JP2001324689A - Multibeam scanning optical system, multibeam scanning device, multibeam scanning method and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize an excellent small-diameter light spot, the high degree of freedom in the layout of optical arrangement and excellent light utilization efficiency required for high speed scanning in multibeam scanning. SOLUTION: This multibeam scanning optical system is provided with a 1st optical system 2 coupling plural beams from a light source side to succeeding optical systems, a 2nd optical system 4 forming the respective beams coupled by the 1st optical system into a line image long in a main scanning direction and separate from each other in a subscanning direction, a light deflector 5 having a deflecting reflection surface near a position where the line image is formed and deflecting the respective beams, and 3rd optical systems 6 and 7 condensing the respective beams deflected by the light deflector 5 onto a surface to be scanned 8 and forming the light spot separated from each other in the subscanning direction on the surface 8. When a pitch in the subscanning direction of a light emitting source in a light source 1 is defined as P1, the pitch of a pixel on the surface 8 is defined as P2 and a skip order is defined as m(>=1), they satisfy a condition: (1) 0.1<P1/(m.P2)<1.0.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a multi-beam scanning optical system, a multi-beam scanning device, a multi-beam scanning method, and an image forming apparatus.

[0002]

2. Description of the Related Art Optical scanning apparatuses are widely known in connection with image forming apparatuses such as digital copying apparatuses and optical printers.
As a method that can speed up the scanning by the optical scanning device, a “multi-beam method” that simultaneously scans a plurality of scanning lines on the surface to be scanned.
Is being realized. For example, using a semiconductor laser array as a light source, beams from each light source are converted into parallel beams by a common coupling lens, and each parallel beam is converged in a sub-scanning direction by a cylindrical lens, and separated from each other in the sub-scanning direction. The image is formed as a long line image in the main scanning direction, deflected by an optical deflector having a deflecting reflection surface at the image forming position of the line image, and each deflected beam is condensed toward a surface to be scanned by an fθ lens. Consider what forms a plurality of light spots separated in the sub-scanning direction on the scanning surface.
Assuming that the pitch of the plurality of light emitting sources is P and the pitch of the light spot on the image plane where the deflected beam forms an image by the fθ lens in the sub-scanning direction is Q, these are the focal length of the coupling lens: f ₁ , the cylindrical Focal length of lens in sub-scanning direction: f ₂ , lateral magnification of fθ lens in sub-scanning direction:
β and the following relationship is satisfied. (4) Q = P (f ₂ / f ₁ ) | β | The pixel pitch on the surface to be scanned (the interval between adjacent scanning lines) is P
_2. Assuming that the interlace order in the multi-beam scanning is m, it is necessary to satisfy Q = mP. In order to realize a desired Q, P, f ₂ , f ₁ , and | β | may be set so as to satisfy the expression (4). Parameters satisfying such conditions: P, f ₂ , Although there are various combinations of f ₁ and | β |, the above parameters are not completely free, and each parameter is regulated.

If the focal length f ₁ is too short, the numerical aperture of the coupling lens becomes large, and it becomes impossible to sufficiently secure the wavefront aberration of the coupling lens. "The luminous flux becomes large, and it becomes difficult to secure the amount of light required for optical scanning.
Further, the focal length: When f ₂ is too short, the layout is difficult cylindrical lens is too close to the optical deflector, and the opening of the aperture of the beam-shaping becomes small, the amount of light is transmitted to the scanned surface side Less. Focal length: When f ₂ is too long, and the optical axis deviation of the coupling lens, susceptible to mounting tolerances of the cylindrical lens, and the like bending of the scanning line is likely to occur. If the lateral magnification: β is too small, the radius of curvature of the fθ lens becomes small, so that wavefront aberration (particularly, tangential coma aberration) tends to occur particularly at the peripheral image height, and it becomes difficult to narrow the spot diameter to a small diameter. In addition, the distance between the fθ lens and the surface to be scanned is reduced, and the restriction on the layout of the optical arrangement is increased. If the lateral magnification: β is too large, “defocusing on the surface to be scanned (defocus)” due to temperature fluctuation and mounting accuracy is likely to occur. In general, since the fθ lens approaches the optical deflector, the beam diameter of the incident beam becomes large, so that it becomes susceptible to wavefront aberration, and it is difficult to reduce the spot diameter to a small value. As described above, in the multi-beam scanning, in order to realize the “desired pitch” of the light spot on the surface to be scanned and to improve the optical performance such as the spot diameter and the layout conditions of the optical system, the parameters of each optical system must be set. Need to optimize.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to realize a small-diameter and good light spot, a large degree of freedom in layout of an optical arrangement, and a good light use efficiency required for high-speed scanning in multi-beam scanning. And

[0005]

