JP4880767B2 - Optical scanning device and image forming apparatus - Google Patents

Description

  The present invention relates to an optical scanning device and an image forming apparatus used for a laser printer, a digital copying machine, a plain paper fax machine, and the like.

In electrophotographic image forming apparatuses used in laser printers, digital copying machines, plain paper fax machines, etc., colorization and speeding up have progressed, and tandem image forming apparatuses having a plurality of (usually four) photoreceptors have become widespread. Yes. As a color electrophotographic image forming apparatus, there is a method in which only one photoconductor is provided and the photoconductor is rotated by the number of colors (4 colors, one drum needs to be rotated four times), but productivity is high. Inferior to
However, in the case of the tandem method, the number of light sources inevitably increases, and accordingly, the number of parts increases, color shift due to wavelength difference between a plurality of light sources, and cost increase.
Further, deterioration of the semiconductor laser is cited as a cause of the failure of the writing unit. As the number of light sources increases, the probability of failure increases and the recyclability deteriorates.

There is an example in which the tandem method is devised so as not to increase the number of light sources (see, for example, Patent Document 1). In this example, a scanned surface is scanned with different beams from a common light source using a pyramid mirror or a flat mirror. However, with this method, the number of light sources can be reduced, but the number of deflecting mirrors is limited to a maximum of two, and there remains a problem with speeding up.
In order to solve the above-described problem, the present invention intends to use polygon mirrors stacked in two stages at different phases as means for scanning a surface to be scanned with different beams from a common light source. There is a conventional technique having a configuration similar to the present invention (see, for example, Patent Document 2).
However, this conventional technique is intended to increase the scanning width and is not intended to scan different surfaces to be scanned.

In order to solve the above problems, the present invention aims at the following points.
1. Provided is an optical scanning device that enables high-speed image output while reducing the number of light sources.
2. At that time, no ghost light is generated, and an excellent image output is enabled.
3. 1 reduces the number of parts and lowers the cost.
4). 1 reduces the failure rate of the entire unit and improves recyclability.

The invention according to claim 1, a light source is modulated driving, and the deflecting means having a plurality of stages of reflecting mirrors of the polygonal in common rotational axis, it divides the beam from the light source in different stages of the deflection means A beam splitting means for making the split beam incident on the reflecting mirror, a plurality of scanned surfaces, a scanning optical system for guiding the beams scanned by the deflecting means to the scanned surface, and scanned by the deflecting means An optical scanning device having a light receiving means for detecting a beam , wherein the beams divided by the beam splitting means scan different surfaces to be scanned, and the multi-surface reflecting mirrors at different stages are mutually rotated. wherein the angle is deviated.

According to a second aspect of the present invention, in the optical scanning device according to the first aspect, the following condition is satisfied.
θ / 2 <2π / M − φ
And,
θ / 2 <φ
And,
θ / 2 <2α
However,
θ: Angle of view including the beam reaching the light receiving means
α: Average incident angle to the reflector in the effective scanning width
φ: Angular misalignment in the rotational direction of the multi-surface reflectors of different stages
M: Number of faces of the multi-faced reflecting mirror In the invention described in claim 3, in the optical scanning device described in claim 2 , the amount of deviation of the angle in the rotation direction is substantially equal to π / M.

  According to a fourth aspect of the present invention, in the optical scanning device according to the third aspect, pitch adjusting means for adjusting a sub-scanning direction pitch of the plurality of scanning lines formed on the surface to be scanned is the light beam dividing means and the light beam dividing means. It is arranged between the deflecting means.

According to a fifth aspect of the present invention, in the optical scanning device according to any one of the first to fourth aspects, the light source to be modulated and driven is an edge-emitting semiconductor laser, and the direction is opposite to the direction of the deflecting means. A light receiving means for monitoring the light emitted to the light source and a means for automatically controlling the light quantity with respect to the light source. When any of the divided beams to the reflecting mirror is not at an incident angle of 0, the light quantity automatic control is performed. It is characterized by performing.
According to a sixth aspect of the present invention, in the optical scanning device according to any one of the first to fifth aspects, each of the scanned surfaces scanned by the beams split by the light beam splitting unit is different. It is characterized in that different amounts of light are set for the surface to be scanned.

  According to a seventh aspect of the present invention, there is provided an image forming apparatus including the optical scanning device according to any one of the first to sixth aspects and having a plurality of image carriers corresponding to the respective scanned surfaces. .

