JP2008015139A - Optical scanner and image forming device using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a compact and high-quality optical scanner, and to provide an image forming device. <P>SOLUTION: This scanner has one or more scanning units having a deflector which deflects a plurality of optical fluxes from light sources, and one or more focusing optical systems having focusing optical elements for focusing the optical flux on the surfaces to scan that match their light sources. On the same deflecting surface, the optical flux enter the plane vertical to the turn axis of the deflector at angles different in the sub-scanning cross section. It has optically effective sections and one or more optically ineffective sections between them where the optical flux do not pass; in the one or more focusing optical elements, the plurality of optical fluxes pass the optically effective section different from each other where the optical flux deflected on the same surface in the sub-scanning cross section; and the distance is made 1.0 mm or smaller in the optical axis direction, from the line connecting the peaks of the optically effective sections to the peaks of the optically ineffective sections between them in the sub-scanning cross section. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an optical scanning device and an image forming apparatus using the same, and is suitable for an image forming apparatus such as a laser beam printer, a digital copying machine, or a multi-function printer (multi-function printer) having an electrophotographic process.

  Conventionally, in an optical scanning device such as a laser beam printer (LBP), a light beam that is light-modulated and emitted from a light source means according to an image signal is periodically deflected by, for example, an optical deflector composed of a rotating polygon mirror (polygon mirror). ing. The deflected light beam is focused in a spot shape on the surface of a photosensitive recording medium (photosensitive drum) by an imaging optical system having fθ characteristics, and image recording is performed by optically scanning the surface.

  FIG. 17 is a schematic view of a main part of a conventional optical scanning device.

  In the figure, a divergent light beam emitted from the light source means 1 is converted into a parallel light beam by a collimator lens 3, and the light beam is limited by a diaphragm 2 and incident on a cylindrical lens 4 having a finite refractive power only in the sub-scanning direction. Yes. Among the parallel light beams incident on the cylindrical lens 4, the light is emitted as it is in the main scanning section. Further, in the sub-scan section, the light beam is focused and formed as a line image on the deflecting surface (reflecting surface) 5a of the optical deflector (rotating polygon mirror) 5 as a deflecting means.

  Then, the light beam deflected by the deflecting surface 5a of the optical deflector 5 is guided onto a photosensitive drum surface 8 as a surface to be scanned through an imaging optical system (imaging lens system) 6 having fθ characteristics. Then, by rotating the optical deflector 5 in the direction of arrow A, the photosensitive drum surface 8 is optically scanned in the direction of arrow B (main scanning direction) to record image information.

  In the above optical scanning device, in order to adjust the timing for starting image formation on the surface of the photosensitive drum 8 before the surface of the photosensitive drum 8 is scanned with the light spot, a beam detector (beam detector) is used as a photodetector. ) A sensor 96 is provided. The synchronization detection sensor 96 scans a synchronization detection light beam that is a part of the light beam reflected and deflected by the optical deflector 5, that is, an area outside the image formation area before the image formation area on the surface of the photosensitive drum 8 is scanned. Receives the luminous flux when

  The synchronization detection light beam is reflected by the synchronization detection mirror 95, condensed by a synchronization detection lens (not shown), and enters the synchronization detection sensor 96. A synchronization detection signal (synchronization signal) is detected from the output signal of the synchronization detection sensor 95, and the image recording start timing on the surface of the photosensitive drum 8 is adjusted based on the synchronization detection signal.

  The imaging optical system 6 in the figure is configured such that the deflecting surface 5a of the optical deflector 5 and the photosensitive drum surface 8 are in a conjugate relationship in the sub-scan section, thereby correcting surface tilt of the deflecting surface 5a. is doing.

  In such an optical scanning device, a printing machine with a high printing speed is desired year by year. For example, in the case of a color LBP, considering the printing speed, a tandem type in which a photosensitive drum corresponding to four colors is scanned and transferred to a transfer drum, rather than a type in which a photosensitive drum is scanned four times and transferred. Is desired.

  Further, in order to save space in the office, a compact optical scanning device is desired, and the entire device is downsized by bending the optical path with a mirror.

  In recent years, further miniaturization is desired, and simplification of optical components such as lenses and motors constituting the scanning optical system and miniaturization of the entire optical system are desired.

  Therefore, in order to reduce the number of lenses and reduce the height of the optical deflector (polygon mirror), a light beam is incident on the deflecting surface of the optical deflector from an oblique direction so that the imaging lens on the optical deflector side is shared ( Double pass) is used. Various types of optical scanning devices of this type have been conventionally proposed (see Patent Document 1).

  Further, as a method for reducing the number of lenses, there is a method in which an imaging lens closer to the surface to be scanned (photosensitive drum surface) is also shared (double pass). However, in the oblique incidence optical system, the sub-scanning is performed in the direction in which the imaging lens is obliquely incident in order to correct the rotation of the spot and the bending of the scanning line caused by the difference in the amount of incident light entering and exiting the deflection surface of the optical deflector. It is eccentric in the direction. Various kinds of optical scanning devices of this type have been conventionally proposed (see Patent Document 2).

