JP2007025165A - Optical scanner and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical scanner which contributes to the reduction in the number of components by reducing the number of light sources, the reduction in cost, and the reduction in the trouble rate of the whole unit, and realizes a high speed out put of an image and an excellent image output by reducing the returning light to the light sources. <P>SOLUTION: While an effective region is scanned by a beam B1 with an upper stage polygon mirror 7a, the other beam divided by a luminous flux division means is reflected on a lower stage polygon mirror 7b and returned to the light source (beam B2' shown by hatching). The radius of the inscribed circle of the polygon mirror and the incident position of the beam are so decided that the beam width ω2 in a main scanning direction of the beam reflected on the lower stage polygon mirror 7b towards the light source is smaller than the beam width ω1 in the main scanning direction of the beam which is made incident to the polygon mirror. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an optical scanning device that scans a surface to be scanned with a light beam from a light source, and an image forming apparatus such as a copying machine, a printer, a facsimile, or a plotter having the optical scanning device.

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. However, four colors and one drum need to be rotated four times. Inferior to
In the case of the tandem method, the number of light sources inevitably increases, resulting in an increase in the number of parts, a color shift due to a wavelength difference between a plurality of light sources, and a 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.

Japanese Patent Laid-Open No. 2002-23085 discloses a configuration in which a scanned surface with different beams from a common light source is scanned using a pyramid mirror or a flat mirror. In this case, the number of light sources can be reduced, but the number of deflecting mirrors is limited to a maximum of two, which is problematic for speeding up.
Japanese Patent Application Laid-Open No. 2001-83452 discloses a configuration in which two-stage polygon mirrors have an angular difference in the deflection rotation plane in order to increase the scanning width.
Japanese Patent Application Laid-Open No. 2005-92129 proposes a new system in which a beam from one light source is divided and the divided beam is guided onto different scanned surfaces.

Japanese Patent Laid-Open No. 2002-23085 Japanese Patent Laid-Open No. 2001-83451 JP 2005-92129 A

According to the method disclosed in Patent Document 3, high-speed image output is possible while reducing the number of light sources.
However, the beam reflected by the rotary polygon mirror returns to the light source, causing problems such as variations in beam output.

  The present invention can contribute to a reduction in the number of parts by reducing the number of light sources, a reduction in cost, a reduction in the failure rate of the entire unit, a high-speed image output, and a reduction in return light to the light sources. An object of the present invention is to provide an optical scanning device that enables excellent image output and an image forming apparatus having the optical scanning device.

In order to achieve the above object, according to the first aspect of the present invention, a light source to be modulated and driven, a deflecting means having a plurality of stages of multi-surface reflecting mirrors and having a common rotation axis, and a common light source A beam splitting unit that splits the beam and makes the split beam incident on a multi-surface reflecting mirror at a different stage of the deflection unit; a scanning optical system that guides the beam scanned by the deflection unit to a surface to be scanned; and the deflection unit And a light receiving means for detecting the beam scanned by the optical scanning device, wherein the split beams from the common light source scan different surfaces to be scanned. The angle is deviated and the following conditions are satisfied.
(1) There is a condition in which one of the beams at the different stages scans the effective range, and the other beam is reflected by the polyhedral reflecting mirror and returns to the light source side.
(2) The beam reflected by the polyhedral reflecting mirror in (1) has a narrower beam width in the main scanning direction than the light beam incident on the polyhedral reflecting mirror.

  According to a second aspect of the present invention, in the optical scanning device according to the first aspect, the light beam splitting unit prevents the light beam incident on the light beam splitting unit from being reflected by the light beam splitting unit and returning to the light source. Is inclined with respect to the incident beam.

  According to a third aspect of the present invention, in the optical scanning device according to the second aspect of the present invention, the light beam splitting means comprises a half mirror prism.

  According to a fourth aspect of the present invention, in the optical scanning device according to any one of the first to third aspects, the beam incident on the multi-faced reflecting mirror and the coating condition of the multi-faced reflecting mirror are set in the effective scanning range. The reflectance of the multi-surface reflecting mirror is set to be larger than the reflectance at the time of vertical incidence.

