K · P / (ρ · cos φ) = 0.01066 × 42.33
The equation (1) is satisfied with 3/14 = 0.03223. Light emitting unit ch1 in Example 3
(Only 21 μm from the optical axis of the coupling lens 123,
FIG. 9 shows the variation of the spot diameter in the sub-scanning direction of the light spot formed by the light beam from (distance in the sub-scanning direction) due to defocusing at each image height position where ± 150 mm is divided into nine equal parts in the main scanning direction. The sub-scanning direction is shown in (a). “Depth margin” is 8.
10 mm, 4.51 mm in the sub-scanning direction, and 0.
Since it is much larger than 9 mm, the spot diameter is stable in both main and sub-scanning directions, so that "adjacent scanning with multiple beams"
It can be performed. Numerical aperture: The value of NAz (source) is
Since it is as small as 0.03223, the influence of the dispersion of the divergence angle for each light emitting unit is effectively avoided. When a photoconductive photoconductor having an exposure energy of 6.3 mJ / m ² is used as the substance of the surface to be scanned, the scanning speed is 380.8.
The threshold energy of exposure is 7.28 mW at m / sec, and the maximum output of the semiconductor laser array used is 10 m.
Since it is W or less, insufficient light quantity for multi-beam scanning does not occur.

Example 4 The optical arrangement of Example 4 is shown in FIG. Reference numeral 114 is a semiconductor laser array, reference numeral 124 is a coupling lens, reference numeral 134 is an aperture, reference numeral 144 is a cylindrical lens, reference numeral 154 is a rotary polygon mirror, reference numerals 164 and 174.
Is a lens forming the scanning image forming optical system, and reference numeral 19 is a surface to be scanned. "Semiconductor laser array as light source" Number of light emitting parts: 4 Arrangement pitch of light emitting parts: ρ = 14 µm Emission wavelength: 780 nm Maximum output: 10 mW Tilt angle: φ = 62.3 degrees "Coupling lens" Lens configuration: 1 element in 1 group Configuration Focal length: 27mm Coupling action: Collimating action "Cylindrical lens" Focal length in sub-scanning direction: 126.18mm "Aperture" Opening width in main scanning direction: 6.56mm Opening width in sub-scanning direction: 2.3mm "Rotation" Polygonal mirror ”Deflection / reflection surface number: 5 Inscribed circle radius: 18 mm Incidence angle (angle formed by the beam incident direction from the light source side and the optical axis of the scanning imaging optical system): 60 degrees Writing density: 1200 dpi scanning direction of the spot diameter: 45 [mu] m "data of optical elements located between the rotary polygon mirror and the scan surface" surface _{number: i R mi R Si X Y} n deflected counter Surface 0 ∞ ∞ 72.56 0.286 Lens 164 1 1616.43 -50.14 35.00 0 1.52398 2 -146.51 -199.81 61.93 0.254 Lens 174 3 400.87 -72.03 14.00 0 1.52398 4 824.88 -27.59 160.56 0 Surface numbers 1 to 3 have surface shape (10), It is specified by the equation (11), and the surface number 4 is specified by the equations (11) to (13). Tables 8 to 12 show the respective constants of the expressions (10) to (13).

[0033]

[Table 8]

[0034]

[Table 9]

[0035]

[Table 10]

[0036]

[Table 11]

[0037]

[Table 12]

In Example 4, the coefficient of conditional expression (2):
K is K = 0.82 × 780 × 10 ⁻³ /45=0.01421, which satisfies the expression (2). K · P / in conditional expression (1)
(ρ · cos φ) is K · P / (ρ · cos φ) = 0.01421 × 21.16
The equation (1) is satisfied with 7/14 · cos (62.3 degrees) = 0.04622. Light emitting unit ch1 in Example 4
A spot diameter in the sub-scanning direction of a light spot formed by a light beam from (a distance of 18.48 μm from the optical axis of the coupling lens 12 in the sub-scanning direction) is divided into nine equal image height positions. FIG. 11A shows the fluctuation due to defocus in the main scanning direction and FIG. 11B shows the sub-scanning direction. The "depth margin" is 3.04 mm in the main scanning direction and 3.93 mm in the sub scanning direction.
Since it greatly exceeds 0.9 mm, "adjacent scanning by multi-beams" can be performed with a stable spot diameter in both the main and sub scanning directions. Since the value of numerical aperture: NAz (source) is as small as 0.04622, the influence of the dispersion of the divergence angle among the light emitting units is effectively avoided. The exposure energy is 6.3 mJ / m as a substance of the surface to be scanned.
When using the ^second photoconductive photosensitive body, scanning speed: 38
The exposure threshold energy is 7.40 mW at 0.8 m / sec.
And the maximum output of the semiconductor laser array used is: 1
Since it is 0 mW or less, insufficient light quantity for multi-beam scanning does not occur.