According to the present invention, it is possible to provide an optical scanning device that enables high-speed and good image output while reducing the number of light sources. Accordingly, the number of parts can be reduced and the cost can be reduced, the failure rate of the entire unit is reduced, and the recyclability is improved. Furthermore, the quality difference between the beams that scan different photoreceptor surfaces can be reduced.
A wide effective scanning width can be secured, and generation of ghost light can be suppressed.
A plurality of scan lines can be formed on the same surface to be scanned by one scan, and high speed and high density can be realized.
The scanning line interval in the sub-scanning direction on the surface to be scanned can be accurately corrected.
It is possible to output an image with an appropriate density and less uneven density.
By adjusting the set light quantity, it is possible to output an image with excellent color reproducibility.

It is a schematic diagram which shows the structure of this invention of this invention. It is a sub-scanning sectional view of a half mirror prism which is an embodiment of the present invention. It is a figure for demonstrating the optical scanning by a two-stage polygon mirror. It is a timing chart of exposure for multiple colors. It is a timing chart for making exposure differ according to a color. It is a figure for demonstrating the scanning angle of a polygon. It is a figure which shows the example of a pitch adjustment means. It is a figure for demonstrating the actual adjustment method. It is a subscanning sectional view showing other embodiments for separating a beam. It is a subscanning sectional view showing other embodiments for separating a beam. 1 is a diagram illustrating a basic configuration of a multicolor image forming apparatus. It is an aberration diagram of a light source image. It is a figure which shows the change of the beam spot for every image height by defocusing. It is a figure which shows the change of the beam spot for every image height by defocusing.

FIG. 1 is a schematic diagram showing the configuration of the present invention.
In the figure, reference numerals 1 and 1 ′ denote a semiconductor laser as a light source, 2 denotes an LD (semiconductor laser) base, 3, 3 ′ denotes a coupling lens, 4 denotes a half mirror prism as a beam splitting means, and 5 and 5 ′ denote cylindrical. Lens, 6 is soundproof glass, 7 is a polygon mirror as deflection means, 8 is a first scanning lens, 9 is a mirror, 10 is a second scanning lens, 11 is a photoreceptor as a surface to be scanned, and 12 is an aperture stop. Show.
The two divergent light beams emitted from the semiconductor lasers 1 and 1 ′ are converted into weak convergent light beams, parallel light beams, or weak divergent light beams by the coupling lenses 3 and 3 ′. The beams exiting the coupling lenses 3 and 3 ′ pass through the aperture stop 12 for stabilizing the beam diameter on the scanned surface and enter the half mirror prism 4. The beams from the common light source incident on the half mirror prism 4 are divided into upper and lower stages, and the beams emitted from the half mirror become a total of four beams.

FIG. 2 is a sub-scan sectional view of the half mirror prism according to the embodiment of the present invention.
The half mirror prism 4 functions as a beam splitting means, and includes a section 41 having a triangular cross section and a section 42 having a parallelogram. The adhesive surface 4a of the portions 41 and 42 is a half mirror, and separates transmitted light and reflected light at a ratio of 1: 1. A surface 4b of the parallelogram portion 42 facing the bonding surface 4a is a total reflection surface and has a function of changing the direction. Here, a half mirror prism is used as the beam splitting means, but a similar system may be configured by using a single half mirror and a normal mirror. Further, the separation ratio of the half mirror is not necessarily 1: 1, and may be set according to the conditions of other optical systems.
The beam emitted from the half mirror prism 4 is converted into a line image that is long in the main scanning direction in the vicinity of the deflecting reflection surface by the cylindrical lenses 5 and 5 ′ arranged on the upper and lower stages. Here, in the deflection means 7, single polygon mirrors 7a and 7b are concentrically arranged on the upper and lower stages, respectively, and the rotation direction angles are shifted from each other. Both polygon mirrors have the same shape, and in principle consist of an arbitrary polygon. The polygons are overlapped so that the vertex of the other polygon corresponds to an angle that bisects the central angle of one side of one polygon. When looking at the vertexes of the opposing polygons that are adjacent to each other in the clockwise direction from the vertices of the respective polygons, if the central angles between the vertices are φ and φ ′ (where 0 <φ ≦ φ ′) If both are symmetrically arranged with respect to an arbitrary vertex, φ = φ ′. In practice, a four-sided polygon mirror is the easiest to use, and here the four-sided polygon mirror is set to φ = φ ′ = 45 deg. These φ and φ ′ are referred to as deviation angles.
Note that the upper and lower polygon mirrors 7a and 7b may be integrally formed, or may be separated and assembled.
In general, the shift angle φ is φ = (2π / M) / 2, that is, π / M, where M is the number of faces of the polygon mirror when both polygon mirrors are evenly shifted. However, if the shift is not uniform, when the smaller shift angle is φ, the larger shift angle φ ′ is φ ′ = 2π / M−φ.