A multi-beam scanning optical system according to the present invention has a first optical system, a second optical system, an optical deflector, and a third optical system. The “first optical system” is an optical system that couples a plurality of beams from the light source to the subsequent optical system. The "second optical system" is an optical system that forms each beam coupled by the first optical system into a line image that is long in the main scanning direction and separated from each other in the sub-scanning direction.
The "optical deflector" has a deflecting / reflecting surface near the image forming position of the line image, and deflects each beam. The “third optical system” is an optical system that condenses each beam deflected by the optical deflector toward the surface to be scanned and forms light spots separated from each other in the sub-scanning direction on the surface to be scanned. . The pitch of the light emitting source in the light source in the sub-scanning direction (interval of the arrangement of the light emitting source in the sub-scanning direction) is P ₁ , the pixel pitch on the surface to be scanned (designed interval between adjacent scanning lines) is P ₂ , the jump order M
When (≧ 1), these satisfy the following condition: (1) 0.1 <P ₁ / (m · P ₂ ) <1.0 (claim 1). The first optical system can be configured as a “coupling lens”, and the second optical system can be configured as a “convex cylindrical lens or a concave cylindrical mirror”. The third optical system should be configured as “one or more lenses”, “imaging mirror having one or more imaging functions”, or “combination of one or more lenses and one or more imaging mirrors”. Can be. For example, the pixel pitch is 21.2 μm when the scanning density is 1200 dpi. “P ₁ / (m · P ₂ )” is the upper limit of the equation (1):
If the value is 0 or more, it is necessary to reduce the “lateral magnification in the sub-scanning direction” of the entire optical system between the light source and the surface to be scanned, and therefore, the positive power in the sub-scanning direction must be increased. As a result, deterioration of wavefront aberration is likely to occur.
If the lower limit of the expression (1) is 0.1 or less, the pitch of the light source in the sub-scanning direction in the light source must be reduced. For example, in a semiconductor laser array, when the pitch of the light emitting sources is smaller than a certain level (for example, 10 μm), the light emitting sources are easily affected by thermal crosstalk and electrical crosstalk between adjacent light emitting sources. In the case of a light source device that performs beam combining, it is difficult to adjust the positions of the light emitting sources.

In the multi-beam scanning optical system according to the first aspect, "the lateral magnification in the sub-scanning direction at the center image height: β" of the third optical system is as follows: (2) 0.5 <| β | < It is preferable to satisfy 1.5 (claim 2) .When "β" is equal to or more than the upper limit of the expression (2): 1.5 or more, the defocus of the light spot on the surface to be scanned due to temperature fluctuation and mounting accuracy. Is easy to occur. In addition, since the third optical system generally approaches the optical deflector, the beam diameter of the deflecting beam incident on the third optical system becomes large, the influence of the wavefront aberration becomes easy, and it becomes difficult to reduce the spot diameter to a small diameter. When “β” is equal to or less than the lower limit of the expression (2): 0.5 or less, the radius of curvature of the third optical system becomes small, so that wavefront aberration (particularly, tangential coma aberration) tends to occur particularly at the peripheral image height. It becomes difficult to narrow the spot diameter to a small diameter. Also,
In general, the distance between the third optical system and the surface to be scanned becomes short, which is a great constraint on the layout of the optical arrangement.

In the multi-beam scanning optical system according to claim 1 or 2, the focal length of the first optical system: f ₁ and the focal length of the second optical system in the sub-scanning direction: f ₂ are as follows: 1.5 <it is preferable to satisfy f ₂ / f ₁ <5.0 (claim 3). When the upper limit value of the expression (3) is 5.0 or more, the optical axis shift of the first optical system and the mounting tolerance of the second optical system are easily affected, and the scanning line is easily bent. When the lower limit of the expression (3) is 1.5 or less, the arrangement of the second optical system is easily affected by the interference of the optical deflector, and the layout of the optical system becomes difficult. In addition, the aperture of the aperture for beam shaping is reduced, and the amount of light transmitted to the surface to be scanned is reduced. In the multi-beam scanning optical system according to any one of claims 1 to 3, the jump order: m can be set to 1 (claim 4). In this case, the multi-beam scanning is so-called “adjacent scanning”. In the adjacent scanning, the position at which each beam scans the third optical system is close to each other in the sub-scanning direction and close to the optical axis, so that the pitch deviation between scanning lines between image heights is small, and environmental fluctuations such as temperature fluctuations occur. The fluctuation of the scanning line pitch due to the fluctuation is small. In the multi-beam scanning optical system according to any one of claims 1 to 4, the coupling action of the first optical system may be "a collimating action for converting each of the plurality of beams from the light source into a parallel beam." (Claim 5). The coupling action of the first optical system is not limited to the collimation action, and may be an action of making each beam from the light source side a “weak divergent beam” or an action of making a “weak convergence beam”.
However, if the coupling action of the first optical system is a collimating action as in the case of the fifth aspect, restrictions on the layout of the optical system thereafter are relaxed.

The multi-beam scanning apparatus according to the present invention is arranged such that "a plurality of beams from a light source device are coupled to a subsequent optical system by a first optical system, and each coupled beam is subjected to a main scanning direction by a second optical system. , Each beam is deflected by an optical deflector having a deflecting / reflecting surface in the vicinity of the imaging position of the line image, and each deflected beam is covered by a third optical system. A multi-beam scanning device that collects light toward a scanning surface, forms light spots separated from each other in the sub-scanning direction on the surface to be scanned, and performs multi-beam scanning with a jump order: m (≧ 1) ” A multi-beam scanning optical system according to any one of claims 1 to 5, wherein the multi-beam scanning optical system guides a plurality of beams from the light source device onto a surface to be scanned to form a plurality of light spots. Features to use To (claim 6). Claim 6
In the described multi-beam scanning device, the light source device can be a “semiconductor laser array”, and the first optical system can be “shared for a plurality of beams from the semiconductor laser array”. In this case, the coupling action of the first optical system can be a “collimating action” (claim 8). In the multi-beam scanning device according to claim 6, 7, or 8, the second optical system may be a "cylindrical lens" (claim 9).

