JP6478627B2 - Optical scanning device and image forming apparatus having the same - Google Patents

Description

  The present invention relates to an optical scanning device used in an image forming apparatus such as a laser beam printer or a copying machine.

  In recent years, there has been proposed an optical scanning device that separates light beams emitted from a light source and deflects the separated light beams by a plurality of deflecting surfaces to scan a plurality of scanned surfaces in a time-division manner.

In Patent Document 1, a light beam emitted from a light source is separated by a light beam separating unit, and each separated light beam is incident on a plurality of deflection surfaces of a four-sided polygon mirror from 45 degrees and deflected. An optical scanning device for time-division scanning a plurality of scanned surfaces is disclosed.
In Patent Document 2, a light beam emitted from a light source is separated by a light beam separating unit, and each separated light beam is incident on a plurality of deflection surfaces of a six-sided polygon mirror from 30 degrees and deflected. An optical scanning device for time-division scanning a plurality of scanned surfaces is disclosed.

JP 2008-257169 A JP 2012-194333 A

However, the optical scanning devices disclosed in Patent Documents 1 and 2 can reduce the cost by writing on a plurality of scanned surfaces from a single light source, but can only secure a scanning angle of view of 45 degrees or less. Therefore, a sufficient scanning field angle cannot be ensured.
Accordingly, an object of the present invention is to provide an optical scanning device capable of efficiently performing time-division scanning while ensuring a sufficient scanning angle of view and reducing the influence of return light to the light source on time-division scanning. And

なる条件式を満たすことを特徴とする。
An optical scanning device according to the present invention includes a separating unit that separates a light beam emitted from one light emitting point into a first light beam and a second light beam, and first and second deflecting surfaces for the first and second light beams, respectively. The first and second imaging optical systems for guiding the first and second light beams deflected by the deflector to the first and second scanned surfaces, respectively, The total number of deflecting surfaces of the deflector is an odd number, and the order of the second deflecting surfaces when counted along the rotation direction of the deflectors with reference to the first deflecting surface is L, and the total number of deflecting surfaces of the deflectors is N, and the angle formed between the first incident direction of the first light beam with respect to the first deflection surface and the second incident direction of the second light beam with respect to the second deflection surface in the main scanning section is θ [degree]. and when,

The following conditional expression is satisfied.

  According to the optical scanning device of the present invention, it is possible to efficiently perform time-division scanning while ensuring a sufficient scanning angle of view and reducing the influence of return light to the light source on time-division scanning.

FIG. 3 is a main scanning sectional view of the optical scanning device according to the first embodiment. The figure explaining the time division scanning in the optical scanning device concerning a first embodiment. The elements on larger scale of the optical scanning device concerning a first embodiment. The figure which showed the structure for performing time division scanning in the optical scanning device which concerns on 1st embodiment. The figure which showed a mode that regular reflection occurred simultaneously by two deflection surfaces in the optical scanning device which concerns on 1st embodiment. The figure which showed the scanning timing chart on each to-be-scanned surface with respect to the rotation angle of the deflector in the optical scanning device which concerns on 1st embodiment. 1 is a schematic view of a main part of a color image forming apparatus equipped with an optical scanning device according to the present invention.

  Hereinafter, an optical scanning device according to the present invention will be described with reference to the drawings. It should be noted that the drawings shown below may be drawn at a scale different from the actual scale so that the present invention can be easily understood.

  In the following description, the main scanning direction (Y direction) corresponds to a direction perpendicular to the rotation axis of the deflector and the optical axis (X direction) of the imaging optical system, and the sub scanning direction (Z direction) is Corresponds to the direction parallel to the rotation axis of the deflector. The main scanning section corresponds to a section perpendicular to the sub-scanning direction, and the sub-scanning section corresponds to a section including the optical axis of the imaging optical system and the sub-scanning direction (a section perpendicular to the main scanning direction).

  In recent years, there has been a demand for speeding up, downsizing, and cost reduction in optical scanning devices.