Example 5 The optical arrangement of Example 5 is shown in FIG. (A) shows the state in the main scanning direction, and (b) shows the state in the sub-scanning direction. Reference numeral 115 is a semiconductor laser array, reference numeral 125 is a coupling lens, reference numeral 135 is an aperture, reference numeral 145 is a cylindrical lens, reference numeral 155 is a rotary polygon mirror, and reference numerals 165, 175, 185, 18M are lenses forming a scanning and imaging optical system. Reference numeral 19 denotes a surface to be scanned and a cylindrical mirror. That is, in this embodiment, the scanning image forming optical system is composed of three lenses 165, 175, 185 and one cylindrical mirror 18M. "Semiconductor laser array as light source" Number of light emitting parts: 4 Arrangement pitch of light emitting parts: ρ = 10 µm Emission wavelength: 670 nm Maximum output: 8 mW Tilt angle: φ = 0 degree "Coupling lens" Lens configuration: 2 groups, 3 elements focus Distance: 22 mm Coupling function: Collimating function "Cylindrical lens" Lens configuration: Two cemented lenses Focal length in sub-scanning direction: 189.77 mm "Aperture" Aperture width in main scanning direction: 10.5 mm Aperture width in sub-scanning direction 1.96 mm “Rotating polygon mirror” Deflection / reflection surface number: 8 Inscribed circle radius: 65 mm Incident angle (angle formed by the beam incident direction from the light source side and the optical axis of the scanning imaging optical system): 60 degrees Writing density : 850 dpi Target spot diameter in sub-scanning direction: 35 μm “Data of optical element between rotary polygon mirror and scanned surface” Surface number: R _mi R _Si X Y n deflecting reflection surface 0 ∞ ∞ 48.50 0.499 lens 165 1 -78.22 spherical 9.80 0 1.58700 2 -1115.4 spherical 3.95 0 lens 175 3 -318.06 spherical 20.6 0 1.78097 4 -112.85 spherical 2.04 0 lens 185 5 639.11 spherical 23.00 0 1.45419 6 -158.15 Spherical surface 315.00 0 Mirror 18M 7 ∞ -169.87 99.97 0 In Example 5, the coefficient K of the conditional expression (2) is: K = 0.82 × 670 × 10 ⁻³ /35=0.01570 And satisfies the expression (2). K · P / in conditional expression (1)
(ρ · cos φ) is K · P / (ρ · cos φ) = 0.01570 × 29.88
2/10 = 0.04691, which satisfies the expression (1). Light emitting unit ch1 in Example 5 (15 μm from the optical axis of the coupling lens 12)
(± 150 mm of the spot diameter in the sub-scanning direction of the light spot formed by the light beam from
13A for the main scanning direction and FIG. 13B for the sub-scanning direction. The "depth margin" is 2.46 mm in the main scanning direction and 2.58 mm in the sub scanning direction, which is much larger than 0.9 mm. "Adjacent scanning" can be performed. Numerical aperture: NAz (source)
Since the value of is as small as 0.04691, the influence of variations in each divergence of each light emitting unit is effectively avoided. The exposure energy is 5.5 mJ as the substance of the surface to be scanned.
Scanning speed: 3 when using a photoconductive photoconductor of / m ²
Exposure threshold energy is 4.96 m at 80.8 m / sec.
The maximum output of the semiconductor laser array used is W:
Since it is 8 mW or less, there is no shortage of light amount in multi-beam scanning.