At this time, if an image forming lens near the surface to be scanned is used in common for the light fluxes directed to the respective photosensitive drums, the lenses are stacked in the vertical direction (sub-scanning direction). Various types of optical scanning devices of this type have been conventionally proposed (see Patent Document 3).
JP 2002-365574 A JP 2004-70108 A JP 2002-160268 A

  As a method for making the imaging optical system compact and simple, there is a method of bringing a plurality of imaging lenses constituting the imaging optical system close to an optical deflector (enlargement optical system). At this time, the distance between the apexes (between surface apexes) of the imaging lenses stacked vertically is relatively short.

  FIG. 18 is an enlarged explanatory view showing a state in which two light beams pass through lens surfaces 181a and 181b of a lens (imaging lens) 181 stacked vertically.

  When the imaging lens 181 is actually molded, considering the sub-scanning cross section, the transferability of the joint portion (B1) of the two arcs may be more deteriorated than the other portions because the angle change is tight. Conceivable. As described above, in the case of an optical system in which the distance between the vertices A11 of the two A parts (optically effective parts) is narrow in the magnifying optical system, the deterioration in transferability of the B part (optically ineffective part) affects the shape of the light beam passing position. Effect. As a result, the wavefront aberration on the photosensitive drum surface is affected, and there is a concern that the spot shape of the spot on the photosensitive drum surface is deteriorated as shown in FIG.

  Therefore, in order to improve the transferability of the B part (optical ineffective part), it is necessary to consider the shape of the imaging lens 181 in the sub-scan section.

  The present invention uses an optical scanning device that is compact and simple, and that does not deteriorate the optical performance without deteriorating the spot shape on the surface to be scanned even if the imaging lens is used in common, and the same. An object is to provide an image forming apparatus.

The optical scanning device of the invention of claim 1
A plurality of light source means, a deflecting means for deflecting and scanning a plurality of light beams emitted from the plurality of light source means, and a plurality of light beams deflected and scanned by the deflecting means on a surface to be scanned corresponding to each light source means An optical scanning device comprising one or more scanning units each having an imaging optical system having one or more imaging optical elements to form an image,
The plurality of light beams are incident on the same deflection surface of the deflecting unit at different angles with respect to a plane perpendicular to the rotation axis of the deflecting unit in the sub-scan section, and the one or more imaging optics The element has a plurality of optically effective portions and one or more optically ineffective portions between the plurality of optically effective portions and through which light flux does not pass,
In the one or more imaging optical elements, a plurality of light beams deflected by the same deflection surface in a sub-scan section pass through different optical effective portions,
In the sub-scan section, the distance in the optical axis direction of the imaging optical element from the line segment connecting the vertices of the plurality of optically effective portions to the vertex of the optically ineffective portion between the plurality of optically effective portions is 1. It is characterized by being configured to be 0 mm or less.

The invention of claim 2 is the invention of claim 1,
A plurality of light source means, a deflecting means for deflecting and scanning a plurality of light beams emitted from the plurality of light source means, and a plurality of light beams deflected and scanned by the deflecting means on a surface to be scanned corresponding to each light source means An optical scanning device comprising one or more scanning units each having an imaging optical system having one or more imaging optical elements to form an image,
The plurality of light beams are incident on the same deflection surface of the deflecting unit at different angles with respect to a plane perpendicular to the rotation axis of the deflecting unit in the sub-scan section, and the one or more imaging optics The element has a plurality of optically effective portions and one or more optically ineffective portions between the plurality of optically effective portions and through which the light beam does not pass,
In the one or more imaging optical elements, a plurality of light beams deflected by the same deflection surface in the sub-scan section pass through different optical effective portions, and the plurality of optical effective elements in the sub-scan section. The distance in the optical axis direction of the imaging optical element from the position through which the principal ray of each light beam passes through the apex of the optically ineffective portion between the plurality of optically effective portions is 1.0 mm or less. It is characterized by having.

The invention of claim 3 is the invention of claim 1 or 2, wherein
The plurality of optically effective portions and the optically ineffective portion are connected so that the inclination is continuous.

The invention of claim 4 is the invention of claim 1, 2 or 3,
The separation amount in the sub-scanning direction when the light beams from the plurality of light source units are incident on the same deflection surface of the deflection unit is 0 mm or more and 1.0 mm or less.

The invention of claim 5 is the invention of any one of claims 1 to 4,
When the imaging magnification in the sub-scan section of the imaging optical system is βs,
1.8 ≦ | βs | ≦ 3.0
It is characterized by satisfying the following conditions.

The color image forming apparatus of the invention of claim 6
Each of the optical scanning devices according to any one of claims 1 to 5 is disposed on a surface to be scanned, and has a plurality of image carriers that form images of different colors.

The invention of claim 7 is the invention of claim 6,
It is characterized by having a printer controller that converts color signals input from an external device into image data of different colors and inputs them to each optical scanning device.

  According to the present invention, it is possible to reduce the overall size of the apparatus and reduce the number of lenses, and to improve the transferability of the lenses and to suppress image deterioration due to the deterioration of wavefront aberration, and the same An image forming apparatus using can be achieved.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a sectional view (main scanning sectional view) of the main part in the main scanning direction according to the first embodiment of the present invention. FIG. 2 is a sectional view (sub-scanning sectional view) of the principal part in the sub-scanning direction of only one scanning unit (scanning optical system) S1 with the optical deflector according to the first embodiment of the present invention interposed therebetween. FIG. 3 is a cross-sectional view (sub-scanning cross-sectional view) of the main part in the sub-scanning direction including the plane mirror according to the first embodiment of the present invention.

