JP2008287092A - Optical scanning apparatus and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the following problems regarding an image forming apparatus for superposing color images through the use of a plurality of image carriers, currently, plastic materials are largely used for an optical device for a scanning optical system, but the shape of the optical device is often deviated from the ideal one due to a molding condition and a temperature condition, etc., further, these errors including an attaching error of the optical element with a housing cause curving of a scanning line and positional deviation; thereby, color drift occurs, and image quality is remarkably reduced. <P>SOLUTION: When the scanning line is tilted, the tilt of the scanning line can be corrected by using the oscillation of a return mirror M with one end thereof as an axis, the level of the correctable tilt is varied in accordance with the size of a deflection angle to reflect a light beam. That is, if the deflection angle is small, the tilt may not be sufficiently corrected even by increasing the oscillation amount. An image light beam having the highest brightness of color is assigned for the return mirror so as not to make the insufficient correction conspicuous. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an optical scanning device such as a digital copying machine, a laser printer, and a laser facsimile, and an image forming apparatus using the same.

In general, an optical scanning device widely known in relation to a laser printer or the like generally deflects a light beam from a light source side by an optical deflector and collects the light beam toward a surface to be scanned by a scanning imaging optical system such as an fθ lens. Thus, a light spot is formed on the surface to be scanned, and the surface to be scanned is optically scanned with this light spot. What constitutes the surface to be scanned is a photosensitive surface of a photosensitive medium such as a photoconductive photosensitive member. The direction in which the light spot moves due to the rotation of the optical deflector is called the main scanning direction, and the direction perpendicular to the plane through which the light beam moves is called the sub-scanning direction. These terms are terms that should originally be defined on the surface to be scanned, but for convenience, these terms are also used at positions between the optical deflector and the surface to be scanned.
As an example of a full-color image forming apparatus, four photoconductors are arranged in the conveyance direction of the recording paper, and light beams emitted from a plurality of light source devices corresponding to the photoconductors are formed by one deflecting unit. A deflection scan is performed, and a plurality of scanning imaging optical systems corresponding to the respective photosensitive members are simultaneously exposed to the respective photosensitive members to form latent images, and these latent images are developed in different colors such as yellow, magenta, cyan, and black. After being visualized by a developing device using an agent, these visible images are sequentially superimposed and transferred and fixed on the same recording paper so that a color image can be obtained. As described above, an image forming apparatus that obtains a multicolor image, that is, a two-color image (for example, red and black) or a three-color or more color image, by using two or more combinations of the optical scanning device and the photosensitive member. Is known as a “tandem image forming apparatus”.

As such a tandem type image forming apparatus, a system in which a plurality of photosensitive media share a single optical deflector is disclosed.
[1] A counter scanning method in which a light beam is incident from both sides of a deflector, and the light beam is distributed and scanned.
[2] A plurality of light beams that are substantially parallel and separated in the sub-scanning direction are incident on the deflector, and a plurality of scanning optical elements corresponding to the plurality of light beams are arranged and scanned in the sub-scanning direction.
[3] A light beam enters from one side of the deflector, and a plurality of scanning optical systems (L1, L2, L3) in L3 and L2 pass through a plurality of light beams directed to different scanning surfaces. It is provided for each scanning plane.
As described above, when the optical deflectors are shared by a plurality of scanned surfaces, it is possible to reduce the number of optical deflectors, thereby reducing the size and cost of the image forming apparatus.

  However, in recent years, plastic materials are often used for optical elements of scanning optical systems. While plastic is excellent in mass productivity, the shape may deviate from the ideal because the temperature distribution in the mold during molding and cooling after removal from the mold are not uniformly performed. Many. In a scanning optical system, there are many optical elements having a long shape in the main scanning direction, and the optical elements may be bent (warped) in the sub-scanning direction. Depending on the holding method, the scanning line inclination, the scanning line bending, etc. The scanning position shifts in the sub-scanning corresponding direction. Further, an error in attaching the optical element to the housing often results in a scanning position shift in the sub-scanning corresponding direction on the scanning surface and cannot be ignored.

Furthermore, in an image forming apparatus having a plurality of scanning means, the amount of scanning position deviation in the sub-scanning corresponding direction such as scanning line bending differs for each scanning means, resulting in color misregistration and a marked reduction in image quality. Let
In addition, in a tandem type full-color copying machine, four photosensitive drums corresponding to each color of cyan (C), magenta (M), yellow (Y), and black (K) are transferred on the transfer belt. And an optical scanning device scans the beam provided corresponding to each photoconductive drum to form an electrostatic latent image on the peripheral surface of the photoconductive drum and develop it with the toner of the corresponding color. Since this is converted into an image and this is sequentially transferred onto a sheet conveyed by a transfer belt to form a multicolor image, the scanning position shift in the sub-scanning corresponding direction is different for each color. Causes image quality degradation and color misregistration.

