JP4522060B2 - Optical scanning device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical scanning device that deflects light from a plurality of light sources by a single deflecting means, and then separates and guides the light onto a plurality of scanning lines, for example, for yellow, magenta, cyan, and black images. The four light beams are deflected by a single polygon mirror and guided onto a plurality of scanning lines to form an image.
[0002]
[Prior art]
A means for scanning a plurality of scanning lines, (1) a system that eliminates the need for arranging a plurality of scanning optical system units and can reduce the number of scanner motors, and (2) adverse effects such as unevenness in the amount of light in the scanning lines. In order not to cause the light source, it is not necessary to change the deflection of the light source and the wavelength (if the wavelength is different, the fθ characteristic, the beam diameter and the like are different), there are the following.
[0003]
Conventional technology A
Patent Document 1 discloses an optical scanning device in which a plurality of light beams are incident on a set of polygon mirrors, and light after deflection (after reflection) is scanned by sharing some post-deflection optical components. Yes. In this optical scanning device, a plurality of light beams incident on the polygon mirror are incident in a direction parallel to the normal line of the polygon mirror reflecting surface.
[0004]
Prior art B, C
As disclosed in Patent Literature 2, Patent Literature 3, Patent Literature 4, Patent Literature 5, Patent Literature 6, and Patent Literature 7, a plurality of remote scans using one polygon mirror and one set of optical elements. A scanning optical system that performs scanning on a line has been proposed. These aim to reduce the thickness of the polygon mirror by allowing the scanning surfaces to cross in the post-deflection optical system, and to give the common lens power in the sub-scanning direction. Is made possible.
[0005]
Conventional technology D
Patent Document 8 describes an invention in which a light beam inclined in the sub-scanning direction is incident on one point on a polygon mirror in a sub-scanning direction, and a plurality of beams are scanned in a state where the polygon mirror thickness is reduced. Yes. In this case, for each light beam, a plurality of mirrors having power in the sub-scanning direction are combined, and the arrangement or curvature thereof is changed to change the lateral magnification in the sub-scanning direction, so that the amount of bending of the scanning line is the same. Or try to eliminate the bend.
[0006]
[Patent Document 1]
US Pat. No. 5,215,055
[0007]
[Patent Document 2]
JP 7-256926 A
[0008]
[Patent Document 3]
JP-A-8-122672
[0009]
[Patent Document 4]
JP-A-8-122673
[0010]
[Patent Document 5]
JP-A-8-136839
[0011]
[Patent Document 6]
JP-A-8-136840
[0012]
[Patent Document 7]
JP 2000-162523 A
[0013]
[Patent Document 8]
JP 2000-180749 A
[0014]
[Problems to be solved by the invention]
In the prior art A, since it is necessary to leave a space on the polygon mirror surface by the space necessary for separating the light beam after the post-deflection optical system, the polygon mirror thickness and the post-deflection optical system are inevitably required. It was necessary to increase the height. When the polygon mirror is thickened, the windage loss when the polygon mirror is rotated increases. Furthermore, in order to rotate the polygon mirror at a high speed, a motor with a large power is required, and power consumption and noise increase. Moreover, since the temperature rise of the motor becomes large, there is a problem that cooling is necessary.
[0015]
Furthermore, the increase in the height of the lens causes problems such as an increase in the cost of the lens and an increase in the size of the unit. In addition, the prior art (FIG. 1) shown here is configured to gather at one point on the polygon mirror surface, but as shown in the problem of the known example of the prior art D, the curve of the scanning line is bent. Will happen. As a result, when multi-color latent images are created and then overlapped, color misregistration caused by scanning line bending (when creating an image by superimposing images of a plurality of color components) If the location is shifted, the hue changes and the thickness of the line or point changes.
[0016]
In the prior art B, Patent Document 2, Patent Document 3, Patent Document 4, Patent Document 5, and Patent Document 6, a plurality of light beams are incident on the polygon mirror so that the scanning surfaces after deflection intersect, An example through a common lens is shown. This is an example in which the bending of the scanning line is suppressed by the characteristics of the post-deflection optical system while suppressing the thickness of the polygon mirror. In these cases, the outermost light on both sides of the sub-scanning direction is configured to be symmetric, and the polygon mirror thickness is still thick. Further, the beam is passed through the principal point in the sub-scanning direction so that the beam position in the sub-scanning direction does not fluctuate with respect to temperature changes and laser wavelength fluctuations. Although improved, the polygon mirror thickness is still thick.
[0017]
Patent Document 7 of Prior Art C is also configured so that the outermost light in the sub-scanning direction is symmetric, and the polygon mirror thickness is still thick.
[0018]
In the method of the prior art D, if the surface to be scanned is an M surface, 2 × M lenses are required only for individual mirrors, and two shared fθ lenses are required. Even when M = 2, six M, = 4 requires 10 optical elements of 8 individual mirrors + 2 fθ lenses, which increases the number of parts and the influence of variations in individual cylindrical mirrors (for example, bending of the bus bar). It has become a thing. In addition, basically, the scanning line is bent, and the amount thereof is to be made the same by the individual cylindrical mirrors.
[0019]
SUMMARY OF THE INVENTION An object of the present invention is to reduce image relative positional shift (color shift) and improve imaging characteristics while maintaining a thin deflection means such as a polygon mirror.
[0020]
[Means for Solving the Problems]
In order to solve the above-described problem, an optical scanning device according to a first aspect of the invention makes light from a plurality of light sources incident on a deflecting unit such that a scanning surface after deflection intersects the sub-scanning direction. Separate the deflected light beams by the separating means, In the sub-scanning direction In an optical scanning device that guides to a plurality of distant scanning lines, out of a plurality of deflected lights deflected by the deflecting means In the image plane Both sides in the sub scanning direction Located in It is characterized in that the outermost light is an asymmetrical optical path.