  In the following description, the main scanning direction is a direction perpendicular to the rotation axis of the optical deflector and the optical axis of the imaging optical system (imaging lens system) (the light deflector reflects and deflects (deflects and scans) the optical deflector). Direction). The sub-scanning direction is a direction parallel to the rotation axis of the optical deflector. The main scanning section is a plane including the main scanning direction and the optical axis of the imaging optical system. The sub-scanning section is a section perpendicular to the main scanning section.

  The optical scanning device of the present embodiment includes two imaging lens systems (imaging optical systems) 15a and 15b with an optical deflector (polygon mirror) 5 interposed therebetween, and two light beams to the imaging lens systems 15a and 15b. And four light beams are simultaneously reflected and deflected by one optical deflector 5. Then, the four light beams are guided to the corresponding photosensitive drum surfaces 8a, 8b, 8c, and 8d, and the tandem type optical scanning device that optically scans the photosensitive drum surfaces 8a, 8b, 8c, and 8d. .

  In the figure, S1 and S2 are first and second scanning units (hereinafter also referred to as “station” or “scanning optical system”).

  Hereinafter, each member of the first and second scanning units S1 and S2 will be described focusing on the first scanning unit S1. Of the members of the second scanning unit S2, the same members as those of the first scanning unit S1 are shown in parentheses.

  The first (second) scanning unit S1 (S2) includes aperture stops 2a and 2c (2b and 2d) for restricting light beams from the light source means 1a and 1c (1b and 1d), and other states of the light beams. The first optical elements 3a and 3c (3b and 3d) for converting to the state of the luminous flux. Further, the first (second) scanning unit S1 (S2) includes second optical elements 4a and 4c (4b and 4d) that form a long line image in the main scanning direction, and an optical deflector 5 as a deflecting unit. And have. Furthermore, it has an imaging lens system 15a (15b) for forming a light beam from the optical deflector 5 in spots on the scanned surfaces 8a, 8c (8b, 8d).

  In the present embodiment, the first and second scanning units S1 and S2 use the same optical deflector 5, and the first and second scanning units S1 and S2 are different from each other in the optical deflector 5. A light beam reflected and deflected (deflected and scanned) by the deflecting surface is used.

  In this embodiment, the writing timing to the photosensitive drum surfaces 8a and 8c (8b and 8d) as the scanned surfaces of the first (second) scanning unit S1 (S2) is determined from the deflection surface of the optical deflector 5. Are detected by the writing position detection means (synchronous detection optical system) 16. The timing for writing on the photosensitive drum surfaces (8a, 8c, 8b, 8d) is determined using a signal from the writing position detection means 16.

  The first and second scanning units S1 and S2 are configured such that the light beam enters the optical deflector 5 from the same direction.

  In the first and second scanning units S1 and S2, the light source means (1a, 1c, 1b, 1d) are each composed of a semiconductor laser, and the light source means (1a, 1c, 1b, 1d) are the same planar substrate 12. Is arranged. The light source means (1a, 1c, 1b, 1d) may be arranged independently.

  The aperture stops (2a, 2c, 2b, 2d) respectively shape the light beams emitted from the light source means (1a, 1c, 1b, 1d) into a specific optimum beam shape.

  The first optical elements (3a, 3c, 3b, 3d) are each composed of a collimator lens, and convert the light beam that has passed through the aperture stop (2a, 2c, 2b, 2d) into a parallel light beam (or a divergent light beam or a convergent light beam). is doing.

  Each of the second optical elements (4a, 4c, 4b, 4d) is formed of a cylindrical lens and has a finite refractive power only in the sub-scanning direction. In the present embodiment, these four cylindrical lenses (4a, 4c, 4b, 4d) are integrally formed by a plastic mold or the like.

  The light source means 1a, 1c (1b, 1d), aperture stops 2a, 2c (2b, 2d), collimator lenses 3a, 3c (3b, 3d), cylindrical lenses 4a, 4c (4b, 4d), etc. Constitutes an element of the incident optical system.

  The optical deflector 5 is composed of, for example, a rotating polygon mirror (polygon mirror) having four deflection surfaces, and is rotated at a constant speed in the direction of arrow A in the figure by a driving means (not shown) such as a motor. In the present embodiment, as described above, the first and second scanning units S1 and S2 use the optical deflector 5 together, and the first and second scanning units S1 and S2 include the optical deflector 5. The light beams reflected and deflected by the different deflecting surfaces 5a and 5b are used.

  Reference numeral 15a (15b) denotes an imaging lens system (fθ lens system) having a light condensing function and an fθ characteristic, and includes first and second imaging lenses 6a and 7a (6b and 7b). . The imaging lens system 15a (15b) forms a plurality of light beams reflected and deflected by the optical deflector 5 in a spot shape on the corresponding scanned surfaces 8a and 8c (8b and 8d). The imaging lens system 15a (15b) has a surface tilt correction function by providing a conjugate relationship between the deflection surface of the optical deflector 5 and the scanned surfaces 8a and 8c (8b and 8d) in the sub-scan section. Have. The first and second imaging lenses 6a and 7a (6b and 7b) are plastic toric lenses (imaging optical elements) having different refractive powers in the main scanning direction and the sub-scanning direction, respectively. It is made up.