FIG. 3 is a diagram for explaining optical scanning by a two-stage polygon mirror.
In the figure, reference numeral 14 denotes a light shielding member.
As shown in the figure, when the upper beam from the common light source scans the photoconductor 11a as the scanned surface, the lower beam prevents the beam from reaching the scanned surface, and preferably a light shielding member. 14 to shield light. Further, when the lower beam from the common light source is scanning the photoconductor 11b different from the upper beam, the upper beam is prevented from reaching the surface to be scanned. Further, when the modulation drive is shifted in the upper stage and the lower stage and the photoconductor 11a corresponding to the upper stage is scanned, the modulation driving of the light source is performed based on the image information of the color (for example, black) corresponding to the upper stage, When scanning the photoreceptor 11b corresponding to the lower stage, the light source is modulated based on image information of a color (for example, magenta) corresponding to the lower stage.

FIG. 4 is a timing chart of exposure for a plurality of colors.
In the figure, the vertical axis represents the amount of light and the horizontal axis represents time.
A time chart in the case where black and magenta exposure is performed with a common light source and all the lights are turned on in the effective scanning region is shown in FIG. A solid line indicates a portion corresponding to black, and a dotted line indicates a portion corresponding to magenta. The writing timing in black and magenta is determined by detecting the scanning beam with the synchronous light receiving means arranged outside the effective scanning width. Although the synchronous light receiving means is not shown, a photodiode is usually used.

FIG. 5 is a timing chart for varying the exposure amount depending on the color.
In FIG. 4, the light amounts in the black and magenta regions are set to be the same. However, since the transmittance and reflectance of the optical element are actually different, if the light amount of the light source is the same, the photosensitive member The amount of light reaching the beam will be different. Therefore, as shown in FIG. 5, when the different photoconductor surfaces are scanned, the light amounts set on the different photoconductor surfaces can be made equal by making the set light amounts different from each other.

FIG. 6 is a diagram for explaining the polygon scanning angle.
In the same figure, α and α ′ are the average incident angles to the reflecting mirror in the effective scanning width, θ is the angle of view including the synchronous light receiving means, and φ is one angle of the rotating direction of the reflecting mirrors at different stages (upper and lower stages). Each shift is shown.
Normally, only a light receiving means for detecting the beam is provided prior to the exposure of the effective scan width, but in order to obtain information for correcting the scan width magnification, the beam is detected after the effective scan width is exposed. Sometimes. In this case, the angle of view includes the beam reaching the light receiving means before the start of scanning and after the start of scanning.
In the figure, the deflecting means rotates at a constant angular speed in the clockwise direction.
First, in order to separate the beam corresponding to the incident beam to the deflection means and the field of view within the deflection rotation plane,
θ / 2 <2α (1)
Need to be satisfied.

Here, the beam A in the figure is the beam at the periphery of the angle of view on the scanning end side, and here is a beam deflected by the upper (hatched) reflecting mirror. At this time, it is necessary that the beam A ′ emitted from the light source common to the upper beam and reflected by the lower reflecting mirror does not expose the surface to be scanned. The angle between the beam A ′ and the beam A indicates 2φ or 2 × (2π / M−φ). In order to prevent the beam A ′ from scanning the surface to be scanned, the beam A ′ is included until synchronization. Must be outside the effective width.
Sunahachi,
θ <2φ, or θ / 2 <φ (2)
And θ <2 × (2π / M−φ), or θ / 2 <2π / M−φ (3)
It is necessary to. However, M is the number of surfaces of the multi-surface reflecting mirror. At this time, the beam may be shielded by the light shielding member 20 as shown in the figure.

