JP2008026410A - Optical scanner, optical write-in device with the optical scanner, and image forming apparatus with the optical scanner or the write-in device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a compact, inexpensive and low-electric driving power optical scanner which forms a high quality image by performing optical scanning with synchronous detection without being affected by external disturbance such as temperature change without specially machining a scanning lens system, and to provide an optical write-in device with the optical scanner and an image forming apparatus with the optical scanner or the optical write-in device. <P>SOLUTION: The optical scanner is provided with; 2n (n≥1) pieces of light sources 2 having m (m≥1) pieces of light emitting parts 1; an optical deflector 4 in which (m×n) luminous fluxes 3 from each light source 2 are oppositely made incident on the rotation center 40; 2n pieces of surfaces 5 to be scanned corresponding to the 2n pieces of light sources 2; a scanning lens system 6 that makes the m pieces of light fluxes 3 of the light emitting parts 1 to form an image on each of the 2n pieces of surfaces 5 to be scanned arranged in a manner opposing the optical deflector 4; and a synchronous light receiving means 8 in which the center 50 of the write-in width on the 2n pieces of surfaces 5 to be scanned and the center 40 of rotation of the optical deflector 4 are arranged to be lined up on one line 7 and in which the deflective luminous flux of the optical deflector 4 is received as the synchronous luminous flux 32 for deciding the write-in timing of the scanning luminous flux 31. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an optical scanning device, an optical writing device including the optical scanning device, and an image forming apparatus including the optical scanning device or the optical writing device. Specifically, an optical scanning device that optically scans the surface to be scanned along the main scanning direction with a plurality of light beams emitted from the light source, and a plurality of light beams that are emitted from the light source with the optical scanning device along the main scanning direction. Optical writing apparatus that scans a surface to be scanned to form an image, and copier, facsimile apparatus, printer, or a combination thereof that forms a recorded image on the optical scanning apparatus or a recording medium that includes the optical writing apparatus The present invention relates to an image forming apparatus.

In a conventional optical scanning device, an optical writing device including the optical scanning device, and an image forming apparatus including the optical scanning device or the optical writing device, the optical scanning device and the optical writing device include a digital copying device, It is widely known in connection with laser printers and the like.
The scanning optical system is an optical system that is used in an optical scanning device and collects a light beam deflected by an optical deflector as a light spot on a surface to be scanned. In recent years, optical scanning devices have been strongly demanded to increase the density of optical scanning, and in order to meet this demand, reduction in the diameter and stabilization of the light spot have been pursued.

In particular, the light spot position affects the color shift when, for example, a multicolor image is formed. Therefore, stabilization along with the light spot diameter is required. In general, a method is widely used in which a synchronous light beam, which is a light beam outside the writing range, is detected by a light receiving element and the writing position on the surface to be scanned is determined.
Since the synchronous light beam is a light beam used as a reference for determining the light spot position, higher stability than the writing light beam is required. When the scanning lens is deformed due to a disturbance such as temperature fluctuation, the light spot is displaced with respect to the light beam passing through the scanning lens.
Therefore, it is desirable that the reference sync beam does not receive the power of the scanning lens. The best method is a method that does not pass through the scanning lens, but due to the miniaturization of the optical scanning device, miniaturization of the scanning lens and the approach to the optical deflector have advanced, and the synchronous light flux that passes outside the scanning lens and the light Since there is a possibility that the optical system in front of the deflector may interfere, it is difficult to construct such a layout.

Therefore, in order to suppress the influence on the synchronous light flux due to the deformation of the scanning lens due to the temperature fluctuation, the following countermeasures have already been proposed.
First, a U-shaped notch is made at the end of the scanning lens (see Patent Document 1).
Next, the passage portion of the synchronous light beam is set to non-power in the main scanning direction (see Patent Document 2).
Further, an inclined portion is provided at the end of the scanning lens (see Patent Document 3).
However, these measures apply processing to the portion outside the effective range of the scanning lens in order to suppress the influence on the synchronous light flux due to deformation of the scanning lens due to temperature fluctuations, so that the accuracy of the peripheral portion of the scanning lens decreases. There are problems such as an increase in the number of processes leading to an increase in cost.
Japanese Patent Laid-Open No. 2002-98921 Japanese Patent Laid-Open No. 10-10445 Japanese Patent No. 3288970