The multi-beam scanning method according to the present invention provides a method of “coupling a plurality of beams from a light source device to a subsequent optical system by a first optical system, and coupling each of the coupled beams by a second optical system in a main scanning direction. , Each beam is deflected by an optical deflector having a deflecting / reflecting surface in the vicinity of the imaging position of the line image, and each deflected beam is covered by a third optical system. A multi-beam scanning method for converging light toward a scanning surface, forming light spots separated from each other in the sub-scanning direction on the surface to be scanned, and performing multi-beam scanning with a jump order: m (≧ 1) ”. The method is performed using the multi-beam scanning device according to any one of claims 6 to 9 (claim 10). 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”. A multi-beam scanning device according to any one of claims 6 to 9 is used as an optical scanning device for optically scanning a surface (claim 11). 12. The image forming apparatus according to claim 11, wherein the photosensitive medium is a photoconductive photoreceptor, and an electrostatic latent image formed by uniform charging of a photosensitive surface and optical scanning by an optical scanning device is visualized as a "toner image". Can be configured to
(Claim 12). 12. The image forming apparatus according to claim 11, wherein the toner image is fixed on a sheet-shaped recording medium (transfer paper or "OHP sheet (plastic sheet for overhead projector)"). In this case, the latent image formed by the optical scanning by the optical scanning device can be visualized by a developing method of a normal silver halide photographic process. Such an image forming device is, for example, an “optical plate making device” or The image forming apparatus according to the twelfth aspect can be embodied as a laser printer, a laser plotter, a digital copying apparatus, a facsimile machine, or the like.

[0010]

FIG. 1 shows an embodiment of a multi-beam scanning apparatus according to the present invention. The light source 1 is a semiconductor laser array in which four light emitting sources are arranged in a line at equal intervals. In this embodiment, the four light emitting sources are arranged in the sub-scanning direction (a direction orthogonal to the drawing). However, the semiconductor laser array 1 is inclined so that the arrangement direction of the light emitting sources is inclined with respect to the main scanning direction. You may. The four beams emitted from the four light sources (the light sources are arranged in a direction perpendicular to the drawing, so that the four beams overlap each other) are mainly in the major axis direction of the elliptical far-field pattern. Coupling lens 2 which is a divergent light beam directed in the scanning direction, but is a "first optical system" common to four beams.
Is coupled to the subsequent optical system. The form of each coupled beam can be a weakly divergent light beam, a weakly convergent light beam, or a parallel light beam, depending on the optical characteristics of the optical system thereafter. The four beams transmitted through the coupling lens 2 are “beam-shaped” by the aperture 3, and are respectively focused in the sub-scanning direction by the operation of the cylindrical lens 4 as the “second optical system”.
In the vicinity of the deflecting and reflecting surface of the polygon mirror 5, which is an "optical deflector", each image is separated from each other in the sub-scanning direction as linear images in the main scanning direction. The four beams deflected at a constant angular velocity by the deflecting reflection surface pass through the two lenses 6 and 7 forming the “third optical system” and are placed on the surface 8 to be scanned (substantially, the photosensitive surface of the photosensitive medium). Are focused as four light spots separated in the sub-scanning direction, and four scanning lines on the surface 8 to be scanned are simultaneously scanned. One of the beams is detected by a "not shown detector" prior to optical scanning, and the writing start timing of the four beams is determined based on the detection result. The “third optical system” is an optical system that condenses four beams simultaneously deflected by the optical deflector 5 as four light spots on the surface 8 to be scanned, and includes two lenses 6 and 7. Is done.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Two specific embodiments of the optical arrangement shown in FIG. 1 will be described below. "Expression formula for specifying lens surface shape of third optical system" in each of the following embodiments.
Will be described. However, the contents of the present invention are not limited to the following expressions. In expressing the lens surface, the coordinates in the main scanning direction near the lens surface are Y, the coordinates in the sub-scanning direction are Z, and the X direction passing through the origin is taken as the optical axis. The general formula of the lens surface is f (Y, Z) = fm (Y) + fs (Y, Z) (5). Here, fm (Y) of the first term on the right side represents “the shape in the main scanning cross section (XY plane)”, and fs (Y, Z) of the second term represents the position at the position of the coordinate: Y in the main scanning direction. "Shape in sub-scan section (plane parallel to XZ plane)" is shown. In the following, as the shape in the main scanning section: fm (Y), a well-known non-arc-shaped equation, that is, the paraxial radius of curvature in the main scanning section in the optical axis: Rm, the main scanning direction from the optical axis in the main scanning direction Distance: Y, cone constant: Km, higher order coefficients: Am1, Am2, Am3, Am4, Am
5, Am6,..., And the depth in the optical axis direction: X is expressed by the following polynomial. ^{fm (Y) = (Y 2} / Rm) / [1 + √ {1- (1 + K) (Y / Rm) 2}] + + Am1 · Y + Am2 · Y 2 + Am3 · Y 3 + Am4 · Y ⁴ + Am ⁵ · Y ⁵ + Am ⁶ · Y ⁶ + (6) In the equation (6), when any of the odd-order coefficients: Am 1, Am 3, Am 5... Is not 0, the non-arc shape is “main scanning direction”. Asymmetrical shape ". In the first and second embodiments, only the even-numbered orders are used, and are symmetric in the main scanning direction. The fs (Y, Z) is represented as follows. fs (Y, Z) = ( Y 2 · Cs) / [1 + √ {1- (1 + Ks) (Y · Cs) 2} + + (F0 + F1 · Y + F2 · Y 2 + F3 · Y ^{3 + F4 · Y 4 + ··} ) · Z + (G0 + G1 · Y + G2 · Y 2 + G3 · Y 3 + G4 · Y 4 + ··) · Z 2 + (H0 + H1 · Y + H2 ^{· Y 2 + H3 · Y 3} + H4 · Y 4 + ··) · Z 3 + (I0 + I1 · Y + I2 · Y 2 + I3 · Y 3 + I4 · Y 4 + ··) · Z 4 + (J0 + J1 · Y + J2 · Y 2 + J3 · Y 3 + J4 · Y 4 + ··) · Z 5 + ··· (7) here, Cs = (1 / Rs0) + B1 · Y + ^{B2 · Y 2 + B3 · Y} 3 + B4 · Y 4 + B5 · Y 5 + ·· (8) Ks = Ks0 + C1 · Y + C2 · Y 2 + C3 · Y 3 + C4 · Y 4 + C5 · Y ⁵ + · · · · a (9), "Rs0" is a paraxial radius of curvature in the sub-scanning cross-section including the optical axis. Odd coefficient of Y: B1, B3, B5
When either of them is other than 0, the curvature in the sub-scan section becomes asymmetric in the main scanning direction. Similarly, coefficients: C1, C3, C
5, ..., F1, F3, F5 ..., G1, G3, G5 ...
When any of the "odd power coefficients of Y" representing the non-arc amount is other than 0, the non-arc amount in the sub-scanning direction becomes asymmetric in the main scanning direction. Example 1 A light source 1 is a semiconductor laser array and has an emission wavelength of 780 nm.
The number of light emitting sources: 4, and the pitch of the light emitting sources: P ₁ = 15 μm. Coupling lens 2 has a focal length of 29.233 m
m indicates a coupling action: a collimating action, and each beam emitted from the coupling lens becomes a parallel beam. The opening width of the aperture 3 is 9.0 m in the main scanning direction.
m, sub-scanning direction: 1.6 mm. The cylindrical lens 4 has a focal length of 58.687 mm. The rotating polygon mirror 5 has 5 deflection reflection surfaces and an inscribed circle radius of 20 m.
m, the rotation center and the deflection starting point (the position of the intersection between the principal ray and the deflecting reflection surface when the principal ray of the deflected light beam is parallel to the optical axes of the lenses 6 and 7) are: Distance in the direction: J = 18.475 mm, distance in the main scanning direction:
h = 8.0 mm apart. In the "state in which the principal ray of the deflected light beam is parallel to the optical axis of the lenses 6 and 7", the angle between the principal ray and the "principal ray of the light beam incident on the deflective reflection surface from the light source side"("to the rotating polygon mirror"). Angle of incidence) is 60 degrees. The angle of view is -38 degrees to +38 degrees.