The beam B in the figure is the beam at the periphery of the angle of view on the scanning start side, but the beam B ′ emitted from the light source common to the upper beam and reflected by the lower reflecting mirror exposes the surface to be scanned. It is necessary to satisfy the above-mentioned equations (2) and (3).
In the above two formulas, 2π / M−φ and φ may be different from each other, but the condition for obtaining the largest θ is 2π / M−φ = φ (4)
In other words, when φ = π / M, where θ <2 × π / M (5)
It becomes. In the case of M = 4, the angle of view θ is smaller than π / 2 rad (90 deg).
By satisfying the expression (4), a wide effective scanning width can be secured and generation of ghost light can be suppressed.
In the figure, a plurality of beams are incident on a common reflecting mirror, but at that time, the plurality of beams must satisfy the condition of the expression (1).
That is, θ / 2 <2α and θ / 2 <2α ′. By satisfying this condition, a plurality of scanning lines can be formed on the same scanning surface in one scan, high speed and high density can be realized, wide effective scanning width can be secured, and ghost light Can be suppressed.

The plurality of beams emitted from the plurality of light sources 1 and 1 ′ shown in FIG. 1 form two scanning lines on two different photoconductors, respectively, by one scan. At this time, it is necessary to adjust the pitch of the scanning lines in the sub-scanning direction according to the pixel density. As a method often used as a pitch adjustment method, the light source unit (1, 1 ′, 2, 3, 3 ′ is one unit) is rotated around an axis perpendicular to the main scanning direction and the sub-scanning direction. There is a method, but in this case, it is possible to set a desired pitch in one photoconductor, but in the other photoconductor, a pitch error occurs due to a shape error, an attachment error, etc. of an optical element after the light beam splitting element. .
In order to solve this problem, it is necessary to provide means for adjusting the pitch in the sub-scanning direction between the beam splitting element and the deflecting means.

FIG. 7 is a diagram showing an example of the pitch adjusting means. The figure (a) is a figure which shows one-side adjustment and the figure (b) is a figure which shows both-side adjustment.
As an example, the cylindrical lens 5 is attached to the housing via intermediate members 21a to 21c. A curable resin (for example, photocurable) is applied in advance to each mounting surface. At this time, 21 a to 21 c can perform “eccentric adjustment around an axis parallel to the main scanning direction” and “adjustment in the optical axis direction” with respect to the housing, and the cylindrical lens 5 can be “on the optical axis” with respect to the intermediate member. “Eccentric adjustment around parallel axes” and “placement adjustment in the sub-scanning direction” are possible, and the cylindrical lens 5 can be adjusted with respect to the intermediate member 21 and at least one of the directions in which the intermediate member can be adjusted with respect to the housing. At least one of the different directions is different. By adopting such a configuration, a plurality of optical characteristics (thickening the beam waist diameter, reducing beam waist position deviation, and beam spot position deviation) can be secured simultaneously, and the cylindrical lens 5 is decentered around the optical axis. By making it adjustable, the scanning line interval in the sub-scanning direction can be set optimally. Further, the surface of the intermediate member 21a that is in contact with the cylindrical lens 5 and the surface that is in contact with the housing are flat and easy to adjust. When the adjustment is completed, the mutual position is fixed by curing the curable resin by a predetermined method (for example, ultraviolet irradiation).

FIG. 8 is a diagram for explaining an actual adjustment method. The figure (a) is a figure which shows one-side adjustment and the figure (b) is a figure which shows both-side adjustment.
The cylindrical lens 5 is held by a jig, and the cylindrical lens 5 is moved in the direction to be adjusted (here, the position in the optical axis direction, the eccentricity around the axis parallel to the optical axis, the position in the sub-scanning direction). Thereafter, the intermediate member 21 to which the ultraviolet curable resin is applied is pressed against the cylindrical lens 5 and the housing, and ultraviolet rays are irradiated to fix the cylindrical lens. With such a configuration, adjustment in a plurality of directions can be easily performed with a simple structure. Here, by making the intermediate member 21 transparent, fixing with an ultraviolet curable resin becomes easier. Although it is possible to hold the optical element by using one intermediate member 21a as shown in FIG. 7a, it is also possible to arrange a plurality of intermediate members 21b and 21c on opposite sides of the light beam. For example, when the linear expansion coefficient of the housing and the intermediate member 21 (assuming resin) is different, stress is generated symmetrically with respect to the optical element with respect to the optical axis even if the temperature rises. The change in the posture of the optical element is reduced.