  According to a fifth aspect of the present invention, in the optical scanning device according to any one of the first to third aspects, a quarter-wave plate is disposed between the light beam dividing unit and the deflecting unit, and the light beam division. The means is a polarization beam splitter.

  According to a sixth aspect of the present invention, in the optical scanning device according to any one of the first to third aspects, a beam emitted from the light source is linearly polarized light, and 1 / between the light source and the deflecting means. A four-wave plate is provided, and a polarizing filter is provided between the light source and the quarter-wave plate.

According to the seventh aspect of the present invention, the light source to be modulated and driven, the deflecting means having a plurality of multi-surface reflecting mirrors and having a common rotation axis, and the beam from the common light source are divided and divided. A beam splitting unit that causes a beam to be incident on a multi-surface reflecting mirror at a different stage of the deflecting unit, a scanning optical system that guides the beam scanned by the deflecting unit to a scanned surface, and a beam scanned by the deflecting unit are detected. An optical scanning device in which beams divided from a common light source scan different surfaces to be scanned, and the different-stage multi-surface reflecting mirrors are offset from each other in the rotational direction angle, and The following conditions are satisfied.
(1) There is a condition in which one of the beams at the different stages scans the effective range, and the other beam is reflected by the polyhedral reflecting mirror and returns to the light source side.
(2) The beam incident on the multi-surface reflecting mirror and the coating conditions of the multi-surface reflecting mirror are set so that the reflectance of the multi-surface reflecting mirror in the effective scanning range is larger than the reflectance at the time of normal incidence.

In the invention described in claim 8, the light source to be modulated and driven, the multi-stage reflecting mirror, the deflecting means having the common rotation axis, and the beam from the common light source are divided and divided. A beam splitting unit that causes a beam to be incident on a multi-surface reflecting mirror at a different stage of the deflecting unit, a scanning optical system that guides the beam scanned by the deflecting unit to a scanned surface, and a beam scanned by the deflecting unit are detected. An optical scanning device in which beams divided from a common light source scan different surfaces to be scanned, and the different-stage multi-surface reflecting mirrors are offset from each other in the rotational direction angle, and The following conditions are satisfied.
(1) There is a condition in which one of the beams at the different stages scans the effective range, and the other beam is reflected by the polyhedral reflecting mirror and returns to the light source side.
(2) The beam incident on the polyhedral reflector is inclined in the sub-scanning direction with respect to the normal line of the polyhedral reflector.

  According to a ninth aspect of the present invention, in the optical scanning device according to the seventh aspect, the light beam splitting unit is arranged so that a beam incident on the light beam splitting unit is reflected by the light beam splitting unit and does not return to the light source. It is characterized by being inclined with respect to the incident beam.

According to a tenth aspect of the present invention, in the optical scanning device according to any one of the first to ninth aspects, at least one transmissive optical element is disposed between the light source and the deflecting unit, and the transmissive optical element is provided. At least one of the above conditions satisfies any of the following conditions.
(1) A coating for reducing transmittance is applied to at least one surface.
(2) At least one surface is not coated.

  According to an eleventh aspect of the present invention, in the multicolor image forming apparatus having an optical scanning device and a plurality of image carriers, the optical scanning device is the one according to any one of the first to tenth aspects. It is characterized by being.

According to the present invention, it is possible to output images at high speed while reducing the number of light sources, and it is possible to reduce the number of parts and reduce the cost.
Further, the failure rate of the entire optical scanning device unit can be reduced, and the recyclability can be improved.
In addition, since the beams from the common light source are divided, the difference in quality between the beams scanned on the different photoreceptor surfaces can be reduced, and high image quality can be realized. At that time, no return light to the light source is generated, and good image output is possible.

A first embodiment of the present invention will be described below with reference to FIGS. First, an outline of the configuration of the optical scanning device 20 in the present embodiment will be described based on FIG. In FIG. 1, reference numerals 1 and 1 ′ denote a semiconductor laser as a light source, 2 denotes a support base of the semiconductor laser, 3, 3 ′ denotes a coupling lens, and 4 denotes a half mirror prism as a beam splitting unit. 5b is a cylindrical lens, 6 is a soundproof glass, 7 is an upper polygon mirror 7a as a polyhedral reflector, and a deflecting means comprising a lower polygon mirror 7b as a polyhedral reflector, and 8a and 8b are scanning optical systems. , 9 denotes a mirror as a scanning optical system, 10a and 10b denote a scanning lens 2 as a scanning optical system, 12K and 12C denote photosensitive members as scanning surfaces, and 25 denotes an aperture stop. ing.
In FIG. 1, only the configuration corresponding to the two photoconductors is shown, but actually, the four photoconductors are scanned by disposing an optical system similar to the illustrated optical system with the deflecting means 7 interposed therebetween. It is like that.