The jump order of multi-beam scanning: m = 1
Is "adjacent scan". Pixel pitch: P ₂ = 21.2 μm Lateral magnification of the third optical system in the sub-scanning direction: β = −0.704 Paraxial radius of curvature of the third optical system: Rm, Rs0, surface interval on the optical axis: x The data for the refractive index n of the lens material are shown below. Surface number Rm Rs0 xn Deflection reflective surface 0 ∞ ∞ 72.560 1 Lens L1 1 1616.426 -50.145 35.0 1.52398 2 -146.513 -199.813 61.933 1 Lens L2 3 400.875 -72.026 14.0 1.52398 4 824.882 -27.588 160.556 1 Is a special toroidal surface whose curvature is asymmetric in the main scanning direction, and the second and third surfaces are "special toroidal surfaces", and the fourth surface has a non-arc shape in the sub-scanning cross section. A special toroidal surface that changes asymmetrically in the main scanning direction. The “special toroidal surface” is a toroidal surface in which the curvature in the sub-scan section changes in the main scanning direction.

The values of the above-mentioned coefficients for specifying the lens surface shape for the above-mentioned first to fourth surfaces are shown below. In the following notation, for example, "E + 2" means "10 squared",
For example, “E-13” represents “10 to the −13 power”. 1 surface (incident surface of the deflector side lens) Rm = 1616.426, K = 1.9758E + 2, Am4 = 1.2807E-8, Am6 = -6.3739E
-13, Am8 = -9.4279E-17, Am10 = 5.9653E-21 Rso = -50.145, B1 = -1.1619E-5, B2 = 2.2760E-6, B3 = 2.7143E-
9, B4 = -1.5441E-10, B5 = -4.2654E-13, B6 = 6.4174E-15, B7 =
9.1795E-19, B8 = -1.2300E-19, B9 = 1.4532E-20, B10 = -1.881
4E-22, B11 = -1.4681E-24, B12 = -2.6702E-26 2 surfaces (exit surface of deflector side lens) Rm = -146.513, K = -1.8570E-1, Am4 = 1.7743E-8, Am6 = 1.3838E
-13, Am8 = -4.3545E-17, Am10 = 7.1684E-21 Rso = -199.813, B2 = -2.1247E-6, B4 = 1.8045E-11, B6 = 2.7156
E-14, B8 = 6.9237E-19, B10 = -2.6853E-22, B12 = -5.7783E-26 3 surfaces (incident surface of the lens to be scanned) Rm = 400.875, K = -1.2603E + 1, Am4 = -7.3492E-9, Am6 = -2.1056
E-13, Am8 = 8.1727E-18, Am10 = 5.4093E-22, Am12 = -1.0819E-
26, Am14 = -2.0391E-32 Rso = -72.026, B2 = -1.9618E-7, B4 = 2.2296E-11, B6 = -1.0216
E-15, B8 = 1.0811E-20, B10 = 6.3632E-25, B12 = -3.6449E-29 4 surfaces (exit surface of lens to be scanned) Rm = 824.882, K = -7.107E + 1, Am4 = -1.3238E-8, Am6 = 9.6624E-
14, Am8 = 1.8875E-17, Am10 = -3.1016E-22, Am12 = 7.2979E-2
7, Am14 = 2.3052E-32 Rso = -27.588, B1 = -8.5460E-7, B2 = 4.1615E-7, B3 = -2.5226E
-11, B4 = -2.9599E-11, B5 = 2.1135E-16, B6 = 1.1604E-15, B7 =
4.3715E-22, B8 = -1.0981E-21, B9 = 5.5597E-24, B10 = -7.784
6E-25, B11 = -1.6169E-29, B12 = 3.2622E-30 Ks0 = -3.9399E-1, C1 = 1.7960E-4, C2 = 2.4246E-6, C3 = 4.4377
E-8, C4 = 4.5838E-10, C5 = -2.4380E-12, C6 = -3.3957E-14, C7
= 4.1317E-17, C8 = 6.8052E-19 I0 = 2.8688E-6, I1 = 4.0115E-11, I2 = 1.6903E-11, I3 = 3.5723
E-14, I4 = -8.7422E-15, I5 = 1.9643E-18, I6 = 8.6034E-19, I7
= 6.1604E-23, I8 = -3.3469E-23, I9 = -3.6931E-28, I10 = 4.53
55E-28 K0 = -1.5263E-9, K1 = -3.1009E-11, K2 = -8.9028E-12, K3 = 5.0
172E-14, K4 = 3.2408E-15, K5 = -7.7026E-18, K6 = -4.1043E-1
9, K7 = 5.1175E-22, K8 = 2.3678E-23, K9 = -1.5500E-26, K10 =-
6.3709E-28, K11 = 1.7480E-31, K12 = 6.5028E-33
.