  The first imaging lenses 6a and 6b are also referred to as anamorphic lenses 1, and the second imaging lenses 7a and 7b are also referred to as anamorphic lenses 2.

  Further, the first and second imaging lenses 6a and 7a (6b and 7b) in the present embodiment each have a region through which a plurality of light beams pass.

  Reference numerals 20a, 21a, and 22a (20b, 21b, and 22b) denote folding mirrors that fold the light beams that have passed through the imaging lens system 15a (15b) toward the corresponding photosensitive drums 8a and 8c (8b and 8d).

  Reference numeral 16 denotes a writing position detection means (synchronous detection optical system). The synchronization detection optical system 16 includes a synchronization detection lens (hereinafter referred to as “synchronization detection lens”) 9, a linear edge portion (hereinafter referred to as “synchronization detection edge”) 11, and synchronization detection. Sensor (hereinafter referred to as “synchronous detection sensor”) 10. The synchronization detection optical system 16 determines the timing of writing to the scanned surfaces 8a and 8c (8b and 8d) of the scanning unit S1 (S2).

  The synchronization detection lens 9 in this embodiment is formed integrally with the cylindrical lenses 4a and 4c (4b and 4d) of each scanning unit S1 (S2), and the synchronization detection light beam reflected and deflected by the deflection surface 5a ( (Synchronization detection light beam) is imaged on the surface of the synchronization detection edge 11. The synchronization detection lens 9 scans on the synchronization detection edge 11 in the main scanning section, and the deflection surface and the synchronization detection edge 11 are conjugate in the sub-scanning section. It has become.

  The synchronization detection edge 11 determines the image writing position.

  The synchronization detection sensor 10 includes a sensor in which a plurality of elements are arranged in a one-dimensional direction. In this embodiment, the synchronization detection sensor 10 and the four light source means (1a, 1c, 1b, 1d) are integrally formed on the same flat substrate 12. The synchronization detection sensor 10 and the four light source means (1a, 1c, 1b, 1d) may be configured independently of each other.

  In the present embodiment, first, in the first station S1, the two light beams emitted and modulated from the light source means 1a and 1c according to the image information are regulated by the aperture stops 2a and 2c. The two regulated light beams are converted into parallel light beams or convergent light beams by the collimator lenses 3a and 3c, and enter the cylindrical lenses 4a and 4c. Out of the light beams incident on the cylindrical lenses 4a and 4c, they are emitted as they are in the main scanning section. Further, in the sub-scan section (plane perpendicular to the rotation axis of the optical deflector), it converges and is incident on the deflecting surface 5a of the optical deflector 5 at different angles (obliquely incident) to form a line image (in the main scanning direction). Longitudinal line image). The two light beams reflected and deflected by the deflecting surface 5a of the optical deflector 5 are spot-formed on the photosensitive drum surfaces 8a and 8c by the imaging lens system 15a via the corresponding folding mirrors 20a, 21a and 22a. Is done. Then, by rotating the optical deflector 5 in the direction of arrow A, optical scanning is performed on the photosensitive drum surfaces 8a and 8c in the direction of arrow B (main scanning direction) at a constant speed. Thus, image recording is performed on the photosensitive drum surfaces 8a and 8c which are recording media.

  At this time, in order to adjust the timing of the scanning start position on the photosensitive drum surfaces 8a and 8c before optical scanning on the photosensitive drum surfaces 8a and 8c, the light beam reflected and deflected by the deflecting surface 5a of the optical deflector 5 is used. A part (synchronous detection light beam) is condensed on the surface of the synchronous detection edge 11 by the synchronous detection lens 9. Thereafter, the light beam condensed on the surface of the synchronization detection edge 11 is guided to the synchronization detection sensor 10. Then, the timing of the scanning start position of image recording on the photosensitive drum surface 8a is adjusted by using the writing position detection signal (synchronization detection signal) obtained by detecting the output signal from the synchronization detection sensor 10. .

  In the second station S2, the two light beams emitted from the light source means 1b and 1d are incident on the deflecting surface 5b of the optical deflector 5 at different angles from the same direction as the incident direction of the first scanning unit S1. . Then, the two light beams reflected and deflected by the deflection surface 5b are imaged in a spot shape on the photosensitive drum surfaces 8b and 8d via the corresponding folding mirrors 20b, 21b and 22b by the imaging lens system 15b, and optically scanned. The As a result, one scanning line is formed on each of the four photosensitive drum surfaces 8a, 8b, 8c, and 8d to perform image recording.

  Next, means and effects for achieving the object of the present embodiment will be described.