As a method for solving the above-described problem, in Japanese Patent Application Laid-Open No. H10-228707, in an image forming apparatus using a plurality of scanning units, the position of each scanning unit (housing) is adjusted with respect to the photosensitive member, and the scanning lines on each photosensitive member are matched. The invention has been described. However, the mechanism for adjustment becomes complicated and it takes time for adjustment, resulting in an increase in cost.
The present applicant has proposed a method of correcting the scanning line curvature by changing the amount of protrusion when a projection is abutted near the center of the lens in Patent Document 2 as a method of correcting the scanning line curvature. However, it is difficult to correct depending on the lens shape (for example, a lens having a thick central wall such as a single-lens scanning lens and short in the main scanning direction).

Further, a method for correcting the bending of the scanning line by bending a mirror that is turned back in the sub-scanning direction toward the surface to be scanned is known (for example, see Patent Document 3). However, if the mirror is curved, it has power in the main scanning direction, so that the curvature of field deteriorates and it is difficult to obtain a high-quality image. This becomes more significant as the adjustment amount (deflection amount) is larger.
As an adjustment of the inclination of the scanning line, there is a method in which the folding mirror is eccentrically adjusted around an axis parallel to the sub-scanning direction. According to this method, the curvature of field is deteriorated by changing the optical path length, and it becomes difficult to obtain a high-quality image.
The inability to obtain a high-quality image means that the resolution is particularly low. When the curvature of field is deteriorated, the beam spot diameter is increased and the resolution is lowered.

JP 2001-133718 A Japanese Patent Laid-Open No. 10-268217 JP 2001-228427 A

  An optical scanning device capable of satisfactorily correcting a scanning line bend caused by the curvature of a scanning lens and a scanning line inclination caused by assembly of an optical element and the like, and a high-quality color image can be obtained, and an image forming apparatus, and the problems It is an object of the present invention to realize an optical scanning device and a color image forming apparatus capable of solving the problem and reducing color misregistration.

In the invention described in claim 1, after the light beams corresponding to the plurality of scanned surfaces are deflected by the optical deflector, the imaging optical system, the folding mirror for folding the optical path and guiding the light beams to the scanned surface, In the optical scanning device that forms a multi-color image by condensing each of the scanning surfaces corresponding to each other, between the optical deflector and the scanned surface of the light beam directed to at least two scanned surfaces, The folding mirror has a rotation mechanism that can rotate around an axis that is not parallel to either the main scanning direction or the traveling direction of the light beam, and among the plurality of folding mirrors having the rotation mechanism, The folding mirror having the smallest deflection angle of the light beam is a folding mirror that reflects and deflects the lightest image beam.
According to a second aspect of the present invention, in the optical scanning device according to the first aspect, the folding mirror that reflects and deflects the lightest image beam is arranged on the axis among the plurality of folding mirrors having the rotating mechanism. On the other hand, it is a folding mirror having the longest distance to the position where the light beam at the outer end is reflected on the folding mirror surface.

According to a third aspect of the present invention, in the optical scanning device according to the first or second aspect, the folding mirror having the rotation mechanism has a bending mechanism that bends so as to have a curvature in the main scanning direction. The folding mirror that reflects and deflects the lightest image beam has the longest scanning line length in the main scanning direction on the mirror surface of the light beam that forms the image among the plurality of folding mirrors having the deflection mechanism. It is a short folding mirror.
In the invention described in claim 4, after the light beams corresponding to the plurality of scanned surfaces are deflected by the optical deflector, the imaging optical system, the folding mirror for folding the optical path and guiding the light beams to the scanned surface, In the optical scanning device that forms a multi-color image by condensing each on the corresponding scanned surface, the folding mirror is disposed between the optical deflector of the light beam directed to at least two scanned surfaces and the scanned surface. The bending mirror having a bending mechanism that bends so as to have a curvature in the main scanning direction, and the folding mirror having the smallest deflection angle of the light beam among the plurality of folding mirrors having the bending mechanism It is a folding mirror that reflects and deflects.

According to a fifth aspect of the present invention, in the optical scanning device according to the fourth aspect, the folding mirror that reflects and deflects the lightest image beam forms an image among the plurality of folding mirrors having the deflection mechanism. It is a folding mirror having the shortest scanning line length in the main scanning direction on the mirror surface of the light beam.
According to a sixth aspect of the present invention, in the optical scanning device according to the fourth or fifth aspect, the plurality of folding mirrors having the bending mechanism are parallel to both the main scanning direction and the traveling direction of the light beam. The folding mirror that has a pivoting mechanism that can pivot about a non-coordinated axis and reflects and deflects the lightest image beam reflects the light beam at the outer end on the folding mirror with respect to the axis. This is a folding mirror having the longest distance to the position.