First, in order to achieve an increase in the speed of the optical scanning device, a multi-beam technique has been proposed in which a plurality of scanning lines can be written at a time.
In particular, recently, a surface emitting semiconductor laser called VCSEL (Vertical Cavity Surface Emitting Laser) (Vertical Cavity Surface Emitting Laser) has been developed. By using the VCSEL, the optical scanning device can include a light source having a number of light emitting points that is difficult to realize with a conventional edge-emitting semiconductor laser.
However, if a multi-beam light source that can write a plurality of scanning lines at a time, such as a VCSEL, is used as the light source in order to increase the speed of the optical scanning device, the cost increases.

  In order to increase the speed of the optical scanning device, it is conceivable to increase the number of polygon mirrors. However, as the number of polygon mirrors increases, the scanning angle of view decreases, so a certain scanning area is secured. In order to achieve this, it is necessary to increase the focal length of the optical element, which is not suitable for miniaturization.

  As described above, in order to achieve speedup of the optical scanning device, even if a multi-beam light source is used or the number of polygon mirrors is increased, the optical scanning device can be reduced in size and reduced while ensuring a scanning angle of view. It is difficult to achieve cost.

  FIG. 1 is a main scanning sectional view of an optical scanning device 100 according to the first embodiment of the present invention.

  The optical scanning device 100 includes a light source 101, a collimator lens 102, a light beam separation element (separating means) 103, cylindrical lenses 104a and 104b, reflection mirrors 105a and 105b, and aperture stops 106a and 106b. The optical scanning device 100 also includes a deflector 107, first fθ lenses 108a and 108b, second fθ lenses 109a and 109b, dustproof means 110a and 110b, and scanned surfaces 111a and 111b. Note that the scanned surfaces 111a and 111b may be the surface of a photoreceptor (not shown).

The light source 101 has at least one light emitting point (first light emitting point). For example, an edge emitting laser, a surface emitting semiconductor laser such as a VCSEL, or the like is used.
The collimator lens 102 converts the light beam emitted from the light source 101 into a substantially parallel light beam. Here, the substantially parallel light beam includes a weak divergent light beam, a weakly convergent light beam, and a parallel light beam.
The light beam separating element 103 separates the light beam that has passed through the collimator lens 102 into two light beams (a first light beam and a second light beam) traveling in different directions. For example, the light beam separation element 103 is configured by a prism or the like.
Each of the cylindrical lenses 104a and 104b has a finite power (refractive power) in the sub-scan section, and condenses each light beam separated by the light beam separation element 103 in the sub-scan direction.
The reflection mirrors 105a and 105b reflect the light beams that have passed through the cylindrical lenses 104a and 104b toward the deflector 107, respectively.
The aperture stops 106a and 106b limit the beam widths of the beams reflected by the reflection mirrors 105a and 105b, respectively.
In this way, each light beam is condensed only in the sub-scanning direction in the vicinity of the deflecting surface of the deflector 107, and is formed as a long line image in the main scanning direction.
The light source 101, collimator lens 102, light beam separation element 103, cylindrical lenses 104a and 104b, reflection mirrors 105a and 105b, and aperture stops 106a and 106b constitute an incident optical system of the optical scanning device 100.

The deflector 107 is rotated in the direction of arrow A in the figure by a motor (not shown), thereby deflecting each light beam incident on different deflection surfaces toward the scanned surfaces 111a and 111b. For example, the deflector 107 is configured by a polygon mirror or the like.
The first fθ lenses 108 a and 108 b and the second fθ lenses 109 a and 109 b are anamorphic imaging lenses having different powers in the main scanning section and the sub-scanning section, and each light beam deflected by the deflector 107. Is condensed (guided) on the scanned surfaces 111a and 111b.
The dustproof means 110a and 110b are provided in order to prevent dust and the like from entering the inside of the optical scanning device 100, and are composed of, for example, a glass plate.
The first fθ lens 108a and the second fθ lens 109a constitute a first imaging optical system of the optical scanning device 100. The first fθ lens 108b and the second fθ lens 109b constitute a second imaging optical system of the optical scanning device 100. In addition, the first imaging optical system and the second imaging optical system may be collectively referred to as an imaging optical system.
Accordingly, the scanned surfaces 111a and 111b are scanned by the deflector 107 and the imaging optical system. Since deflector 107 rotates in the direction of arrow A in the figure, scanned surfaces 111a and 111b are scanned in the direction of arrow B in the figure.
It should be noted that the movement of the exposure location in the sub-scanning direction on the scanned surfaces 111a and 111b causes the scanned surfaces 111a and 111b to be sub-scanned each time the first and second imaging optical systems are scanned and exposed in the main scanning direction. It is executed by moving in the scanning direction.