Example 6 The optical arrangement of Example 6 is shown in FIG. Reference numeral 116 is a semiconductor laser array, reference numeral 126 is a coupling lens, reference numeral BX is a beam expander, reference numeral 136 is an aperture, reference numeral 146 is a cylindrical lens, reference numeral 156 is a rotary polygon mirror, and reference numerals 166, 176 and 186 are scanning and imaging optics. Reference numeral 19 denotes a surface to be scanned, which is a lens constituting the system. "Semiconductor laser array as a light source" Number of light emitting parts: 4 Array pitch of light emitting parts: ρ = 10 µm Emission wavelength: 780 nm Maximum output: 10 mW Tilt angle: φ = 81.14 degrees "Coupling lens" Lens configuration: 3 elements in 2 groups Configuration Focal length: 35 mm Coupling action: Action to make multiple divergent beams from the semiconductor laser array into divergent beams with weaker divergence "Beam expander" Beam expander function: The beam diameter of the light beam from the coupling lens Enlarge only in the main scanning direction. It does not work in the sub-scanning direction. Magnification: 10x "Cylindrical lens" Focal length in the sub-scanning direction: 149.43 mm "Aperture" Aperture width in the main scanning direction: 2.04 mm Aperture width in the sub-scanning direction: 17.4 mm "Rotating polygonal mirror" Deflection reflection surface Number: 8 Inscribed circle radius: 75 mm Incident angle (angle formed by the beam incident direction from the light source side and the optical axis of the scanning imaging optical system): 50 degrees Writing density: 1200 dpi Spot diameter in the target sub-scanning direction: 35 μm “Data of optical element between rotating polygon mirror and surface to be scanned” Surface number: i R _mi R _Si X Y n Deflection / reflection surface 0 ∞ ∞ 108.00 0.381 Lens 166 1 -126.00 Spherical surface 13.10 0 1.58201 2 ∞ 142.95 10.60 0 Lens 176 3 -2450.0 Spherical Surface 22.50 0 1.49282 4 -150.00 Spherical Surface 5.60 0 Lens 186 5 ∞ ∞ ∞ 27.00 0 1.70400 6 -294.00 -81.10 655.10 0 Corner: φ
= 81.14 degrees, which is close to 90 degrees. That is, the far field pattern of the coupled light beam is close to that shown in FIG. 3D, and the light beam diameter is short in the main scanning direction and long in the sub scanning direction. Since the coupling alone is insufficient to obtain the required spot diameter in the main scanning direction, a beam expander is used to expand the light beam diameter in the main scanning direction. Therefore, the aperture shape of the aperture becomes “a shape elongated in the sub-scanning direction” as shown in FIG.

In Example 6, the coefficient of conditional expression (2):
K is K = 0.82 × 780 × 10 ⁻³ /35=0.01827, which satisfies the expression (2). K · P / in conditional expression (1)
(ρ · cos φ) is K · P / (ρ · cos φ) = 0.01827 × 21.16
7/1 cos (81.14 degrees) = 0.25108, which satisfies the expression (1). Light emitting unit ch1 in Example 6 (12.5 from the optical axis of the coupling lens 12)
The distance from the spot diameter in the sub-scanning direction of the light spot formed by the light beam from
The variation due to defocus at each image height position obtained by dividing 0 mm into 9 parts is shown in FIG. 15A for the main scanning direction and in FIG. 15B for the sub scanning direction. "Depth margin" is 2.22 mm in the main scanning direction and 1.65 m in the sub scanning direction.
m, which is much larger than 0.9 mm, so
"Adjacent scanning by multi-beams" can be performed with a stable spot diameter in both the sub-scanning direction. Numerical aperture: NAz (s
Since the value of ource) is as small as 0.25108, the influence of variations in each divergence of each light emitting unit is effectively avoided.
As the substance of the surface to be scanned, the exposure energy is 4.
When a photoconductive material having a photoconductivity of 4 mJ / m ² is used, the threshold energy for exposure is 9.80 at a scanning speed of 380.8 m / sec.
Since it is 38 mW and the maximum output of the semiconductor laser array used is 10 mW or less, insufficient light quantity for multi-beam scanning does not occur. The scanning and imaging optical systems of Examples 1 to 6 have a function of making the optical scanning uniform.