[0014] Condition (1) _{Parameters: P 1 / (m · P} 2) of the values: P ₁ / a _{(m · P 2) = 15} / (21.2 × 1) = 0.71 Condition (2) magnification: | β | = 0.704 parameter condition _{(3): f 2 / f} 1 values: the _{f 2 / f 1 = 58.687 /} 29.233 = 2.0 Figure 2, the image for example 1 Surface curvature (solid line is the sub-scanning direction, broken line is the main scanning direction) and uniform velocity (solid line is linearity, broken line is fθ characteristic). As is clear from the figure, the first embodiment has extremely good curvature of field and uniform speed. FIG. 4 shows that in the first embodiment, the depth margin of the semiconductor laser array with respect to the beam from the light emitting source 22.5 μm (outside) from the optical axis of the coupling lens is determined in the main scanning direction (a) and the sub-scanning direction ( b). The horizontal axis in the figure represents the defocus amount of the light spot with respect to the scanned surface (the difference between the beam waist position and the scanned surface), and the vertical axis represents the spot diameter. Both the main and sub scanning directions have a sufficiently large depth margin.

Embodiment 2 The light source 1 is a semiconductor laser array having an emission wavelength of 655 n.
m, the number of light-emitting sources: 4, and these four light-emitting sources are arranged in the sub-scanning direction. Light emitting source pitch: P ₁ = 30 μm. The coupling lens 2 has a focal length of 27.000.
In mm, the coupling action is a collimating action, and the light beam emitted from the coupling lens becomes a parallel light beam.
The aperture width of the aperture 3 is 7.84 m in the main scanning direction.
m, sub-scanning direction: 2.76 mm. The cylindrical lens 4 has a focal length of 85.400 mm.
For the rotating multi-surface 5, the number of deflecting / reflecting surfaces: 5, the inscribed circle radius: 18
mm, and the rotation center and the deflection starting point are arranged at a distance of J = 16.628 mm in the optical axis direction and at a distance of h = 7.2 mm in the main scanning direction. The angle of incidence on the rotating polygon mirror is 60 degrees, and the angle of view is -38 degrees to +38 degrees. "5th-order interlaced scanning" with the interlaced order of multi-beam scanning: m = 5. Pixel pitch: P ₂ = 21.2 μm Lateral magnification in the sub-scanning direction of the third optical system: β = −1.117 Paraxial radius of curvature relating to the third optical system: Rm, Rs0, surface interval on the optical axis: x, The data for the refractive index of the lens material: n are listed below. Surface number Rm Rs0 xn Deflection reflection surface 0 ∞ ∞ 72.492 1 Lens L1 1 1617.537 -259.916 35.0 1.52718 2 -146.526 -80.074 62.911 1 Lens L2 3 413.676 -59.597 13.940 1.52718 4 824.882 -30.107 159.706 1 1 and 2 The surface is a “special toroidal surface in which the curvature in the sub-scanning section changes asymmetrically in the main scanning direction”.
The surface is a “special toroidal surface in which the shape in the sub-scanning cross section is a non-arc shape, and the non-arc shape changes asymmetrically in the main scanning direction”. The values of the above-described coefficients for specifying the lens surface shapes for the above-described first to fourth surfaces are shown below. One surface (incident surface of the deflector side lens) Rm = 1617.537, K = 1.8499E + 2, Am4 = 1.2841E-8, Am6 = -6.0170E
-13, Am8 = -8.0398E-17, Am10 = 5.1378E-21 Rso = -295.916, B1 = 0, B2 = 7.4192E-7, B3 = 0, B4 = -9.0134E-1
1, B5 = 0, B6 = 7.4572E-15, B7 = 0, B8 = 5.0851E-19, B9 = 0, B10 =
4.3322E-22, B11 = 0, B12 = -4.6324E-26 2 surfaces (exit surface of deflector side lens) Rm = -146.526, K = -1.9337E-1, Am4 = 1.7905E-8, Am6 = 2.8474 E
-13, Am8 = -3.7228E-17, Am10 = 5.9304E-21 Rso = -80.074, B1 = 3.8163E-6, B2 = -8.9442E-7, B3 = -7.1778E
-10, B4 = 1.0620E-10, B5 = 8.0561E-14, B6 = -9.5854E-15, B7 =
-1.2058E-17, B8 = -2.9218E-19, B9 = 8.5505E-22, B10 = 3.400
8E-22, B11 = 2.2597E-26, B12 = 1.0818E-27 3 surfaces (incident surface of lens to be scanned) Rm = 413.676, K = -1.3947E + 1, Am4 = -6.7899E-9, Am6 = -2.0465
E-13, Am8 = 7.4657E-18, Am10 = 5.2824E-22, Am12 = -8.1428E-
27, Am14 = -3.7707E-33 Rso = -59.597, B1 = 2.8847E-6, B2 = -1.1609E-7, B3 = -1.9647E
-10, B4 = 1.4403E-11, B5 = 1.1509E-14, B6 = -8.9639E-16, B7 =
-4.6935E-19, B8 = 1.1227E-20, B9 = 1.3265E-23, B10 = 1.3121
E-24, B11 = -2.2260E-28, B12 = -7.3153E-29 4 surfaces (exit surface of the lens to be scanned) Rm = 824.882, K = -6.9066E + 1, Am4 = -1.3483E-8 , Am6 = 8.9530E
-14, Am8 = 1.9362E-17, Am10 = -2.8403E-22, Am12 = 6.0443E-2
7, Am14 = 1.0767E-31 Rso = -30.107, B1 = 2.5964E-7, B3 = -2.2608E-11, B5 = 1.0492E