  Next, various characteristics of the incident optical system and the imaging optical system of the optical scanning device 100 according to the present embodiment are shown in Table 1 and Table 2 below, respectively.

In Tables 1 and 2, the optical axis direction, the axis orthogonal to the optical axis in the main scanning section, and the optical axis in the sub-scanning section when the intersection of each lens surface and the optical axis is the origin. The orthogonal axes are the X axis, Y axis, and Z axis, respectively. In Tables 1 and 2, “E-x” means “× 10 ^−x ”.

  The collimator lens 102 of this embodiment is a rotationally symmetric glass mold lens having an aspherical shape for aberration correction. The shape is represented by the following formula (1).

ここで、Ｒは曲率半径、ｋは離心率、Ｃ_ｉ（ｉ＝２，４，６）は非球面係数である。

Here, R is a radius of curvature, k is an eccentricity, and C _i (i = 2, 4, 6) is an aspherical coefficient.

  The aspherical shape in the main scanning section of each lens surface in the first fθ lenses 108a and 108b and the second fθ lenses 109a and 109b is expressed by the following equation (2).

Here, R is a radius of curvature, k is an eccentricity, and B _i (i = 4, 6, 8,..., 16) is an aspheric coefficient. When the coefficient B _i is different between the positive side and the negative side with respect to y, as shown in Table 2, the subscript u is added to the positive side coefficient (that is, B _iu ), and the subscript is added to the negative side coefficient. l is attached (ie, B _il ).

  The aspherical shape in the sub-scan section of each lens surface in the first fθ lenses 108a and 108b and the second fθ lenses 109a and 109b is expressed by the following formula (3).

_Here, M _{j_4} (j = 0,2,4,6,8) are aspherical coefficients. When the coefficient M _{j_4} is different between the positive side and the negative side with respect to y, as shown in Table 2, the subscript u is attached to the positive side coefficient (that is, M _{j_4u} ), and the subscript is added to the negative side coefficient. l is attached (that is, M _{j — 4l} ).
Further, the radius of curvature r ′ of the sub-scan section changes continuously according to the y coordinate of the lens surface as in the following formula (4).

Here, r is the radius of curvature of the sub-scanning section on the optical axis, and E _j (j = 2, 4, 6, 8, 10) is the coefficient of change in the radius of curvature of the sub-scanning section. When the coefficient E _j is different between the positive side and the negative side with respect to y, as shown in Table 2, the subscript u is added to the positive side coefficient (that is, E _ju ), and the subscript is added to the negative side coefficient. l is attached (ie, E _jl ).

  Next, in the optical scanning device 100 according to the present embodiment, a configuration in which time-division scanning is performed so that a light beam returning from the deflector 107 to the light source 101 (hereinafter referred to as return light) is not generated will be described.

  2A and 2B are diagrams for explaining time-division scanning in the optical scanning device 100 according to the present embodiment. Specifically, FIG. 2A shows a state where the light beam deflected by the deflector 107 starts to scan the scanned surface 111a, and FIG. 2B shows the state where the light beam deflected by the deflector 107 is scanned. A state in which the scanning surface 111a has been scanned is shown.

  Here, as shown in FIGS. 2A and 2B, time-division scanning refers to an image area (on the other surface to be scanned 111b) when a light beam is scanning on the surface to be scanned 111a. This means a scanning method in which the luminous flux does not reach the effective scanning area.