The multi-beam scanning devices of the first to sixth embodiments described above scan a plurality of beams from the semiconductor laser array (111 etc.) through a common optical system including an optical deflector (151 etc.). In a multi-beam scanning device in which a plurality of light spots separated in the sub-scanning direction are guided to the surface 19 and simultaneously deflected by an optical deflector, the surface to be scanned 19 simultaneously scans a plurality of scanning lines adjacent to each other. The laser array is arranged with the arrangement direction of the light emitting portions with respect to the sub-scanning direction with an inclination angle of φ (90> φ ≧ 0 unit: degree), the scanning line pitch is P, and the arrangement pitch of the light emitting portions in the semiconductor laser array. Is ρ, and K and P and ρ are defined by K = 0.82λ / ωz according to the emission wavelength of the semiconductor laser array: λ and the target spot diameter in the sub-scanning direction: ωz. Conditions: (1) 0.01 <K · P / (ρ · cosφ) <0.30 (2) satisfies 0.011 <K <0.030 (claim 1). Further, a coupling lens (121 or the like) for coupling a plurality of beams from the semiconductor laser array (111 or the like) to a subsequent optical system, and an aperture (131 or the like) for beam shaping the plurality of beams transmitted through the coupling lens, A line image forming optical system (141 etc.) for converging each beam-shaped beam in the sub-scanning direction and forming an image as a long line image in the main scanning direction, and deflection reflection in the vicinity of the image forming position of each line image. Optical deflector having a surface (151
Etc.) and the scanning and imaging optical system (161, 17) for converging each beam deflected by the optical deflector toward the surface to be scanned.
1, 181) and the like (claim 2). The tilt angle of the semiconductor laser array is 0 in Examples 1, 3 and 5, and the tilt angle φ of the semiconductor laser array is φ> 0 in Examples 2, 4, and 6. (Claim 4). In Examples 1 to 5, the coupling action of the coupling lens is a collimating action (claim 5), and in Example 6, the coupling action of the coupling lens causes a plurality of divergent beams from the semiconductor laser array, respectively. This is an action of forming a divergent beam with weak divergence (claim 6). In each of Examples 1 to 6, the optical deflector is a rotating mirror, the scanning imaging optical system has a function of equalizing the speed of scanning by the light spot (claim 7), and the optical deflector is a rotating mirror and the scanning connection is performed. The image optical system is an fθ lens (claim 8). Further, in each of Examples 1 to 6, the line image forming optical system is a cylindrical lens (141 or the like) (claim 9). Further, in the sixth embodiment, the tilt angle φ of the semiconductor laser array 116 is close to 90 degrees, and the optical path between the coupling lens and the optical deflector is
A main-scanning-direction beam expander BX for expanding the light beam diameter in the main-scanning direction is provided (claim 10).

Further, the light source devices in Examples 1 to 6 are
A semiconductor laser array (111 or the like) provided by inclining the arrangement direction of a plurality of light emitting portions arranged in one row at an arrangement pitch: ρ with respect to the sub-scanning direction by an inclination angle: φ (≧ 0), and this semiconductor laser. Coupling lens (121 etc.) that couples multiple beams from the array to the subsequent optical system
And an aperture (131, etc.) for beam-shaping a plurality of beams transmitted through this coupling lens, and the numerical aperture in the sub-scanning direction defined by the aperture: NAz
(source) satisfies the following condition: (3) 0.01 <NAz (source) <0.30 (claim 11). Further, in the light source device according to the first, third, and fifth embodiments, the inclination angle of the semiconductor laser array is φ = 0 (claim 12).
In the light source devices of Nos. 4 and 6, the inclination angle of the semiconductor laser array is φ> 0 (claim 13). In the light source devices of Examples 1 to 5, the coupling action of the coupling lens is a collimating action (claim 14).
In the light source device according to items 4 to 4, the coupling lens is composed of one lens (claim 15). In the light source device of the sixth embodiment, the coupling action of the coupling lens is an action of making each of the plurality of divergent beams from the semiconductor laser array into a divergent beam with weak divergence (claim 16). In the light source devices of Examples 5 and 6, the arrangement pitch of the light emitting portions in the semiconductor laser array:
ρ is 10 μm (claim 17). In addition, Example 2,
In the light source device of No. 5, the emission wavelength: λ in the semiconductor laser array is 700 nm or less (claim 18).
The arrangement pitch of the light emitting portions in the semiconductor laser array is 10
If it is smaller than μm, the modulation of the emission intensity of the adjacent light emitting portions may interfere with each other to cause “crosstalk”. Therefore, the arrangement pitch of 10 μm as in Examples 5 and 6 is equal to the arrangement pitch. It is an example of the lower limit. Then, according to the multi-beam scanning devices of Embodiments 1 to 6, a plurality of beams from the semiconductor laser array (111 or the like) is scanned through the common optical system including the optical deflector (151 or the like) to be scanned surface (19). ), A plurality of light spots separated in the sub-scanning direction are formed, and simultaneously deflected by an optical deflector, whereby a multi-beam scanning method is performed in which the surface to be scanned is simultaneously scanned adjacent to a plurality of scanning lines ( Claim 19).

