JP2008191435A - Optical scanning device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical scanning device enabling high speed image output while attaining a low cost by reducing the number of light sources. <P>SOLUTION: The optical scanning device has: the modulation driven light sources 1-1, 1-2; a deflection means 7 having multi-face reflection mirrors 7a, 7b on a common rotating shaft in a plurality of stages; a light flux division means 4 for entering a light beam divided into the different stage reflection mirrors 7a, 7b of the deflection means 7 by dividing the light beam from the common light source; a plurality of faces to be scanned 11a, 11b; and scanning optical systems 8, 9, 10a, 10b for guiding the light beam scanned by the deflection means 7 to the corresponding face to be scanned. In the optical scanning device, the light beam scanning the different faces to be scanned 11a, 11b, the different stage multi-face reflection mirrors 7a, 7b displace in an angle of θ of a mutually rotating direction, and the light beam divided from the common light source has the angle in each sub-scanning direction to the normal of the multi-face reflection mirrors 7a, 7b. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an optical scanning device provided in an electrophotographic image forming apparatus, and image formation of a digital copying machine, a laser printer, a laser plotter, a laser facsimile, or a composite machine including these optical scanning devices. Relates to the device.

An electrophotographic image forming apparatus has been put into practical use as a digital copying machine, a laser printer, a laser plotter, a laser facsimile, or a complex machine thereof. However, in these electrophotographic image forming apparatuses, in recent years, With the progress of colorization and high speed, tandem color image forming apparatuses having a plurality of photoconductors (four mainstream) are becoming popular.
However, in the optical scanning device provided in the tandem image forming apparatus, the number of light sources increases corresponding to each photoconductor, so that the cost increases due to the increase in the number of parts and the color shift caused by the wavelength difference between the multiple light sources. There is a problem that it occurs.

In general, the cost of the light source unit in the optical scanning device is expensive because it includes a base for modulating the semiconductor laser, which is a harmful effect in the case of aiming to reduce the cost and size of the entire device. .
Further, the cause of the failure of the optical scanning device is the deterioration of the semiconductor laser used as the light source. As the number of light sources increases, the establishment of failure increases, which is disadvantageous for recycling.

  As an example of a device that does not increase the number of light sources in an optical scanning device that supports the tandem method, an optical scanning device described in Patent Document 1 has been proposed. In this prior art, a scanning surface with different light beams from a common light source is scanned using a pyramid mirror or a flat mirror. However, with this method, the number of light sources can be reduced, but the number of deflecting mirrors is limited to a maximum of two, and there remains a problem with speeding up.

  In order to solve the above-mentioned problems, the present invention uses a deflecting means having a polygon mirror (polygonal mirror) stacked in two stages as a means for scanning a surface to be scanned with different light beams from a common light source. It is. As a technique similar to the present invention, a conventional technique described in Patent Document 2 is disclosed. However, this conventional technique aims to increase the scanning width and is not intended to scan different surfaces to be scanned.

More recently, in an optical scanning device of a color image forming apparatus, a light beam is incident (obliquely incident) at an angle in the sub-scanning direction on the deflection reflection surface of the optical deflector as in the prior art described in Patent Document 3. An oblique incidence optical system is known. In this oblique incidence optical system, after a plurality of light beams are deflected and reflected by the deflecting / reflecting surfaces, they are separated and guided to corresponding scanning surfaces (photoconductors) by folding mirrors or the like. At this time, the angle of each light beam in the sub-scanning direction (the angle at which the light beam obliquely enters the optical deflector) is set to an angle at which each light beam can be separated by the mirror.
However, the oblique incidence method has problems such as occurrence of “scanning line bending” and an increase in the deviation between the image heights of the beam spot diameter due to “deterioration of wavefront aberration”. The amount of bending of the scanning line varies depending on the oblique incident angle of each light beam in the sub-scanning direction, and color misregistration occurs when a latent image drawn with each light beam is visualized by overlaying with each color toner. Appears. In addition, the oblique incident light causes the light beam to be twisted and incident on the scanning lens, thereby increasing the wavefront aberration. Particularly, the optical performance is significantly deteriorated at the peripheral image height, the beam spot diameter is increased, and the image quality is improved. It becomes a factor to prevent.

As a method of correcting the “large scanning line bending” inherent to the oblique incidence method, the scanning imaging optical system “changes the inherent inclination of the lens surface in the sub-scan section in the main scanning direction so as to correct the scanning line bending. Including a lens having a curved lens surface (Patent Document 4) or “inherent inclination of the reflecting surface in the sub-scanning section is changed in the main scanning direction to correct the scanning line curvature” in the scanning imaging optical system. A method of including a “corrected reflecting surface having a reflected surface” (Patent Document 5) has been proposed.
Further, in the prior art described in Patent Document 6, the obliquely incident light beam passes through the off-axis of the scanning lens, and scanning is performed using a surface that changes the aspherical amount of the scanning lens child line along the main scanning direction. A method for aligning the positions of lines has been proposed. In the prior art described in Patent Document 6, an example in which correction is performed by one scanning lens is given, and the scanning line bending can be corrected. However, a beam spot diameter due to an increase in wavefront aberration described below. There is no description of the degradation of.

  Another problem with the oblique incidence method is that a large wavefront aberration is likely to occur at the peripheral image height (near both ends of the scanning line) due to the light beam skew. When such wavefront aberration occurs, the spot diameter of the light spot increases at the peripheral image height. That is, an image height deviation of the beam spot diameter occurs. If this problem cannot be solved, it will not be possible to achieve the "high image quality" that has been strongly demanded recently. In the optical scanning device described in Patent Document 6, a large scanning line curve peculiar to the oblique incidence method is corrected well, but the correction of the wavefront aberration is not sufficient.

As an optical scanning device that can satisfactorily correct the above-mentioned “scan line bending and wavefront aberration degradation”, which can be said to be a problem with the oblique incidence method, the scanning imaging optical system includes a plurality of rotationally asymmetric lenses, and lenses of these rotationally asymmetric lenses. There has been proposed a shape in which a generatrix connecting the child vertexes of a surface is curved in the sub-scanning direction (Patent Document 7).
However, the lens having the “lens surface curved in the sub-scanning direction of the generatrix connecting the child vertexes” solves various problems by curving the generatrix, and an individual scanning lens corresponding to the incident light beam Therefore, when applied to a tandem scanning optical system, the number of scanning lenses increases. In other words, when a plurality of light beams directed to different scanning surfaces are incident on the same lens, the problem is solved for one of the light beams by curving the shape of the generatrix, but the other light beam is scanned. It is difficult to reduce line bending and wavefront aberration.

Also, since it has a curvature in the sub-scanning direction, if the light beam incident on the lens shifts in the sub-scanning direction due to the effects of assembly errors, processing errors, environmental fluctuations, etc., the influence of the refractive power of the lens in the sub-scanning direction Therefore, there is a problem that the shape of the scanning line curve changes, the effect of suppressing the initial (or design) color shift in the color image cannot be obtained, and color shift occurs.
Further, in the correction of wavefront aberration, a change in the skew state of the light beam is large due to the fluctuation of the incident light beam on the surface having the curvature, and it is difficult to stably obtain a good beam spot diameter.

  Also in the prior art described in Patent Document 3 which is the oblique incidence method described above, the scanning line bending is corrected using the same surface as in Patent Document 7. However, as described above, it is difficult to stably obtain a good beam spot diameter.

Japanese Patent Laid-Open No. 2002-23085 Japanese Patent Laid-Open No. 2001-83451 JP 2003-5114 A Japanese Patent Laid-Open No. 11-14932 Japanese Patent Laid-Open No. 11-38348 JP 2004-70109 A Japanese Patent Laid-Open No. 10-73778

The present invention has been made in view of the above circumstances, and has as its first object the realization of an optical scanning device that enables high-speed image output while reducing the number of light sources and reducing the cost.
In addition, the present invention provides a novel configuration of optical scanning that can effectively correct scanning line bending and wavefront aberration deterioration in an oblique incidence type optical scanning device that can prevent malfunction of the light source and realize good image output. The realization of the device is a second object.
Furthermore, a third object of the present invention is to provide an optical scanning device in consideration of the environment such as a reduction in failure rate, improvement in recyclability, and low power consumption.
Furthermore, a fourth object of the present invention is to realize an image forming apparatus having a novel configuration provided with an optical scanning device capable of achieving the first to third objects.