In the invention described in claim 7, after the light beams corresponding to the plurality of scanned surfaces are deflected by the optical deflector, the imaging optical system, the folding mirror for folding the optical path and guiding the light beams to the scanned surface, In the optical scanning device that forms a multi-color image by condensing each on the corresponding scanned surface, the folding mirror is disposed between the optical deflector of the light beam directed to at least two scanned surfaces and the scanned surface. A rotation mechanism that can rotate around an axis that is not parallel to either the main scanning direction or the traveling direction of the light beam, and among the plurality of folding mirrors having the rotation mechanism, On the other hand, the folding mirror having the longest distance to the position where the light beam at the outer end is reflected on the folding mirror surface is a folding mirror that reflects and deflects the lightest image beam.
According to an eighth aspect of the present invention, in the optical scanning device according to the seventh aspect, the folding mirror having the rotation mechanism has a bending mechanism that bends so as to have a curvature in the main scanning direction, and the maximum brightness. The folding mirror that reflects and deflects the image beam is a folding mirror that has the shortest scanning line length in the main scanning direction on the mirror surface of the light beam that forms the image among the plurality of folding mirrors having the deflection mechanism. It is a mirror.
In the invention according to claim 9, after the light beam corresponding to the plurality of scanned surfaces is deflected by the optical deflector, the imaging optical system, the folding mirror for folding the optical path and guiding the light beam to the scanned surface, In the optical scanning device that forms a multi-color image by condensing each on the corresponding scanned surface, the folding mirror is disposed between the optical deflector of the light beam directed to at least two scanned surfaces and the scanned surface. , Having a bending mechanism for bending so as to have a curvature in the main scanning direction, and scanning the light beam forming the image on the mirror surface in the main scanning direction among a plurality of folding mirrors having the bending mechanism The folding mirror with the shortest line length is a folding mirror that reflects and deflects the lightest image beam.

According to a tenth aspect of the present invention, in the optical scanning device according to any one of the first to ninth aspects, the multicolor includes three colors of yellow, magenta, and cyan, and the lightest image beam. Is a yellow image beam.
According to an eleventh aspect of the present invention, in the optical scanning device according to any one of the first to tenth aspects, the imaging optical system is composed of a single scanning lens.
According to a twelfth aspect of the present invention, there is provided an image forming apparatus for forming an image by executing an electrophotographic process, and means for performing an exposure process of the electrophotographic process according to any one of the first to eleventh aspects. An image forming apparatus including the optical scanning device described above is characterized.
According to a thirteenth aspect of the present invention, in the image forming apparatus according to the twelfth aspect, the image forming apparatus has at least three photoconductors as the surface to be scanned, and forms a color image.

  According to the present invention, when scanning line inclination adjustment for color misregistration reduction is performed, a decrease in resolution in a multicolor image due to field curvature variation and beam spot diameter degradation is reduced, and a high-quality image is obtained. An optical scanning device that can be realized can be provided.

FIG. 1 is a diagram for explaining an embodiment of an optical scanning device of the present invention.
In the figure, reference numeral 1 is a light source, 2 is a coupling lens, 3 is a cylindrical lens, 4 is a polygon mirror, 4a is a reflecting surface of the polygon mirror, 5 is an imaging optical system, 6 is a scanning optical system, 7 is a photoconductor, Reference numeral 7a denotes a surface to be scanned.
This figure shows the optical path from the light source to the surface to be scanned developed on the same plane.
The divergent light beam L emitted from the semiconductor laser 1 as the light source is converted into a light beam form suitable for the subsequent optical system by the coupling lens 2. The form of the light beam converted by the coupling lens 2 can be a parallel light beam, or a light beam with weak divergence or weak convergence.
The light beam L from the coupling lens 2 is condensed in the direction of the paper surface of the figure by the cylindrical lens 3 and is incident on the deflection reflection surface 4a of the polygon mirror 4 as an optical deflector.
The light beam L ′ reflected by the deflecting / reflecting surface 4a is deflected at a constant angular velocity as the polygon mirror 4 rotates at a constant speed, passes through the imaging optical system 5, and is condensed on the scanned surface 7a. As a result, the deflected light beam L ′ forms a light spot on the scanned surface 7a, and performs optical scanning of the scanned surface 7a. As described above, scanning in this direction is called main scanning. The direction orthogonal to the main scanning direction on the scanned surface 7a is called sub-scanning. Actually, the light traveling direction is changed by a folding mirror (the folding mirror is not shown in the figure), so the “main scanning direction” and “sub-scanning direction” are relative to each other in the light traveling direction. Used as

  When the scanning lens is made of a plastic material, the shape often deviates from an ideal one because the temperature distribution in the mold at the time of molding and the cooling after taking out from the mold are not uniformly performed. Specifically, the scanning lens is bent (warped) in the sub-scanning direction, and the generatrix is bent, so that the light beam incident on the scanning lens is displaced and incident in the sub-scanning direction. The scan line tilts or bends on 7a. In addition, the inclination of the scanning line and the bending of the scanning line also occur due to variations in assembly of the optical elements.