The divergent light beam emitted from the semiconductor lasers 1 and 1 ′ is converted into a weak convergent light beam, a parallel light beam, or a weak divergent light beam by the coupling lenses 3 and 3 ′. The beams exiting the coupling lenses 3 and 3 ′ pass through an aperture stop 25 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 prism 4 become a total of four beams.
FIG. 2 is a sub-scan sectional view of the half mirror prism 4. Reference numeral 4a denotes a half mirror, which separates transmitted light and reflected light at a ratio of 1: 1. Reference numeral 4b denotes a total reflection surface and has a function of changing the direction.
Although the half mirror prism 4 is used here, a similar system may be configured 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 5a and 5b provided in the upper and lower stages. Here, the deflecting means 7 is provided with polygon mirrors 7a and 7b on the upper and lower stages, respectively, which are offset from each other in the rotational direction by an angle (φ). Here, the four polygon mirrors are shifted by φ = 45 deg. The upper and lower polygon mirrors 7a and 7b may be integrally formed or may be assembled separately.

As shown in FIG. 3A, when the upper beam B1 from the common light source is scanning the photosensitive member surface (scanned surface), the lower beam B2 is prevented from reaching the scanned surface. Desirably, light is shielded by the light shielding member 13.
As shown in FIG. 3B, when the lower beam B2 from the common light source scans the photosensitive surface (scanned surface) different from the upper one, the upper beam B1 does not reach the scanned surface. To.
Furthermore, the modulation drive of the semiconductor laser is also shifted in timing between the upper and lower stages, and when scanning the photoconductor corresponding to the upper stage, the modulation of the light source (semiconductor laser) is performed based on the image information of the color corresponding to the upper stage (for example, black) When the photosensitive member corresponding to the lower stage is scanned, the light source is modulated based on the image information of the color (for example, magenta) corresponding to the lower stage.

FIG. 4 is a time chart in the case where black and magenta exposure are performed with a common light source, and all lights are turned on in the effective scanning region. A solid line indicates a portion corresponding to black, and a dotted line indicates a portion corresponding to magenta.
The writing start timing in black and magenta is determined by detecting the scanning beam with a synchronous light receiving means (not shown) arranged outside the effective scanning width. A photodiode is normally used as the synchronous light receiving means.
In FIG. 4, the light quantity in the black and magenta areas is set to be the same, but in reality, the light quantity of the light source is the same because the transmittance and reflectance of the optical element (half mirror prism 4 etc.) are relatively different. If this is the case, the amount of light beams reaching the photoconductor 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.

The present embodiment will be described in detail with reference to FIGS. However, FIG. 7 is a comparative example.
6 and 7, the upper polygon mirror 7a reflects the other beam divided while scanning within the effective range with the beam B1 and returns to the light source by the lower polygon mirror 7b (in hatching). Displayed beam B2 ').
In FIG. 7 (comparative example), the inscribed circle radius of the polygon mirror is large, and the beam width ω1 ′ in the main scanning direction incident on the polygon mirror is reflected in the main scanning direction reflected by the lower polygon mirror toward the light source. The beam width ω2 ′ has not changed. In this case, the light quantity of the beam B2 ′ returning to the light source becomes large, causing the following problems.
(1) The light returns to the light source (semiconductor laser), the output of the light source varies, and density unevenness occurs.
(2) The beam reflected again by the light source reaches the photosensitive member.
In order to solve these problems, it is necessary to reduce the amount of return light to the light source as much as possible. In the present embodiment, as shown in FIG. 6, the beam width ω2 in the main scanning direction reflected toward the light source by the lower polygon mirror 7b is different from the beam width ω1 in the main scanning direction incident on the polygon mirror. The inscribed circle radius of the polygon mirror and the incident position of the beam are set so as to be narrow. Thereby, the problems (1) and (2) can be greatly improved.