In order to achieve the above object, the present invention employs the following technical means.
The first means of the present invention includes a light source to be modulated and driven, a deflecting means having a plurality of stages of reflecting mirrors on a common rotation axis, and a stage different from the deflecting means by dividing a light beam from the common light source. A light beam splitting unit that causes the split light beam to enter, a plurality of scanned surfaces, and a scanning optical system that guides the light beam scanned by the deflecting unit to the corresponding scanned surface, In the optical scanning device in which the divided light beams scan different surfaces to be scanned, the multi-surface reflecting mirrors of the different stages are shifted in rotation angle with respect to each other, and the light beams divided from a common light source are Each of them has an angle in the sub-scanning direction with respect to the normal of the reflecting mirror.

According to a second means of the present invention, in the optical scanning device of the first means, at least one surface of at least one scanning lens constituting the scanning optical system faces the periphery in the main scanning direction and enters the scanning lens. A special surface composed of a surface in which the angle of the light beam emitted from the scanning lens with respect to the normal line of the multi-surface reflector is larger than the angle of the multi-surface reflector mirror with respect to the normal line of the multi-surface reflector. It has a surface.
According to a third means of the present invention, in the optical scanning device of the second means, the special surface is shared by all the light beams directed to different scanned surfaces.

According to a fourth means of the present invention, in the optical scanning device according to any one of the first to third means, the light beams divided from the common light source are respectively subordinate to the normal line of the multi-surface reflecting mirror. It has a different sign angle in the scanning direction.
According to a fifth means of the present invention, in the optical scanning device of any one of the first to fourth means, a light beam path is deflected and divided by the light beam dividing means from the common light source. The angle in the sub-scanning direction with respect to the normal line of the multi-faced reflecting mirror is smaller than the angle in the sub-scanning direction with respect to the normal line of the multi-faced reflecting mirror of the light beam whose beam path is not deflected by the beam splitting means. It is characterized by.
Furthermore, a sixth means of the present invention is the optical scanning device of any one of the first to fifth means, comprising a plurality of the light sources, and the light beams from each light source are symmetrical in the sub-scanning direction. It is incident on a multi-surface reflecting mirror having a common rotation axis corresponding to an angle.

According to a seventh means of the present invention, in the optical scanning device of any one of the first to sixth means, the plurality of light sources are provided, and the scanning optical system is arranged for each light beam from the plurality of light sources. And at least one surface of the lens disposed for each light beam from the plurality of light sources is a surface having a different amount of shift eccentricity in the sub-scanning direction in the main scanning direction.
According to an eighth means of the present invention, in the optical scanning device according to any one of the first to sixth means, the light source includes a plurality of light sources, and the scanning optical system includes light beams from the light sources. The lens arranged for each light beam from the plurality of light sources does not have power in the sub-scanning direction, and has a surface with a different amount of tilt eccentricity in the sub-scanning direction in the main scanning direction. It is characterized by having.

According to a ninth means of the present invention, in the optical scanning device of any one of the first to eighth means, a multi-beam light source that emits a plurality of light beams is used as the light source.
According to a tenth means of the present invention, in the optical scanning device according to any one of the first to ninth means, different scanned surfaces corresponding to a plurality of light sources are constituted by at least four photosensitive members. It is characterized by.

  According to an eleventh means of the present invention, in the image forming apparatus for forming an image by executing an electrophotographic process, any one of the first to tenth means as a means for executing an exposure process of the electrophotographic process. The optical scanning device is provided.

According to the present invention, the light beam from the common light source is split into two light beams by the light beam splitting means, and deflected by the deflecting means having a multi-stage polygon mirror to simultaneously scan different scanning surfaces. It is possible to simultaneously scan four scanned surfaces using two light sources, and to realize an optical scanning device that enables high-speed and good image output while reducing the number of light sources. Therefore, according to the present invention, the number of parts of the optical scanning device can be reduced and the cost can be reduced, the failure rate of the entire unit is reduced, and the recyclability is improved. Further, in the present invention, since the surface shape of the scanning lens constituting the scanning optical system is devised, scanning line bending and wavefront aberration deterioration in an oblique incidence type optical scanning device can be effectively corrected. The difference in quality between the beams that scan the surface to be scanned (photoreceptor surface) can be reduced.
Furthermore, according to the present invention, by using a multi-beam light source as a light source, a plurality of scanning lines can be formed on the same scanned surface by one scan, and the high-speed and high-density of the image forming apparatus. Can be realized. In addition, according to the present invention, it is possible to realize an image forming apparatus capable of outputting an image with an appropriate density and with little density unevenness. Further, an image forming apparatus capable of outputting an image with excellent color reproducibility by adjusting the set light amount can be realized.

  Hereinafter, specific configurations, operations, and effects of the present invention will be described in detail based on illustrated embodiments.

[Example 1 (Example of the first means)]
FIG. 1 is a schematic configuration diagram of a main part of an optical scanning device according to an embodiment of the present invention. In the figure, reference numerals 1-1 and 1-2 denote a semiconductor laser (LD) as a light source, 2 denotes an LD (semiconductor laser) base, 3-1 and 3-2 denote coupling lenses, and 4 denotes a light beam as light beam dividing means. Dividing elements (half mirror prism in the example shown), 5-1 and 5-2 are cylindrical lenses, 6 is soundproof glass, and 7 is an optical deflector having multi-stage polygon mirrors (polygon mirrors) 7a and 7b as deflecting means. , 8 is a first scanning lens, 9 is a mirror, 10 is a second scanning lens, 11a and 11b are photoreceptors as scanning surfaces, and 12 is an aperture stop (aperture). The two divergent light beams emitted from the semiconductor lasers 1-1 and 1-2 are converted into weak convergent light beams, parallel light beams, or weak divergent light beams by the coupling lenses 3-1 and 3-2. The light beams exiting the coupling lenses 3-1 and 3-2 pass through the aperture stop 12 for stabilizing the beam diameter on the scanned surface and enter the half mirror prism 4. Since the light beam from the common light source (semiconductor laser 1-1 or 1-2) incident on the half mirror prism 4 is divided into two in the upper and lower stages and emitted, all the light beams emitted from the half mirror prism 4 are emitted. There are four light beams.

  In FIG. 1, only two optical systems after the optical deflector 7 are shown, and only two photoconductors 11a and 11b are shown as scanning surfaces. However, the optical scanning device is a tandem type which will be described later. When mounted on the image forming apparatus, as shown in FIG. 5B or FIG. 9B, four photoconductors 11Y, 11M, 11C, and 11K are arranged as the scanning surface, and the scanning optical system has four. It becomes a system. FIG. 5B shows an example of the one-side scanning method, and FIG. 9 shows an example of the counter scanning method.

  FIG. 2A is a sub-scan sectional view of a light beam splitting element (half mirror prism) 4 which is an embodiment of the light beam splitting means according to the present invention. The half mirror prism 4 shown in FIG. 2 (a) functions as a beam splitting means, and is composed of a section 41 having a triangular cross section and a section 42 having a parallelogram shape. The adhesive surface 4a of the portions 41 and 42 is a half mirror, and separates transmitted light and reflected light at a ratio of 1: 1. A surface 4b of the parallelogram portion 42 facing the bonding surface 4a is a total reflection surface and has a function of changing the direction of the light beam. Here, the half mirror prism 4 is used as the beam splitting means, but a similar system may be configured by using a single half mirror and a normal mirror. Further, the separation ratio of the half mirror is not necessarily 1: 1, and may be set according to the conditions of other optical systems. Further, the shape of the parallelogram portion 42 may be a quadrangle other than the parallelogram, for example, as shown in FIG. 2B (inclination angles of the half mirror surface 4a and the total reflection surface 4b are different. As the shape, the angles in the sub-scanning direction at the time of emission of the divided light beams from the light beam dividing unit may be arbitrarily changed. The effect in this case will be described later.