In a conventional optical scanning device, an optical writing device including the optical scanning device, and an image forming apparatus including the optical scanning device or the optical writing device, the influence on the synchronous light flux due to the deformation of the scanning lens due to temperature variation In order to suppress this, processing is performed on a portion outside the effective range of the scanning lens, so that problems have arisen that the accuracy of the peripheral portion of the scanning lens is lowered and the increase in the number of steps leads to an increase in cost.
Therefore, an object of the present invention is to solve such problems. In other words, a compact, low-cost, low drive power optical scanning device that forms a high-quality image by performing optical scanning with synchronous detection that is not affected by disturbances such as temperature fluctuations without special processing on the scanning lens system And an optical writing device including the optical scanning device, and an image forming apparatus including the optical scanning device or the optical writing device.

In order to achieve the above object, the present invention described in claim 1 is an optical scanning device that optically scans a surface to be scanned along a main scanning direction with a plurality of light beams emitted from a light source. 1) 2n (where n ≧ 1) light source units having one light emitting unit, and an optical deflector in which (m × n) light beams from each of the light source units are incident to face the rotation center And 2n (where n ≧ 1) scanned surfaces corresponding to 2n (where n ≧ 1) light sources, and m (where m ≧ 1) luminous fluxes of the light emitting unit are A scanning lens system that forms an image on 2n (where n ≧ 1) scanning surfaces arranged to face the optical deflector, and 2n (where n ≧ 1) scanning surfaces The writing beam center of the optical deflector is arranged so that the writing width center on the surface and the rotation center of the optical polarizer are aligned in a straight line, and the scanning light beam is written. Characterized in that an optical scanning apparatus comprising a synchronizing light receiving means for receiving a synchronizing light beam to determine the observed time.
Alternatively, the present invention described in claim 2 is the optical scanning device according to claim 1, wherein the light source unit includes a semiconductor laser array in which a plurality of the light emitting units are arranged in a line. It is characterized by that.
Alternatively, according to a third aspect of the present invention, in the optical scanning device according to the first or second aspect, the scanning optical system of the optical deflector causes the light spot on the surface to be scanned to be constant speed in the main scanning direction. It is an optical scanning device provided with a function of optically scanning.
Alternatively, according to a fourth aspect of the present invention, in the optical scanning device according to the first, second, or third aspect, the scanning optical system of the optical deflector corrects the surface tilt of the optical deflector in the sub-scanning direction. It is an optical scanning device provided with the function to perform.
Alternatively, according to a fifth aspect of the present invention, in the optical scanning device according to any one of the first to fourth aspects, the scanning lens system includes the light of the scanning lens system including one or more scanning lenses L. Scanning lenses L1, L2,... Lj (j = 1.2,...) In order from the deflector and one or more scanning lenses facing the scanning lens system with respect to the rotation center of the optical deflector. The scanning having the same shape in any j of scanning lenses M1, M2,... Mj (j = 1.2,...) In the order closer to the optical deflector of the other scanning lens system composed of M. It is an optical scanning device including a lens Lj and the scanning lens Mj.
Alternatively, according to a sixth aspect of the present invention, in the optical scanning device according to any one of the first to fifth aspects, the scanning lens system is an optical scanning device having an anamorphic surface. To do.
Alternatively, according to a seventh aspect of the present invention, in the optical scanning device according to any one of the first to sixth aspects, at least one surface of the scanning lens system has a center of curvature in the sub-scanning section as a main scanning section. It is an optical scanning device provided with a special toric surface in which a line connecting within is non-linear.