[0021]
With the above configuration, the outermost light beams on both sides in the sub-scanning direction after deflection are made asymmetrical optical paths, so that light from a plurality of light sources does not concentrate on one point of the deflection surface of the deflecting means. Thereby, the bending of the scanning line is suppressed, the color shift (relative positional shift of the image) due to the bending of the scanning line can be prevented, and the imaging characteristics are improved.
[0036]
DETAILED DESCRIPTION OF THE INVENTION
The best mode of the optical scanning device according to the present invention will be described below.
[0037]
FIG. 1 is a sectional view in the sub-scanning direction of the optical path of the post-deflection optical system, and is enlarged in the sub-scanning direction. FIG. 2 is a plan view in which the optical path of the optical scanning device is viewed from the plane direction by unfolding the mirror. FIG. 3 shows a state viewed from a direction orthogonal to the plane direction shown in FIG. 2 (a direction perpendicular to the rotation axis of the optical deflecting device). It is the side view which looked at the position where the deflection angle by an optical deflection | deviation apparatus is 0 degree regarding the light beam which passes through the optical member arrange | positioned from to a to-be-scanned surface. FIG. 4 shows the relationship between the entrance and exit of the reflecting surface 5a of the optical deflecting device 5, the emission angle in the sub-scanning direction from the optical deflecting device 5, the characteristics of the post-deflection optical system 21 in the sub-scanning direction, and the deviation of the scanning position in the sub-scanning direction. It is a figure for demonstrating. FIG. 5 is a graph obtained by calculating the optical path when the output height from the light deflecting device 5 is constant and the output height is changed by using a paraxial ray tracing equation. FIG. 6 is a graph showing the optical path difference when the light beam height difference at the optical element principal point position is fixed at 1, and the incident height difference and inclination difference are varied. FIG. 7 is a cross section in the sub-scanning direction of the optical path diagram according to the first embodiment, which is enlarged in the sub-scanning direction. FIG. 8 is a cross section in the sub-scanning direction of the optical path diagram of the principal ray according to the first embodiment, which is enlarged in the sub-scanning direction. FIG. 9 is a cross section in the sub-scanning direction of the optical path diagram according to the second embodiment, which is enlarged in the sub-scanning direction. FIG. 10 is a cross section in the sub-scanning direction of the optical path diagram of the principal ray according to the second embodiment, which is enlarged in the sub-scanning direction. FIG. 11 is an enlarged view of the vicinity of the intersection of FIG. 12 to 15 are tables showing values such as inclination around the axis. 16 to 21 are tables showing values such as inclination around the axis.
[0038]
The optical scanning device according to this embodiment is a device that scans a laser beam. For example, it is an optical scanning device suitable for use in an electrophotographic image forming apparatus, particularly an image forming apparatus that forms a latent image corresponding to an image using a laser beam and visualizes the latent image to obtain an image.
[0039]
The optical scanning apparatus mainly includes a pre-deflection optical system, an optical deflection apparatus, and a post-deflection optical system. The pre-deflection optical system, the optical deflection apparatus, and the post-deflection optical system will be outlined.
[0040]
The pre-deflection optical system is an optical system for guiding a plurality of laser beams from a light source to an optical deflecting device. This pre-deflection optical system includes a plurality of semiconductor laser elements as a light source, a plurality of lenses, an aperture stop having a predetermined shape opening, and the like. The pre-deflection optical system adjusts the beam cross-sectional shape of each laser beam from each light source to a predetermined shape, and guides each laser beam toward a predetermined position of the optical deflection apparatus.
[0041]
The optical deflection apparatus is an apparatus for deflecting the laser beam from the pre-deflection optical system to the post-deflection optical system. Here, the laser beam is reflected using a polygon mirror to deflect in a predetermined direction. In some cases, refraction is used. A galvanometer mirror or the like may be used.
[0042]
Specifically, the light deflection apparatus includes a polygon mirror having a plurality of (rarely one) reflectors (mirror surfaces) and a motor that rotates the polygon mirror at a predetermined speed. The optical deflecting device continuously reflects (deflects) individual laser beams (laser beams whose cross-sectional beam shape is adjusted to a predetermined shape) from the pre-deflection optical system while continuously rotating the individual reflectors. Let Thus, a laser beam guided from one end to the other end in the width direction of the latent image holding member is generated along the rotation direction (main scanning direction) of the reflector. That is, the individual laser beams applied to the respective reflectors of the polygon mirror are deflected in the main scanning direction by continuously changing the reflection angle by rotating the respective reflectors of the polygon mirror.
[0043]
The post-deflection optical system is an optical system for separating the laser beam deflected by the optical deflecting device and guiding it to each latent image holder to form an image. The post-deflection optical system includes an fθ lens or an fθ mirror that is long in the main scanning direction, and a plurality of mirrors that are long in the main scanning direction. With this fθ lens or the like, the reflection point of each reflector of the polygon mirror (the reflection point that continuously changes according to the rotation angle of the reflector), and the imaging position where each laser beam reaches on the latent image holding member, Regardless of the distance between them, each laser beam continuously reflected by the reflector is connected to a predetermined position on the latent image holder while being scanned substantially linearly in a direction along the axial direction. Let me image. In many cases, each laser beam is bent between the optical deflecting device and the photosensitive drum by an arbitrary number of times by a plurality of plane mirrors due to the size restriction of the optical scanning device. A line formed by connecting a point where the surface to be scanned and the principal ray of the laser beam intersect while each laser beam is continuously emitted is called a scanning line. By turning on / off the laser beam scanned on the scanning line in accordance with the image, a latent image can be written at a predetermined position on the scanning line.
[0044]
Next, it will be described in detail with reference to the drawings.
[0045]
FIG. 2 shows a state in which the optical path of the optical scanning device incorporated in the color printer apparatus is viewed from the plane direction (rotational axis direction of the optical deflecting device described below) by unfolding the mirror. FIG. 3 shows a state viewed from a direction orthogonal to the plane direction shown in FIG. 2 (a direction perpendicular to the rotation axis of the optical deflecting device). 3 shows a state in which the light beam passing through the optical member disposed between the scanning surface and the surface to be scanned is viewed at a position where the deflection angle by the light deflecting device is 0 °.