  As shown in FIG. 4, the second imaging lens 7a (7b) is configured to deviate the lens surface 20 up and down in the sub-scanning direction as shown in FIG. It has lens surfaces (outgoing surfaces) 21 and 22 that are separated into two parts. The cross sections of the two lens surfaces 21 and 22 are circular arcs. Considering the state shown in FIG. 4, the portion (connecting portion) 23 connecting the two lens surfaces 21 and 22 is not continuous and has an angle. For this reason, the direction of contraction is different in the central portion 24 of the connecting portion 23 after molding. For this reason, the shape of the central portion 24 in the sub-scanning direction includes a habit that includes an aspherical component (fourth order or higher) with respect to the original arc shape, and the light rays on the lens surface 21 and the lens surface 22 are generated. There is a possibility that the wavefront aberration of the light beam is deteriorated by affecting the shape of the position through which the light passes.

  In FIG. 4, Y1 and Y2 are optically effective portions (optically effective surfaces). In this embodiment, the two light beams deflected by the deflecting surface 5a are incident on the corresponding optical effective portions Y1 and Y2. The optically effective portions Y1 and Y2 are included in the lens surfaces 21 and 22, respectively.

  Y3 is an optical ineffective portion (optical ineffective surface) through which the light beam does not pass, and is between the optical effective portions Y1 and Y2. The optically ineffective portion Y3 is included in the connecting portion 23.

  In this embodiment, as shown in FIG. 4, the lens surface 21 and the lens surface 22 are connected by a smooth curve (for example, an arc or a polynomial) so that the inclination is continuous. The influence of the habit of the joint is reduced.

  The continuity of the slope described here means that the slopes at the connection points of the two curves are equal. In addition, the influence of the habit can be reduced by reducing the distance from the connecting portion 23 to the lens surface 21 and the lens surface 22.

  Next, specific contents will be described.

In FIG. 4, the vertex of the lens surface 21 is A21, the vertex of the lens surface 22 is A22, and the vertex of the joint 23 is B. In order to simplify the concept, the lens surface 21, the lens surface 22, and the connecting portion 23 are considered as arcs. The radius of curvature of the lens surface 21 and the lens surface 22 is R ₂₁ , and the radius of curvature of the optically effective portions Y 1 and Y 2 is also R ₂₁ . Further, the radius of curvature of the connecting portion 23 is R ₂₃ , and the radius of curvature of the optically ineffective portion Y 3 is also R ₂₃ . Further, when the distance from the vertex A21 to the vertex A22 is H, the distance (sag amount) z in the optical axis direction from the line segment connecting the vertex A21 and the vertex A22 to the vertex B can be expressed as follows.

With respect to a plane perpendicular to the rotation axis of the optical deflector 5, light beams L1 and L2 obliquely incident at ± γ degrees in the vertical direction in the sub scanning direction from the position where the light beams L1 and L2 enter the lens surface 21 and the lens surface 22 to the deflection surface 5a When the distance is L, the distance h between the passing positions of the two light beams is h = 2L · tanγ.
It is represented by In order to make the scanning optical system (scanning unit) compact, it is preferable to bring the imaging lens system 15a (15b) closer to the optical deflector 5 (enlargement optical system). Further, in order to prevent the light beam reflected by the plane mirror from interfering with the imaging lens system 15a (15b), it is necessary to reduce the distance from the optical deflector 5 to the imaging lens system 15a (15b) to about 60 mm. is there.

  Considering the separation of each light beam after exiting the imaging lens system 15a (15b), the oblique incident angle γ is preferably 2.5 degrees or more. Accordingly, the distance h between the two light beams in the imaging lens system 15a (15b) is relatively small, about 2 to 3 mm. When the imaging lens system 15a (15b) is close to the optical deflector 5, the light passing is relatively close to the apex of the lens surface. Therefore, assuming that H≈h, (Equation A) can be rewritten as follows.

The power of the exit surface of the imaging lens system 15a (15b) is increased for correction of spot rotation and scanning line bending, and the radius of curvature R is generally about 10-50. If stacked lenses in two stages, it is necessary to approximate the radius of curvature R ₂₃ of the higher curvature tighter optical invalid portion Y3 (connecting portion 23) to the radius of curvature R ₂₁ of the optically effective portion Y1 (lens surfaces 21, 22) So
R ₂₁ = 10,
_{R 23} ≧ R 21/4
From (Equation B), z ≦ 1.0mm (1)
It becomes.

  However, the sag amount z is 0 mm <z.

  Thus, the two lens surfaces 21, so that the distance z in the optical axis direction from the line segment connecting the vertex A21 of the lens surface 21 and the vertex A22 of the lens surface 22 to the vertex B of the connecting portion 23 is suppressed to 1.0 mm or less. By connecting 22 smoothly, the influence of shrinkage after molding can be reduced. Thereby, deterioration of wavefront aberration can be reduced. Further, by providing the imaging lens system 15a (15b) close to the optical deflector 5 and sharing the second imaging lens 7a (7b) with two light beams, a more compact optical scanning device than the conventional one is provided. can do.

The above conditional expression (1) is further changed to z ≦ 0.5 mm (1a)
If it is set to, the influence on shrinkage after molding can be further reduced, which is desirable.

  Table 1 shows various amounts of the optical system of Example 1 of the present invention.

  In this embodiment, as shown in FIG. 5, the exit surface 21 and the surface vertex axis c1 and the surface vertex axis c2 of the exit surface 22 and the exit surface 22 of the second imaging lens (anamorphic lens 2) 7a (7b) become the lens optical axis c0. On the other hand, it is eccentric by 1.4 mm vertically in the sub-scanning direction.