FIG. 2 is a diagram for explaining the first embodiment of the present invention.
In the figure, A and B are optical path length variations corresponding to the mirrors, M is a folding mirror, Δθ is a displacement amount of the folding mirror (hereinafter referred to as eccentricity), P is a pivot point, and Z is an optical axis. Each is shown.
The present invention intends to solve the problem by configuring one end of the folding mirror M to be rotatable.
This figure explains how the optical path length to the surface to be scanned of a light beam incident on a position with a different distance from the rotation fulcrum P changes with the same mirror rotation amount Δθ. FIG. 4A shows a case where the distance from the fulcrum P is short, and FIG. 4B shows a case where the distance from the fulcrum P is long. The fulcrum P represents one point on the plan view of the shaft provided at one end of the mirror M, and as will be described later, the shaft is not always perpendicular to the paper surface in FIG.
According to the present invention, the folding mirror M is arranged between the optical deflector of the light beam directed to at least two or more scanned surfaces of the optical scanning device having the folding mirror M and the scanned surface. It has a turning mechanism that can turn around an axis that is not parallel to the beam traveling direction. As shown in the figure, when the folding mirror M is rotated about an axis parallel to the reflecting surface of the mirror M as a fulcrum P, the inclination of the scanning line on the scanned surface 7a changes. When a multicolor image is formed, if each has a different inclination on the photoconductor as each surface to be scanned, color misregistration occurs when the respective colors are superimposed, and the image quality is significantly reduced. In other words, it is possible to reduce the color shift by adjusting the scanning line inclination on the surface to be scanned corresponding to each color by the folding mirror M.
In addition to the configuration in which the rotation axis is parallel to the reflecting surface of the mirror M, depending on the configuration of the housing, it can be modified as appropriate, for example, by providing the shaft in the vertical direction or the like so that it can be easily adjusted from the side or top surface of the housing. is there.

In the scanning line inclination adjusting mechanism, color misregistration can be reduced. However, when the scanning line inclination is adjusted in the adjustment, the optical path length of the light beam L ′ directed toward the scanned surface 7a changes (difference caused by A1 and A2 in the figure). When the optical path length changes, the curvature of field changes, which causes a phenomenon that the beam spot diameter on the surface to be scanned increases. As a result, the resolution of the image is lowered, and the image quality is different from the color shift.
Therefore, in the present invention, among the plurality of folding mirrors that can be rotated around an axis that is not parallel to the main scanning direction and the traveling direction of the light beam, the folding mirror having the smallest deviation angle of the light beam A folding mirror that reflects and deflects a light beam corresponding to a surface to be scanned that forms a high color image (hereinafter referred to as a beam for maximum brightness image).

FIG. 3 is a diagram for explaining a difference in adjustment amount due to a difference in deflection angle of the folding mirror.
In order to reduce the field curvature fluctuation, it is necessary to reduce the eccentric adjustment amount of the folding mirror M and to reduce the change in the optical path length. If the change in the optical path length is small, the field curvature fluctuation can be reduced and the beam spot diameter fluctuation can be reduced. In order to reduce the decentering adjustment amount of the folding mirror, it is necessary to increase (obtuse) the deflection angle (hereinafter simply referred to as the deflection angle) of the light beam by the folding mirror. As shown in the figure, when the same amount (B in the figure) of the scanning position change is given on the surface to be scanned with a mirror having a large declination and a small mirror, the decentering amount of the folding mirror M is a mirror having a large declination. Is smaller. That is, the adjustment sensitivity is high. Looking at the change in the optical path length at this time, it can be seen that the portion indicated by the dotted line in the figure is larger for the mirror having a small declination. That is, in a mirror with a small declination, a change in the optical path length, in other words, a field curvature variation becomes large and the beam spot diameter deteriorates. In the figure, a light beam far from the eccentric axis of the adjustment mirror is extracted and shown. When viewed in the main scanning section, it is an explanatory diagram at the position A1 or A2 in FIG.
In the figure, three arrows in the sub-scanning direction are shown. This is because the direction perpendicular to the light traveling direction in the drawing of FIG.