[0046]
Only one optical deflection device 5 is provided. The light deflecting device 5 reflects the laser beam L (Y, M, C and B) and continuously changes the direction. Each of the laser beams LY, LM, LC, and LB is a light beam corresponding to image data for each color component, and each of the first to fourth semiconductor laser elements (actually two light emission units as described below). The laser array is a light source including a chip) and is emitted from 3Y, 3M, 3C and 3B. Four groups, that is, four colors (two for each) of laser beams L (Y, M, C, and B) emitted from each laser array 3 (Y, M, C, and B) and reflected by the optical deflector 5, The light is continuously deflected at a predetermined linear velocity toward each photosensitive drum 4 (Y, M, C, and B) accommodated in the corresponding image forming unit.
[0047]
Each laser array 3Y, 3M, 3C and 3B is provided with two light emitting chips (not shown) in one package. Accordingly, two laser beams L (a) and L (b), that is, LY (a + b), LM (a + b), LC (a + b), and LB (a + b) are emitted corresponding to the image data for each color component. It is supposed to be. However, the two laser beams LY (a + b), LM (a + b), LC (a + b) and LB (a + b) emitted from the individual laser arrays 3 (Y, M, C and B) are actually , Generally overlap. Therefore, when it is not necessary to identify and explain each laser beam, the laser beams LY, LM, LC, and LB are displayed for each color component.
[0048]
Each laser array 3 (Y, M, C and B) is arranged as shown in FIG. The yellow image laser array 3 </ b> Y is disposed at a position where the emitted laser beam LY is directly incident on the reflection surface of the optical deflector 5. The magenta image laser array 3M, the cyan image laser array 3C, and the black image laser array 3B are arranged at a predetermined angle with respect to the laser beam LY of the yellow image laser array 3Y. Synthesis mirrors 7M, 7C, and 7B are provided on the laser beam LY line of the yellow image laser array 3Y, respectively. Each of the composite mirrors 7M, 7C, and 7B is disposed at a predetermined angle. The laser beams LM, LC, and LB from the laser arrays 3M, 3C, and 3B are folded back by the synthetic mirrors 7M, 7C, and 7B so as to substantially overlap the laser beam LY when viewed from the planar direction. Each laser beam L (Y, M, C, and B) is arranged at a set angle in the sub-scanning direction (direction orthogonal to the direction deflected by the optical deflecting device 5). Specifically, it will be described later.
[0049]
Between each laser array 3 (Y, M, C and B) and each combining mirror 7M, 7C and 7B, a laser beam L (Y, M, from the laser array 3 (Y, M, C and B)) is provided. Pre-deflection optical systems 9Y, 9M, 9C and 9B which are light source side optical systems for adjusting the cross-sectional beam shape of C and B) to a predetermined shape are arranged.
[0050]
Each pre-deflection optical system 9Y, 9M, 9C and 9B includes collimating lenses 11Y, 11M, 11C and 11B, diaphragms 13Y, 13M, 13C and 13B, and cylinder lenses 15Y, 15M, 15C and 15B. .
[0051]
The collimating lenses 11Y, 11M, 11C, and 11B collimate the laser beams L (Y, M, C, and B) from the respective laser arrays 3 (Y, M, C, and B). Each of the collimating lenses 11Y, 11M, 11C, and 11B is a finite focus lens or a positive power that suppresses the divergence by appropriately selecting the materials and shapes of a plurality of lenses used in the post-deflection optical system 21 described later. It is also possible to replace the lens with a lens.
[0052]
The respective apertures 13Y, 13M, 13C, and 13B are provided at the rear focal points of the respective collimating lenses 11Y, 11M, 11C, and 11B, and are collimated by the respective collimating lenses 11Y, 11M, 11C, and 11B. , C and B) are formed into a predetermined cross-sectional beam shape.
[0053]
Each cylinder lens 15Y, 15M, 15C, and 15B guides each laser beam L (Y, M, C, and B) to the reflecting surface 5a of the light deflecting device 5 while converging at least in the sub-scanning direction.
[0054]
Each pre-deflection optical system 9Y, 9M, 9C and 9B guides each laser beam L (Y, M, C and B) to the reflecting surface 5a of the optical deflecting device 5 in a predetermined cross-sectional beam shape. Reflected by. At this time, since the reflecting surface 5a is rotating, each laser beam L (Y, M, C, and B) is sequentially reflected on the photosensitive drum 4 (Y, M, C, and B) while its reflection direction is changed. It is continuously scanned along the axial direction.
[0055]
A post-deflection optical system 21 is provided on the downstream side of the light deflection apparatus 5. The post-deflection optical system 21 includes first to fourth imaging lenses 23, 25, 27, and 29. Each imaging lens 23, 25, 27, and 29 is an optical medium including a non-planar surface. By the imaging lenses 23, 25, 27 and 29, the traveling direction (imaging position) of each laser beam L (Y, M, C and B) is changed. That is, each laser beam L (Y, M, C, and B) reflected by the reflecting surface 5a of the light deflecting device 5 and sequentially passing through the imaging lenses 23, 25, 27, and 29 is at least in the sub-scanning direction. The traveling direction (image forming position) can be changed.
[0056]
Next, FIG. 3 shows an example in which the light beam is divided into a plurality of scanning lines after passing through one set of optical deflecting device 5 and one set of post-deflection optical system 21. Here, by tilting the incident light to the optical deflecting device 5 in the sub-scanning direction, the beam interval on the reflecting surface 5a of the optical deflecting device 5 is reduced, and the thickness of the optical deflecting device 5 is reduced.
[0057]
As can be seen from this figure, the locations where multiple beams are spatially separated in the sub-scanning direction are created at intervals of about half the scanning line interval (in this case, the same as the drum interval). Each of the optical path folding plane mirrors 33Y, 33M, 33C, 33B, 35Y, 35M, 35C, 37Y, 37M and 37C is inserted to separate the beams.
[0058]
That is, by the respective imaging lenses 23, 25, 27 and 29 of the post-deflection optical system 21.