  In this embodiment, the rotation of the spot is corrected as shown in FIG. 6 by decentering the emitting surface 21 up and down in the sub-scanning direction. The spots are represented by contour lines of 5%, 10%, 13.5%, 36.8%, and 50% with respect to the peak light quantity.

  FIG. 7 is an explanatory diagram showing the amount of sag at the joint portion according to the first embodiment of the present invention. As shown in the figure, the sag amount z of the optically ineffective portion Y3 up to the joint portion with respect to the surface apex portion is as small as 50 μm. The lens surface 21 and the lens surface 22 may be connected as they are, but in consideration of convenience when processing the mold, the inclination of the optically effective portions Y1 and Y2 through which the light beam passes and the optical ineffective portion Y3 through which the light beam does not pass It is desirable to adjust with a small diameter (loose curvature) R or a polynomial so that is continuous.

  At this time, since the sag amount z of the optically ineffective portion Y3 is further reduced, the influence of the joint by the molding is small, and the deterioration of the spot shape due to the deterioration of the wavefront aberration can be prevented. Further, since the second imaging lens 7a (7b) is close to the optical deflector 5, the length of the lens can be shortened compared to the conventional one.

In order to suppress the distance from the optical deflector 5 to the second imaging lens 7a (7b) to a certain extent and avoid interference with the lens due to folding of the light beam, the imaging lens system 15a (15b) in the sub-scan section It is desirable to set the imaging magnification βs to 1.8 or more. Also, if the imaging magnification βs becomes too large, the second imaging lens 7a (7b) becomes too close to the optical deflector 5 and the separation of the light flux becomes disadvantageous, so the sub-scanning magnification βs should be suppressed to 3.0 or less. Is desirable. That is, the imaging magnification βs in the sub-scan section of the imaging lens system 15a (15b) is
1.8 ≦ | βs | ≦ 3.0 (2)
It is better to satisfy the following conditions.

  In order to facilitate light beam separation, it is conceivable to increase the amount of light beam separation when a plurality of light beams reflect the deflection surface, but the height of the deflection surface in the sub-scanning direction increases. Therefore, considering the increase in the rotational resistance of the motor and the increase in the height of the second imaging lens 7a (7b), the separation amount of the plurality of light beams on the deflection surface is 0 mm or more and 1.0 mm or less. It is desirable to do.

In the present embodiment, the case where the lens surface of the second imaging lens 7a (7b) has two stages is shown, but the present invention is not limited to this, and the lens surface may have three or more stages. For example, in a system in which three or more light beams are separated after passing through the second imaging lenses 7a and 7b, the lens surface may have three or more stages. Smooth connection can reduce the influence of the habit of molding.
[Modification]
FIG. 8 is a sectional view (sub-scanning sectional view) of the principal part in the sub-scanning direction of a modification of the first embodiment of the present invention. In the figure, the same elements as those shown in FIG.

  The modification differs from the first embodiment described above in that the imaging optical system 15 is composed of a single imaging lens (anamorphic lens 1) 6. Other configurations and optical actions are the same as those in the first embodiment.

  Table 2 shows various amounts of the optical system of the modification.

  In the modification, since the number of lenses constituting the imaging optical system 15 is one, the degree of freedom in correcting the optical performance on the scanned surface of the lens surface is reduced. Therefore, in this embodiment, in order to correct the rotation of the spot as shown in FIG. 10, the surface vertex axes c3 and c4 of the incident surfaces 21a and 22a of the imaging lens 6 are set to the lens optical axis (lens) as shown in FIG. Center) 2.9 mm up and down in the sub-scanning direction with respect to c0. Similarly, the surface vertex axes c5 and c6 of the emission surfaces 21b and 22b are decentered by 2.7 mm vertically in the sub-scanning direction with respect to the lens optical axis c0.

  In FIG. 10, spots are represented by contour lines of 5%, 10%, 13.5%, 36.8%, and 50% with respect to the peak light quantity.

  Here, the distance (sag amount) z in the optical axis direction of the joint between the incident surfaces 21a and 22a and the exit surfaces 21b and 22b of the imaging lens 6 is shown in FIGS. From FIGS. 5A and 5B, the sag amount z from the surface apex to the joint is about 0.3 mm on both sides.

  Since the light beam passing position is close to the lens optical axis c0 as shown in FIG. 9, in order to reduce the influence of the connecting portions 23a and 23b, the optical effective portions Y1 and Y2 through which the light passes and the optical ineffective portion through which the light does not pass. It is desirable to adjust with a small diameter (loose curvature) R or a polynomial so that the slope of Y3 is continuous.

  Thus, by reducing the sag amount with respect to the surface apexes of the connecting portions 23a and 23b, it is possible to reduce the influence due to the habit when forming the connecting portions 23a and 23b on both surfaces.

  FIG. 12 is a sectional view (sub-scanning sectional view) of the principal part in the sub-scanning direction of only one scanning unit (scanning optical system) S1 with the optical deflector according to the second embodiment of the present invention interposed therebetween, and FIG. It is a sub-scan sectional view of a lens (anamorphic lens 2). 12 and 13, the same elements as those shown in FIGS. 2 and 5 are denoted by the same reference numerals.