As shown in FIG. 2A, when the light beam 201a starts to scan the image area of the scanned surface 111a, the light beam 201b does not enter the image area of the scanned surface 111b and the image area of the scanned surface 111b. Scan outside.
As shown in FIG. 2B, when the light beam 202a finishes scanning the image area of the surface to be scanned 111a, the light beam 202b does not enter the image area of the surface to be scanned 111b. Scan outside the image area. The light beam 202c reflected by the deflecting surface adjacent to the deflector 107 does not enter the image area of the scanned surface 111b.
Further, while the light beam scans the surface to be scanned 111a, regular reflection in which the light beam 202c is reflected in the normal direction of the deflection surface does not occur, and therefore, no return light to the light source 101 is generated.

  Subsequently, when the light beam scans the image area of the scanned surface 111b, the light beam scans outside the image area of the scanned surface 111a without entering the image area of the scanned surface 111a, and the light source 101 No return light is generated.

  Next, in the optical scanning device 100 according to the present embodiment, an arrangement condition and the like of each optical element for enabling time-division scanning without generating return light to the light source 101 will be described.

  FIG. 3 is a partially enlarged view of the optical scanning device 100 according to the present embodiment.

  In FIG. 3, θ is an angle between the light beam reflected by the reflection mirror 105a and the light beam reflected by the reflection mirror 105b. Θin is an angle between the light beam reflected by the reflection mirror 105a and the optical axis of the first fθ lens 108a.

In the optical scanning device 100 according to the present embodiment, θ and θin are set to 56 degrees and 62 degrees, respectively. By arranging in this way, time-division scanning as shown in FIG. 2 can be performed.
In order to explain the reason, a geometrical condition for enabling time-division scanning without generating return light to the light source 101 will be described next.

  FIG. 4 shows a configuration for performing time-division scanning in the optical scanning device 100 according to the present embodiment.

Incident light beams 401a and 401b are light beams incident on the deflecting surfaces 403 and 405 of the deflector 107, respectively. The outgoing light beams 402a and 402b are light beams that are reflected and emitted by the deflecting surfaces 403 and 405 of the deflector 107, respectively.
Point O is the rotation center of the deflector 107. Point D is an intersection of incident light beam 401 a and deflecting surface 403. Point E is the intersection of incident light beam 401 b and deflecting surface 405. Point F is the intersection of the extension line of the incident light beam 401a and the extension line of the incident light beam 401b.
The deflector 107 is a regular polygonal polygon mirror having an N angle (that is, N is the total number of deflection surfaces of the deflector 107) and having an outer angle β. The deflection surface 403 is the mth (m is an arbitrary integer) surface of the deflector 107, and the deflection surface 404 is the m + Lth (L is an arbitrary integer) surface of the deflector 107. The deflecting surface 405 is a deflecting surface when the deflecting surface 404 rotates around the point O by 1/2 of the external angle β.
The angle between the incident light beam 401a and the outgoing light beam 402a is 2α. The angle between the normal line of the deflection surface 403 and the normal line of the deflection surface 404 is Lβ. The angle between the incident light beam 401a and the incident light beam 401b is θ1.

  When the deflector 107 is a regular polygonal polygon mirror, after the scanning surface is scanned by the mth deflection surface, when the deflector 107 rotates by the external angle β, the (m + 1) th surface changes the scanning surface. Start scanning. That is, the scanning period of the deflector 107 corresponds to the outer angle β.

In order to perform time-division scanning with the highest efficiency, it is necessary to alternately scan each surface to be scanned.
For this purpose, after one surface to be scanned is scanned by the mth deflection surface, it is only necessary to start scanning the other surface to be scanned by shifting the m + Lth deflection surface by a half of the scanning period.

  Therefore, in order to perform time-division scanning with the highest efficiency, after one surface to be scanned is scanned by the mth deflection surface 403, the other surface to be scanned is m + Lth deflection surface 404 having an outer angle β of 1. It is only necessary to start scanning by the state rotated by / 2, that is, by the deflection surface 405.

  From FIG. 4, the angle θ1 (degrees) is expressed by the following equation (5).

  Further, the angle α (degree) is expressed by the following formula (6).