-15, B7 = -9.2108E-22, B9 = -1.4922E-24, B11 = 2.0387E-29 Ks0 = -3.7766E-1, C1 = 5.1394E-6, C2 = -4.7466E-5, C3 = -5.54
10E-8, C4 = 3.5948E-8, C5 = 4.3084E-11, C6 = -6.0684E-12, C7
= -5.7729E-15, C8 = 2.3739E-16, C9 = 1.6716E-19, C10 = 1.778
0E-20, C11 = 3.3715E-24, C12 = -1.0989E-24 I0 = 2.1618E-6, I1 = 3.6416E-10, I2 = 9.3075E-10, I3 = -3.167
2E-13, I4 = -4.6925E-13, I5 = 3.6532E-17, I6 = 1.0567E-16, I
7 = 3.2030E-21, I8 = -1.1714E-20, I9 = -6.3093E-25, I10 = 6.3
027E-25, I11 = 2.3556E-29, I12 = -1.3187E-29 K0 = 9.1006E-9, K1 = -1.3347E-11, K2 = -4.8215E-11, K3 = 3.55
35E-15, K4 = 2.5809E-14, K5 = 6.1734E-18, K6 = -5.5228E-18,
K7 = -1.2408E-21, K8 = 5.4705E-22, K9 = 6.8910E-26, K10 = -2.
4762E-26, K11 = -9.0920E-31, K12 = 4.0593E-31
.

[0016] Condition (1) _{Parameters: P 1 / (m · P} 2) of the _{values: P 1 / (m · P} 2) = 30 / (21.2 × 5) = 0.28
Magnification of three conditions (2): | β | = 1.117 parameter condition _{(3): f 2 / f} 1 values: the _{f 2 / f 1 = 85.4 /} 27.00 = 3.16 Figure 3 FIG. 2 shows the curvature of field and the constant velocity in Example 2. As is clear from FIG. 3, the second embodiment has extremely good field curvature and constant speed. In FIG. 5, in the second embodiment, the depth margin of the semiconductor laser array with respect to the beam from the light emitting source 45 μm away (outside) from the optical axis of the coupling lens is determined by the main scanning direction (a) and the sub-scanning direction (b). Is shown in FIG. Also in the second embodiment, the depth margin is sufficiently large. FIG. 6 shows a state of adjacent scanning in the first embodiment, and FIG. 7 shows a state of “fifth interlaced scanning” in the second embodiment. B1 to B4 indicate light spots. In FIG. 7, broken lines indicate scanning lines that are not optically scanned. Finally, FIG. 8 shows an embodiment of the image forming apparatus. This image forming apparatus is a “laser printer”. The laser printer 100 has a “photoconductive photosensitive member formed in a cylindrical shape” as the photosensitive medium 111. Around the photosensitive medium 111, a charging roller 11 as a charging unit is provided.
2. A developing device 113, a transfer roller 114, and a cleaning device 115 are provided. A well-known "corona charger" can be used as the charging means. Further, a multi-beam scanning device 117 using a laser beam LB is provided, and “exposure by multi-beam scanning” is performed between the charging roller 112 and the developing device 113.
8, reference numeral 116 denotes a fixing device, reference numeral 118 denotes a cassette, reference numeral 119 denotes a pair of registration rollers, reference numeral 120 denotes a paper feed roller, reference numeral 121 denotes a conveyance path, reference numeral 122 denotes a pair of paper discharge rollers, reference numeral 123 denotes a tray, and reference numeral P Denotes transfer paper as a recording medium. When performing image formation, the photosensitive medium 111, which is a photoconductive photoconductor, is rotated clockwise at a constant speed, and the surface thereof is uniformly charged by the charging roller 112.
An electrostatic latent image is formed by receiving writing exposure by scanning of the multi-beam LB of the multi-beam scanning device 117. The formed electrostatic latent image is a so-called “negative latent image”, and the image portion is exposed. This electrostatic latent image is reversely developed by the developing device 113, and a toner image is formed on the image carrier 111. The cassette 118 storing the transfer paper P is detachable from the main body of the image forming apparatus 100. When the cassette 118 is mounted as shown in FIG. Is done. The fed transfer paper P has its leading end held by a pair of registration rollers 119. The registration roller pair 119 sends the transfer paper P to the transfer section in time with the movement of the toner image on the image carrier 111 to the transfer position. The transferred transfer paper P is superimposed on the toner image at the transfer section, and the toner image is electrostatically transferred by the operation of the transfer roller 114. The transfer paper P to which the toner image has been transferred is sent to the fixing device 116, where the toner image is fixed.
23. The surface of the image carrier 111 after the transfer of the toner image is cleaned by the cleaning device 115 to remove residual toner, paper dust, and the like. The above-described OHP sheet or the like can be used instead of the transfer paper, and the transfer of the toner image can be performed via an “intermediate transfer medium” such as an intermediate transfer belt. By using the multi-beam scanning device of the embodiment as the optical scanning device 117, good image formation can be performed.