Alternatively, according to an eighth aspect of the present invention, in the optical scanning device according to the seventh aspect, the scanning lens system changes the curvature of the special toric surface in the sub-scan section along the main scanning direction. It is an optical scanning device provided as a non-object with respect to the optical axis of the surface.
Alternatively, according to a ninth aspect of the present invention, in the optical scanning device according to any one of the first to eighth aspects, the scanning lens system includes the scanning lens constituted by a single lens. It is characterized by being.
Alternatively, according to a tenth aspect of the present invention, in the optical scanning device according to any one of the first to ninth aspects, the scanning lens system includes the scanning lens formed of a resin. It is characterized by being.
Alternatively, the present invention according to claim 11 is the optical scanning device according to any one of claims 1 to 10, wherein the scanning lens system is inclined with respect to the normal line of the surface to be scanned. It is an optical scanning device provided with at least 1 piece of the said scanning lens which has these.
Alternatively, according to a twelfth aspect of the present invention, in the optical scanning device according to any one of the first to eleventh aspects, the synchronous light receiving unit does not pass through the scanning lens system used for determining the write timing. It is an optical scanning device provided with a light beam.
Alternatively, according to a thirteenth aspect of the present invention, in the optical scanning device according to any one of the first to twelfth aspects, the luminous flux is in a sub-scanning direction with respect to the normal line of the reflecting surface of the optical deflector. It is an optical scanning device provided with an angle.
Alternatively, the present invention described in claim 14 is an optical writing apparatus for forming an image by scanning a surface to be scanned along a main scanning direction with a plurality of light beams emitted from a light source. An optical writing device comprising: the optical scanning device according to claim 1; and an image writing unit that optically scans the surface to be scanned by the optical scanning device and writes an image.
Alternatively, the present invention according to claim 15 is the optical writing device according to claim 14, wherein the optical scanning device is an optical writing device comprising a plurality of layers stacked in the sub-scanning direction. To do.
Alternatively, the present invention described in claim 16 is the optical writing device according to claim 15, wherein each of the optical scanning devices stacked in the sub-scanning direction includes the optical deflector having a common rotation axis. It is an insertion device.
Alternatively, the present invention according to claim 17 is the optical writing device according to claim 15 or 16, wherein each of the optical scanning devices stacked in the sub-scanning direction is incident on the same phase plane of the optical deflector. It is an optical writing device having different incident angles in the main scanning direction of the lower light beam.
Alternatively, the present invention according to claim 18 is the optical writing device according to claim 15, 16 or 17, wherein each of the optical scanning devices stacked in the sub-scanning direction is incident on the same phase plane of the optical deflector. An optical writing device having different reflection points deflected in the main scanning direction of the upper and lower light fluxes.
Alternatively, the present invention according to claim 19 is the optical writing device according to claim 14, wherein the two optical scanning devices are arranged in parallel so that the main scanning planes are the same. It is an insertion device.
Alternatively, the invention according to claim 20 is an image forming apparatus for forming a recorded image on a recording medium, wherein the optical scanning device according to any one of claims 1 to 13 or the claims 14 to 14 is provided. 20. An image forming apparatus comprising: the optical writing device according to claim 19; and an image forming unit that forms a recorded image on a recording medium by the optical scanning device or the optical writing device. To do.
Alternatively, according to a twenty-first aspect of the present invention, in the image forming apparatus for forming a color recording image on a recording medium, the optical scanning device 10 according to any one of the first to thirteenth aspects or the present invention. Item 20. An image forming apparatus comprising: the optical writing device according to any one of Items 14 to 19; and an image forming unit that forms a color recording image on a recording medium by the optical scanning device or the optical writing device. It is characterized by being.