  Therefore, from the equations (5) and (6), the angle θ1 is expressed by the following equation (7).

  Here, since the angle β (degree) is an outside angle of a regular N-gon, Expression (7) can be rewritten as Expression (8) below.

  Therefore, time division scanning can be performed most efficiently by setting the angle θ1 as shown in Expression (8).

  Next, a condition for minimizing the influence of return light to the light source 101 on time-division scanning will be discussed.

First, return light to the light source 101 is generated when the incident direction of the incident light beam on the deflection surface coincides with the normal line of the deflection surface.
Therefore, in time-division scanning with respect to each scanning surface facing each other, in order to minimize the influence of the return light to the light source 101, regular reflection is simultaneously generated by each deflection surface scanning each scanning surface facing each other. Is preferred.

  FIG. 5 shows a state in which regular reflection is simultaneously generated by the deflection surfaces 503 and 504 in the optical scanning device 100 according to the present embodiment.

Incident light beams 501a and 501b are light beams incident on the deflection surfaces 503 and 504 of the deflector 107, respectively.
Point O is the rotation center of the deflector 107. Point D is an intersection of the incident light beam 501a and the deflecting surface 503. Point E is an intersection of the incident light beam 501b and the deflecting surface 504.
The deflection surface 503 is the mth (m is an arbitrary integer) surface of the deflector 107, and the deflection surface 504 is the m + Lth (L is an arbitrary integer) surface of the deflector 107.
The angle between the incident light beam 501a and the incident light beam 501b is θ2.

  In FIG. 5, the angle θ2 (degrees) is expressed by the following equation (9).

  Here, since the angle β (degree) is an outside angle of a regular N-gon, Expression (9) is rewritten as Expression (10) below.

  From the above, it is preferable that the angle θ (degree) between the light beam reflected by the reflection mirror 105a and the light beam reflected by the reflection mirror 105b satisfies the following formula (11).

  In other words, in order to efficiently perform time-division scanning while reducing the influence of return light to the light source on time-division scanning, the optical scanning device 100 according to the present embodiment is configured so that the angle θ satisfies Expression (11). It is preferable to arrange each of the optical elements.

  Therefore, substituting Equation (8) and Equation (10) into Equation (11) yields the following Equation (12).

  However, in order to satisfy the conditional expression of Expression (12), the relation of 0 <L <(N / 2) −1 is satisfied from (2L + 1) × (360 / N) −180 <L × (360 / N). Must be met.

  If the angle θ is less than the lower limit of the equation (12), the scanning of the image area on each surface to be scanned overlaps without being separated, that is, time-division scanning cannot be performed. On the other hand, even if the angle θ exceeds the upper limit of Expression (12), it is possible to efficiently perform time-division scanning while reducing the influence on the time-division scanning of the return light to the light source. Must not.

  The conditional expression of Expression (11) is that the angle θin (degree) between the light beam reflected by the reflection mirror 105a and the optical axis of the first fθ lens 108a satisfies the following Expression (13). In other words.

  Here, γ (degree) is an angle between the incident light beam 501a and the optical axis of the first fθ lens 108a.

  Here, when each optical element is arranged so that each incident light beam to the deflector 107 and each optical axis of the first fθ lenses 108a and 108b are symmetric with respect to the yz plane, an angle 2α (degrees). ) Can be written as the following equation (14).

  Further, the angle γ (degree) can be expressed as the following formula (15).

  Therefore, equation (13) can be rewritten as equation (16) below.

  However, in order to satisfy the conditional expression of Expression (16), 90− (L / 2) × (360 / N) <180 − ((2L + 1) / 2) × (360 / N), 0 <L < The relationship (N / 2) -1 must be satisfied.

In this embodiment, the deflector 107 is a regular pentagonal polygon mirror, and performs time-division scanning with two adjacent deflection surfaces. Therefore, N and L are 5 and 1, respectively.
Therefore, Expression (12) and Expression (16) are as shown in Expression (17) and Expression (18) below, respectively.

  Next, the influence of conditional expressions (17) and (18) on actual time-division scanning in the optical scanning device 100 according to the present embodiment will be discussed.