Implementation data of the optical system in the present embodiment 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)
The average incident angle to the reflector α = 28.225 (deg) = π × 28.225 / 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 deflecting means is shown below.
The first surface of the scanning lens 1 and the both surfaces of the scanning lens 2 are expressed by equations (1) and (2).
Main scanning non-arc type The surface shape in the main scanning surface is a non-arc shape, the paraxial radius of curvature in the main scanning surface 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 + ·· (1)
Here, when numerical values other than zero are substituted for odd-order A1, A3, A5,..., They have 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 (2) 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 + ・ ・ (2)
Here, when the odd odd power coefficients As1, As3, As5... Are substituted with numerical values other than zero, the radius of curvature of the sub-scanning becomes asymmetric in the main scanning direction.

The second surface of the scanning lens 1 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 expressed as 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 + ··
(3)
Scan lens 1 first surface shape 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

Scan lens 1 second surface shape 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

Scanning lens 2 first surface shape 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

Scan lens 2 second surface shape 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

The refractive indexes of the scanning lenses at the used wavelength are all 1.52724.

The optical arrangement is shown below.
Distance d1: 64 mm from the deflection surface to the first surface of the scanning lens 1
Center thickness d2 of the scanning lens 1: 22.6 mm
Distance d3 from scan lens 1 second surface to scan lens 2 first surface: 75.9 mm
Center thickness d4 of the scanning lens 2: 4.9 mm
Distance from scanning lens 2 second surface to surface to be scanned d5: 158.7 mm
In addition, a soundproof glass 6 and a dustproof glass having a refractive index of 1.514 and a thickness of 1.9 mm are disposed, and the soundproof glass 6 is inclined by 10 degrees with respect to a direction parallel to the main scanning direction in the deflection rotation plane.
The dustproof glass is not shown, but is disposed between the scanning lens 2 and the surface to be scanned.

FIG. 8 shows aberration diagrams of the light sources 1 and 1 ′ (left: field curvature (dotted line is main scanning field curvature, solid line is sub-scanning field curvature), right: constant velocity characteristic (dotted line is fθ characteristic, solid line is linearity). )). As is apparent from the figure, both are corrected satisfactorily.
An aperture having a main scanning width of 7 mm and a sub-scanning width of 2.14 mm is disposed between the coupling lenses 3 and 3 ′ and the cylindrical lenses 5 and 5 ′.
The intersection of the principal ray of the incident beam and the polygon mirror when the beam is reflected to the light source side is 7.74 mm on the scanned surface side in the optical axis direction of the scanning optical system, and in the optical axis direction of the scanning optical system. The vertical direction is shifted 3.27 mm toward the light source. At this time, the main scanning width ω1: 7 mm of the incident beam is 5.35 mm with respect to the main scanning width ω2: 7 of the reflected beam, and the amount of light returning to the light source can be reduced, thereby returning to the light source (semiconductor laser). Variations in the output of the light source due to light and the influence of the beam reflected again by the light source can be reduced.

As shown in FIGS. 1 and 2, the half mirror prism 4 is used as the light beam dividing means, whereby the light beam can be divided with a simple configuration, and high-speed image output is possible while reducing the number of light sources.
At this time, as shown in FIG. 2, when the incident beam to the half mirror prism 4 is incident perpendicularly to the incident surface or the exit surface, the output variation of the light source and the ghost light described above are generated when returning to the light source side. .
In order to solve this, in the present embodiment, as shown in FIG. 9, the light beam splitting means is inclined at an angle θ with respect to the incident beam to the light beam splitting means (half mirror prism 4), and the return light is sent to the light source side. It is set not to return. Specifically, the incident beam is prevented from being perpendicular to the incident surface and the exit surface of the light beam splitting means. Thereby, the return light to a light source can be reduced and the above-mentioned malfunction can be solved.