  According to the present invention, a compact, low-cost, low driving power that forms a high-quality image by performing optical scanning with synchronous detection that is not affected by disturbances such as temperature fluctuations without special processing on the scanning lens system An optical scanning device, an optical writing device including the optical scanning device, and an image forming apparatus including the optical scanning device or the optical writing device can be provided.

Embodiments of the present invention will be described below in detail with reference to the drawings.
FIG. 1 is a basic configuration diagram showing an optical arrangement in a main scanning section of an optical scanning device 10 according to an embodiment of the present invention.
FIG. 2 is a perspective view of the basic configuration of the single beam system of the optical scanning device 10 or the optical writing device 100 including the optical scanning device 10 according to the embodiment of the present invention.
FIG. 3 is a perspective view of the basic configuration of the multi-beam system of the optical scanning device 10 or the optical writing device 100 including the optical scanning device 10 according to the embodiment of the present invention.
FIG. 4 is a graph showing the field curvature (a) and constant velocity characteristic (b) of the optical scanning device 10 according to the embodiment of the present invention.
FIG. 5 is a graph showing a depth curve (a) of the spot diameter in the main scanning direction and a depth curve (b) of the spot diameter in the sub-scanning direction of the optical scanning device 10 according to the embodiment of the present invention.
FIG. 6 is a basic configuration diagram of an optical writing device 100 including the oblique incidence type optical scanning device 10 according to the embodiment of the present invention.
FIG. 7 is a basic configuration diagram in which a crossing angle is given to the optical scanning device 10 according to the embodiment of the present invention and the reflection points of the upper and lower light fluxes 3 are different.
FIG. 8 is a basic configuration diagram of an optical writing device 100 provided with a plurality of optical scanning devices 10 according to an embodiment of the present invention which are superposed in the upper and lower stages.
FIG. 9 is a basic configuration diagram of an optical writing device 100 provided with a plurality of optical scanning devices 10 according to an embodiment of the present invention arranged in parallel on the same main scanning plane.
FIG. 10 is a basic configuration diagram of an image forming apparatus that includes the optical scanning device 10 or the optical writing device 100 according to the embodiment of the present invention and forms a recorded image on a recording medium.
FIG. 11 shows an image in which a plurality of optical scanning devices 10 or optical writing devices 100 according to an embodiment of the present invention are provided in parallel on the same main scanning plane to form a color recording image on a recording medium. 1 is a basic configuration diagram of a forming apparatus 300. FIG.
FIG. 12 is a chart showing data of the optical system between the optical polarizer 4 and the scanned surface 5 of the optical scanning device 10 according to the embodiment of the present invention.
FIG. 13 is a chart showing coefficients in the main scanning direction of the incident surface (surface number: i = 1) of the optical scanning device 10 according to the embodiment of the present invention.
FIG. 14 is a chart showing coefficients in the main scanning direction and the sub-scanning direction of the exit surface (surface number: i = 2) of the optical scanning device 10 according to the embodiment of the present invention.

In FIG. 1, an optical scanning device 10 that optically scans a surface to be scanned along a main scanning direction with a plurality of light beams emitted from a light source includes 2n (provided that m ≧ 1) light emitting units 1. n ≧ 1) light source sections 2, optical deflectors 4 on which (m × n) light beams 3 from each light source section 2 are incident on the rotation center 40, and 2n (where n ≧ 1) 1) 2n (where n ≧ 1) scanned surfaces 5 corresponding to one light source unit 2 and m (where m ≧ 1) light beams 3 of the light emitting unit 1 are transmitted to the optical deflector 4. A scanning lens system 6 that forms an image on 2n (where n ≧ 1) scanned surfaces 5 arranged to face each other, and writing on 2n (where n ≧ 1) scanned surfaces 5 The width center 50 and the rotation center 40 of the optical polarizer 4 are arranged so as to be aligned on a straight line 7 to determine the writing timing of the scanning light beam 31 with the deflected light beam of the optical deflector 4. And a synchronous receiving means 8 for receiving as Kikotaba 32.
The optical scanning device 10 is arranged so that the writing width center 50 on the two scanned surfaces 5 arranged to face the optical deflector 4 and the rotation center 40 of the optical polarizer 4 are aligned on a substantially straight line 7. ing. Since the writing width centers 50 on the scanning surface 50 arranged on both sides of the optical deflector 4 are aligned, it is possible to perform optical scanning suitable for a tandem image forming apparatus 300 described later (see FIG. 11). ).

Since the optical scanning device 10 easily secures a spatial margin between the optical system in front of the optical deflector 4 and the scanning optical system by such an optical arrangement, special processing is performed on the end of the scanning lens system 6 and the like. The optical path of the synchronous light flux 32 that does not pass through the scanning lens system 6 can be ensured without performing the above.
In addition, it is possible to avoid deterioration of the processing accuracy of the peripheral portion of the scanning lens system 6 when special processing is performed on the end portion of the scanning lens system 6, and to reduce the cost by not performing processing. .
Furthermore, in general, it is preferable to bring the scanning lens system 6 closer to the optical deflector 4 in order to reduce the size of the apparatus. At this time, it becomes difficult to secure a passage portion of the synchronous light beam 32.
However, since the optical scanning device 10 of the present invention can secure the optical path of the synchronous light flux 32 that does not pass through the scanning lens system 6 received by the synchronous light receiving means 8 only by the arrangement of the scanning lens system 6, temperature fluctuations and the like. Thus, it is possible to realize a synchronous optical system that is not affected by the deformation of the scanning lens system 6 due to the disturbance of the lens, and to achieve both downsizing of the apparatus and stabilization of the synchronous light flux 32 with respect to temperature.