  In FIG. 1, the light beam emitted from the half mirror prism 4 is converted into a line image that is long in the main scanning direction in the vicinity of the deflecting reflection surface by the cylindrical lenses 5-1 and 5-2 provided on the upper and lower stages respectively. . Here, in the optical deflector 7 which is a deflecting means, single polygon mirrors 7a and 7b are arranged concentrically on the upper and lower stages, respectively, and the rotation direction angles are shifted from each other by a predetermined angle θ. Both polygon mirrors 7a and 7b have the same shape, and are in principle formed by polygons having an arbitrary number of faces (in the example shown in the figure, it is a quadrangle, but is not limited to a quadrangle). The polygons are overlapped so that the vertex of the other polygon corresponds to an angle that bisects the central angle of one side of one polygon. When looking at the vertexes of the polygons on the opposite side that are adjacent to each other in the clockwise direction from the vertices of each polygon, if the central angles for each of the vertices are φ, φ ′ (where 0 <φ ≦ φ ′) If both are symmetrically arranged with respect to an arbitrary vertex, φ = φ ′. In practice, a four-sided polygon mirror is the easiest to use, and here, the four-sided polygon mirror is set to φ = φ ′ = 45 deg. These φ and φ ′ are referred to as deviation angles. The upper and lower polygon mirrors 7a and 7b may be integrally formed or may be assembled separately.

  FIG. 3 is a diagram for explaining optical scanning by the two-stage polygon mirrors 7a and 7b. In the figure, reference numeral 14 denotes a light shielding member. As shown in FIG. 5A, when a light beam incident from a common light source and reflected by the upper polygon mirror 7a is scanning the photoconductor 11a which is the surface to be scanned, the lower polygon mirror 7b is used. The reflected light beam does not reach the surface to be scanned, and is preferably shielded by the light shielding member 14. Further, as shown in FIG. 5B, when the light beam incident from a common light source and reflected by the lower polygon mirror 7b is scanning the photoconductor 11b different from the upper stage, the upper polygon mirror 7a. The light beam reflected by the light beam does not reach the surface to be scanned, and is preferably shielded by the light shielding member 14. Further, when the modulation drive is shifted in timing by the upper and lower polygon mirrors 7a and 7b and the photosensitive member 11a corresponding to the upper polygon mirror 7a is scanned, the color corresponding to the upper polygon mirror 7a (for example, black) ) Based on the image information, the light source is modulated and driven to scan the photoconductor 11b corresponding to the lower polygon mirror 7b. Based on the image information of the color (for example, magenta) corresponding to the lower polygon mirror 7b, Modulates the light source.

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

Usually, a semiconductor laser used in an image forming apparatus performs automatic light amount control (Auto Power Control: hereinafter referred to as APC) to stabilize light output. APC is a system in which the light output of a semiconductor laser is monitored by a light receiving element, and the forward current of the semiconductor laser is controlled to a desired value by a detection signal of a light receiving current proportional to the light output of the semiconductor laser.
When the semiconductor laser is an edge emitting semiconductor laser, the light receiving element often uses a photodiode for monitoring light emitted in the direction opposite to the direction emitted toward the coupling lens. However, when performing APC, it is unnecessary. When ghost light is incident, the amount of light detected by the light receiving element increases. For example, when the incident angle of the light beam to the upper polygon mirror 7a is 0, the reflecting surface of the polygon mirror 7a is directly facing the light source direction. When APC is performed at this position, the upper polygon mirror 7a The reflected beam returns to the light source, and the amount of light detected by the light receiving element increases. For this reason, the laser output from the lower polygon mirror 7b on which the writing is performed becomes a light emission output that is less than the target, and the image density becomes thin or density unevenness occurs. Similarly, when the incident angle of the light beam to the lower polygon mirror 7b becomes 0, the same problem occurs with respect to the laser output from the upper polygon mirror 7a.

Therefore, in the present invention, the light beams split from the common light source (semiconductor laser 1-1 or 1-2) are respectively in the sub-scanning direction with respect to the normal lines of the multi-surface reflecting mirrors (polygon mirrors) 7a and 7b. The above problem is solved by adopting a configuration having an angle. All the light beams incident on the multi-surface reflecting mirrors (polygon mirrors) 7a and 7b have an angle in the sub-scanning direction with respect to the normal line of the multi-surface reflecting mirrors (polygon mirrors) 7a and 7b. Thus, for example, even when the incident angle of the light beam to the upper reflecting mirror (polygon mirror) 7a is 0, the reflected beam from the upper reflecting mirror (polygon mirror) 7a does not return to the light source and is sub-scanned. Move away with distance in the direction. For this reason, the amount of light detected by the light receiving element does not increase, and the laser output from the lower reflecting mirror (polygon mirror) 7b that performs writing becomes a light emission output that is less than intended, resulting in a low image density. There is no problem that the density becomes uneven or uneven density occurs.
Also, when the incident angle of the light beam to the lower reflecting mirror (polygon mirror) 7b becomes 0, the reflected beam returns to the light source in the same manner with respect to the laser output from the upper reflecting mirror (polygon mirror) 7a. In addition, the amount of light detected by the light receiving element is stable, and there is no problem that the image density becomes thin or density unevenness occurs.

[Embodiment 2 (embodiments of second and third means)]
A problem in terms of optical performance when the oblique incidence method (incident with an angle in the sub-scanning direction with respect to the normal lines of the multi-surface reflecting mirrors (polygon mirrors) 7a and 7b) will be described.
In the present method in which the conventional horizontal incidence is obliquely incident in the sub-scanning direction, there is a problem that “scanning line bending” is large. The amount of bending of the scanning line varies depending on the oblique incident angle of each light beam in the sub-scanning direction, and color misregistration occurs when the latent images drawn by the respective light beams are visualized by superimposing them with respective color toners. Will appear. In addition, the oblique incident light causes the light beam to be twisted and incident on the scanning lens, thereby increasing the wavefront aberration. Particularly, the optical performance is significantly deteriorated at the peripheral image height, the beam spot diameter is increased, and the image quality is improved. It becomes a factor to prevent.

  Here, with reference to FIG. 5, the generation of the scanning line bending in the oblique incidence optical system will be described. For example, the shape of the incident surface of the scanning lens constituting the scanning optical system, particularly the scanning lens having a strong refractive power in the sub-scanning direction (second scanning lens L2 in FIG. 5) in the main scanning direction is an optical deflector (polygon mirror). The distance from the deflecting reflecting surface of the optical deflector 7 to the scanning lens incident surface varies depending on the lens height in the main scanning direction, unless the arc shape is centered on the reflecting point of the light beam on the deflecting reflecting surface 7). Usually, it is difficult to make the scanning lens in the above shape in order to maintain optical performance. That is, as shown in FIG. 5, a normal light beam is deflected and scanned by the optical deflector 7 and is perpendicularly incident on the lens surface at each image height in the main scanning section (FIG. 5A). Instead, it is incident with an incident angle in the main scanning direction. Further, as shown in FIG. 5B, the light beam deflected and reflected by the optical deflector 7 is deflected by the image height because it has an angle in the sub-scanning direction (because it is obliquely incident). The distance from the deflecting and reflecting surface of the device 7 to the incident surface of the scanning lens is different, and the incident height in the sub-scanning direction to the scanning lens is higher or lower than the center (having the light beam in the sub-scanning direction). Depending on the direction of the angle). As a result, when passing through a surface having refracting power in the sub-scanning direction, the refracting power received in the sub-scanning direction differs and scanning line bending occurs. In the case of normal horizontal incidence, the light beam travels horizontally with respect to the scanning lens even if the distance from the deflecting / reflecting surface to the scanning lens incidence surface is different. There is no occurrence of bending of the scanning line. Note that FIG. 5 is described using a general scanning optical system, and the light beam splitting element according to the present invention is not shown.

Next, the wavefront aberration deterioration in the oblique incidence optical system will be described. As described above, unless the shape in the main scanning direction of the entrance surface of the scanning lens constituting the scanning optical system is an arc shape centering on the reflection point of the light beam on the deflection reflection surface, The distance from the deflecting / reflecting surface to the scanning lens entrance surface is different. Usually, it is difficult to make the scanning lens in the above shape in order to maintain optical performance. That is, a normal light beam is deflected and scanned by the optical deflector 7 and does not enter the lens surface perpendicularly at each image height in the main scanning section, but with an incident angle in the main scanning direction. .
The light beam of the light beam deflected and reflected by the optical deflector 7 has a width in the main scanning direction, and the light beams at both ends in the main scanning direction in the light beam are scanned from the deflection reflection surface of the light deflector 7 to the scanning lens. Since the distance to the incident surface is different and has an angle in the sub-scanning direction (because it is obliquely incident), it is incident on the scanning lens in a twisted state. As a result, the wavefront aberration is significantly degraded and the beam spot diameter is increased. As shown in FIG. 5A, the incident angle in the main scanning direction becomes tighter toward the peripheral image height, and the incident positions of the light beams on both ends in the main scanning direction of the light beam on the scanning lens in the sub-scanning direction are greatly shifted. Therefore, the twist of the light beam increases, and the beam spot diameter increases due to the deterioration of the wavefront aberration toward the periphery.