A tandem multicolor image forming apparatus using the above-described optical scanning device will be described with reference to FIG.
The multicolor image forming apparatus has four photoconductors 12Y, 12M, 12C, and 12K juxtaposed along the moving direction of the transfer belt 11. Around the photoreceptor 12Y for yellow image formation, a charger 13Y, a developer 14Y, a transfer unit 15Y, and a cleaning unit 16Y are arranged in this order in the rotation direction indicated by the arrow. The other colors have the same configuration, and are distinguished by adding European letters (M: magenta, C: cyan, K: black) for each color, and a description thereof is omitted.
The charger 13 is a charging member constituting a charging device for uniformly charging the surface of the photoreceptor. Between the charging unit 13 and the developing unit 14, the surface of the photosensitive member is irradiated with a beam by the optical scanning device 20, and an electrostatic latent image is formed on the photosensitive member 12.
Based on the electrostatic latent image, a toner image is formed on the surface of the photoreceptor by the developing device 14. The transfer unit 15 sequentially transfers the transfer toner images of the respective colors onto the recording medium (transfer sheet) conveyed by the transfer belt 11, and finally the superimposed image is fixed on the transfer sheet by the fixing unit 17.

A second embodiment will be described with reference to FIG. Note that the same parts as those in the above embodiment are denoted by the same reference numerals, and unless otherwise specified, description of the configuration and functions already described is omitted, and only the main part will be described (the same applies to other embodiments below).
In order to reduce the influence of the return light to the light source on the image as much as possible, it is necessary to reduce the light amount of the beam returning to the light source side as much as possible with respect to the light amount of the beam toward the scanning surface.
For this purpose, it is necessary to set the reflectivity of the multi-surface reflecting mirror in the effective scanning range to be larger than the reflectivity at the time of normal incidence with respect to the beam incident on the multi-surface reflecting mirror and the coating conditions of the multi-surface reflecting mirror. Specifically, the incident beam to the polyhedral reflector may be made as S-polarized light.
FIG. 11 is a graph in which the horizontal axis represents the angle of incidence on the polygon mirror and the vertical axis represents the reflectance from the polygon mirror (SIO single layer (film thickness: λ / 2) on the aluminum substrate). By making S-polarized light incident on the polygon mirror, the reflectance can be increased as the incident angle increases.
That is, by making S-polarized light incident on the polygon mirror, the light amount of the beam toward the surface to be scanned can be set large, and the light amount of the beam returning to the light source side can be set small.

A third embodiment will be described with reference to FIG.
In this embodiment, a polarizing beam splitter 40 is used as the light beam dividing means, and the quarter wavelength plate 18 is disposed between the light beam dividing means 40 and the deflecting means 7.
In the polarization beam splitter 40, reference numeral 40a denotes a polarization plane that transmits P-polarized light and reflects S-polarized light. Now, if a beam having a P-polarized component and an S-polarized component of 1: 1 with respect to the polarization plane 40a is incident on the beam splitting means, the polarization direction rotates 45 degrees after passing through the λ / 4 plate 18 once. When the return light reflected by the mirror reaches the polarization plane 40a again, the polarization direction is rotated by 90 degrees, and none of them can return to the light source side.
In order to make the incident beam to the beam splitting means 4 have a P-polarized component and an S-polarized component of 1: 1 with respect to the polarization plane 40a, the active layer (active layer and polarized light) of the semiconductor laser as the light source is used. (The direction is parallel) may be inclined 45 degrees around the optical axis with respect to the sub-scanning direction, or the active layer of the semiconductor laser may be parallel to the sub-scanning direction, and a half-wavelength plate may be inserted between the light source and the beam splitting means. .

A fourth embodiment will be described with reference to FIG.
The beam emitted from the light source is linearly polarized in the sub-scanning direction, and a polarizing filter 19 that allows the beam to pass only in the direction parallel to the linearly polarized light is provided. 18 is inserted.
Since the polarization direction of the return light reflected by the polygon mirror is orthogonal to the sub-scanning direction, it does not pass through the polarization filter 19. Therefore, the beam reflected by the polygon mirror does not return to the light source side. Of course, the light beam splitting means is the half mirror prism 4 at this time.

A fifth embodiment will be described with reference to FIG.
The beams incident on the polyhedral reflecting mirrors 7a and 7b are inclined in the sub-scanning direction with respect to the normal line of the polyhedral reflecting mirrors 7a and 7b. With such a configuration, the beams reflected by the polygon mirrors 7a and 7b can be prevented from returning to the polygon mirror.
Further, by adopting the configuration shown in FIG. 9, the return light to the light source side can be further reduced.