FIGS. 6A, 6B, and 6C show scanning timing charts on each scanning surface with respect to the rotation angle of the deflector 107 in the optical scanning device 100 according to the present embodiment. Specifically, FIG. 6A shows a scanning timing chart when each optical element is arranged so that θ is 56 degrees and θin is 62 degrees. FIG. 6B shows a scanning timing chart in the case where the optical elements are arranged so that θ is 36 degrees and θin is 72 degrees. FIG. 6C shows a scanning timing chart when each optical element is arranged so that θ is 72 degrees and θin is 54 degrees.
That is, FIG. 6B shows a scanning timing chart in the case where each optical element is arranged so that time division scanning can be performed most efficiently. On the other hand, FIG. 6C shows a scanning timing chart in the case where each optical element is arranged so as to minimize the influence of the return light to the light source 101 in the time-division scanning with respect to each opposed scanning surface. ing.
The arrangement of each optical element corresponding to FIG. 6A (θ is 56 degrees and θin is 62 degrees) satisfies Expressions (17) and (18). On the other hand, the arrangement of each optical element corresponding to FIG. 6B (θ is 36 degrees and θin is 72 degrees) and the arrangement of each optical element corresponding to FIG. 6C (θ is 72 degrees and θin is 54 degrees). Degree) does not satisfy the equations (17) and (18).

6A, 6 </ b> B, and 6 </ b> C, the image region of the surface to be scanned 111 a is scanned at the rotation angle of the deflector 107 in the region surrounded by 601, 602, and 603. In the area 601, the image area of the scanned surface 111 a is scanned by the first surface of the deflector 107. In the area 602, the image area of the scanned surface 111 a is scanned by the second surface of the deflector 107. In the area 603, the image area of the scanned surface 111a is scanned by the third surface of the deflector 107.
Further, the image area of the surface to be scanned 111b is scanned at the rotation angle of the deflector 107 in the area surrounded by 604, 605, and 606. In the area 604, the image area of the scanned surface 111b is scanned by the fifth surface of the deflector 107. In the area 605, the image area of the scanned surface 111b is scanned by the first surface of the deflector 107. In the area 606, the image area of the scanned surface 111b is scanned by the second surface of the deflector 107.
Reference numerals 607, 608, 609, and 610 denote rotation angle regions of the deflector 107 in which return light to the light source 101 is generated. In the region 607, the light beam specularly reflected by the first surface of the deflector 107 passes through the aperture stop 106a and returns to the light source 101. In the region 608, the light beam specularly reflected by the second surface of the deflector 107 is reflected. The light passes through the aperture stop 106a and returns to the light source 101. In the region 609, the light beam specularly reflected by the fifth surface of the deflector 107 passes through the aperture stop 106b and returns to the light source 101. In the region 610, the light beam specularly reflected by the first surface of the deflector 107 is obtained. The light passes through the aperture stop 106b and returns to the light source 101.

  From FIG. 6A, it can be seen that the regions 601 to 610 can all be separated without overlapping. Therefore, by arranging each optical element so that θ is 56 degrees and θin is 62 degrees, it is possible to efficiently perform time-division scanning while reducing the influence of the return light to the light source on time-division scanning. .

On the other hand, from FIG. 6B, it can be seen that the optical scanning apparatus 100 according to the present embodiment can perform the time division scanning most efficiently in the regions 601 to 606. However, since the regions 607, 608, 609 and 610 overlap with the regions 605, 606, 601 and 602, respectively, return light to the light source 101 is generated during time-division scanning of the image regions of the scanned surfaces 111a and 111b. You can see that
When the return light to the light source 101 is generated, the light emission of the light source 101 becomes unstable. Generally, when the return light to the light source 101 is generated, the light source 101 does not emit light.
Therefore, in the arrangement corresponding to FIG. 6B, the return light to the light source 101 cannot be avoided during the time-division scanning of the image areas of the scanned surfaces 111a and 111b. For this reason, a time region in which the light source 101 does not emit light is formed during image formation on the scanned surfaces 111a and 111b, and good image formation cannot be performed.