FIG. 4 is a view for explaining an optical path when four photoconductors are used.
In the figure, reference numeral 7 denotes a photosensitive member having a scanned surface.
As shown in the figure, for example, in the optical paths of light beams directed to four different scanned surfaces 7a, the deflection angles of a plurality of adjustment folding mirrors (hatched folding mirrors in the figure) are common to each light beam. That is difficult and impractical. That is, there are a light beam in which a mirror with high adjustment sensitivity is arranged and a light beam in which a mirror with low adjustment sensitivity is arranged. This means that there are always a color image with a large variation in field curvature and a color image with a small variation in field curvature, that is, a color image with a large deterioration in beam spot diameter and a small color image. Therefore, in the present invention, the folding mirror for adjustment having the smallest deflection angle of the light beam (lowest adjustment sensitivity) is a folding mirror that reflects and deflects the lightest image beam. By adopting the form of this method, the color image with the greatest resolution degradation in the multi-color image is changed to the most inconspicuous color, that is, the color with the highest brightness (for example, cyan, magenta, yellow, and black). In the case of yellow). A reduction in resolution with a low-lightness color causes a significant reduction in quality in the image, but a color with a high lightness has a relatively small effect on the resolution. According to the present invention, it is possible to minimize degradation of resolution, and it is possible to realize an optical scanning device that can obtain good image quality from both sides of color shift and resolution.

The folding mirror that reflects and deflects the lightest image beam (hereinafter referred to as beam Y for convenience) is a folding mirror that is farthest from the pivot point P to the reflection point of the beam Y. desirable.
In the image forming apparatus, the structure of the optical system housing is complicated, and therefore the lengths of the folding mirrors cannot often be made the same. Since the position of the axis is provided at the end of the mirror, the distance from the axis to the light beam incident position (beam reflection point) may differ depending on the mirror.
In other words, in the optical paths of the light beams directed to four different scanning surfaces, it is possible to match the distances between the rotation fulcrums P of the plurality of folding mirrors that can be rotated about the axis and the optical axis. This is a major limitation in designing the housing. For this reason, it is conceivable that the position of the rotation fulcrum P differs depending on each folding mirror.
The distance from the turning fulcrum P of the folding mirror to the reflection position of the light beam at the image end opposite to the fulcrum on the folding mirror in the main scanning direction (hereinafter referred to as the outer end beam for convenience) is long. In this case, as shown in FIG. 2, when the amount of eccentricity Δθ for adjustment is the same, the change in the optical path length becomes larger than when the distance is short (A <B in the figure). Since the problem when the change in the optical path length is large is the same as that described above, it is omitted. In the figure, the light beam is originally reflected by the mirror, but for the sake of explanation, it is shown as being transmitted.

In other words, when the adjustment sensitivity of the folding mirror for adjustment is low as in the first embodiment, and the distance to the reflection position of the outer end beam is long, the field curvature variation becomes larger and the resolution degradation also increases.
Therefore, in the present invention, the folding mirror that reflects and deflects the beam Y is a folding mirror that is farthest from the outer end beam reflection position. According to the present invention, degradation in resolution can be minimized, and an optical scanning device that can obtain good image quality from both sides of color misregistration and resolution in a multicolor image can be realized.

The scanning line inclination correction has been described so far. Next, scanning line curve correction will be described.
As described above, when the scanning lens is made of a plastic material, the shape is not ideal because the temperature distribution in the mold at the time of molding and the cooling after taking out from the mold are not uniformly performed. There are many. Specifically, the scanning lens is bent (warped) in the sub-scanning direction, and the generatrix is bent, so that the light beam incident on the scanning lens is displaced and incident in the sub-scanning direction. Scan line bending occurs above. In addition, scanning line bending also occurs due to variations in assembly of optical elements.

  In the present invention, between the optical deflector of the light beam directed to at least two or more scanned surfaces and the scanned surface, the folding mirror has a bending mechanism that bends so as to have a curvature in the main scanning direction. The scanning line can be bent on the surface to be scanned by bending the folding mirror so as to have a curvature in the main scanning direction. That is, in other words, it is possible to correct the generated scanning line curve to a state close to a straight line.

  In the scanning line curve adjustment mechanism, color misregistration can be reduced. However, when the folding mirror is bent in order to adjust the scanning line bending, the folding mirror has a convex or concave refractive power, and the field curvature in the main scanning direction in particular varies. As described in the first embodiment, if the field curvature variation is large, the beam spot diameter is deteriorated and the resolution is lowered.