Next, a sixth embodiment will be described.
Usually, the coupling lenses 3 and 3 ′ and the cylindrical lenses 5 and 5 ′ are coated with an antireflection film to improve the transmittance, but conversely, by reducing the transmittance, the return light to the light source can be reduced. Can be reduced.
For example, if the coupling lenses 3 and 3 ′ and the cylindrical lenses 5 and 5 ′ are not coated, the transmittance is reduced from 97% to about 90%. Thereby, the return light can be reduced.

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 adjusting method, a light source unit (the semiconductor lasers 1 and 1 ′, the support base 2 and the coupling lenses 3 and 3 ′ are set as one unit) is perpendicular to the main scanning direction and the sub-scanning direction. There is a method of rotating around a certain axis. In this case, a certain photosensitive member can have a desired pitch. However, for the other photosensitive member, an optical element after the light beam dividing means (light beam dividing element) is used. Pitch error occurs due to the shape error, mounting error, etc.
In order to solve this problem, it is necessary to provide means for adjusting the pitch in the sub-scanning direction between the light beam dividing means and the deflecting means.
One example is shown in FIGS. The cylindrical lens 5 is attached to the housing 33 of the optical scanning device via an intermediate member 32. The intermediate member 32 has a triangular prism shape, and includes a flat portion 32 a that contacts the cylindrical lens 5 and a flat portion 32 b that is orthogonal to the flat portion 32 a and contacts the housing 33.
The cylindrical lens 5 has one end in the longitudinal direction fixed to the intermediate member 32 in a cantilever manner. However, in the state before being fixed to the flat portion 32a of the intermediate member 32, the cylindrical lens 5 is in the sub-scanning direction. Arrangement adjustment in the direction of arrow D1, arrangement adjustment in the main scanning direction (arrow D2 direction), and eccentric adjustment around the axis parallel to the optical axis (arrow D3 direction) are possible.

In other words, the intermediate member 32 has a flat surface portion 32a that is a plane perpendicular to the optical axis of the cylindrical lens 5, thereby adjusting the eccentric direction around the optical axis of the cylindrical lens 5 and the optical axis. The vertical direction can be adjusted.
As shown in FIG. 16, the intermediate member 32 is arranged and adjusted in the optical axis direction (arrow D4 direction) in the state before being fixed with respect to the upper surface of the fixing convex portion 34 of the housing 33, and main scanning. The arrangement adjustment in the direction (arrow D2 direction) and the eccentric adjustment around the axis parallel to the sub-scanning direction (arrow D5 direction) are possible. The intermediate member 32 is formed of a transparent material (for example, a plastic material).

Therefore, there are two or more adjustable directions of the cylindrical lens 5 with respect to the intermediate member 32, and there are two or more adjustable directions of the intermediate member 32 with respect to the housing 33.
Further, at least one of the directions in which the intermediate member 32 can be adjusted with respect to the housing 33 is different from at least one of the directions in which the cylindrical lens 5 can be adjusted with respect to the intermediate member 32.
By adopting such a support configuration, a plurality of optical characteristics (thickening the beam waist diameter, reducing beam waist position deviation, and beam spot position deviation) can be secured at the same time, and the cylindrical lens 5 is rotated around the optical axis. By making the eccentricity adjustable, the scanning line interval in the sub-scanning direction can be set optimally.
In FIG. 16, reference numerals 36 and 37 denote adhesive application surfaces (fixed surfaces or fixed surfaces).

An actual adjustment method will be described with reference to FIG. The cylindrical lens 5 is held by a jig (not shown), 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 32 coated with the ultraviolet curable resin on the coating surface 36 is pressed against the flat surface portion 5a of the cylindrical lens 5 and the coating surface 37 of the housing 33 coated with the ultraviolet curable resin on the coating surface 37 (temporarily fixed). The cylindrical lens 5 and the intermediate member 32 are fixed by irradiating ultraviolet rays.
Since the intermediate member 32 is formed of a transparent material, the degree of freedom of ultraviolet irradiation is large and easy, and fixing can be performed quickly and uniformly.