Further, in the optical arrangement of the optical scanning device 10 according to the present invention, the scanning lens system 6 includes L1, L2,... In the order closer to the optical deflector 4 of the scanning lens system 60 including one or more scanning lenses L. The optical deflector 4 of the scanning lens system 61 including one or more scanning lenses M facing the scanning lens system 60 with respect to Lj (j = 1.2,...) And the rotation center 40 of the optical deflector 4. .., Mj (j = 1.2,...) In the order of M1, M2,...
Since the two scanning optical systems of the scanning lens system 60 and the scanning lens system 61 are thus arranged rotationally symmetrically with respect to the rotation center 40 of the optical deflector 4, scanning is performed corresponding to the rotation of the optical deflector 4. Thus, the equivalent light beam 3 is scanned on both sides of the optical deflector 4. That is, the scanning lens system 60 and the scanning lens system 61 for providing a desired imaging performance on the scanned surface 5 arranged on both sides are completely equivalent.
That is, since the scanning lens system 60 and the scanning lens system 61 having the same shape can be applied to both scanning optical systems, the shape of the lens to be molded is made the same, and the number of mold forming points is reduced, thereby reducing the production cost. .
The scanning lens system 6 in the optical scanning device 10 includes an anamorphic surface capable of independently correcting wavefront aberrations in the main and sub-scanning directions in order to obtain good imaging characteristics with the above optical arrangement.
Therefore, it is possible to provide the optical scanning device 10 that efficiently suppresses the wave optical aberration by the scanning lens system 6.

The scanning lens system 6 has at least one surface, for example, a surface on the scanned surface 5 side that is a special toric surface, and a line that connects the center of curvature in the sub-scanning section in the main scanning section is non-linear. The change in the main scanning direction of the curvature in the sub-scanning section is prepared for the non-object with respect to the optical axis of the scanning lens (L, M) surface.
The special toric surface of the scanning lens system 6 is a lens surface whose curvature in the sub-scanning section changes continuously in the main scanning direction. That is, it is a lens surface whose curvature in the sub-scanning direction changes according to the position of the sub-scanning cross section when the position of the sub-scanning cross section is changed in the main scanning direction. With this shape, it is possible to suppress the wave optical aberration in the sub-scanning direction and reduce the influence of an optical sag described later on the imaging performance.
Further, the scanning lens system 6 can correct the wavefront aberration with a single scanning lens (L, M) to obtain a good imaging performance, and also can reduce the number of scanning lenses (L, M) and the number of steps. This leads to a reduction in molding costs.

The scanning optical system of the optical deflector 4 included in the optical scanning device 10 has a function of optically scanning the light spot on the surface to be scanned 5 at a constant speed in the main scanning direction, and the optical deflector 4 in the sub scanning direction. Has a function to correct the tilting.
Therefore, it is possible to provide the optical scanning device 10 that can ensure uniform velocity characteristics in the main scanning direction and is resistant to surface tilt of the optical deflector 4.
Further, the scanning lens system 6 includes scanning lenses (L, M) molded from resin. Molding using a resin has the advantages of low cost and the ability to mold complex shapes.

The scanning lens system 6 includes at least one scanning lens (L, M) having an optical axis that is tilted with respect to the normal line of the surface to be scanned 5, and therefore an optical sag described later. Thus, it is possible to provide the optical scanning device 10 that suppresses wave optical aberration due to the above by a simple method.
Since the light source unit 2 includes the monolithic semiconductor laser array 11 in which the plurality of light emitting units 1 are arranged in a line, optical writing can be performed by high-speed optical scanning.
When the multi-beam method is used for speeding up, a light source unit 2 having a plurality of light emitting units 1 is required. Since the monolithic semiconductor laser array 11 has a plurality of light emitting portions 1 provided in a single element, the stability to attachment is good.