Usually, a semiconductor laser used in an image forming apparatus performs automatic light amount control (Auto Power Control: hereinafter referred to as APC) to stabilize light output. APC is a system in which the light output of a semiconductor laser is monitored by a light receiving element, and the forward current of the semiconductor laser is controlled to a desired value by a detection signal of a light receiving current proportional to the light output of the semiconductor laser.
When the semiconductor laser is an edge emitting semiconductor laser, the light receiving element often uses a photodiode for monitoring light emitted in the direction opposite to the direction emitted toward the coupling lens. However, when performing APC, it is unnecessary. When ghost light is incident, the amount of light detected by the light receiving element increases.
For example, when the incident angle of the beam to the upper reflecting mirror is 0, the reflecting surface of the reflecting mirror faces the light source direction, so if APC is performed at this position, the reflected beam at the upper stage returns to the light source. The amount of light detected by the light receiving element increases. For this reason, the laser output from the lower reflecting mirror in which writing is performed becomes a light emission output that is less than the target, and the image density becomes thin or density unevenness occurs. Similarly, when the beam incident angle to the lower reflecting mirror becomes 0, the same problem occurs with respect to the laser output from the upper reflecting mirror.
Therefore, any reflector is set not to perform APC when the incident angle is zero. By adopting this configuration, it is possible to output an image with an appropriate density and with little density unevenness.

9 and 10 are sub-scan sectional views showing other embodiments for separating beams.
In the figure, reference numeral 13 denotes a prism.
The light source 1 to the aperture stop 12 are shown. The beam emitted from the coupling lens 3 passes through a plurality of aperture stops 12a and 12b separated vertically in the sub-scanning direction. As a result, the light beam can be separated without using a half mirror, so that the amount of light can be easily secured, and the cost can be reduced and the number of parts can be reduced.
FIG. 9 shows an example in which the aperture stops 12a and 12b are separated by an amount corresponding to the level difference of the polygon mirror. FIG. 10 shows that both aperture stops are approaching a narrower interval, and the prism 13 is moved after one beam exits the aperture. By passing through, an interval corresponding to the step of the polygon mirror can be given. The configuration of FIG. 10 can use a portion closer to the center of the light beam than the configuration of FIG.

FIG. 11 is a diagram showing a basic configuration of a multicolor image forming apparatus.
In the figure, reference numeral 31 is a photosensitive member, 32 is a charger, 34 is a developing unit, 35 is a cleaning unit, 36 is a transfer charging unit, 39 is a transfer belt, 40 is a fixing unit, 50 is a writing unit, and S is a recording unit. Each paper is shown. Y, M, C, and K represent image colors, and indicate yellow, magenta, cyan, and black, respectively.
The photoreceptors 31Y, 31M, 31C, and 31K rotate in the direction of the arrow, and in the order of rotation, the chargers 32Y, 32M, 32C, and 32K, the developers 34Y, 34M, 34C, and 34K, and the transfer charging units 36Y, 36M, 36C, and 36K. Cleaning means 35Y, 35M, 35C, and 35K are provided.
The chargers 32Y, 32M, 32C, and 32K are charging members that constitute a charging device for uniformly charging the surface of the photoreceptor. The writing unit irradiates the surface of the photosensitive member between the charger and the developing units 34Y, 34M, 34C, and 34K with a writing unit so that an electrostatic latent image is formed on the photosensitive member. Then, based on the electrostatic latent image, a toner image is formed on the surface of the photoreceptor by the developing device. Further, the respective transfer toner images are sequentially transferred onto the recording paper S by the transfer charging means 36Y, 36M, 36C, 36K, and finally the image is fixed on the recording test S by the fixing means 40.

The implementation data of the optical system is shown below.
・ Light source wavelength: 655 nm
・ Coupling lens focal length: 15mm
-Coupling action: Collimating action-Polygon mirror Number of deflecting reflective surfaces: 4
Inscribed circle radius: 7mm
The angle difference φ between the upper and lower stages is 45 (deg) = 45 × π / 180 (rad)
-Average incident angle to the reflector α = 28.225 (deg) = π x 28.225 / 180 (rad)
α ′ = 29.775 (deg) = π × 29.775 / 180 (rad)
In addition, a cylindrical lens having a focal length of 110 mm is provided between the beam splitting unit and the deflecting unit, and forms a long line image in the main scanning direction in the vicinity of the reflecting mirror.