Therefore, in the present invention, wavefront aberration correction is performed on a special surface that increases the angle in the sub-scanning direction of the light beam incident on the scanning lens toward the periphery in the main scanning direction.
As an example of the special surface, one surface of the shared lens (first scanning lens L1 in FIG. 5) is a surface in which the curvature in the sub-scanning direction changes according to the main scanning direction, and the periphery of the same surface in the main scanning direction A surface constituted by a surface having a negative refractive power that increases toward the surface will be described.

  As described above, the incident angle in the main scanning direction to the scanning lens becomes tighter as the height of the peripheral image increases, the twist of the light beam increases, and as the height of the peripheral image increases, the beam spot diameter increases due to the deterioration of wavefront aberration. Becomes bigger. Deterioration of the wavefront aberration is greatly caused by twisting of the light beam when entering a scanning lens having a strong refractive power especially in the sub-scanning direction. In order to correct the wavefront aberration, it is necessary to correct the height of incidence on the scanning lens having a strong refractive power in the sub-scanning direction so that the light is condensed at one point on the surface to be scanned. For this reason, the special surface used for correcting the wavefront aberration is a lens (second scanning lens L2 in FIG. 5) on the optical deflector side from the scanning lens (second scanning lens L2 in FIG. 5) having the strongest refractive power in the sub-scanning direction. It is desirable to provide the first scanning lens L1). The first scanning lens L1 jumps up a peripheral light beam and makes it incident on a high position of the second scanning lens L2, thereby correcting the deterioration of wavefront aberration (twisting of the light beam). (Within the same light beam) can be condensed at one point.

  The special surface of the first scanning lens L1 is represented by the following shape formula. This special surface is a surface whose curvature in the sub-scanning direction changes according to the main scanning direction, and the main scanning of the same surface. It is a surface where the negative refractive power increases toward the periphery of the direction. However, the content of the present invention is not limited to the following shape formula, and the same surface shape can be specified using another shape formula.

  The surface shape of the special surface of the first scanning lens L1 includes the optical axis, and the paraxial radius of curvature in the “main scanning section”, which is a plane section parallel to the main scanning direction, is RY, and the distance in the main scanning direction from the optical axis. Is Y, higher order coefficients are A, B, C, D..., And RZ is the paraxial radius of curvature in the “sub-scanning cross section” orthogonal to the main scanning cross section.

X (Y, Z) = Y ² · Cm / {1 + √ [1- (1 + K) · (Y · Cm) ² ]}
+ A · Y ⁴ + B · Y ⁶ + C · Y ⁸ + D · Y ¹⁰ + E · Y ¹² + ...
+ (Cs (Y) · Z ² ) / {1 + √ [1- (Cs (Y) · Z) ² ]}
However,
Cm = 1 / RY
Cs (Y) = 1 / RZ + a · Y + b · Y ² + c · Y ³ + d · Y ⁴ + e · Y ⁵ + f · Y ⁶
+ G · Y ⁷ + h · Y ⁸ + i · Y ⁹ + j · Y ^10.
And

  As described above, this special surface is used for the first scanning lens L1. This special surface is a surface in which the curvature in the sub-scanning direction changes according to the main scanning direction, and the surface where the negative refractive power increases toward the periphery in the main scanning direction on the same surface, the transmitted light beam is It becomes possible to jump the light beam toward the periphery of the main scanning direction in the sub-scanning direction. As a result, as described above, the incident height in the sub-scanning direction to the second scanning lens L2 having a strong refractive power in the sub-scanning direction can be adjusted, and the wavefront aberration can be corrected satisfactorily.

  As described above, when the wavefront aberration correction is performed by changing the incident position of the light beam on the second scanning lens L2, in the configuration in which the light beam passes on the optical axis (reference axis) of the special surface, the imaging position It is difficult to adjust the incident height in the sub-scanning direction to the second scanning lens L2 only by changing the above. Therefore, the path of the light beam can be deflected by using the change in curvature of the special surface in the main scanning direction in the sub-scanning direction and further transmitting the light beam off the reference axis.

  Next, a shared lens used for the first scanning lens L1 will be described. The advantage of using a shared lens for the first scanning lens L1 is that a scanning lens is provided for each light beam directed to a plurality of scanned surfaces (for example, the photoconductors 11Y, 11M, 11C, and 11K in FIG. 5B). This is because the number of scanning lenses can be reduced, and a low-cost optical scanning device can be provided. The first scanning lens L1 close to the optical deflector 7 is shared by the light beams directed to different scanned surfaces, and the oblique incident angle is set as small as possible, thereby suppressing the occurrence of wavefront aberration and scanning line bending. Is possible. Although wavefront aberration can be corrected by the special surface, it goes without saying that the correction amount should be small. In order to set the oblique incident angle small, it is advantageous to reduce the number of shared light beams and reduce the oblique incident angle as an opposed scanning method. However, by sharing all the light beams, the number of scanning lenses can be minimized, which is advantageous for low cost. Either of these can be selected according to the specifications required for the scanning optical system.

  If the first scanning lens L1 is not shared, scanning lenses corresponding to each light beam from different light source devices, that is, for each light beam directed to different photoconductors 11Y, 11M, 11C, and 11K must be arranged in the sub-scanning direction. There is. In the counter scanning method, at least two steps are required, and in the one-sided scanning method, four steps are required. At this time, each scanning lens requires a rib outside the effective range of the lens surface corresponding to each light beam, the distance between adjacent light beams in the sub-scanning direction increases, the oblique incident angle increases, and the optical performance deteriorates. Will become bigger. In order to widen the interval between adjacent light beams without changing the oblique incident angle, it is necessary to move the first scanning lens L1 away from the optical deflector 7, and in particular, it is necessary to increase the refractive power in the main scanning direction. As a result, the scanning lens increases in size and costs. Furthermore, there are also problems in assembling such as an adhesion process for fixing the lenses to be overlapped and accurate positioning.

  In addition, by integrally molding the shared lens, the number of parts can be reduced, and variations among parts can be suppressed to a small value. For example, in the one-side scanning method as shown in FIG. 5B, the photoreceptors 11Y, 11M, 11C, and 11C as scanning surfaces of yellow (Y), magenta (M), cyan (C), and black (K) are used. By sharing all of the light beam directed to 11K with a single lens, the number of scanning lenses can be greatly reduced. In the opposed scanning method, as shown in FIG. 9, the number of scanning lenses can be reduced by sharing the first scanning lens L1 with light beams for two colors. That is, variation in component tolerances between the light beams corresponding to the respective colors can be reduced, and stable optical performance can be obtained between the respective colors. Further, as in the present invention, the first scanning lens L1 is shared, and a plurality of light beams are transmitted outside the reference axis in the sub-scanning direction of the shared lens. Wavefront aberration can be corrected.

  As described above, the special surface needs to transmit the light beam outside the reference axis, and by using the special surface for the shared lens, it is possible to achieve wavefront aberration correction that is a problem in the oblique incidence optical system. In addition, a compact optical system and a low-cost optical system can be achieved. Further, by reducing the number of lenses, it is possible to reduce the influence of component variations and to realize stable optical performance.

[Example 3 (Examples of the fourth, fifth, and sixth means)]
The light beams split from the common light source 1-1 (or 1-2) have different signs in the sub-scanning direction with respect to the normal lines of the multi-surface reflecting mirrors (polygon mirrors) 7a and 7b of the optical deflector 7. The angle of the light beam having an angle and the beam path being deflected by the beam splitting means from a common light source in the sub-scanning direction with respect to the normal line of the polygonal mirrors 7a and 7b is the beam flux. It is desirable that the angle of the light beam whose beam path is not deflected by the dividing means is smaller than the angle in the sub-scanning direction with respect to the normal of the polygonal mirrors 7a and 7b.