The multi-beam scanning optical system according to the embodiment shown in FIG.
As a multi-beam scanning optical system, a first optical system 2 for coupling a plurality of beams from a light source side to an optical system thereafter.
And a second optical system 4 for forming each beam coupled by the first optical system into a line image that is long in the main scanning direction and separated from each other in the sub-scanning direction. Optical deflector 5 having a deflecting / reflecting surface and deflecting each beam
And third optical systems 6 and 7 for condensing each beam deflected by the optical deflector toward the surface 8 to be scanned and forming light spots separated from each other in the sub-scanning direction on the surface to be scanned. When the pitch of the light emitting source in the light source 1 in the sub-scanning direction is P ₁ , the pixel pitch on the surface to be scanned is P ₂ , and the jump order is m (≧ 1), these conditions are: (1) 0 .1 <P ₁ / (m · P ₂ ) <1.0 (claim 1). In addition, the third optical systems 6 and 7
The lateral magnification in the sub-scanning direction at the center image height: β satisfies the condition: (2) 0.5 <| β | <1.5 (claim 2), and the focal length of the first optical system 2:
f ₁ , the focal length of the second optical system in the sub-scanning direction: f ₂ satisfies the condition: (3) 1.5 <f ₂ / f ₁ <5.0 (claim 3). In the multi-beam scanning device of the first embodiment, the jump order: m is 1 (Claim 4).
The coupling action of the optical system 2 is a collimation action for converting a plurality of beams from the light source side into parallel beams (claim 5).

In the above-described embodiment, the multi-beam scanning device uses a plurality of beams from the light source device 1 as the first beam.
The optical system 2 couples the beams to the subsequent optical systems. The second optical system 4 forms the coupled beams into line images that are long in the main scanning direction and separated from each other in the sub-scanning direction. Each beam is deflected by an optical deflector 5 having a deflecting / reflecting surface in the vicinity of the image forming position, and each of the deflected beams is condensed by a third optical system 6 and 7 toward a surface 8 to be scanned. A multi-beam scanning apparatus that forms light spots separated from each other in the sub-scanning direction and performs multi-beam scanning with a jump order: m (≧ 1), wherein a plurality of beams from the light source device 1 are scanned on the surface 8 to be scanned. As a multi-beam scanning optical system for guiding light to form a plurality of light spots.
A multi-beam scanning optical system according to any one of the fifth to fifth aspects is used (claim 6). The light source device 1 is a semiconductor laser array, and the first optical system 2 is
Common to a plurality of beams from the semiconductor laser array 1 (Claim 7), the coupling action of the first optical system 2 is a collimating action (Claim 8), and the second optical system 4 is a cylindrical lens (Claim 8). Item 9). According to the above embodiment, the plurality of beams from the light source device 1 are coupled to the subsequent optical systems by the first optical system 2, and the coupled beams are transmitted by the second optical system 4 in the main scanning direction. Long, form a line image separated from each other in the sub-scanning direction,
Each beam is deflected by an optical deflector 5 having a deflecting / reflecting surface in the vicinity of the image forming position of the line image, and the respective deflected beams are condensed by a third optical system 6 and 7 toward a surface 8 to be scanned. Form light spots separated from each other in the sub-scanning direction on the surface,
A multi-beam scanning method for performing multi-beam scanning with a jump order: m (≧ 1) is performed using the multi-beam scanning device according to any one of claims 6 to 9 (claim 1).
0).

The image forming apparatus 100 of the embodiment shown in FIG. 8 forms a latent image by performing optical scanning on a photosensitive surface of a photosensitive medium 111 by an optical scanning device, and visualizes the latent image to obtain an image. An image forming apparatus using the multi-beam scanning device according to any one of claims 6 to 9 as an optical scanning device for optically scanning a photosensitive surface of a photosensitive medium 111 (claim 11). ), The photosensitive medium 111 is a photoconductive photosensitive member, and an electrostatic latent image formed by uniform charging of the photosensitive surface and optical scanning by the optical scanning device is visualized as a toner image.

[0020]

As described above, according to the present invention, a novel multi-beam scanning optical system, a multi-beam scanning apparatus, a multi-beam scanning method, and an image forming apparatus can be realized. According to the multi-beam scanning optical system, the multi-beam scanning device, and the multi-beam scanning method of the present invention, a small-diameter and good light spot, a large degree of freedom in layout of an optical arrangement, and a good light use efficiency required for high-speed scanning. Can be realized. The image forming apparatus of the present invention can form a good image by using the multi-beam scanning device.