FIG. 5 is a diagram for explaining a third embodiment of the present invention.
This figure is a diagram for explaining the difference in bending displacement due to the difference in deflection angle of the folding mirror.
FIG. 6 is a diagram for explaining the relationship between the curvature of the folding mirror and the curvature of field on the surface to be scanned.
In order to reduce the field curvature fluctuation, it is necessary to reduce the bending amount of the folding mirror and to reduce the refractive power of the convex or concave of the folding mirror. If the refracting power of the folding mirror is small, the field curvature fluctuation can be reduced and the beam spot diameter fluctuation can be reduced. In order to reduce the bending amount of the folding mirror, it is necessary to increase (obtuse) the deflection angle of the light beam by the folding mirror. As shown in the figure, the amount of fluctuation in the scanning line curve (B, B 'in the figure) when the same amount of deflection (A in the figure) is given by the mirror having a large declination and the small mirror. Is larger for a mirror having a larger declination (B ′). That is, the adjustment sensitivity of a mirror with a declination being an obtuse angle is high, and the adjustment sensitivity of a mirror with a declination being an acute angle is low. The two mirrors (actually one mirror is bent) and the surface to be scanned 7a described with reference to FIG. 6 correspond to positions C and D in FIG. 6, respectively.

  For example, in the optical paths of light beams directed to four different surfaces to be scanned, it is difficult and unrealistic to make the deflection angle of the folding mirror common to each light beam. That is, there are a light beam in which a mirror with high adjustment sensitivity is arranged and a light beam in which a mirror with low adjustment sensitivity is arranged. This means that there are always a color image with a large variation in field curvature and a color image with a small variation in field curvature, that is, a color image with a large deterioration in beam spot diameter and a small color image. Therefore, in the present invention, the folding mirror for adjustment having the smallest deflection angle of the light beam (lowest adjustment sensitivity) is a folding mirror that reflects and deflects the beam Y. By adopting the form of this method, the resolution deterioration in the multi-color image is the least noticeable color, that is, the color with the highest brightness (for example, yellow in the case of a four-color image of cyan, magenta, yellow, and black). be able to. A reduction in resolution with a low-lightness color causes a significant reduction in quality in the image, but a color with a high lightness has a relatively small effect on the resolution. According to the present invention, it is possible to minimize degradation of resolution, and it is possible to realize an optical scanning device that can obtain good image quality from both sides of color shift and resolution.

FIG. 7 is a diagram for explaining the amount of deflection when the folding mirror is bent.
In the present invention, in the folding mirror, the folding mirror having the shortest scanning line length in the main scanning direction on the mirror surface of the light beam forming the image is a folding mirror that reflects and deflects the beam Y.
The amount of deflection used below means the amount of displacement in the optical axis direction (direction toward the center of the surface to be scanned) of the center of the mirror with respect to a line connecting both ends of the mirror. The depth amount refers to the amount of displacement in the optical axis direction at the center of the mirror with respect to a line connecting both ends of the scanning line.
When the amount of deflection of the adjustment mirror is the same, the depth shown in the figure is different between the case where the length of the scanning line on the mirror surface is long and the case where the length is short (A <A ′ in the figure). Changes. Specifically, when the length of the scanning line on the mirror surface is short (A in the figure), the correction sensitivity of the scanning line bending becomes low. In this case, in order to obtain the same correction amount (in order to obtain the same amount of A as A ′, the curvature becomes strong), it is necessary to increase the amount of deflection. When the deflection amount is increased, the refractive power of the convex or concave in the main scanning direction of the folding mirror is increased, and the beam spot diameter is greatly deteriorated and the resolution is lowered.

  Therefore, in the present invention, in the folding mirror, the folding mirror having the shortest scanning line length in the main scanning direction on the mirror surface of the light beam forming the image is the beam Y, that is, for the most bright image. A folding mirror that reflects and deflects the beam is used, and the maximum resolution degradation in a multicolor image is assigned to the color with the highest brightness (for example, yellow for a four-color image of cyan, magenta, yellow, and black). A reduction in resolution with a low-lightness color causes a significant reduction in quality in the image, but a color with a high lightness has a relatively small effect on the resolution. According to the present invention, it is possible to reduce color misregistration by correcting the occurrence of scanning line bending, and to reduce deterioration in resolution in a multicolor image due to fluctuations in field curvature and beam spot diameter degradation. It is possible to provide an optical scanning device that can realize the above.

So far, scanning line inclination and scanning line bending have been described separately, but even when adjustment is performed using different folding mirrors, satisfactory image quality can be satisfied by satisfying the above description. That is, the above-described relationship is established between the scanning line bending correction folding mirrors, and the above-described description relationship is established between the scanning line tilt correction folding mirrors, thereby realizing a good image quality.
Further, the scanning line bending and the scanning line tilt adjusting mirror may be implemented by the same mirror. In this case, it goes without saying that good image quality can be realized by establishing the relationship of the present invention.
That is, providing a turning mechanism at one end of the folding mirror and bending the folding mirror is not a contradiction, and assigning a folding mirror with the smallest declination to the lightest image beam, It is not necessarily a tradeoff between allocating the folding mirror with the longest distance to the position where the light beam at the outer edge is reflected and allocating the folding mirror with the shortest scanning line length in the main scanning direction on the mirror surface. . Therefore, various combinations exist.