  Therefore, in this embodiment, as shown in FIG. 6, the light beam dividing element 4 is used as the light beam dividing means, and all the light beams are sub-scanned with respect to the normal lines of the polygonal mirrors 7a and 7b. Is incident at an angle. Here, a description will be given using the one-side scanning method. At this time, the light beams split from the common light source 1-1 (or 1-2) have different signs (+ or different) in the sub-scanning direction with respect to the normal lines of the multi-surface reflecting mirrors (polygon mirrors) 7a and 7b. With the angle of −), the multi-surface reflecting mirrors (polygon mirrors) 7a and 7b can be used in the respective light beams deflected and reflected by the multi-surface reflecting mirrors (polygon mirrors) 7a and 7b of the optical deflector 7. The angle in the sub-scanning direction with respect to the line can be set to the smallest. That is, for example, as shown in FIG. 6B, the light beam from the light source 1-1 has a large angle counterclockwise in the figure in the sub-scanning direction, and the divided light beam has a small angle clockwise. ing. For this reason, the interval between the light beams adjacent in the sub-scanning direction after deflection reflection by the multi-surface reflecting mirrors (polygon mirrors) 7a and 7b of the optical deflector 7 is as shown in FIG. A mirror installation space for separating and folding the scanning surface is required. For this reason, when each light beam is reflected and emitted from the optical deflector 7, the interval between the adjacent light beams in the sub-scanning direction is set to be widened, while the angle in the sub-scanning direction is set small. The space between adjacent light beams is required to secure a mirror installation space for separating and folding back to the corresponding scanned surfaces. Originally, it is possible to minimize the angle in the sub-scanning direction because the center two light beams are horizontal, but as described above, since light returning to the light source is generated and image degradation occurs, all It is desirable that the light beam has an angle in the sub-scanning direction.

  Further, the light beam whose path is deflected and split by the light beam splitter 4 from the common light source 1-1 (or 1-2) with respect to the normal lines of the polygonal mirrors 7a and 7b. The angle in the sub-scanning direction is preferably set smaller than the angle in the sub-scanning direction with respect to the normal line of the multi-surface reflecting mirrors (polygon mirrors) 7a and 7b of the light beam whose beam path is not deflected by the light beam splitting element 4. . The influence of the angle change in the sub-scanning direction on the optical performance is large, and the larger the angle is, the larger the optical performance deterioration is. Therefore, in the present invention, the angle in the sub-scanning direction of the light beam that is folded back by the half mirror of the light beam splitting element 4 is set to be small, and the deterioration of the optical performance is reduced even when the variation items due to tolerance increase. Have achieved.

  In addition, the tandem-compatible optical scanning device usually has a plurality of light sources (two in this embodiment) in order to correspond to the four photoconductors 11Y, 11M, 11C, and 11K, and each of the light sources 1-1 and 1 is provided. It is desirable that the light beam from -2 is incident on multiple reflecting mirrors (polygon mirrors) 7a and 7b having a common rotation axis corresponding to an angle symmetrical to the sub-scanning direction. With this configuration, as shown in FIG. 7, the incident light to the scanning lens is symmetrical with respect to the optical axis in the sub-scanning direction, and wavefront aberration correction using the same special surface is possible. Of course, for each light beam or, for example, as shown in FIG. 8A or 8B, the upper side (2 beams) and the lower side (2 beams) in the sub-scanning direction with respect to the optical axis, or the upper stage outside And the inside (2 beams), the lower surface outside and inside (2 beams) may be divided.

Up to this point, the description has been given by taking the two-lens scanning lens (the first scanning lens L1 and the second scanning lens L2) as an example. However, in the case of the one-lens scanning lens, the strongest refractive power in the sub-scanning direction The same effect can be obtained if a special surface is provided on the side of the optical deflector with respect to the surface.
In addition, by forming a special surface on the scanning lens close to the optical deflector 7, the light beam width in the main scanning direction is particularly wide, so that the shape setting of the special surface and the correction of wavefront aberration can be satisfactorily achieved. In order to correct the wavefront aberration, it is necessary to deflect the angle of the light beam in the sub-scanning direction within the light beam. As described above, correction (deflection of the light beam in the sub-scanning direction) is performed using a special surface. However, if the width of the light beam is small, the correction becomes difficult. In other words, even if a special surface is introduced at a position where the light beam width in the main scanning direction is narrowed, that is, a position close to the surface to be scanned (photosensitive member), the direction of the light beam can be changed. It is difficult to deflect in the sub-scanning direction.

  In other words, the scanning lens closest to the optical deflector is shared by a plurality of light beams, and a special surface is used for the incident surface, thereby realizing good wavefront aberration correction, stable optical performance, and a low-cost optical scanning device. Would be the most desirable above. However, the present invention is not limited to the present embodiment, and is within the scope of the present invention as long as similar effects can be obtained.

[Embodiment 4 (Another embodiment of the second means)
Next, another embodiment of the special surface of the first scanning lens L1 will be described. By using a surface having no power in the sub-scanning direction and having a different amount of tilt eccentricity in the sub-scanning direction in the main scanning direction (hereinafter referred to as a special tilt surface), the same effect as the special surface described in the second embodiment is obtained. It is done.
The surface shape of the special surface of the first scanning lens L1 is according to the following shape formula. However, the content of the present invention is not limited to the following shape formula, and the same surface shape can be specified using another shape formula.

  The surface shape of the special surface of the first scanning lens L1 includes the optical axis, and the paraxial radius of curvature in the “main scanning section” which is a plane section parallel to the main scanning direction is RY, and the distance in the main scanning direction from the optical axis Is Y, higher order coefficients are A, B, C, D..., And RZ is the paraxial radius of curvature in the “sub-scanning cross section” orthogonal to the main scanning cross section.

X (Y, Z) = Y ² · Cm / {1 + √ [1- (1 + K) · (Y · Cm) ² ]}
+ A · Y ⁴ + B · Y ⁶ + C · Y ⁸ + D · Y ¹⁰ + E · Y ¹² + ...
+ (Cs (Y) · Z ² ) / {1 + √ [1- (Cs (Y) · Z) ² ]}
+ (F0 + F1 · Y + F2 · Y 2 + F3 · Y 3 + F4 · Y 4 + ··) Z
However,
Cm = 1 / RY
Cs (Y) = 1 / RZ
And
Incidentally, (F0 + F1 · Y + F2 · Y 2 + F3 · Y 3 + F4 · Y 4 + ··) Z is a moiety represents a tilt amount, when no tilt amount, F0, F1, F2, · · · is All are zero. When F1, F2,... Are not 0, the tilt amount changes in the main scanning direction.

Furthermore, the reason why the shape of the special tilt surface of the first scanning lens L1 in the sub-scanning direction is a planar shape having no curvature will be described.
When curvature is added in the sub-scanning direction, the shape in the main-scanning direction changes greatly for each height in the sub-scanning direction, and the incident position of the light beam shifts in the sub-scanning direction due to temperature fluctuations and optical element assembly errors In the color machine, the beam spot position shifts between the colors and the color shift occurs. Therefore, as in the present invention, the surface shape of the special surface in the sub-scanning direction is a planar shape having no curvature, so that the shape error in the main scanning direction can be reduced for each height in the sub-scanning direction, and The variation in magnification error when the incident position of the light beam is deviated can be reduced, and the occurrence of color misregistration can be suppressed.

  Actually, the main scanning shape changes depending on the height in the sub-scanning direction by using a special surface, but the amount is small, and the change in the main scanning shape is smaller than when a curvature is added in the sub-scanning direction. it can. As a result, the difference in magnification fluctuation between the light beams due to the temperature distribution can be reduced, and by synchronizing, the color shift at the intermediate image height when the writing position and the writing end position are matched with each light beam is reduced. can do.

  Further, as shown in FIG. 7B, when the incident light beam is shifted in the sub-scanning direction, the special surface does not have a refractive power, so only the traveling direction of the light beam is shifted, and the change in the direction is small. On a surface having a curvature in the sub-scanning direction, that is, having a refractive power, as shown in FIG. 7A, when the incident light beam is shifted in the sub-scanning direction, the traveling direction of the light beam is changed by changing the refractive power. If the amount of change in the advancing direction is different at each image height, the scanning line is greatly bent. In addition, a skew of the light flux occurs, which causes deterioration of wavefront aberration and beam spot diameter. For the above reasons, the shape in the sub-scanning direction on the special surface needs to be a planar shape having no curvature.

When this special surface is used for a shared lens, it is desirable to set a special surface for each light beam. Since the special surface of Example 2 is a surface having a curvature, even if the angle in the sub-scanning direction incident on the scanning lens is different, the incident height is also different, so that the wavefront aberration can be corrected on the same surface. Further, if the sub-scanning cross section has a non-arc shape, a better correction can be made. However, in this embodiment, it is difficult to set an optimum tilt amount in the sub-scanning direction for each angle in the sub-scanning direction on a common special surface.
Therefore, by adopting this special surface for the scanning lens L1 of the optical scanning apparatus of the counter scanning type as shown in FIG. 9, it is sufficient to use a two-stage special surface, and a low-cost scanning lens can be used. In this case, the light beams divided by the light beam splitter 4 from the same light source 1-1 (or 1-2) may have the same angle. Further, the scanning lens L1 is not limited to one, but may be a two-layered one.
Of course, even in the one-side scanning type optical scanning apparatus as shown in FIG. 5B, a special surface for each light beam may be set on the first scanning lens L1.