1) The image plane substantially coincides with the image plane over the entire scanning plane.
2) When the light is deflected by the light deflecting device 5, the image surface is irradiated with an image height that is substantially proportional to the deflection angle (the fθ characteristic is good).
3) A beam emitted from one point of each laser array 3 (Y, M, C, and B) is condensed at approximately one point at the imaging point.
4) The reflection point of the reflection surface 5a and the image plane have a conjugate relationship over the entire scanning line so that the tilting of the reflection surface 5a of the optical deflector 5 does not affect the beam position in the sub-scanning direction.
Each of the laser beams L (Y, M, C, and B) having the various characteristics set optimally corresponds to the respective optical path folding plane mirrors 33Y, 33M, 33C, which are located at the subsequent stage corresponding to the individual color components. 33B, 35Y, 35M, 35C, 37Y, 37M, and 37C are sequentially folded and guided to the outer peripheral surface of the corresponding photosensitive drum 4 (Y, M, C, and B).
[0059]
Note that dustproof glasses 39Y, 39M, 39C, and 39B are provided on the downstream side of the first to fourth imaging lenses 23, 25, 27, and 29 to protect the inside of the optical scanning device 1 from dust. These dust-proof glasses 39Y, 39M, 39C and 39B prevent the toner from the image forming unit, paper dust or the like (paper to be transferred) from becoming fine powder from entering the optical scanning device 1.
[0060]
As the optical path at this time, the outermost light in the sub-scanning direction is set as an asymmetric optical path. As a result, the required characteristics of a general scanning optical system are fθ characteristics, surface tilt characteristics, imaging characteristics, and a plurality of scanning lines. The linearity of the scanning lines required for the color scanning optical system that forms and superimposes the latent images, the relative positional deviation in the main scanning direction of the plurality of beams is small (fθ characteristics are uniform), and the plurality of beams It has been confirmed that performance such as a small relative positional deviation in the sub-scanning direction can be obtained (a scanning line bends and has the same inclination).
[0061]
Using the paraxial optical theory, if the distance between the beams on the optical element is the same, it will be examined how the light beam interval on the light deflecting device 5 can be reduced. FIG. 1 is a sectional view in the sub-scanning direction of the optical path of the post-deflection optical system 21 in FIG. 3 and enlarged in the sub-scanning direction.
[0062]
A place indicated by a hatched ellipse in the figure is a place where a space for inserting each of the optical path folding plane mirrors 33Y, 33M, and 33C is secured in order to separate the light rays. In order to secure this place, it is necessary to take the optical path in the direction indicated by the arrow in FIG.
[0063]
On the other hand, when the incident angle to the reflecting surface 5a of the light deflecting device 5 increases, the reflection surface 5a enters and exits (the distance from the rotation axis center of the light deflecting device 5 to the reflection point of the laser beam varies). The beam position fluctuation in the sub-scanning direction becomes large.
[0064]
The relationship between the sub-scanning direction magnification and the sub-scanning direction beam position deviation due to the entrance / exit of the reflecting surface 5a is as follows.
[0065]
Incident angle of the laser beam with respect to the optical deflecting device 5 (incident light of the laser beam in a projection view along a perpendicular line of the reflecting surface 5a of the optical deflecting device 5 and extending in the sub-scanning direction perpendicular to the reflecting surface 5a) Assuming that the angle between the vertical line and the vertical line is α, the beam position in the sub-scanning direction on the reflecting surface 5a is shifted by δ × tan α due to the entry / exit δ of the reflecting surface 5a as shown in FIG.
[0066]
If the lateral magnification in the sub-scanning direction between the reflecting surface 5a of the light deflector 5 and the image surface (the surface of the photosensitive drum 4) is β, the beam position on the image surface varies by β × δ × tan α in the sub-scanning direction. Resulting in. As a result, as α increases, the beam position on the image plane fluctuates greatly, and the relative positional shift (color shift) of the image increases and the imaging characteristics deteriorate. Therefore, it is desirable that the incident angle α be small.
[0067]
For this reason, the thickness of the light deflecting device 5 can be reduced in a state where the incident angle α is kept small and the relative position shift (color shift) of the image is reduced to improve the imaging characteristics. To consider. That is, under the condition that the laser beams (LY and LB in FIG. 1) have the same (or almost the same) tilt angle and the signs are reversed, the direction of the arrow in FIG. Whether the thickness of the optical deflecting device 5 can be reduced by moving the laser beam and reducing the beam interval on the reflecting surface 5a of the optical deflecting device 5 will be examined using the paraxial ray tracing method.
[0068]
The height at the reflecting surface 5a of the optical deflector 5 is h0, the incident angle is u0, the reflecting surface 5a is the object point, the scanned surface is the image plane, and the combined power in the sub-scanning direction of the post-deflection optical system 21 is 1. / F, e1 is the distance between the object point and the combined object point side principal point of the post-deflection optical system 21 in the sub-scanning direction, and e1 is the distance to the combined image plane side principal point of the post-deflection optical system 21 in the sub-scanning direction. If the distance is e2,
The height and inclination of the synthesized object point principal point in the sub-scanning direction of the post-deflection optical system 21 are
h1 = h0−e1 × u0
u1 = u0
The height and inclination of the synthesized image plane side principal point in the sub-scanning direction of the post-deflection optical system 21 are
h1 '= h1
u1 ′ = (1 / f) × h1 + u1
The height and inclination on the image plane are
h2 = h1′−e2 × u1 ′
u2 = u1 '
It is expressed.
[0069]
Since the post-deflection optical system 21 has a surface tilt correction function, it is necessary to maintain a conjugate relationship between the object point and the image plane in the sub-scanning direction.
(1 / e1) + (1 / e2) = 1 / f
The distance between the object point and the image plane is 1, and the magnification is −2.669090309.
e1 = 0.725254121
e2 = 0.72745879
After all,
1 / f = 5.043749794
It becomes.