  In the case of two scanning lenses, there is a method proposed by the present applicant that a projection is abutted near the center of the scanning lens and the amount of projection is changed to correct the scanning line bending. In the case of a scanning lens having a configuration, it is difficult to correct depending on the lens shape (for example, a lens having a thick central thickness such as a scanning lens and a short lens in the main scanning direction). In such an optical scanning device using a single-lens scanning lens, scanning line bending correction by a folding mirror as in the present invention that does not require lens deformation is particularly effective.

FIG. 8 is a view showing an example of an image forming apparatus using the optical scanning device according to the present invention.
The present embodiment is an example in which the optical scanning device according to the present invention is applied to a tandem type full-color laser printer. In the figure, a conveying belt 17 for conveying transfer paper (not shown) fed from a paper feeding cassette 13 disposed in the horizontal direction is provided on the lower side in the apparatus. On the conveying belt 17, a photosensitive member 7Y for yellow Y, a photosensitive member 7M for magenta M, a photosensitive member 7C for cyan C, and a photosensitive member 7K for black K are sequentially arranged from the upstream side in the conveying direction of the transfer paper. They are arranged at equal intervals. Hereinafter, subscripts Y, M, C, and K are appropriately added to the reference numerals for distinction. These photoreceptors 7Y, 7M, 7C, and 7K are all formed to have the same diameter, and process members that perform each process according to the electrophotographic process are sequentially arranged around the photoreceptors. Taking the photoconductor 7Y as an example, a charging charger 8Y, an optical scanning optical system 6Y, a developing device 10Y, a transfer charger 11Y, a cleaning device 12Y, and the like are sequentially arranged. The same applies to the other photoconductors 7M, 7C, and 7K. That is, in the present embodiment, the surfaces of the photoconductors 7Y, 7M, 7C, and 7K are to be scanned surfaces 7a set for the respective colors, and four optical scanning optical systems are provided for each photoconductor. 6Y, 6M, 6C, and 6K are provided in a one-to-one correspondence. In addition, a registration roller 16 and a belt charging charger 20 are provided around the transport belt 17 on the upstream side of the photoconductor 7Y, and are positioned on the downstream side in the rotation direction of the belt 17 with respect to the photoconductor 7K. A belt separation charger 21, a static elimination charger 8, a cleaning device 12 and the like are provided in this order. Further, a fixing device 24 is provided downstream of the belt separation charger 21 in the transfer paper conveyance direction, and is connected to a paper discharge tray 26 by a paper discharge roller 25.

In such a schematic configuration, for example, in the case of the full color mode (multiple color mode), each of the photoconductors 7Y, 7M, 7C, and 7K is based on image signals of colors Y, M, C, and K, respectively. In this optical scanning device 6Y, 6M, 6C, 6K, an electrostatic latent image corresponding to each color signal is formed on the surface of each photoconductor. These electrostatic latent images are developed with color toners by the corresponding developing devices to become toner images, which are superposed by being sequentially transferred onto transfer paper that is electrostatically attracted onto the transport belt 17 and transported. As a result, a full-color image is formed on the transfer paper. This full-color image is fixed by the fixing device 24 and then discharged to a discharge tray 26 by a discharge roller 25.
By using the optical scanning optical systems 6Y, 6M, 6C, and 6K of the image forming apparatus as the optical scanning apparatus according to the above-described embodiment, scanning line bending, scanning line inclination, and field curvature deterioration can be effectively corrected. Therefore, it is possible to realize an image forming apparatus that can ensure high-quality image reproducibility without color misregistration.

It is a figure for demonstrating one Embodiment of the optical scanning device of this invention. It is a figure for demonstrating the 1st Example of this invention. It is a figure for demonstrating the difference in the adjustment amount by the difference in the deflection angle of a folding mirror. It is a figure for demonstrating the optical path in the case of using four photoconductors. It is a figure for demonstrating the 3rd Example of this invention. It is a figure for demonstrating the relationship between the curvature of a folding mirror, and the curvature of field in a to-be-scanned surface. It is a figure for demonstrating the deflection amount at the time of bending a folding mirror. 1 is a diagram illustrating an example of an image forming apparatus using an optical scanning device according to the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Light source 2 Coupling lens 3 Cylindrical lens 4 Polygon mirror 5 Imaging optical system 6 Scanning surface 7 Photoconductor

Claims (13)