The optical scanning device 10 is provided with the folding mirrors 111 and 112 of the image writing unit 101 that optically scans the surface to be scanned 5 and writes an image by the optical scanning device 10, thereby main scanning a plurality of light beams emitted from the light source. An optical writing device 100 as shown in FIGS. 6, 8, and 9 that scans the surface to be scanned along the direction to form an image can be configured.
First, the optical writing device 100 shown in FIG. 8 can be configured by using a plurality of optical scanning devices 10 and overlapping them in the upper and lower stages in the sub-scanning direction.
In this case, writing can be performed on four or more scanned surfaces 5 for forming an image of four or more colors, and the rotating shaft 41 of the optical deflector 4 is common in the upper and lower stages. Among them, the number of parts of the relatively expensive optical deflector 4 can be reduced, resulting in cost reduction.

In the optical writing device 100 that superimposes a plurality of optical scanning devices 10 in the sub-scanning direction in the upper and lower stages, the incident angles of the light beams 3 on the upper and lower stages to the optical deflector 4 are made different (hereinafter referred to as “giving a crossing angle”). By doing so, it becomes possible to reduce the interval between the upper and lower stages to be equal to or less than the interval between the light emitting points, thereby realizing miniaturization (see FIG. 7A).
Naturally, the upper and lower light beams 3 given the crossing angles also differ in their optical characteristics and deflection angles by the optical deflector 4. In particular, vignetting may occur in one of the upper and lower stages in the synchronous light flux near the end of the deflection angle range. Therefore, by slightly changing the reflection points of the upper and lower light beams 3, the difference can be reduced and the deviation of the optical characteristics of each scanning optical system can be suppressed (see FIG. 7 (b)).

In addition to the configuration of the optical writing device 100 described above, there is also an optical writing device 100 having a configuration in which a plurality of optical scanning devices 10 are arranged in parallel on the same main scanning plane (see FIG. 9). In this configuration, since four or more scanned surfaces 5 are already in parallel, the number can be reduced only by the folding mirror 111 of the image writing means 101 after the scanning lens system 6, and the cost can be reduced. At the same time, the optical writing device 100 which is strong against mechanical fluctuation can be realized.
In addition, there is an advantage that the degree of freedom of the interval between the photosensitive drums of the image carrier 211 that is the surface to be scanned 5 is increased when configuring the image forming apparatus. In consideration of extending the life of the photosensitive drum of the image carrier 211, a photosensitive drum of the image carrier 211 having a large diameter is required. In this case, the optical path length of the scanning optical system of the optical writing device 100 is required. Are strongly restricted. Image formation that realizes a longer life of the photosensitive drum of the image carrier 211 by using the optical writing device 100 configured to apply an arrangement in which a plurality of optical scanning devices 10 are arranged in parallel on the same main scanning plane. An apparatus can be configured.

The optical scanning device 10 included in the optical writing device 100 described so far has a configuration in which the light beam 3 is incident and deflected parallel to the normal line of the reflection surface of the optical deflector 4.
However, the optical scanning device 10 included in the optical writing device 100 of the present invention illustrated in FIG. 6 employs a method in which the light beam 3 is incident and deflected at an angle with respect to the normal line of the reflecting surface of the optical deflector 4. . This method is called an oblique incidence method.
As an advantage of this oblique incidence method, four-color images can be written by the one-stage optical deflector 4, so that the cost for configuring the optical writing device 100 can be reduced. When this oblique incidence method is applied, scanning line bending and wavefront aberration deterioration are unavoidable problems, so the surface shape of the scanning lens system 6 must correspond to the obliquely incident light beam 3. However, the effects of the present invention can be used as they are, and the cost can be reduced by combining them.