Finally, FIG. 16 shows one embodiment of the image forming apparatus. This image forming apparatus is a "laser printer". The laser printer 1000 has a “photoconductive photosensitive member formed in a cylindrical shape” as the photosensitive medium 1110. Around the photosensitive medium 1110, a charging roller 1121 as a charging unit, a developing device 1131, a transfer roller 1
141 and a cleaning device 1151 are provided.
A well-known "corona charger" can be used as the charging means. Further, a multi-beam scanning device 1171 by the laser beam LB is provided, and “exposure by multi-beam writing” is performed between the charging roller 1121 and the developing device 1131. In FIG. 16, reference numeral 1161 is a fixing device, reference numeral 1181 is a cassette, reference numeral 1
Reference numeral 191 is a pair of registration rollers, reference numeral 1201 is a paper feed roller,
Reference numeral 1211 is a conveyance path, reference numeral 1221 is a pair of discharge rollers,
Reference numeral 1231 indicates a tray, and reference numeral P indicates a transfer sheet as a recording medium. When forming an image, a photosensitive medium 1110 which is a photoconductive photoconductor is rotated at a constant speed in a clockwise direction, its surface is uniformly charged by a charging roller 1121, and multi-beam scanning of a laser beam LB of an optical scanning device 1171 is performed. An electrostatic latent image is formed by receiving the exposure of writing by. The formed electrostatic latent image is a so-called "negative latent image", and the image portion is exposed. This electrostatic latent image is transferred to the developing device 11
Inverse development is performed by 31, and a toner image is formed on the image carrier 1110. Cassette 118 containing transfer paper P
1 is detachable from the main body of the image forming apparatus 1000, and in the mounted state as shown in FIG.
The uppermost one of the sheets is fed by the feeding roller 1201.
The leading end of the fed transfer paper P is a registration roller pair 119.
Can be changed to 1. The pair of registration rollers 1191 feeds the transfer paper P to the transfer portion at the same timing as the toner image on the image carrier 1110 moves to the transfer position. The transferred transfer paper P is superposed on the toner image at the transfer portion, and the toner image is electrostatically transferred by the action of the transfer roller 1141. Transfer paper P on which the toner image is transferred
Is sent to a fixing device 1161, the toner image is fixed in the fixing device 1161, and the toner image is discharged onto a tray 1231 by a discharge roller pair 1221 through a conveying path 1211. The surface of the image carrier 1110 after the transfer of the toner image is cleaned by the cleaning device 1151 to remove residual toner, paper dust and the like. The above-mentioned OHP sheet may be used instead of the transfer paper, and the transfer of the toner image may be performed via an "intermediate transfer medium" such as an intermediate transfer belt. Optical scanning device 117
As No. 1, good image formation can be performed by using the multi-beam scanning device of the embodiment.

That is, the image forming apparatus shown in FIG. 16 is an image forming apparatus which forms a latent image by performing optical scanning on the photosensitive surface of the photosensitive medium 1110 by the optical scanning device 1171 and visualizes the latent image. Therefore, the multi-beam scanning device according to any one of claims 1 to 10 is used as an optical scanning device that optically scans the photosensitive surface of the photosensitive medium 1110 (claim 20). Is a photoconductive photoreceptor, and an electrostatic latent image formed by uniform charging of the photosensitive surface and optical scanning of an optical scanning device is visualized as a toner image (claim 21).