[0070]
The influence of the entrance / exit of the reflecting surface 5a is proportional to the incident angle α with respect to the optical deflecting device 5 and the lateral magnification β in the sub-scanning direction, so that the exit angle from the optical deflecting device 5 in the sub-scanning direction is made as small as possible. It is desirable to keep the thickness of the light deflecting device 5 thin.
[0071]
For this reason, it is assumed that the inclination angles of the laser beams (light rays) at both ends of the plurality of laser beams are substantially the same and the signs are reversed, the emission angle u0 from the optical deflecting device 5 is constant, and the emission height h0 is set to be constant. What was shaken is shown in FIG.
[0072]
From this figure, we can conclude as follows.
[0073]
The light beam (LB in FIG. 1) separated most on the image plane side needs to be far away from the optical axis of the post-deflection optical system 21 at a location close to the image plane, and the light beam height on the reflection surface 5a is also high. Although it must be high, the light beam (LY in FIG. 1) separated most on the optical system 21 side after deflection has little effect even if the light beam height at the reflecting surface 5a is lowered.
[0074]
The light beam (LY in FIG. 1) separated most on the post-deflection optical system 21 side has a small distance from the optical axis of the post-deflection optical system 21 and is separated on the most image plane side (referred to in FIG. 1). And LB) take a large distance.
[0075]
Further, the position where the principal ray of the light ray passing through both ends in the sub-scanning direction intersects with the optical axis of the post-deflection optical system 21 is set as follows. That is, the point at which the light beam (LY in FIG. 1) separated most on the post-deflection optical system 21 and the optical axis of the post-deflection optical system 21 intersect is the light beam separated on the most image plane side (in FIG. In other words, it was set at a position closer to the optical deflection device 5 side than the point where LB) and the optical axis of the post-deflection optical system 21 intersect.
[0076]
On the other hand, the pre-deflection optical systems 9Y, 9M, 9C and 9B and the post-deflection optical system 21 are composed of a plurality of lenses. However, the light beams are evenly distributed to the respective lenses by changing the location where each light beam intersects the optical axis. There are cases where the light does not enter and exit. In this case, the beam position fluctuates due to refractive index fluctuations due to temperature changes of the respective lenses and wavelength fluctuations of the semiconductor laser. In order to alleviate this, each lens is a lens in which glass materials having different Abbe numbers are combined. Further, the lens having the smallest Abbe number is given negative power in the sub-scanning direction.
[0077]
Next, the difference in separation location between LY and LM, and LC and LB will be considered.
[0078]
Considering a different light beam from the previous equation, the height and slope of the post-deflection optical system 21 at the synthesized object point principal point in the sub-scanning direction are:
H1 = H0−e1 × U0
U1 = U0
The height and inclination of the synthesized image plane side principal point in the sub-scanning direction of the post-deflection optical system 21 are
h1 '= h1
U1 ′ = (1 / f) × H1 + U1
The height and inclination on the image plane are
H2 = H1′−e2 × U1 ′
U2 = U1 '
It is expressed.
[0079]
Taking the difference from the beam expressed in the previous equation,
Δh0 = h0−H0
Δu0 = u0−U0
Δh1 = h1−H1 = (h0−e1 × u0) − (H0−e1 × U0)
= (H0−H0) −e1 × (u0−U0) = Δh0−e1 × Δu0
Δu1 = u1-U1
Δh1 ′ = h1′−H1 ′ = h1−H1 = Δh1
Δu1 ′ = u1′−U1 ′ = {(1 / f) × h1 + u1} − {(1 / f) × H1 + U1}
= (1 / f) × (h1−U1) + (u1−U1) = (1 / f) × Δh1 + Δu1
The height and inclination on the image plane are
Δh2 = (h1′−e2 × u1 ′) − (H1′−e2 × U1 ′)
= (H1'-H1 ')-e2 * (u1'-U1') = [Delta] h1'-e2 * [Delta] u1 '
Δu2 = u2−U2 = u1′−U1 ′ = Δu1 ′
Thus, it can be seen that the same equation can be used for the difference in beam position and the application formula for the beam position.
[0080]
Here, FIG. 6 shows the optical path difference when the light beam height difference at the optical element principal point position is fixed at 1, and the incident height difference Δh0 and inclination difference Δu0 are swung. The object point corresponds to 0 on the horizontal axis, and the image plane corresponds to 1.
[0081]
The following can be seen from FIG.
[0082]
If the distance between the beams on the optical element is the same, it will be examined how the light beam interval on the reflection surface 5a of the light deflector 5 can be reduced.
[0083]
The two light beams (LC and LB in FIG. 1) separated on the most image plane side (downstream of the optical path) need to be greatly separated from each other at a location close to the image plane. Although the distance must be large, the two rays (LY and LM in FIG. 1) separated on the post-deflection optical system 21 side have little effect even if the distance on the reflecting surface 5a is reduced.
[0084]
Two light rays (LC and LB in FIG. 1) separated on the most image plane side (downstream side of the optical path) have a large distance on the reflecting surface 5a, and the most post-deflection optical system 21 side ( The two light rays (LY and LM in FIG. 1) separated on the upstream side of the optical path take a small distance on the reflection surface 5a.
[0085]
The point where the scanning surfaces of the two light beams separated on the image plane side intersect is farther from the reflecting surface 5a than the point where the scanning lines of the two light beams separated on the post-deflection optical system 21 side intersect.
[0086]
On the other hand, the pre-deflection optical systems 9Y, 9M, 9C and 9B and the post-deflection optical system 21 are constituted by a plurality of lenses. However, since the light beam and the optical axis intersect with each other, the light beam is evenly distributed to each lens. There are cases where the light does not enter and exit. In this case, the beam position fluctuates due to refractive index fluctuations due to temperature changes of the respective lenses and wavelength fluctuations of the semiconductor laser. In order to alleviate this, each lens is a lens in which glass materials having different Abbe numbers are combined. Further, the lens having the smallest Abbe number is given negative power in the sub-scanning direction. Beam position variation is corrected by appropriately combining lenses having different Abbe numbers and positive and negative powers.