In the above example, the cylindrical lens 5 is fixed to the one intermediate member 32 by the cantilever method. However, the cylindrical lens 5 may be fixed to the plurality of intermediate members 32. This example is shown in FIGS.
As shown in FIG. 17, the dimensions of the outer shape of the cylindrical lens 5 are long in the main scanning direction and the sub-scanning direction so as to be positioned on opposite sides of the light beam passing through the cylindrical lens 5. Two intermediate members 32 are arranged at an interval in one direction (here, the sub-scanning direction), and each end of the cylindrical lens 5 is fixed to each flat surface portion 32a.
One intermediate member 32 is fixed to the upper surface of the convex portion 34 of the housing 33, and the other intermediate member 32 is fixed to the upper surface of the convex portion 35.
As in the above example, after fixing the cylindrical lens 5, the intermediate member 32 is brought into contact and irradiated with ultraviolet rays.
By adopting such a fixing (supporting) configuration, for example, when the linear expansion coefficient of the housing 33 and the intermediate member (here, synthetic resin) 32 is different, the optical axis is optically affected even if the temperature rises. Since stress is generated at the symmetrical portion of the element (cylindrical lens 5), the change in the attitude of the optical element due to temperature fluctuation is reduced.
Further, by adopting a configuration in which two intermediate members 32 are arranged at intervals in the direction of the longer outer shape of the cylindrical lens 5 in the main scanning direction and the sub-scanning direction, the tolerance for the arrangement error is obtained. Can be improved and the eccentric error can be reduced.

  In each of the embodiments described above, two beams are used to scan one photoconductor, but one beam may be used to scan one photoconductor.

FIG. 2 is a perspective view of a part of the optical scanning device according to the first embodiment of the present invention omitted. It is a figure which shows the function of a light beam splitting means. It is a schematic diagram which shows suppressing one of the several beam from a common light source. It is a time chart at the time of all lighting of the system exposed using a common light source. It is the time chart which changed the light quantity of the light source according to the color. It is a schematic diagram which shows suppressing the return light to a light source. It is a figure which shows a comparative example. It is a figure which shows the aberration of each light source. It is a figure which shows the function at the time of inclining a light beam splitting means with respect to an incident beam. 1 is a schematic front view of a tandem type image forming apparatus having an optical scanning device. It is a graph which shows the relationship between the reflectance from the polygon mirror in 2nd Embodiment, and the incident angle to a polygon mirror. It is a figure which shows the beam splitting function of the site | part of the light beam splitting means in 3rd Embodiment. It is a figure which shows the beam splitting function of the site | part of the light beam splitting means in 4th Embodiment. It is a figure which shows the positional relationship of the incident beam and polyhedral reflecting mirror in 5th Embodiment. It is a figure which shows the position adjustment structure of the optical element (cylindrical lens) between a light beam splitting means and a deflection | deviation means, and is a perspective view which shows the fixed state of a cylindrical lens and an intermediate member. It is a figure which shows the position adjustment structure of the optical element (cylindrical lens) between a light beam splitting means and a deflection | deviation means, and is a perspective view which shows the fixed state of the intermediate member with respect to a housing. It is a figure which shows the other example of the position adjustment structure of the optical element (cylindrical lens) between a light beam splitting means and a deflection | deviation means, and is a perspective view which shows the fixed state of a cylindrical lens and an intermediate member. It is a figure which shows the other example of the position adjustment structure of the optical element (cylindrical lens) between a light beam splitting means and a deflection | deviation means, and is a perspective view which shows the fixed state of the intermediate member with respect to a housing.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 1 'Semiconductor laser as light source 7 Deflection means 4 Half mirror prism as light beam splitting means 7a, 7b Polyhedral reflecting mirror 8 Scanning lens 1 as scanning optical system
10 Scanning lens 2 as scanning optical system
18 1/4 wavelength plate 19 Polarizing filter 40 Polarizing beam splitter as beam splitting means

Claims (11)