[0046]

As described above, according to the present invention, a novel multi-beam scanning device, a multi-beam scanning method, a light source device for a multi-beam scanning device, and an image forming apparatus can be realized. Multi-beam scanning device of the present invention
The multi-beam scanning method uses a semiconductor laser array as a light source and secures a sufficiently large depth margin while effectively reducing or preventing the influence of the dispersion of the divergence angle of each light emitting unit, and achieving a stable multi-beam with a stable spot diameter. Beam scanning can be realized. The light source device of the present invention enables the multi-beam scanning device to be realized. Further, the image forming apparatus of the present invention can form an excellent image quality by using the multi-beam scanning apparatus of the present invention.

[Brief description of drawings]

FIG. 1 is a diagram for explaining one embodiment of a multi-beam scanning device of the present invention.

FIG. 2 is a diagram for explaining image formation in an auxiliary scanning direction of an optical system from a light source to a surface to be scanned.

FIG. 3 is a diagram for explaining a relationship between a semiconductor laser array, a far-field pattern of a radiated light beam, and an aperture.

FIG. 4 is a diagram showing an optical arrangement of the multi-beam scanning device of the first embodiment.

FIG. 5 is a diagram showing a depth margin according to the first embodiment.

FIG. 6 is a diagram showing an optical arrangement of a multi-beam scanning device according to a second embodiment.

FIG. 7 is a diagram showing a depth margin according to the second embodiment.

FIG. 8 is a diagram showing an optical arrangement of a multi-beam scanning device according to a third embodiment.

FIG. 9 is a diagram showing a depth margin according to the third embodiment.

FIG. 10 is a diagram showing an optical arrangement of a multi-beam scanning device according to a fourth embodiment.

FIG. 11 is a diagram showing a depth margin according to the fourth embodiment.

FIG. 12 is a diagram showing an optical arrangement of a multi-beam scanning device according to a fifth embodiment.

FIG. 13 is a diagram showing a depth margin according to the fifth embodiment.

FIG. 14 is a diagram showing an optical arrangement of a multi-beam scanning device according to a sixth embodiment.

FIG. 15 is a diagram showing a depth margin according to the sixth embodiment.

FIG. 16 is a diagram showing an embodiment of an image forming apparatus.

[Explanation of symbols] 1 Semiconductor laser array 2 coupling lens 3 Aperture 4 Cylindrical lens 5 rotating polygon mirror 6,7 Scanning imaging optical system 9 Photosensitive medium

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI H04N 1/113 H04N 1/04 104A (72) Inventor Akihisa Itabashi 1-3-6 Nakamagome, Ota-ku, Tokyo In Ricoh (56) Reference JP-A-5-53068 (JP, A) JP-A-6-273688 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) G02B 26/10

Claims (21)