The image forming apparatus 200 of the present invention including the optical scanning device 10 or the optical writing device 100 illustrated in FIG. 10 is configured to scan the photosensitive drum of the photosensitive image carrier 211 that is the scanning surface 5. A latent image is formed by performing optical scanning according to, and the latent image is visualized by the developing means 213 to obtain an image.
Further, the image forming apparatus 300 of the present invention including the optical scanning device 10 or the optical writing device 100 shown in FIG. 11 is a photosensitive image carrier (yellow, magenta, cyan, blank) that is a plurality of scanned surfaces 5. ) 211 (Y, M, C, Bk) photosensitive drums are optically scanned by the optical scanning device 10 to form latent images corresponding to the respective colors (yellow, magenta, cyan, blank). A latent image corresponding to yellow, magenta, cyan, and blank) is visualized by developing means (yellow, magenta, cyan, and blank) 213 (Y, M, C, and Bk) to obtain a color image.

Various photosensitive image carriers 211 that are the scanning surface 5 can be used. For example, a silver salt film can be used as the image carrier 211. In this case, a latent image is formed by writing by optical scanning, and this latent image can be visualized by processing by a normal silver salt photographic process. Such an image forming apparatus can be implemented as an optical plate making apparatus or an optical drawing apparatus that draws a CT scan image or the like.
As the photosensitive image carrier 211, it is also possible to use a color developing medium (positive printing paper) that develops color by the thermal energy of the light spot during optical scanning. In this case, a visible image is directly displayed by optical scanning. Can be formed.
As the photosensitive image carrier 211, a photoconductive photosensitive member can also be used. As the photoconductive photosensitive member, a sheet-like one such as zinc oxide paper can be used, or a drum-like or belt-like one such as a selenium photosensitive member or an organic optical semiconductor can be used. it can.

When a photoconductive photoconductor is used as the image carrier 211, an electrostatic latent image is formed by uniform charging of the photoconductor and optical scanning by the optical scanning device 10. The electrostatic latent image is visualized as a toner image by development. The toner image is directly fixed on the photoconductor when the photoconductor is in the form of a sheet such as zinc oxide paper. If the photoconductor can be used repeatedly, the transfer paper or the OHP sheet is used. It is transferred and fixed on a sheet-like recording medium such as a plastic sheet for an overhead projector.
The transfer of the toner image from the photoconductive photosensitive member to the sheet-like recording medium may be directly transferred from the photosensitive member to the sheet-like recording medium (direct transfer method), or may be temporarily transferred from the photosensitive member to an intermediate transfer belt or the like. After transfer to the intermediate transfer medium, transfer from the intermediate transfer medium to a sheet-like recording medium (intermediate transfer method) may be performed. Such an image forming apparatus can be implemented as an optical printer, an optical plotter, a digital copying apparatus, or the like.
In addition, the image forming apparatus 300 including the optical scanning device 10 or the optical writing device 100 of the present invention includes a plurality of photosensitive drums of the image carrier 211 arranged along the conveyance path of the sheet-like recording medium. An electrostatic latent image is formed for each photoconductive drum of the image carrier 211 using the optical scanning device 10 or the optical writing device 100, and a toner image obtained by visualizing the electrostatic latent image is formed on the same sheet-like recording medium. The image forming apparatus can be implemented as a tandem type image forming apparatus that obtains a color image or a multicolor image synthetically by transferring and fixing.

  When the optical scanning device 10 or the optical writing device 100 is assembled to the image forming apparatuses 200 and 300 shown in FIGS. 10 and 11, cost reduction is also an important issue. As a form for realizing the cost reduction of the optical scanning device 10, the present invention uses a single optical deflector 4 and two scanning optical systems opposed to the optical deflector 4, and a sub scanning method, sub scanning. An oblique incidence method in which the light beam 3 enters the optical deflector 4 at an angle within the cross section is employed. In any case, it can be said that the number of the optical deflectors 4 occupying a relatively large cost of the optical scanning device 10 is reduced. Regarding the configuration of the optical writing apparatus 100 capable of writing an image of four colors or more, the opposed scanning method requires two or more stages of optical deflectors 4, whereas the oblique incidence system has one stage of optical deflectors. There is a cost advantage in molding in that it is sufficient to use 4.