[Example 5 (Example of the seventh means)]
Regarding scanning line bending, which is another problem of the oblique incidence optical system, after passing through the first scanning lens (common lens) L1, each light beam directed to different scanning surfaces (photosensitive members 11Y, 11M, 11C, and 11K). Can be corrected by the second scanning lens L2.
For example, as shown in FIG. 5B, the second scanning lens L2 arranged for each light beam directed to different scanned surfaces (photosensitive members 11Y, 11M, 11C, and 11K) is shifted in the sub-scanning direction. Alternatively, tilt eccentricity may be performed. It is known that the scanning line bending is improved by this. Note that the occurrence of scanning line bending is omitted here since it has been described above.

According to the present invention, at least one surface of a lens arranged for each light beam from a plurality of light source devices is a surface having a different amount of shift eccentricity in the sub-scanning direction in the main scanning direction, that is, in the main scanning direction. The position of the image point at each image height is corrected in the sub-scanning direction, and the scanning line bending can be corrected.
By using the surface, the path of the light beam can be changed in the sub-scanning direction. That is, by optimally providing the shift eccentricity in the sub-scanning direction in the main scanning direction, the light beam scanned in the main scanning direction can be deflected in a desired direction (sub-scanning), and the scanning line bending is corrected. Is possible.

The surface for correcting the scanning line bending is desirably used for the scanning lens closest to the surface to be scanned (second scanning lens L2 in FIG. 5). As the light beam approaches the scanned surface 11 (photosensitive members 11Y, 11M, 11C, and 11K), the size (light beam diameter) decreases. For this reason, even if the traveling direction of the light beam is changed for correcting the scanning line bending, the influence on the light beam is small, and the wavefront is generated on the special surface of the scanning lens (first scanning lens L1 in FIG. 5) close to the optical deflector 7. It is possible to prevent the aberration-corrected state from being deteriorated (the corrected light flux is greatly skewed and the wavefront is not disturbed).
That is, for correcting the wavefront aberration, a scanning lens (first scanning lens L1 in FIG. 5) close to the optical deflector 7 having a large beam diameter and easy to correct the traveling direction of the light beam in the beam is effective.
Furthermore, in the scanning lens close to the scanning surface 11 (second scanning lens L2 in FIG. 5), the light beams directed to the respective image heights are further separated, and the overlapping of the adjacent light beams is small. For this reason, it is possible to finely set the shift eccentricity in the sub-scanning direction, and it is possible to satisfactorily correct the scanning line bending correction.

The surface shape of the scanning lens (second scanning lens L2 in FIG. 5) close to the scanned surface 11 will be described. The surface shape of the scanning lens is according to the following shape formula. However, the content of the present invention is not limited to the following shape formula, and the same surface shape can be specified using another shape formula.
The surface shape of this scanning lens includes the optical axis, and the paraxial radius of curvature in the “main scanning section”, which is a flat section parallel to the main scanning direction, is RY, the distance from the optical axis to the main scanning direction is Y, and higher order If the coefficients are A, B, C, D... And the paraxial radius of curvature in the “sub-scanning cross section” orthogonal to the main scanning cross section is RZ, it can be expressed by the following shape formula.

X (Y, Z) = Y ² · Cm / {1 + √ [1- (1 + K) · (Y · Cm) ² ]}
+ A · Y ⁴ + B · Y ⁶ + C · Y ⁸ + D · Y ¹⁰ + E · Y ¹² + ...
+ (Cs (Y). [Z-Z0 (Y)] ² ) / {1 + √ [1-Cs (Y) ^2. (Z-Z0 (Y)) ² ]}
+ (F0 + F1 · Y + F2 · Y 2 + F3 · Y 3 + F4 · Y 4 + ··) Z
However,
Cm = 1 / RY
Cs (Y) = 1 / RZ + a · Y + b · Y ² + c · Y ³ + d · Y ⁴ + e · Y ⁵ + f · Y ⁶
+ G · Y ⁷ + h · Y ⁸ + i · Y ⁹ + j · Y ^10.
Z0 (Y) = D0 + D1 · Y + D2 · Y 2 + D3 · Y 3 + D4 · Y 4 + ···
And

Incidentally, (F0 + F1 · Y + F2 · Y 2 + F3 · Y 3 + F4 · Y 4 + ··) Z is a moiety represents a tilt amount, when no tilt amount, F0, F1, F2, · · · is All are zero. When F1, F2,... Are not 0, the tilt amount changes in the main scanning direction.
Z0 (Y) = D0 + D1 · Y + D2 · Y ² + D3 · Y ³ + D4 · Y ⁴ +... Represents a shift amount in the sub-scanning direction. Will change direction.
Cs (Y) = 1 / RZ + a · Y + b · Y ² + c · Y ³ + d · Y ⁴ + e · Y ⁵ + f · Y ⁶
+ G · Y ⁷ + h · Y ⁸ + i · Y ⁹ + j · Y ^10.
Means that the curvature in the sub-scanning direction changes in the main scanning direction.

However, when the shape in the sub-scanning direction is a plane, the surface shape does not change even if the shift is decentered (even if the coefficient of D is set). At this time, it is not within the scope of the present invention.
That is, the scanning optical system has at least one surface of the scanning lens (second scanning lens L2 in FIG. 5) close to the surface to be scanned arranged for each light beam from the plurality of light source devices in the main scanning direction in the sub scanning direction. By making the surfaces different in shift eccentricity, it is possible to correct the scanning line bending favorably.

[Embodiment 6 (Embodiment of Eighth Means)]
Next, another example of scanning line curve correction will be described. By using a surface that does not have power in the sub-scanning direction but has a different amount of tilt eccentricity in the sub-scanning direction in the main scanning direction (hereinafter referred to as a special tilt surface) instead of the curved surface of the bus line, scanning line bending can be corrected more effectively. Is possible.
That is, the path of the light beam can be changed in the sub-scanning direction by changing the tilt eccentricity in the sub-scanning direction in the main scanning direction. By optimally varying the tilt amount in the main scanning direction, the light beam scanned in the main scanning direction can be deflected in a desired direction (sub-scanning), and the scanning line bending can be corrected. Similar to the bus curve surface described in the third embodiment, it is desirable to use the special tilt surface for the scanning lens closest to the surface to be scanned. The reason is as described in the above-described fifth embodiment, and therefore the description is omitted here.

The surface shape of the special tilt surface is according to the following shape formula. However, the content of the present invention is not limited to the following shape formula, and the same surface shape can be specified using another shape formula.
The surface shape of the special tilt surface includes the optical axis and the paraxial radius of curvature in the “main scanning section”, which is a flat section parallel to the main scanning direction, is RY, the distance from the optical axis to the main scanning direction is Y, and higher order If the coefficients are A, B, C, D... And the paraxial radius of curvature in the “sub-scanning cross section” orthogonal to the main scanning cross section is RZ, it can be expressed by the following shape formula.

X (Y, Z) = Y ² · Cm / {1 + √ [1- (1 + K) · (Y · Cm) ² ]}
+ A · Y ⁴ + B · Y ⁶ + C · Y ⁸ + D · Y ¹⁰ + E · Y ¹² + ...
+ (Cs (Y) · Z ² ) / {1 + √ [1- (Cs (Y) · Z) ² ]}
+ (F0 + F1 · Y + F2 · Y 2 + F3 · Y 3 + F4 · Y 4 + ··) Z
However,
Cm = 1 / RY
Cs (Y) = 1 / RZ
And

Incidentally, (F0 + F1 · Y + F2 · Y 2 + F3 · Y 3 + F4 · Y 4 + ··) Z is a moiety represents a tilt amount, when no tilt amount, F0, F1, F2, · · · is All are zero. When F1, F2,... Are not 0, the tilt amount changes in the main scanning direction.
Further, the reason why the special tilt surface in the sub-scanning direction is a planar shape having no curvature is the same as described above, and the description thereof will be omitted.