Lens data after the deflector is shown below.
The first surface of the first scanning lens and both surfaces of the second scanning lens are expressed by the following equations (6) and (7).
Main scanning non-arc type The surface shape in the main scanning plane is a non-arc shape, the paraxial radius of curvature in the main scanning plane on the optical axis is Rm, the distance in the main scanning direction from the optical axis is Y, and the cone When the constant is K and the higher-order coefficients are A1, A2, A3, A4, A5, A6,..., The depth in the optical axis direction is X and is expressed by the following polynomial.
X = (Y ² / Rm) / [1 + √ {1- (1 + K) (Y / Rm) ² } +
+ A1 ・ Y + A2 ・ Y ² + A3 ・ Y ³ + A4 ・ Y ⁴ + A5 ・ Y ⁵ + A6 ・ Y ⁶ + ・ ・
(6)
Here, when a numerical value other than zero is substituted for the odd-order coefficients A1, A3, A5,..., It has an asymmetric shape in the main scanning direction.
In Examples 1, 2, and 3, only the even order is used, which is a symmetric system in the main scanning direction.

Sub-scanning curvature formula (7) shows a formula in which the sub-scanning curvature changes in accordance with the main scanning direction.
Cs (Y) = 1 / Rs (0) + B1 · Y + B2 · Y ² + B3 · Y ³ + B4 · Y ⁴ + B5 · Y ⁵ + ···· (7)
Here, when a value other than zero is substituted for the odd odd power coefficients B1, B3, B5,..., The radius of curvature of sub-scanning becomes asymmetric in the main scanning direction.
Further, the second surface of the first scanning lens is a rotationally symmetric aspherical surface and is expressed by the following equation.
A rotationally symmetric aspheric surface The paraxial radius of curvature of the optical axis is R, the distance from the optical axis in the main scanning direction is Y, the cone constant is K, the higher order coefficients are A1, A2, A3, A4, A5, A6,. When represented by the following polynomial, the depth in the optical axis direction is X.
X = (Y ² / R) / [1 + √ {1- (1 + K) (Y / Rm) ² } +
+ A1 ・ Y + A2 ・ Y ² + A3 ・ Y ³ + A4 ・ Y ⁴ + A5 ・ Y ⁵ + A6 ・ Y ⁶ + ・ ・ ・ (8)

Shape of first surface of first scanning lens Rm = −279.9, Rs = −61.
K -2.900000E + 01
A4 1.755765E-07
A6-5.491789E-11
A8 1.087700E-14
A10-3.183245E-19
A12 -2.6635276E-24

B1 -2.066347E-06
B2 5.727737E-06
B3 3.152201E-08
B4 2.280241E-09
B5 -3.729852E-11
B6 -3.283274E-12
B7 1.765590E-14
B8 1.372959E-15
B9 -2.889722E-18
B10 -1.98431E-19

Shape of second surface of first scanning lens R = −83.6
K -0.549157
A4 2.748446E-07
A6 -4.502346E-12
A8-7.366455E-15
A10 1.803003E-18
A12 2.727900E-23

Shape of first surface of second scanning lens Rm = 6950, Rs = 110.9
K 0.000000 + 00
A4 1.549648E-08
A6 1.292741E-14
A8-8.811446E-18
A10-9.18212E-22

B1 -9.593510E-07
B2-2.135322E-07
B3-8.079549E-12
B4 2.390609E-12
B5 2.881396E-14
B6 3.693775E-15
B7-3.258754E-18
B8 1.814487E-20
B9 8.72085E-23
B10-1.340807E-23

Shape of second surface of second scanning lens Rm = 766, Rs = −68.22
K 0.000000 + 00
A4-1.150396E-07
A6 1.096926E-11
A8-6.5542135E-16
A10 1.984438E-20
A12 -2.411512E-25
B2 3.644079E-07
B4 -4.847051E-13
B6 -1.666159E-16
B8 4.534859E-19
B10 2.819319E-23

Further, the refractive indices of the scanning lenses at the used wavelength are all 1.52724.

The optical arrangement is shown below.
Distance d1 from the deflection surface to the first surface of the first scanning lens d1: 64 mm
Center wall thickness d2 of the first scanning lens: 22.6 mm
Distance d3 from the second surface of the first scanning lens to the first surface of the second scanning lens d3: 75.9 mm
Center wall thickness d4 of second scanning lens: 4.9 mm
Distance from second scanning lens second surface to surface to be scanned d5: 158.7 mm
In addition, a soundproof glass and a dustproof glass having a refractive index of 1.514 and a thickness of 1.9 mm are disposed, and the soundproof glass is inclined by 10 degrees with respect to the direction parallel to the main scanning direction in the deflection rotation plane.
The dustproof glass is not shown, but is disposed between the second scanning lens and the surface to be scanned.