  Light beams corresponding to a plurality of scanned surfaces are deflected by an optical deflector and then collected on the corresponding scanned surfaces by an imaging optical system and a folding mirror that folds the optical path and guides the light beams to the scanned surface. In the optical scanning device that forms a multicolor image by emitting light, the folding mirror is disposed between the optical deflector and the scanned surface of the light beam directed to at least two scanned surfaces. A turning mechanism capable of turning about an axis that is not parallel to any of the beam traveling directions, and a turning-back light beam having the smallest deflection angle among a plurality of turning mirrors having the turning mechanism. An optical scanning device characterized in that the mirror is a folding mirror that reflects and deflects the lightest image beam.   2. The optical scanning device according to claim 1, wherein the folding mirror for reflecting and deflecting the lightest image beam is outside of the plurality of folding mirrors having the rotation mechanism on the folding mirror surface with respect to the axis. An optical scanning device characterized by being a folding mirror having a longest distance to a position where an end light beam is reflected.   3. The optical scanning device according to claim 1, wherein the folding mirror having the rotating mechanism has a bending mechanism that bends so as to have a curvature in the main scanning direction, and reflects and deflects the lightest image beam. The folding mirror is a folding mirror having the shortest scanning line length in the main scanning direction on the mirror surface of the light beam forming the image among the plurality of folding mirrors having the bending mechanism. Optical scanning device.   Light beams corresponding to a plurality of scanned surfaces are deflected by an optical deflector and then collected on the corresponding scanned surfaces by an imaging optical system and a folding mirror that folds the optical path and guides the light beams to the scanned surface. In an optical scanning device that forms a multicolor image by irradiating light, the folding mirror has a curvature in the main scanning direction between the optical deflector and the scanned surface of the light beam directed to at least two scanned surfaces. The folding mirror having the smallest deflection angle of the light beam is a folding mirror that reflects and deflects the lightest image beam. An optical scanning device.   5. The optical scanning device according to claim 4, wherein the folding mirror that reflects and deflects the lightest image beam is formed on the mirror surface of the light beam that forms an image among the plurality of folding mirrors having the deflection mechanism. An optical scanning device characterized by being a folding mirror having the shortest scanning line length in the main scanning direction.   6. The optical scanning device according to claim 4, wherein the plurality of folding mirrors having the bending mechanism are rotatable around an axis that is not parallel to either the main scanning direction or the traveling direction of the light beam. A folding mirror that reflects and deflects the lightest image beam has a longest distance from the axis to the position where the outer end light beam is reflected on the folding mirror. An optical scanning device characterized by being a mirror.   Light beams corresponding to a plurality of scanned surfaces are deflected by an optical deflector and then collected on the corresponding scanned surfaces by an imaging optical system and a folding mirror that folds the optical path and guides the light beams to the scanned surface. In an optical scanning device that forms a multicolor image by emitting light, the folding mirror is disposed between the optical deflector and the scanned surface of the light beam directed to at least two scanned surfaces, in the main scanning direction and the traveling of the light beam. A rotation mechanism that can rotate around an axis that is not parallel to any of the directions, and out of the plurality of folding mirrors having the rotation mechanism on the folding mirror surface with respect to the axis An optical scanning device characterized in that the folding mirror having the longest distance to the position where the end light beam is reflected is a folding mirror that reflects and deflects the lightness image beam.   8. The optical scanning device according to claim 7, wherein the folding mirror having the rotation mechanism has a bending mechanism that bends so as to have a curvature in the main scanning direction, and reflects and deflects the beam for maximum brightness image. Is a folding mirror that has the shortest scanning line length in the main scanning direction on the mirror surface of the light beam forming the image among the plurality of folding mirrors having the bending mechanism. Scanning device.   Light beams corresponding to a plurality of scanned surfaces are deflected by an optical deflector and then collected on the corresponding scanned surfaces by an imaging optical system and a folding mirror that folds the optical path and guides the light beams to the scanned surface. In an optical scanning device that forms a multicolor image by irradiating light, the folding mirror has a curvature in the main scanning direction between the optical deflector and the scanned surface of the light beam directed to at least two scanned surfaces. A folding mirror having the shortest scanning line length in the main scanning direction on the mirror surface of the light beam forming the image, among the plurality of folding mirrors having the deflection mechanism Is a folding mirror that reflects and deflects the lightest image beam.   10. The optical scanning device according to claim 1, wherein the multicolor includes three colors of yellow, magenta, and cyan, and the lightest image beam is a yellow image beam. An optical scanning device.   11. The optical scanning device according to claim 1, wherein the imaging optical system is composed of a single scanning lens.   12. An image forming apparatus for forming an image by executing an electrophotographic process, comprising the optical scanning device according to claim 1 as means for performing an exposure process of an electrophotographic process. An image forming apparatus.   13. The image forming apparatus according to claim 12, wherein the image forming apparatus has at least three photoconductors as the scanning surface and forms a color image.

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