[0087]
The features of the present invention are as follows.
[0088]
Light from three or more light sources (here, four light sources) enters the deflecting means (light deflecting device 5) in the post-deflection optical system 21 so that the scanning surfaces after the deflection of the plurality of light beams intersect. The deflected light from the deflecting means is imaged on three or more scanning lines having a predetermined distance by the post-deflection optical system 21, and a plurality of light beams are separated downstream of the optical path of the post-deflection optical system 21. In a scanning optical system having a means for arranging the mirrors at positions where the light beams are spatially separated and having means for guiding them onto scanning lines that are separated from each other, the outermost light in the sub-scanning direction is an asymmetric optical path.
[0089]
On the reflection surface 5a of the light deflecting device 5, a light ray (LY in FIG. 1) that is the principal ray of the outermost ray in the sub-scanning direction and is separated on the most upstream side (light deflecting device 5 side) of the optical path. The distance in the sub-scanning direction from the optical axis of the post-deflection optical system 21 is smaller than the above distance of the light beam (LB in FIG. 1) separated on the most downstream side (image surface side) of the optical path.
[0090]
In addition, the position where the principal ray of the outermost ray in the sub-scanning direction intersects the optical axis of the post-deflection optical system 21 is separated at the most upstream side of the optical path (on the side of the optical deflection device 5) (in FIG. 1). LY) is on the upstream side (closer to the polygon mirror side) than the light beam (LB in FIG. 1) separated on the most downstream side (image plane side) of the optical path.
[0091]
The chief ray of the outermost ray in the sub-scanning direction is emitted from the reflecting surface 5a of the light deflecting device 5 toward the optical axis of the post-deflection optical system 21 with substantially the same inclination in the sub-scanning direction (the inclination direction is reverse). .
[0092]
The distance between the light beams separated on the most downstream side (image surface side) (LC and LB in FIG. 1) is the distance between the light beams separated on the most upstream side (image forming optical means side) (FIG. The distance on the reflecting surface 5a of the light deflector 5 is larger than that of LY and LM.
[0093]
The point at which the scanning plane formed by the principal rays of the two rays (LC and LB in FIG. 1) separated on the most downstream side (image plane side) of the optical path is the most upstream side of the optical path (after the deflection). It is on the downstream side of the optical path (far from the deflecting surface of the deflector) than the point where the scanning plane formed by the principal rays of the two rays (LY and LM in FIG. 1) separated on the image optical element side.
[0094]
The post-deflection optical system 21 is composed of a plurality of lenses in which glass materials having different Abbe numbers are combined. Of these lenses, the lens with the smallest Abbe number is given negative power in the sub-scanning direction.
[0095]
The imaging lenses 23, 25, 27 and 29 of the post-deflection optical system 21 are set as follows.
[0096]
The first imaging lens 23 is a free-form curved lens that is a molded lens including a non-arc shape, which is set independently with the curvature in the main scanning direction and the sub-scanning direction other than 0. The material is optical glass BK7. The Abbe number is νd = 64.1 and νe: 63.9. Both the main scanning direction and the sub-scanning direction have positive power, but the power value differs between the main scanning direction and the sub-scanning direction.
[0097]
The second imaging lens 25 has a concave cylinder surface with a curvature in the main scanning direction on the incident surface and a concave cylinder surface with a curvature in the sub-scanning direction on the output surface. The glass material is SF6. The Abbe number is νd = 25.4 and νe: 25.2, which is smaller than the other lenses (23, 27, 29). Although the main scanning direction and the sub-scanning direction have negative power, the power value differs between the main scanning direction and the sub-scanning direction.
[0098]
In the third imaging lens 27, the incident surface is a cylinder surface, the output surface is a spherical surface, and the planar shape is biconvex. Has positive power in the main scanning direction. The material is optical glass BK7. The Abbe number is νd = 64.1 and νe: 63.9.
[0099]
The fourth imaging lens 29 is a lens having a curvature in the sub-scanning direction. That is, it is a cylinder lens having a positive power in the sub-scanning direction in which one surface is flat and the other surface is convex. The material is BK7 of optical glass material. The Abbe number is νd = 64.1 and νe: 63.9.
[0100]
Here, the tables shown in FIGS. 12 to 15 will be described.
[0101]
If there is an eccentricity or inclination in the same row, it indicates that the eccentricity is performed on the surface and then the inclination is performed. “←” indicates that the value is the same because the common component or the same component is shared. In the pre-deflection optical systems 9Y, 9M, 9C, and 9B, the light beam travels in the + direction in the x direction, and in the post-deflection optical system 21, the light beam travels in one direction in the x direction. Here, the y direction indicates the main scanning direction, and the z direction indicates the sub scanning direction. When the curvature in the z direction (sub-scanning direction) is “←”, it indicates that the curvature is the same as that in the main scanning direction and that the surface is spherical.
[0102]
As can be seen from the inclination around the Y axis in Table 1, LY is -0.0263329935 (the display is -0.03 due to the number of significant digits), LB is 0.024883296 radian (LM: 0.01600004). , LC: 0.025289228) and is incident on the deflecting surface of the deflector (reflecting surface 5a of the optical deflector 5). The emitted light from the light deflecting device 5 at this time is LY: -0.02634343, LB: -0.024893637 radian, (LM: -0.060111416, LC) in the sub-scanning direction at the center value of the swing angle. : -0.025303195), the emission angle in the sub-scanning direction from the reflecting surface 5a of the light deflector 5, which is the deflecting surface of the deflector for the two light beams LY and LB passing through the outermost contour in the sub-scanning direction. Are opposite in sign and have almost the same absolute value.
[0103]
Next, the light beam position on the reflecting surface 5a of the light deflector 5 will be described with reference to FIG.
[0104]
The outermost light beams LY and LB in the sub-scanning direction are asymmetrical in the sub-scanning direction with respect to the optical axis of the post-deflection optical system 21.