A modulation-driven light source;
A deflecting means having a plurality of stages of multi-surface reflecting mirrors and having a common rotation axis;
A beam splitting unit that splits a beam from a common light source and makes the split beam enter a multi-surface reflecting mirror at a different stage of the deflection unit;
A scanning optical system for guiding the beam scanned by the deflecting means to the surface to be scanned;
A light receiving means for detecting the beam scanned by the deflecting means;
In the optical scanning device in which the beam divided from the common light source scans different scanning surfaces,
The optical scanning device according to claim 1, wherein the polygon mirrors at different stages have different rotational angles and satisfy the following condition.
(1) There is a condition in which one of the beams at the different stages scans the effective range, and the other beam is reflected by the polyhedral reflecting mirror and returns to the light source side.
(2) The beam reflected by the polyhedral reflecting mirror in (1) has a narrower beam width in the main scanning direction than the light beam incident on the polyhedral reflecting mirror. The optical scanning device according to claim 1,
An optical scanning apparatus characterized in that the light beam splitting means is tilted with respect to the incident beam so that the light beam incident on the light beam splitting means is reflected by the light flux splitting means and does not return to the light source. The optical scanning device according to claim 2,
The light beam splitting means comprises a half mirror prism. The optical scanning device according to any one of claims 1 to 3,
An optical scanning characterized in that the beam incident on the polyhedral reflector and the coating conditions of the polyhedral reflector are set such that the reflectance of the polyhedral reflector in the effective scanning range is larger than the reflectance at the time of vertical incidence. apparatus. The optical scanning device according to any one of claims 1 to 3,
A quarter wave plate is provided between the light beam splitting means and the deflecting means, and the light beam splitting means is a polarization beam splitter. The optical scanning device according to any one of claims 1 to 3,
The beam emitted from the light source is linearly polarized light, a quarter wavelength plate is disposed between the light source and the deflecting means, and a polarizing filter is disposed between the light source and the quarter wavelength plate. An optical scanning device characterized by the above. A modulation-driven light source;
A deflecting means having a plurality of stages of multi-surface reflecting mirrors and having a common rotation axis;
A beam splitting unit that splits a beam from a common light source and makes the split beam enter a multi-surface reflecting mirror at a different stage of the deflection unit;
A scanning optical system for guiding the beam scanned by the deflecting means to the surface to be scanned;
A light receiving means for detecting the beam scanned by the deflecting means;
In the optical scanning device in which the beam divided from the common light source scans different scanning surfaces,
The optical scanning device according to claim 1, wherein the polygon mirrors at different stages have different rotational angles and satisfy the following condition.
(1) There is a condition in which one of the beams at the different stages scans the effective range, and the other beam is reflected by the polyhedral reflecting mirror and returns to the light source side.
(2) The beam incident on the multi-surface reflecting mirror and the coating conditions of the multi-surface reflecting mirror are set so that the reflectance of the multi-surface reflecting mirror in the effective scanning range is larger than the reflectance at the time of normal incidence. A modulation-driven light source;
A deflecting means having a plurality of stages of multi-surface reflecting mirrors and having a common rotation axis;
A beam splitting unit that splits a beam from a common light source and makes the split beam enter a multi-surface reflecting mirror at a different stage of the deflection unit;
A scanning optical system for guiding the beam scanned by the deflecting means to the surface to be scanned;
A light receiving means for detecting the beam scanned by the deflecting means;
In the optical scanning device in which the beam divided from the common light source scans different scanning surfaces,
The optical scanning device according to claim 1, wherein the polygon mirrors at different stages have different rotational angles and satisfy the following condition.
(1) There is a condition in which one of the beams at the different stages scans the effective range, and the other beam is reflected by the polyhedral reflecting mirror and returns to the light source side.
(2) The beam incident on the polyhedral reflector is inclined in the sub-scanning direction with respect to the normal line of the polyhedral reflector. The optical scanning device according to claim 7.
An optical scanning device characterized in that the beam splitting means is tilted with respect to the incident beam so that the beam incident on the beam splitting means is not reflected by the beam splitting means and returned to the light source. The optical scanning device according to any one of claims 1 to 9,
An optical scanning device, wherein at least one transmission optical element is provided between the light source and the deflection unit, and at least one of the transmission optical elements satisfies any of the following conditions.
(1) A coating for reducing transmittance is applied to at least one surface.
(2) At least one surface is not coated. In a multi-color image forming apparatus having an optical scanning device and a plurality of image carriers,
The image forming apparatus according to claim 1, wherein the optical scanning device is one according to claim 1.

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