  This embodiment is different from the first embodiment described above in that the surface apex B of the second imaging lens 27a is composed of one. Other configurations and optical functions are the same as those in the first embodiment, and the same effects are obtained.

  That is, in the drawing, reference numeral 27a denotes a second imaging lens (anamorphic lens 2), and in this embodiment, as shown in FIG. 13, the surface vertex B of the second imaging lens 27a is composed of one. .

  k1 and k2 are the principal ray passing positions, respectively.

  When the oblique incident angle γ is increased due to the light beam separation, the light beam tends to pass through a position where the inclination of the lens surface is tighter in order to correct the spot rotation and the scanning line curve, so that the light beam is the apex of the original lens surface 21. It passes a position far away from A1.

  Therefore, when the two lens surfaces 21 and 22 are stacked, the vertex A1 of the original lens surface 21 is in the optically effective portion Y2 of the other lens surface 22, and therefore does not substantially exist. However, since sinking of the joint portion 23 due to shrinkage after molding can occur, it is necessary to smoothly connect the two lens surfaces 21 and 22, so that the shape of the surface vertex as shown in FIG. 13 exists in the center. A lens surface with

  Table 3 shows various amounts of the optical system of Example 2.

  In this embodiment, the surface vertex axis c1 of the exit surface 21 of the second imaging lens 27a and the surface vertex axis c2 of the exit surface 22 are vertically moved in the sub-scanning direction with respect to the lens optical axis c0 as shown in FIG. Is eccentric by 3.3 mm. At the same time, the apex in the direction of the strand is bent by about 50 μm, so that spot rotation due to oblique incidence is suppressed as shown in FIG.

  In FIG. 14, the spots are represented by contour lines of 5%, 10%, 13.5%, 36.8%, and 50% with respect to the peak light quantity.

  FIG. 15 is an explanatory diagram showing a sag amount at a joint portion according to the second embodiment of the present invention. In the figure, the same elements as those shown in FIG.

  As shown in the figure, since the distance from the joint to the light ray passing positions k1 and k2 is as long as 4.7 mm with respect to the lens optical axis c0, there is no need to leave the joint 23.

  Therefore, the optically ineffective portion Y3 through which the light beam does not pass is connected by a straight line, or the optically effective portion Y1, Y2 through which the light beam passes and the optical ineffective portion Y3 has a gentle curvature (R) or a polynomial so that the inclination is continuous. Just connect them. At this time, in the sub-scan section, the distance (sag amount) z in the optical axis direction from the ray passing positions k1 and k2 of the principal rays to the surface apex B of the optical ineffective portion Y3 is as small as 0.1 mm or less. The influence of the ineffective portion Y3 is very small.

  If the sag amount z is 1.0 mm or less, the object of the present invention can be achieved. More preferably, the sag amount z is set to 0.5 mm or less. However, the sag amount z is 0 mm <z.

  Further, since the second imaging lens 27a is close to the optical deflector 5, the length of the lens can be shortened compared to the conventional one. Further, the increase in the oblique incident angle γ is advantageous for separating the upper and lower light beams in the sub-scanning direction.

  In the first and second embodiments, the scanning unit (scanning optical system) is provided with the optical deflector 5 interposed therebetween. However, the present invention is not limited to this.

[Color image forming apparatus]
FIG. 16 is a schematic view of a main part of a color image forming apparatus according to an embodiment of the present invention. This embodiment is a tandem type color image forming apparatus in which four optical scanning devices are arranged in parallel and image information is recorded on a photosensitive drum surface as an image carrier. In FIG. 16, 360 is a color image forming apparatus, and 311 and 312 are scanning units each having one of the configurations shown in the first and second embodiments. 341, 342, 343, and 344 are photosensitive drums as image carriers, 321, 322, 323, and 324 are developing units, and 351 is a conveyor belt.

  In FIG. 16, R (red), G (green), and B (blue) color signals are input to the color image forming apparatus 360 from an external device 352 such as a personal computer. These color signals are converted into C (cyan), M (magenta), Y (yellow), and B (black) image data (dot data) by a printer controller 353 in the apparatus. These image data are input to the scanning units 311 and 312 respectively. From these scanning units, light beams 331, 332, 333, and 334 modulated according to each image data are emitted, and the photosensitive surfaces of the photosensitive drums 341, 342, 343, and 344 are mainly emitted by these light beams. Scanned in the scanning direction.

  The color image forming apparatus according to the present embodiment has two scanning units 311 and 312 arranged in correspondence with each color of C (cyan), M (magenta), Y (yellow), and B (black). In parallel, image signals (image information) are recorded on the surfaces of the photosensitive drums 341, 342, 343, and 344, and color images are printed at high speed.

  As described above, the color image forming apparatus according to the present embodiment uses the light beams based on the respective image data by the two scanning units 311 and 312 to respectively correspond to the photosensitive drums 341, 342, 343, and 344 corresponding to the latent images of the respective colors. Formed on top. Thereafter, a single full color image is formed by multiple transfer onto a recording material.