Example 7 (Example of Ninth Means)
In recent years, optical scanners and image forming apparatuses have been increased in speed and density. When a polygon scanner is used as the optical deflector 7, it is possible to cope with high speed and high density by rotating the multi-surface reflecting mirrors (polygon mirrors) 7a and 7b at high speed. However, the number of rotations is limited, and the present invention scans the same surface to be scanned with a plurality of light beams as means for increasing the speed and density without increasing the number of rotations of the polygon scanner.

  In the optical scanning device according to the present invention, the light source is, for example, a semiconductor laser array having a plurality of light emission points, a multi-beam light source device using a single light emission point or a plurality of light sources having a plurality of light emission points, and a plurality of light beams. May be configured to simultaneously scan the surface of the photoconductor. By doing so, it is possible to configure an optical scanning device and an image forming apparatus that are increased in speed and density, and even when such an optical scanning device and an image forming apparatus are configured, the same effects as described above are obtained. The effect of can be obtained.

Here, a cross-type multi-beam light source device will be described as an example. FIG. 10 is an exploded perspective view showing an example of a light source unit constituting the multi-beam light source device.
In FIG. 10, two semiconductor lasers (LD) 403 and 404 that are light sources are individually fitted into fitting holes 405-1 and 405-2 formed in the base member 405 from the back side of the base member. . The fitting holes 405-1 and 405-2 are inclined at a predetermined angle in the main scanning direction, in this embodiment, about 1.5 °, and the semiconductor lasers 403 and 404 fitted in the fitting holes are also included. It is inclined about 1.5 ° in the main scanning direction. The semiconductor lasers 403 and 404 have notches formed in the cylindrical heat sink portions 403-1 and 404-1, and the protrusions 406-1 and 407-1 formed in the center round holes of the pressing members 406 and 407 are provided. The alignment direction of the light emitting sources is adjusted by matching the notches of the heat sinks 403-1 and 404-1. The holding members 406 and 407 are fixed to the base member 405 from the back side thereof with screws 412, so that the semiconductor lasers 403 and 404 are fixed to the base member 405. The collimating lenses 408 and 409 are adjusted in the direction of the optical axis along the semicircular mounting guide surfaces 405-4 and 405-5 of the base member 405. Positioned and bonded so as to be a parallel light beam.

In the example shown in FIG. 10, since the light beams from the respective semiconductor lasers are set so as to intersect within the main scanning plane, the fitting holes 405-1 and 405-2 and the semicircular shape are formed along the light beam direction. The attachment guide surfaces 405-4 and 405-5 are formed to be inclined.
Further, the cylindrical engaging portion 405-3 of the base member 405 is engaged with the holder member 410, and the screw 413 is passed through the through hole 410-2 and screwed into the screw holes 405-6, 405-7 of the base member 405. By doing so, the base member 405 is fixed to the holder member 410 to constitute a light source unit.

  The holder member 410 of the light source unit has a cylindrical portion 410-1 fitted into a reference hole 411-1 provided in the mounting wall 411 of the optical housing, and a spring 611 is inserted from the front side of the mounting wall 411 to stop the stopper member 612. Is held in close contact with the back side of the mounting wall 411, thereby holding the light source unit in the optical housing. One end of the spring 611 is hooked on the protrusion 411-2 of the mounting wall 411, and the other end of the spring 611 is hooked on the light source unit, thereby generating a rotational force about the center of the cylindrical portion in the light source unit. An adjustment screw 613 provided to lock the rotational force of the light source unit is provided, and the adjustment screw 613 rotates the whole unit in the θ direction around the optical axis to adjust the beam pitch. It is configured to be able to. An aperture 415 is disposed in front of the light source unit, and the aperture 415 is provided with a slit corresponding to each semiconductor laser, and is configured to be attached to an optical housing to define an emission diameter of the light beam.

  Although an example of a multi-beam light source device has been described above, a semiconductor laser array (LD array) having a plurality of emission points may be used as the semiconductor laser, and in that case, further multi-beam conversion is possible. It becomes.

[Example 8 (Examples corresponding to the tenth and eleventh means)]
Next, an embodiment of an image forming apparatus using the optical scanning device according to the present invention will be described with reference to FIG.
In this embodiment, an optical scanning device according to the present invention (for example, a one-side scanning optical scanning device as shown in FIG. 5B) is applied to a tandem type full-color laser printer. In FIG. 11, a conveying belt 27 for conveying a recording material (for example, transfer paper) S fed from a paper feeding cassette 23 disposed in the horizontal direction is provided on the lower side in the apparatus. A yellow (Y) photosensitive member 11Y, a magenta (M) photosensitive member 11M, a cyan (C) photosensitive member 11C, and a black (K) photosensitive member 11K are transferred onto the transfer belt 27. S is arranged at equal intervals in order from the upstream side in the transport direction to the downstream side. Hereinafter, subscripts Y, M, C, and K are appropriately added to the reference numerals for distinction. These photoconductors 11Y, 11M, 11C, and 11K are all formed to have the same diameter, and process members that perform each process in accordance with the electrophotographic process are sequentially arranged around the photoconductors 11Y, 11M, 11C, and 11K. Taking the photoconductor 11Y as an example, a charging charger 18Y, a scanning imaging optical system 19Y of the optical scanning device 19, a developing device 20Y, a transfer charger 21Y, a cleaning device 22Y, and the like are sequentially arranged. The same applies to the other photoconductors 11M, 11C, and 11K.

In this embodiment, the surfaces of the photoconductors 11Y, 11M, 11C, and 11K are used as scan surfaces (or irradiated surfaces) that are set for the respective colors, and the photoconductors 11Y, 11M, 11C, and 11K are provided. On the other hand, scanning imaging optical systems 19Y, 19M, 19C, and 19K of the optical scanning device 19 are provided in a one-to-one correspondence relationship.
However, the optical deflector 7 and the first scanning lens L1 are commonly used by the four scanning imaging optical systems 19Y, 19M, 19C, and 19K, and are turned back to turn back the optical paths of the second scanning lens L2 and the respective optical systems. The mirrors M1 and M2 are provided in each optical system. Although not shown, on the incident side of the optical deflector 7 of the optical scanning device 19, a plurality of light sources 1-1 and 1-2, coupling lenses 3-1 and 3-1 as shown in FIG. 3-2, an aperture stop 12, a beam splitting element 4, cylindrical lenses 5-1 and 5-2, and the like are provided.

  The conveyor belt 27 is supported by a driving roller 28 and a driven roller 29 and is rotated in the direction of the arrow in the figure. Around the periphery thereof, a registration roller 26 and a belt charging charger 30 are positioned upstream of the photoreceptor 11Y. A belt separation charger 31, a belt neutralization charger 32, a belt cleaning device 33, and the like are provided in this order so as to be positioned downstream of the photoreceptor 11K in the rotation direction of the belt 27. A fixing device 34 including a heating roller 34 a and a pressure roller 34 b is provided downstream of the belt separation charger 31 in the transfer paper conveyance direction, and is connected to a paper discharge tray 36 by a paper discharge roller 35.

  In the laser printer having such a schematic configuration, for example, in the full color mode (multiple color mode), each of the photoconductors 11Y, 11M, 11C, and 11K is charged by the chargers 18Y, 18M, 18C, and 18K, The light beams of the scanning imaging optical systems 19Y, 19M, 19C, and 19K of the optical scanning device 19 based on the image signals of the respective colors Y, M, C, and K for the photoreceptors 11Y, 11M, 11C, and 11K. By electrostatic scanning, an electrostatic latent image corresponding to each color signal is formed on the surface of each photoconductor. These electrostatic latent images are developed with toners of respective colors Y, M, C, and K by the corresponding developing devices 20Y, 20M, 20C, and 20K to form toner images. The transfer paper S in the paper feed cassette 23 is fed by the paper feed roller 24 and the transport roller 25 in accordance with the timing of this image forming process, and sent to the transport belt 27 by the registration roller 26. The transfer sheet S fed to the transport belt 27 is electrostatically attracted to the transport belt 27 by the action of the belt charger 30 and transported toward the photoconductors 11Y, 11M, 11C, and 11K. , 11M, 11C, and 11K are sequentially transferred onto the transfer paper S so that they are superimposed, and a full-color image is formed on the transfer paper S. The transfer sheet S on which the full-color image has been transferred is separated from the transport belt 27 by the belt separation charger 31 and transported to the fixing device 34. After the full-color image is fixed to the transfer paper S by the fixing device 34, the discharge roller 35 is discharged. As a result, the paper is discharged to the paper discharge tray 36.