[0105]
The positions on the reflecting surface 5a of the light deflecting device 5 which is a deflecting surface are LY: -3.706, LM: -1.5805, LC: 2.128, LB: 4.98. After the deflection on the reflecting surface 5a of the principal ray of the outermost ray in the sub-scanning direction and separated on the most upstream side (post-deflection optical system 21 side) of the optical path (in this embodiment, LY) The distance 3.706 in the sub-scanning direction from the optical axis of the optical system 21 is the above-mentioned distance 4.98 of the light beam (LB in this embodiment) separated on the most downstream side (image surface side) of the optical path. Is smaller than
[0106]
Further, the position at which the principal ray of the outermost ray in the sub-scanning direction intersects the optical axis is a ray (LY in this example) separated on the most upstream side (post-deflection optical system 21 side) of the optical path. This is located on the upstream side (light deflector 5 side) of the light beam (LB in this embodiment) separated on the most downstream side (image plane side) of the optical path.
[0107]
The positions in the sub-scanning direction on the reflection surface 5a of the light deflector 5 are LY: -3.706, LM: -1.5805, LC: 2.128, LB: 4.98, and the sub-scanning position on the reflection surface 5a. The distance between LY and LM in the scanning direction is 2.1255, the distance between LM and LC is 3.7085, and the distance between LC and LB is 2.852. The distance between the light beams separated on the most downstream side (image surface side) (LC and LB in this embodiment) is the distance between the light beams separated on the most upstream side (imaging optical means side) ( In this embodiment, the distance on the reflecting surface 5a is larger than LY and LM).
[0108]
The point where the scanning plane formed by the principal rays of the two rays (LC and LB in this embodiment) separated on the most downstream side (image plane side) of the optical path is the most upstream side ( The downstream side of the optical path (the reflection of the optical deflecting device 5) from the point where the scanning plane formed by the principal rays of the two light rays (LY and LM in this embodiment) separated by the post-deflection imaging optical element side Located far from the surface 5a).
[0109]
The difference between this and the known technology is as follows.
[0110]
In the prior art A, since the polygon incident light is perpendicular to the sub-scanning direction, the polygon thickness is increased and the windage loss is increased as described above.
[0111]
In the prior arts B and C, the optical path passing through the outermost contour in the sub-scanning direction is symmetric, and the polygon mirror thickness becomes thicker than when the present invention is used. Further, the point where LY and LM cross each other and the point where LC and LB cross are almost the same.
[0112]
In the prior art D, since the last two lenses and optical elements are different for each scanning line, if there are variations in the inclination of the mounting of each component, warpage, etc., the inclination of the scanning line, the bending of the scanning line, etc. Variation and color misregistration occur. Also, in such an arrangement, the scanning line is bent and how to match it, but the bending direction of the light beam scanned by different mirror surfaces is opposite on the image plane. Therefore, the occurrence of color misregistration is inevitable.
[0113]
Next, an example in which the post-deflection optical system 21 is a double lens assembly will be described.
[0114]
The first imaging lens was a free-form curved lens, which is a molded lens including a non-arc shape, which has a curvature other than 0 in the main scanning direction and the sub-scanning direction and is set independently. The glass material is S-FTM16. The Abbe number is νd = 35.3 and νe: 35.0, which is smaller than that of the second lens. Although the main scanning direction and the sub-scanning direction have negative power, the power value differs between the main scanning direction and the sub-scanning direction.
[0115]
The second imaging lens is a free-form curved lens that is a molded lens including a non-circular arc shape that has a curvature other than 0 in the main scanning direction and the sub-scanning direction and is set independently. The material is optical glass BK7. The Abbe number was set to νd = 64.1 and νe: 63.9. Both the main scanning direction and the sub-scanning direction have positive power, but the power value differs between the main scanning and sub-scanning directions.
[0116]
As described above, the post-deflection optical system 21 is composed of two lenses in which glass materials having different Abbe numbers are combined. The lens with the smallest Abbe number (first lens) was given negative power in the sub-scanning direction.
[0117]
Here, Table 2 (FIGS. 16 to 21) will be described.
[0118]
As can be seen from the tilt around the Y axis in Table 2, LW is -0.053951729 radian, LB is 0.0545553095 radian, (LM: -0.0176656744, LC: 0.018259439) and the reflection of the light deflector 5. The light enters the surface 5a (the reflective surface of the polygon mirror). The emitted light from the optical deflecting device 5 at this time is LY: 0.058975285, LB: -0.06043285radian (LM: 0.01910102133, LC: -0) in the sub-scanning direction when the center value of the swing angle is obtained. .021227532), the emission angles of the two light beams LY and LB passing through the outermost contour in the sub-scanning direction from the polygon mirror reflecting surface, which is the deflecting surface of the deflector, have opposite signs. The absolute values are almost the same.
[0119]
As a result, the light from the plurality of light sources is not concentrated on one point of the reflection surface 5a of the light deflecting device 5, and the bending of the scanning line is suppressed, and the color shift (relative position of the image) caused by the bending of the scanning line is suppressed. Deviation) can be prevented, and the imaging characteristics are improved.
[0120]
Further, since the light from the plurality of light sources is deflected without being concentrated on one point of the reflection surface 5a, the plurality of light after deflection can be efficiently separated.
[0121]
Next, a second embodiment will be described.
[0122]
FIG. 9 is a cross section in the sub-scanning direction of the optical path diagram according to the second embodiment, which is extended in the sub-scanning direction. FIG. 10 is a cross section in the sub-scanning direction of the optical path diagram of the principal ray according to the second embodiment, which is enlarged in the sub-scanning direction. FIG. 11 is an enlarged view of the vicinity of the intersection of FIG.
[0123]
The outermost light beams LY and LB in the sub-scanning direction are optical paths that are asymmetric in the sub-scanning direction with respect to the optical axis of the post-deflection optical system.