  6C, the regions 607 and 609 and the regions 608 and 610 overlap with each other at the same angle region, and the regions 607 to 610 do not overlap with the regions 601 to 606. Therefore, it can be seen that the influence of the return light to the light source 101 is the smallest in the time-division scanning with respect to the opposed scanned surfaces 111a and 111b. However, it can be seen that time-division scanning cannot be performed because part of the regions 601 and 604, part of the regions 602 and 605, and part of the regions 603 and 606 overlap.

  FIG. 7 is a schematic view of a main part of a color image forming apparatus 90 on which an optical scanning device according to the present invention is mounted. A color image forming apparatus according to the present invention is a tandem type color image forming apparatus in which a plurality of optical scanning devices are arranged and image information is recorded on a photosensitive drum surface as an image carrier in parallel.

  The color image forming apparatus 90 includes optical scanning devices 11 and 12 according to the present invention, and photosensitive drums (photosensitive members) 23, 24, 25, and 26 as image carriers. The color image forming apparatus 90 includes developing devices 15, 16, 17, 18, a conveyance belt 91, a fixing device 94, and a paper cassette 95.

  The color image forming apparatus 90 receives R (red), G (green), and B (blue) color signals (code data) from an external device 92 such as a personal computer. These color signals output from the external device 92 are converted into C (cyan), M (magenta), Y (yellow), and K (black) image data (image signals) by a printer controller 93 in the apparatus. Is done. These image data are input to the optical scanning devices 11 and 12, respectively. Light beams 19, 20, 21, and 22 modulated according to each image data are emitted from the optical scanning devices 11 and 12, and the photosensitive surfaces of the photosensitive drums 23, 24, 25, and 26 are caused by these light beams. Scanned in the main scanning direction.

  The photosensitive drums 23 to 26 are rotated by a motor (not shown). With this rotation, the photosensitive surfaces of the photosensitive drums 23 to 26 move in the sub-scanning direction perpendicular to the main scanning direction with respect to the light beams 19 to 22. Above the photosensitive drums 23 to 26, a charging roller (not shown) for uniformly charging the surfaces of the photosensitive drums 23 to 26 is provided so as to contact the surfaces. The surfaces of the photosensitive drums 23 to 26 charged by the charging roller are irradiated with light beams 19 to 22 emitted from the optical scanning devices 11 and 12.

  As described above, the light beams 19 to 22 are modulated based on the image data, and the electrostatic latent images are formed on the surfaces of the photosensitive drums 23 to 26, that is, the photosensitive surfaces by irradiating the light beams 19 to 22. Is formed. The electrostatic latent image is developed into toner by developing units 15 to 18 arranged so as to come into contact with the photosensitive drums 23 to 26 further downstream in the rotation direction of the photosensitive drums 23 to 26 than the irradiation positions of the light beams 19 to 22. Developed as an image.

  The toner images developed by the developing units 15 to 18 are transferred onto a transfer material by a transfer roller (transfer unit) (not shown) disposed below the photosensitive drums 23 to 26 so as to face the photosensitive drums 23 to 26. The images are sequentially transferred onto a sheet of paper (not shown). The paper is stored in a paper cassette 95 in front of the photosensitive drums 23 to 26 (lower side in FIG. 7), but can be fed manually. A paper feed roller (not shown) is provided at the end of the paper cassette 95, and the paper in the paper cassette 95 is sent to the transport belt 91 by the paper feed roller. Transport to 26.

  The sheet on which the unfixed toner image is transferred as described above is further conveyed to the fixing device 94 behind the photosensitive drums 23 to 26 (left side in FIG. 7). The fixing device 94 includes a fixing roller having a fixing heater (not shown) inside and a pressure roller disposed so as to be in pressure contact with the fixing roller. Then, the conveyed sheet is heated while being pressed by the press contact portion between the fixing roller and the pressure roller, thereby fixing the unfixed toner image on the sheet. Further, a paper discharge roller (not shown) is disposed behind the fixing device 94 and discharges the fixed paper to the outside of the image forming apparatus 90.