[Brief description of the drawings]

FIG. 1 is a diagram showing one embodiment of a multi-beam scanning device according to the present invention.

FIG. 2 is a diagram illustrating field curvature and constant velocity characteristics according to a first embodiment.

FIG. 3 is a diagram illustrating field curvature and constant velocity characteristics according to a second embodiment.

FIG. 4 is a diagram illustrating a depth margin relating to the first embodiment.

FIG. 5 is a diagram illustrating a depth margin according to a second embodiment.

FIG. 6 is a diagram schematically illustrating a writing state by adjacent scanning according to the first embodiment.

FIG. 7 is a diagram schematically illustrating a writing state by fifth-order interlaced scanning according to the second embodiment.

FIG. 8 is a diagram illustrating an embodiment of an image forming apparatus.

[Explanation of symbols]

 Reference Signs List 1 light source (semiconductor laser array) 2 first optical system (coupling lens) 3 aperture 4 second optical system (cylindrical lens) 5 optical deflector (rotating polygon mirror) 6, 7 third optical system 8 surface to be scanned

Continued on the front page (72) Inventor Koji Sakai 1-3-6 Nakamagome, Ota-ku, Tokyo, Ricoh Co., Ltd. (72) Inventor Shinkane 1-3-6 Nakamagome, Ota-ku, Tokyo, Equity F-term in Ricoh Company (reference) 2C362 AA13 AA36 AA40 BA58 BA60 BA61 BA86 2H045 AA01 BA22 BA33 CA04 CA68 2H087 KA08 LA22 PA02 PB02 QA03 QA06 QA12 QA21 QA33 QA41 RA07 RA13

Claims (12)

[Claims] 1. A first optical system for coupling a plurality of beams from a light source side to an optical system thereafter, and each beam coupled by the first optical system is
A second optical system that is long in the main scanning direction and forms a line image separated from each other in the sub-scanning direction; and an optical deflector that has a deflecting / reflecting surface near the image forming position of the line image and deflects each beam. A third optical system that condenses each beam deflected by the optical deflector toward the surface to be scanned and forms, on the surface to be scanned, light spots separated from each other in the sub-scanning direction; P ₁ in the sub-scanning direction pitch of the light-emitting sources in the light source, P ₂ a pixel pitch on the surface to be scanned, the jump order m
When (≧ 1), these conditions satisfy the following condition: (1) 0.1 <P ₁ / (m · P ₂ ) <1.0. 2. The multi-beam scanning optical system according to claim 1, wherein the lateral magnification of the third optical system in the sub-scanning direction at the center image height is β.
Satisfies the following condition: (2) 0.5 <| β | <1.5. 3. The multi-beam scanning optical system according to claim 1, wherein the focal length of the first optical system: f ₁ and the focal length of the second optical system in the sub-scanning direction: f ₂ are: A multi-beam scanning optical system, wherein 1.5 <f ₂ / f ₁ <5.0 is satisfied. 4. The multi-beam scanning optical system according to claim 1, wherein the jump order: m is 1. 5. The multi-beam scanning optical system according to claim 1, wherein the coupling action of the first optical system is a collimating action for converting a plurality of beams from the light source side into parallel beams. A multi-beam scanning optical system, comprising: 6. A plurality of beams from a light source device are coupled to a subsequent optical system by a first optical system, and each coupled beam is elongated in a main scanning direction by a second optical system.
An image is formed on line images separated from each other in the sub-scanning direction, and each beam is deflected by an optical deflector having a deflecting / reflecting surface in the vicinity of the image forming position of the line image.
A multi-beam scanning apparatus that condenses light toward a surface to be scanned, forms light spots separated from each other in the sub-scanning direction on the surface to be scanned, and performs multi-beam scanning with a jump order: m (≧ 1). The multi-beam scanning optical system according to any one of claims 1 to 5, as a multi-beam scanning optical system that guides a plurality of beams from a light source device onto a surface to be scanned to form a plurality of light spots. A multi-beam scanning device characterized by using: 7. The multi-beam scanning device according to claim 6, wherein the light source device is a semiconductor laser array, and the first optical system is:
A multi-beam scanning device, which is common to a plurality of beams from the semiconductor laser array. 8. The multi-beam scanning device according to claim 7, wherein the coupling action of the first optical system is a collimation action. 9. The multi-beam scanning device according to claim 6, wherein the second optical system is a cylindrical lens. 10. A plurality of beams from a light source device are coupled to a subsequent optical system by a first optical system, and each coupled beam is elongated by a second optical system in a main scanning direction and is extended in a sub-scanning direction. An image is formed on a line image separated from each other, each beam is deflected by an optical deflector having a deflecting / reflection surface near the image forming position of the line image, and each deflected beam is directed toward a surface to be scanned by a third optical system. A multi-beam scanning method for converging light, forming light spots separated from each other in the sub-scanning direction on the surface to be scanned, and performing multi-beam scanning with a jump order: m (≧ 1), wherein: 9. A multi-beam scanning method, wherein the method is performed using the multi-beam scanning device according to any one of 9 above. 11. 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, wherein the light on the photosensitive surface of the photosensitive medium is provided. An image forming apparatus using the multi-beam scanning device according to any one of claims 6 to 9 as an optical scanning device that performs scanning. 12. The image forming apparatus according to claim 11, wherein the photosensitive medium is a photoconductive photoreceptor, and an electrostatic latent image formed by uniform charging of a photosensitive surface and optical scanning by an optical scanning device is:
An image forming apparatus which is visualized as a toner image.