  As the external device 352, for example, a color image reading device including a CCD sensor may be used. In this case, the color image reading apparatus and the color image forming apparatus 360 constitute a color digital copying machine.

Main scanning sectional view of Embodiment 1 of the present invention Sub-scan sectional view of Embodiment 1 of the present invention Sub-scan sectional view of Embodiment 1 of the present invention The figure explaining the connection method of the eccentric lens surfaces of Example 1 of this invention Explanatory drawing of the surface eccentricity of the lens in Example 1 of the present invention Spot diagram in Example 1 of the present invention The sag figure of the connection part in Example 1 of this invention Sub-scan sectional view in a modification of Embodiment 1 of the present invention Explanatory drawing of the surface eccentricity of the lens in the modification of Example 1 of this invention Spot diagram in a modification of the first embodiment of the present invention The sag figure of the connection part in the modification of Example 1 of this invention Sub-scan sectional view of Embodiment 2 of the present invention Explanatory drawing of the surface eccentricity of the lens in Example 2 of the present invention Spot diagram in Example 2 of the present invention Sag figure of the joint part in Example 2 of the present invention 1 is a schematic view of a main part of a color image forming apparatus according to an embodiment of the present invention. Schematic diagram of main parts of a conventional optical scanning device Enlarged view of stacked lens surfaces A diagram for explaining deterioration of spot shape due to transfer deterioration

Explanation of symbols

1a, 1b, 1c, 1d Light source means 2a, 2b, 2c, 2d Aperture stop 3a, 3b, 3c, 3d Condensing lens (collimator lens)
4a, 4b, 4c, 4d Cylindrical lens 5 Deflection means (polygon mirror)
15a, 15b Imaging optical system (fθ lens system)
6a, 6b First imaging lens (fθ lens)
7a, 7b Second imaging lens (fθ lens)
8a, 8b, 8c, 8d Scanned surface (photosensitive drum surface)
DESCRIPTION OF SYMBOLS 9 Lens for synchronous detection 11 Edge for synchronous detection 10 Sensor 311 for synchronous detection Scan unit 341,342,343,344 Image carrier (photosensitive drum)
321, 322, 323, 324 Developer 331, 332, 333, 334 Light beam 351 Conveyor belt 352 External device 353 Printer controller 360 Color image forming apparatus

Claims (7)

A plurality of light source means, a deflecting means for deflecting and scanning a plurality of light beams emitted from the plurality of light source means, and a plurality of light beams deflected and scanned by the deflecting means on a surface to be scanned corresponding to each light source means An optical scanning device comprising one or more scanning units each having an imaging optical system having one or more imaging optical elements to form an image,
The plurality of light beams are incident on the same deflection surface of the deflecting unit at different angles with respect to a plane perpendicular to the rotation axis of the deflecting unit in the sub-scan section, and the one or more imaging optics The element has a plurality of optically effective portions and one or more optically ineffective portions between the plurality of optically effective portions and through which light flux does not pass,
In the one or more imaging optical elements, a plurality of light beams deflected by the same deflection surface in a sub-scan section pass through different optical effective portions,
In the sub-scan section, the distance in the optical axis direction of the imaging optical element from the line segment connecting the vertices of the plurality of optically effective portions to the vertex of the optically ineffective portion between the plurality of optically effective portions is 1. An optical scanning device configured to be 0 mm or less. A plurality of light source means, a deflecting means for deflecting and scanning a plurality of light beams emitted from the plurality of light source means, and a plurality of light beams deflected and scanned by the deflecting means on a surface to be scanned corresponding to each light source means An optical scanning device comprising one or more scanning units each having an imaging optical system having one or more imaging optical elements to form an image,
The plurality of light beams are incident on the same deflection surface of the deflecting unit at different angles with respect to a plane perpendicular to the rotation axis of the deflecting unit in the sub-scan section, and the one or more imaging optics The element has a plurality of optically effective portions and one or more optically ineffective portions between the plurality of optically effective portions and through which the light beam does not pass,
In the one or more imaging optical elements, a plurality of light beams deflected by the same deflection surface in the sub-scan section pass through different optical effective portions, and the plurality of optical effective elements in the sub-scan section. The distance in the optical axis direction of the imaging optical element from the position through which the principal ray of each light beam passes through the apex of the optically ineffective portion between the plurality of optically effective portions is 1.0 mm or less. An optical scanning device characterized by comprising:   3. The optical scanning device according to claim 1, wherein the plurality of optically effective portions and the optically ineffective portion are connected so as to have a continuous inclination. 4.   The distance in the sub-scanning direction when the light beams from the plurality of light source units are incident on the same deflection surface of the deflection unit is 0 mm or more and 1.0 mm or less, according to claim 1, 2, or 3 The optical scanning device described. When the imaging magnification in the sub-scan section of the imaging optical system is βs,
1.8 ≦ | βs | ≦ 3.0
5. The optical scanning device according to claim 1, wherein the following condition is satisfied.   6. A color image comprising: a plurality of image carriers, each of which is disposed on a surface to be scanned of the optical scanning device according to claim 1 and forms images of different colors. Forming equipment. 7. The color image forming apparatus according to claim 6, further comprising a printer controller that converts color signals input from an external device into image data of different colors and inputs the converted image data to each optical scanning device.

Images