(57) [Claims] 1. A plurality of beams from a semiconductor laser array,
The light is guided to a surface to be scanned through a common optical system including an optical deflector to form a plurality of light spots separated in the sub-scanning direction,
In a multi-beam scanning device in which a plurality of scanning lines on the surface to be scanned are simultaneously and adjacently scanned by simultaneously deflecting the light by the optical deflector, a semiconductor laser array has an arrangement direction of its light emitting portions with respect to a sub-scanning direction. : Φ (90> φ ≧ 0 unit: degree), where P is the scanning line pitch and ρ is the arrangement pitch of the light emitting portions in the semiconductor laser array, the emission wavelength of the semiconductor laser array is λ, and the sub scanning direction is Target spot diameter: K = 0.82 according to ωz
K defined by λ / ωz and the above P and ρ satisfy the following condition: (1) 0.01 <K · P / (ρ · cosφ) <0.30 (2) 0.011 <K <0.030 A multi-beam scanning device characterized in that 2. The multi-beam scanning device according to claim 1, wherein a coupling lens for coupling a plurality of beams from the semiconductor laser array to a subsequent optical system, and an aperture for beam-shaping the plurality of beams transmitted through the coupling lens. Then, each beam shaped beam is focused in the sub-scanning direction,
A line image forming optical system for forming a long line image in the main scanning direction, an optical deflector having a deflection reflection surface near the image forming position of each line image, and each beam deflected by this optical deflector. A multi-beam scanning device, comprising: a scanning image forming optical system for condensing light toward a surface to be scanned. 3. The multi-beam scanning device according to claim 2, wherein the tilt angle of the semiconductor laser array is zero. 4. The multi-beam scanning device according to claim 2, wherein the tilt angle: φ of the semiconductor laser array is φ> 0. 5. The multi-beam scanning device according to claim 2, 3 or 4, wherein the coupling action of the coupling lens is a collimating action. 6. The multi-beam scanning device according to claim 2, 3 or 4, wherein the coupling action of the coupling lens causes each of the plurality of divergent beams from the semiconductor laser array to be a divergent beam with weaker divergence. A multi-beam scanning device characterized in that it is an action. 7. The multi-beam scanning device according to claim 2, 3 or 4, wherein the optical deflector is a rotating mirror, and the scanning imaging optical system has a function of making scanning by a light spot uniform. Characteristic multi-beam scanning device. 8. The multi-beam scanning device according to claim 5, wherein the optical deflector is a rotating mirror and the scanning imaging optical system is an fθ optical system. 9. The multi-beam scanning device according to any one of claims 2 to 8, wherein the line image forming optical system is a cylindrical lens. 10. The multi-beam scanning device according to claim 4, wherein the inclination angle of the semiconductor laser array: φ is close to 90 degrees, and the beam diameter is main-scanned on the optical path between the coupling lens and the optical deflector. A multi-beam scanning device having a main-scanning direction beam expander that expands in a direction. 11. A light source device for use in a multi-beam scanning device according to claim 1, wherein an arrangement direction of a plurality of light emitting portions arranged in one row at an arrangement pitch: ρ is tilted with respect to a sub-scanning direction. : A semiconductor laser array inclined by φ (≧ 0), a coupling lens for coupling a plurality of beams from this semiconductor laser array to a subsequent optical system, and a beam for transmitting the plurality of beams transmitted through the coupling lens. And a numerical aperture in the sub-scanning direction defined by the above-mentioned aperture, NAz (source) satisfies the following condition: (3) 0.01 <NAz (source) <0.30. And a light source device for a multi-beam scanning device. 12. A light source device for a multi-beam scanning device according to claim 11, wherein the tilt angle of the semiconductor laser array is φ = 0. 13. A light source device for a multi-beam scanning device according to claim 11, wherein the tilt angle of the semiconductor laser array is φ> 0. 14. A light source device for a multi-beam scanning device according to claim 11, 12 or 13, wherein the coupling action of the coupling lens is a collimating action. 15. A light source device for a multi-beam scanning device according to claim 14, wherein the coupling lens is composed of one lens. 16. The light source device according to claim 11, 12 or 13, wherein the coupling action of the coupling lens is such that each of the plurality of divergent beams from the semiconductor laser array becomes a divergent beam with weak divergence. A light source device for a multi-beam scanning device, characterized in that 17. A light source device for a multi-beam scanning device according to any one of claims 11 to 16, wherein an arrangement pitch of light emitting portions in the semiconductor laser array: ρ is 10 μm. 18. The light source device according to any one of claims 11 to 17, wherein the emission wavelength in the semiconductor laser array: λ is 700 nm.
A light source device for a multi-beam scanning device, characterized in that: 19. A plurality of beams from a semiconductor laser array are guided to a surface to be scanned through a common optical system including an optical deflector to form a plurality of light spots separated in the sub-scanning direction, and the light deflection is performed. By deflecting simultaneously with the instrument,
A multi-beam scanning method for simultaneously scanning a plurality of scanning lines on the surface to be scanned at the same time, wherein the multi-beam scanning device according to any one of claims 1 to 10 is used. . 20. An image forming apparatus for forming a latent image by performing optical scanning on a photosensitive surface of a photosensitive medium by an optical scanning device and visualizing the latent image to obtain an image. An image forming apparatus using the multi-beam scanning device according to any one of claims 1 to 10 as an optical scanning device for scanning. 21. The image forming apparatus according to claim 20, wherein the photosensitive medium is a photoconductive photosensitive member, and the electrostatic latent image formed by uniform charging of the photosensitive surface and optical scanning of the optical scanning device,
An image forming apparatus which is visualized as a toner image.