[0124]
The positions on the reflecting surface 5a of the optical deflecting device 5 that are the deflecting surfaces are LY: -0.8675, LM: -0.338, LC: 0.1305, LB: 1.074, and are in the sub-scanning direction. Deflection on the reflecting surface 5a of the light deflecting device 5 of a light ray (LY in this embodiment) separated by the principal ray of the outermost ray and separated on the most upstream side (post-deflection optical system 21 side) of the optical path The distance 0.8675 in the sub-scanning direction from the optical axis of the rear optical system 21 is the above-described distance 1. of the light beam (LB in this embodiment) separated on the most downstream side (image plane side) of the optical path. 074 or less.
[0125]
The position where the principal ray of the outermost ray in the sub-scanning direction intersects the optical axis is the light beam (LY in this example) that is separated on the most upstream side (post-deflection optical system 21 side) of the optical path. It is located upstream of the light beam (LB in this embodiment) separated on the most downstream side (image plane side) of the optical path. That is, the position is close to the light deflecting device 5 side.
[0126]
The sub-scanning direction positions on the reflection surface 5a of the light deflector 5 are LY: -0.8675, LM: -0.338, LC: 0.1305, LB: 1.074, and the sub-scanning position on the reflection surface 5a. In the scanning direction, the distance between LY and LM is 0.5295, the distance between LM and LC is 0.4685, and the distance between LC and LB is 0.9435. The distance between the light beams separated on the most downstream side (image plane side) (LC and LB in this embodiment) 0.9435 is the distance between the light beams separated on the most upstream side (imaging optical means side). The distance on the reflecting surface 5a of the light deflector 5 is larger than the distance (LY and LM in this embodiment) 0.5295.
[0127]
The point at which the scanning plane formed by the principal rays of the two rays (LC and LB in this embodiment) separated on the most downstream side (image plane side) of the optical path is the most upstream side (after deflection) It is located on the downstream side of the optical path from the point where the scanning plane formed by the principal rays of the two rays (LY and LM in this embodiment) separated by the optical system 21 side. That is, the position is far from the reflecting surface 5 a of the light deflecting device 5.
[0128]
Also in this case, the same operations and effects as the first embodiment are obtained.
[0129]
【The invention's effect】
As described above, according to the present invention, the following excellent effects can be achieved.
[0130]
By making the outermost beams on both sides in the sub-scanning direction after deflection into asymmetrical optical paths, light from multiple light sources will not concentrate on one point on the deflection surface of the deflecting means, and scanning line bending will be suppressed. Thus, the color shift (relative image position shift) due to the bending of the scanning line can be prevented, and the imaging characteristics are improved.
[0131]
Further, since the light from the plurality of light sources is deflected without being concentrated on one point of the deflection surface of the deflecting means, the plurality of light after deflection can be efficiently separated.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view in the sub-scanning direction of an optical path of a post-deflection optical system.
FIG. 2 is a plan view of the optical path of the optical scanning device as viewed from the plane direction by developing folding by a mirror.
3 is a state viewed from a direction orthogonal to the plane direction shown in FIG. 2 (a direction perpendicular to the rotation axis of the optical deflecting device), and does not unfold by the mirror, and is a reflection point of the optical deflecting device. It is the side view which looked at the position where the deflection angle by an optical deflection | deviation apparatus is 0 degree regarding the light beam which passes through the optical member arrange | positioned from to a to-be-scanned surface.
FIG. 4 shows the relationship between the entrance and exit of the reflecting surface 5a of the optical deflecting device 5, the emission angle in the sub-scanning direction from the optical deflecting device 5, the characteristics of the post-deflection optical system 21 in the sub-scanning direction, and the deviation of the scanning position in the sub-scanning direction. It is a figure for demonstrating.
FIG. 5 is a graph obtained by calculating the optical path when the output height from the light deflecting device 5 is constant and the output height is changed by using a paraxial ray tracing equation.
FIG. 6 is a graph showing the optical path difference when the difference in the light beam height at the optical element principal point position is fixed at 1, and the difference in the incident height and the difference in inclination are applied.
FIG. 7 is a cross section in the sub-scanning direction of the optical path diagram according to the first embodiment, which is extended in the sub-scanning direction.
FIG. 8 is a cross section in the sub-scanning direction of the optical path diagram of the principal ray according to the first embodiment, which is enlarged in the sub-scanning direction.
FIG. 9 is a cross section in the sub-scanning direction of the optical path diagram according to the second embodiment, which is enlarged in the sub-scanning direction.
FIG. 10 is a cross section in the sub-scanning direction of the optical path diagram of the principal ray according to the second embodiment, which is enlarged in the sub-scanning direction.
11 is an enlarged view near the intersection of FIG. 10;
FIG. 12 is a chart showing values such as a tilt around an axis.
FIG. 13 is a chart showing paraxial power of a lens.
FIG. 14 is a chart showing lens surface coefficients.
FIG. 15 is a chart showing lens surface coefficients.
FIG. 16 is a chart showing values such as a tilt around an axis.
FIG. 17 is a chart showing paraxial power of a lens.
FIG. 18 is a chart showing lens surface coefficients.
FIG. 19 is a chart showing lens surface coefficients.
FIG. 20 is a chart showing lens surface coefficients.
FIG. 21 is a chart showing lens surface coefficients.
[Explanation of symbols]
L: Laser beam, 3: Laser array, 4: Each photosensitive drum, 5: Optical deflecting device, 7: Composite mirror, 9: Pre-deflection optical system, 11: Collimating lens, 13: Aperture, 15: Cylinder lens, 5a : Reflective surface, 21: post-deflection optical system, 23, 25, 27, 29: imaging lens, 33, 35, 37: plane mirror for turning back the optical path, 39: dustproof glass.

Claims (1)

Light from a plurality of light sources is incident on a deflecting unit such that the scanning surface after deflection intersects the sub-scanning direction, and the plurality of deflected lights deflected by the deflecting unit are separated by the separating unit, respectively. In an optical scanning device that leads onto a plurality of scanning lines that are separated in a direction,
An optical scanning device characterized in that outermost light positioned on both sides in the sub-scanning direction on the image plane among a plurality of deflected light deflected by the deflecting means has an asymmetric optical path.

Images