  In addition to the data conversion described above, the printer controller 93 is not only a motor for driving the photosensitive drums 23 to 26, but also each component in the image forming apparatus 90 and the optical scanning apparatuses 11 and 12. Control the polygon motor.

  Further, as the external device 92, for example, a color image reading device including a CCD sensor may be used. In this case, the color image reading apparatus and the color image forming apparatus 90 constitute a color digital copying machine.

  The recording density of the image forming apparatus used in the present invention is not particularly limited. However, considering that the higher the recording density is, the higher the image quality is required, the configuration of the optical scanning device according to the present invention is more effective in an image forming apparatus of 1200 dpi or more.

  As mentioned above, although preferable embodiment of this invention was described, this invention is not limited to these embodiment, A various deformation | transformation and change are possible within the range of the summary.

  In the optical scanning device 100 according to the first embodiment of the present invention, the light beam emitted from the light source 101 is separated into two light beams that travel in different directions by the light beam separation element 103, and each light beam has two surfaces to be scanned. 111a and 111b were scanned. However, the present invention is not limited to this, and the light beam emitted from the light source is separated into three or more light beams traveling in different directions by the light beam separation element, and each light beam scans three or more scanned surfaces. It can also be configured as follows.

  Further, the present invention is effective for an optical scanning device including a deflector having an odd number of deflection surfaces.

DESCRIPTION OF SYMBOLS 100 Optical scanning device 101 Light source 103 Light beam separation element (separation means)
107 Polarizer 108a First fθ Lens (First Imaging Optical System)
108b First fθ lens (second imaging optical system)
109a Second fθ lens (first imaging optical system)
109b Second fθ lens (second imaging optical system)
111a Scanned surface (first scanned surface)
111b Scanned surface (second scanned surface)

Claims (9)

Separating means for separating a light beam emitted from one light emitting point into a first light beam and a second light beam;
A deflector for deflecting each of the first and second light beams by first and second deflection surfaces;
A first imaging optical system and a second imaging optical system for guiding the first and second light beams deflected by the deflector to the first and second scanned surfaces, respectively.
The total number of deflection surfaces of the deflector is an odd number;
The order of the second deflection surfaces when counted along the rotation direction of the deflector with reference to the first deflection surface is L, the total number of deflection surfaces of the deflector is N, and the number of the deflection surfaces in the main scanning section is N. When the angle formed by the first incident direction of the first light beam with respect to the first deflection surface and the second incident direction of the second light beam with respect to the second deflection surface is θ [degrees],

An optical scanning device characterized by satisfying the following conditional expression: When the angle formed by the first incident direction and the optical axis direction of the first imaging optical system in the main scanning section is θ _in [degrees],

The optical scanning device according to claim 1, wherein the following conditional expression is satisfied.   The first incident direction and the second incident direction in a main scanning section are symmetric with respect to a plane perpendicular to the optical axis direction of the first imaging optical system. Item 3. The optical scanning device according to Item 1 or 2. The optical axis of the first imaging optical system in the optical axis direction and the second imaging optical system in the main scanning section, of claims 1 to 3, characterized in that parallel to each other physician The optical scanning device according to claim 1.   2. The second light flux is not incident on an effective scanning area on the second scanned surface when the first light flux is incident on an effective scanning area on the first scanned surface. 5. The optical scanning device according to any one of claims 1 to 4. The optical scanning device according to any one of claims 1 to 5, characterized in that it has a light source including a plurality of light emitting points. The optical scanning device according to claim 6 , wherein the light source is a surface emitting laser. An optical scanning device according to any one of claims 1 to 7 , and a developing device that develops the electrostatic latent images formed on the first and second scanned surfaces by the optical scanning device as a toner image. An image forming apparatus comprising: a transfer device that transfers the developed toner image onto a transfer material; and a fixing device that fixes the transferred toner image onto the transfer material. To the optical scanning device according to any one of claims 1 to 7, characterized in that by converting the code data outputted from an external device into an image signal and a printer controller to be input to the optical scanning device Image forming apparatus.

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