In this embodiment, the optical scanning device 19 of the image forming apparatus configured as described above is configured as the optical scanning device described in the first to seventh embodiments, so that scanning line bending and wavefront aberration are reduced. It is possible to realize an image forming apparatus that is effectively corrected, has no color misregistration, and can ensure high-quality image reproducibility.
Here, the description has been given by taking the one-side scanning type optical scanning device 19 as an example, but in addition to this, a counter scanning type optical scanning device having the configuration shown in FIG. 9 may be used. A deflector 7 is arranged in the center, Y and M scanning imaging optical systems (scanning lenses, mirrors, etc.) are arranged on one side with the optical deflector 7 in between, and C on the other side. If a scanning imaging optical system for K (scanning lens, mirror, etc.) is arranged, one optical deflector 7 can distribute four light beams in two directions and simultaneously perform deflection scanning. Also in this case, the scanning imaging optical system of each color is configured as the optical scanning device described in the first to seventh embodiments, so that the scanning line bending and the wavefront aberration can be effectively corrected, and the color An image forming apparatus that can ensure high-quality image reproducibility without deviation can be realized.

As described above based on the embodiments, according to the present invention, the light beam from the common light source 1-1 or 1-2 is divided into two light beams by the light beam dividing means 4, and a multistage polygon mirror is used. Since different scanning surfaces 11a and 11b are deflected by the deflecting means 7 having 7a and 7b and simultaneously scanned, for example, four scanning surfaces (photoconductors) 11Y, using two light sources 1-1 and 1-2 are used. 11M, 11C, and 11K can be scanned simultaneously, and an optical scanning device that enables high-speed and good image output while reducing the number of light sources can be realized. Therefore, according to the present invention, the number of parts of the optical scanning device can be reduced and the cost can be reduced, the failure rate of the entire unit is reduced, and the recyclability is improved. Further, in the present invention, the surface shape of the scanning lens constituting the scanning optical system is devised as in the above-described embodiment, so that the scanning line bending and the wavefront aberration deterioration in the oblique incidence type optical scanning device are effectively prevented. It is possible to correct, and it is possible to reduce the difference in quality between beams that scan different scanned surfaces (photosensitive member surfaces).
Furthermore, according to the present invention, by using a multi-beam light source as the light sources 1-1 and 1-2, it is possible to form a plurality of scanning lines on the same surface to be scanned by one scan. High speed and high density of the forming apparatus can be realized. In addition, according to the present invention, it is possible to realize an image forming apparatus capable of outputting an image with an appropriate density and with little density unevenness. Further, an image forming apparatus capable of outputting an image with excellent color reproducibility by adjusting the set light amount can be realized.

1 is a schematic configuration diagram of an essential part of an optical scanning device according to an embodiment of the present invention. FIG. 3 is a diagram illustrating the configuration of a light beam splitting element (half mirror prism) that is an embodiment of the light beam splitting unit according to the present invention. It is a figure for demonstrating the optical scanning by the optical deflector (2-stage polygon mirror) of the optical scanning apparatus shown in FIG. It is a figure which shows an example of the timing chart of the exposure for multiple colors. It is explanatory drawing at the time of using an oblique-incidence optical system with the optical scanning device of a one side scanning system. It is explanatory drawing at the time of using a light beam splitting means for the optical scanning device of an oblique incidence optical system. When the incident light to an optical element shifts in the sub-scanning direction, it is an explanatory diagram of scanning line bending and beam diameter deterioration when the surface of the optical element has or does not have refractive power in the sub-scanning direction. It is explanatory drawing of the special surface of a scanning lens. It is explanatory drawing at the time of using a grazing incidence optical system and a light beam splitting means with the optical scanning device of a counter scanning system. It is a disassembled perspective view which shows an example of the light source unit which comprises a multi-beam light source device. 1 is a diagram illustrating an embodiment of an image forming apparatus using an optical scanning device according to the present invention, and is a schematic configuration diagram of a tandem type color laser printer.

Explanation of symbols

1-1, 1-2: Light source (semiconductor laser)
2: LD (semiconductor laser) base 3-1, 3-2: Coupling lens 4: Beam splitting element (half mirror prism) as beam splitting means
5-1, 5-2: Cylindrical lens 6: Soundproof glass 7: Optical deflector as deflecting means 7a, 7b: Multi-surface reflecting mirror (polygon mirror)
8, L1: first scanning lens 9, M1, M2: folding mirrors 10a, 10b, L2: second scanning lens 11: scanned surface 11a, 11b: photoconductor as scanned surface 11Y, 11M, 11C, 11K: Photoconductor 12 as scanning surface: Aperture stop (aperture)
14: light shielding member 18Y, 18M, 18C, 18K: charging charger 19: optical scanning device 20Y, 20M, 20C, 20K: developing device 21Y, 21M, 21C, 21K: transfer charger 22Y, 22M, 22C, 22K: cleaning device 23 : Paper feeding cassette 24: Paper feeding roller 25: Carrying roller 26: Registration roller 27: Carrying belt 28: Driving roller 29: Driven roller 30: Belt charging charger 31: Belt separation charger 32: Static elimination charger 33: Belt cleaning device 34: Fixing device 35: paper discharge roller 36: paper discharge tray S: transfer paper

Claims (11)

A light source that is driven to be modulated, a deflecting means having a plurality of stages of reflecting mirrors on a common rotation axis, and a light beam that is divided into different stages of reflecting mirrors by dividing the light beam from the common light source A beam splitting means for making the incident light, a plurality of scanned surfaces, and a scanning optical system for guiding the light beam scanned by the deflecting means to the corresponding scanned surface, wherein the divided light beams are differently scanned. In an optical scanning device for scanning a surface,
The angles of the rotational direction of the multi-surface reflecting mirrors of the different steps are shifted from each other,
An optical scanning device characterized in that light beams split from a common light source each have an angle in the sub-scanning direction with respect to the normal line of the multi-surface reflecting mirror. The optical scanning device according to claim 1,
At least one surface of at least one scanning lens constituting the scanning optical system has an angle in a sub-scanning direction with respect to a normal line of the multi-surface reflecting mirror of a light beam incident on the scanning lens toward the periphery in the main scanning direction, An optical scanning device comprising: a special surface configured by a surface in which an angle of a sub-scanning direction of a light beam emitted from the scanning lens with respect to a normal line of the multi-surface reflecting mirror is large. The optical scanning device according to claim 2.
The special surface is shared by all the light beams directed to different surfaces to be scanned. The optical scanning device according to any one of claims 1 to 3,
The light beam splitting from the common light source has a different sign angle in the sub-scanning direction with respect to the normal line of the multi-surface reflecting mirror. In the optical scanning device according to any one of claims 1 to 4,
The angle of the light beam from the common light source that is deflected and divided by the light beam dividing means in the sub-scanning direction with respect to the normal of the multi-surface reflecting mirror is determined by the light beam dividing means. An optical scanning device characterized in that an angle of a non-deflected light beam is smaller than an angle in a sub-scanning direction with respect to a normal line of the multi-surface reflecting mirror. In the optical scanning device according to any one of claims 1 to 5,
An optical scanning apparatus comprising: a plurality of light sources, wherein light beams from the respective light sources are incident on a multi-surface reflecting mirror having a common rotation axis at an angle symmetrical to the sub-scanning direction. In the optical scanning device according to any one of claims 1 to 6,
The scanning optical system has a plurality of lenses arranged for each light beam from the plurality of light sources, and at least one surface of the lens arranged for each light beam from the plurality of light sources is An optical scanning device characterized in that the shift eccentricity in the sub-scanning direction is different from the main scanning direction. In the optical scanning device according to any one of claims 1 to 6,
The scanning optical system includes a plurality of light sources, and the scanning optical system includes a lens disposed for each light beam from the plurality of light sources, and the lens disposed for each light beam from the plurality of light sources includes a sub-scanning direction. The optical scanning device is characterized in that it has a surface that has no power and has a different tilt eccentric amount in the sub-scanning direction in the main scanning direction. In the optical scanning device according to any one of claims 1 to 8,
A multi-beam light source that emits a plurality of light beams is used as the light source. The optical scanning device according to any one of claims 1 to 9,
An optical scanning device characterized in that different scanned surfaces corresponding to a plurality of light sources are composed of at least four photosensitive members. In an image forming apparatus that forms an image by executing an electrophotographic process,
An image forming apparatus comprising the optical scanning device according to claim 1 as means for executing an exposure process of the electrophotographic process.

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