FIG. 12 is an aberration diagram of the light source image. FIGS. 4A and 4C are diagrams showing field curvature, and FIGS. 4B and 4D are diagrams showing constant velocity. FIGS. 4A and 4B show characteristics relating to the light source 1, and FIGS. 2C and 2D show characteristics relating to the light source 1 ′.
In FIGS. 4A and 4C, the solid line indicates the field curvature in the sub-scanning direction, and the broken line indicates the field curvature in the main scanning direction. In FIGS. 2B and 2D, the solid line indicates linearity, and the broken line indicates F-θ characteristics.
Both curves show the state corrected satisfactorily.

13 and 14 are diagrams showing changes in the beam spot for each image height due to defocusing. FIG. 13 is a diagram showing characteristics relating to the light source 1, and FIG. 14 is a diagram showing characteristics relating to the light source 1 ′. In both figures, (a) shows the beam spot diameter in the main scanning direction, and (b) shows the beam spot diameter in the sub-scanning direction. In each figure, the vertical axis represents the beam spot diameter (unit μm), and the horizontal axis represents the defocus amount (unit mm).
This data was obtained under the condition that an aperture having a main scanning width of 5.25 mm and a sub scanning width of 2.14 mm was disposed between the coupling lens and the cylindrical lens.
In this embodiment, beam receiving means are provided on both the scanning start side and the scanning end side, and the angle of view θ including the light receiving means is 79.4 (deg) = 79.4 × π / 180. (Rad) ≈1.386 (rad).
Each parameter, θ, M, φ, α, α ′ used in this example satisfies all the conditional expressions (1) to (4).
In the present invention, two beams are used to scan one photoconductor, but one beam may be used to scan one photoconductor. In addition, FIG. 1 discloses only a diagram corresponding to two photoconductors, but scanning four photoconductors by arranging an optical system similar to the optical system illustrated with a polygon mirror interposed therebetween. can do.

DESCRIPTION OF SYMBOLS 1 Semiconductor laser 4 Half mirror prism 7 Polygon mirror 12 Aperture stop 13 Prism

Japanese Patent Laid-Open No. 2002-23085 Japanese Patent Laid-Open No. 2001-83451

Claims (7)

Incident light source is modulated driving, and the deflecting means having a plurality of stages of reflecting mirrors of the polygonal in common axis of rotation, the beam is divided into reflector different stages of the deflection means to divide the beam from the light source has a beam splitting means for a plurality of the scanning surface, a scanning optical system for guiding the scanned the beam to the surface to be scanned by the deflecting means and light receiving means for detecting the beam scanned by said deflection means In an optical scanning device,
Optical scanning apparatus characterized by is shifted split beam so as to scan different scanned surface, the angle of the reflecting mirror is rotated directions of the different stages of the polygonal at the beam splitting means. The optical scanning device according to claim 1,
An optical scanning device characterized by satisfying the following conditions.
θ / 2 <2π / M − φ
And,
θ / 2 <φ
And,
θ / 2 <2α
However,
θ: Angle of view including the beam reaching the light receiving means
α: Average incident angle to the reflector in the effective scanning width
φ: Angular misalignment in the rotational direction of the multi-surface reflectors of different stages
M: Number of faces of the polyhedral reflector The optical scanning device according to claim 2, wherein the amount of angular deviation in the rotation direction is substantially equal to π / M.   4. The optical scanning device according to claim 3, wherein pitch adjusting means for adjusting a sub-scanning direction pitch of a plurality of scanning lines formed on the surface to be scanned is disposed between the light beam dividing means and the deflecting means. An optical scanning device characterized by the above.   5. The optical scanning device according to claim 1, wherein the light source to be modulated and driven is an edge-emitting semiconductor laser, and light receiving means for monitoring light emitted in a direction opposite to the direction of the deflection means. And a means for automatically controlling the amount of light with respect to the light source, wherein the light amount is automatically controlled when any of the divided beams to the reflecting mirror is not at an incident angle of 0. . 6. The optical scanning device according to claim 1, wherein when the beams divided by the light beam dividing means scan different scanned surfaces, the scanned surfaces are different from each other. An optical scanning device characterized in that the amount of light is set.   7. An image forming apparatus comprising: the optical scanning device according to claim 1; and a plurality of image carriers corresponding to respective scanned surfaces.

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