In order that the diameter of the light spot in the sub-scanning direction does not change greatly depending on the image height on the surface to be scanned 5, the lateral magnification β in the sub-scanning direction of the scanning optical system needs not to change greatly depending on the image height. It is.
Further, the variation of the lateral magnification β in the sub-scanning direction due to the image height causes a problem that the scanning line pitch of the scanning lines simultaneously scanned with the image height changes with the image height in the multi-beam optical scanning. Therefore, in order to suppress the variation of the scanning line pitch due to the image height in the multi-beam optical scanning, it is necessary to correct the lateral magnification in the sub-scanning direction of the scanning optical system to be constant between the image heights.
This can be achieved in the scanning lens system 6 by adopting a special toric surface as at least one surface. Further, since the rotation center 40 of the general polygon mirror as the optical deflector 4 is set off the optical axis of the scanning optical system, the reflection point on the deflecting reflection surface is displaced along with the light beam deflection, and the deflection is made. An optical sag is generated in which the starting point of deflection of the light beam fluctuates. When a sag exists, the path through which the light beam 3 passes is different between the + image height side and the −image height side with respect to the optical axis of the scanning optical system, and the lateral magnification in the sub-scanning direction changes asymmetrically in the main scanning direction.

  This asymmetric lateral magnification change can be corrected by using the above-mentioned special toric surface and making the change in the curvature in the sub-scan section along the main scanning direction an asymmetric surface with respect to the optical axis. A surface in which the change in the curvature in the sub-scan section along the main scanning direction is asymmetric with respect to the optical axis is, for example, (a) monotonically increasing asymmetrically as the radius of curvature in the sub-scan section crosses from the optical axis in the main scanning direction. (B) a surface in which the radius of curvature in the sub-scanning section monotonically decreases as the distance from the optical axis increases in the main scanning direction, and (c) a change in the radius of curvature in the sub-scanning section along the main scanning direction. A surface where the extreme value is outside the optical axis, (d) a surface where the change in the radius of curvature in the sub-scanning section along the main scanning direction monotonically increases from the + image height side toward the −image height side, A surface in which the change in the radius of curvature in the scanning section along the main scanning direction is monotonically decreased from the + image height side to the -image height side, (f) a change in the curvature radius in the sub-scanning section along the main scanning direction. Various surfaces such as a surface having two or more extreme values are conceivable. It refers to all surfaces having no rotation symmetry axis. Which of these is adopted as the asymmetrical surface of the curvature change depends on the design conditions.

Note that the optical axis in such an asymmetric lens is a reference axis orthogonal to the main scanning and sub-scanning directions in the reference coordinate system for determining the lens surface shape.
In the present invention, the special toric surface is a surface in which the change in the curvature in the sub-scanning section along the main scanning direction is asymmetric with respect to the optical axis, so that the influence of the optical sag on the optical performance in the sub-scanning direction. This makes it possible to finely adjust the light condensing action in each sub-scan section of each light beam 3.
The optical sag changes the optical path length connecting the reflection point on the surface of the optical deflector 4, the scanning lens system 6, and the surface to be scanned 5 with respect to the light beam 3 in the main scanning direction according to the image height. It affects the change of horizontal magnification of.
That is, constant velocity characteristics such as constant velocity characteristics in the main scanning direction are not constant with respect to the surface to be scanned 5 due to the influence of optical sag. In order to correct this, a method of tilting the scanning lens system 6 itself with respect to the normal line of the surface to be scanned 5 is effective.

In addition, when the optical scanning device 10 of the present invention is applied to the multi-beam method, the line image imaging optical system to the scanning optical system are shared by a plurality of light beams for each of the coupled light beams 3. Since the image forming optical system and below can be configured in the same manner as the single beam type optical scanning device 10, it is possible to realize the multi-beam type optical scanning device 10 that is extremely stable against mechanical fluctuations.
When the multi-beam method is used, the same writing speed can be realized with a smaller number of rotations of the optical deflector 4 than a single beam. Therefore, the optical deflector 4 can be driven with low power, and the energy saving optical scanning device 10 can be realized.

As a light source of the multi-beam type optical scanning device 10, an LD array type or a beam combining type can be used. When an LD array type light source is used, it is possible to effectively reduce the thermal and electrical influences between the light emitting sources and perform good multi-beam optical scanning by setting the interval between the light emitting sources to 10 μm or more. It becomes possible.
The oblique incidence type optical scanning device 10 can constitute an optical writing device 100 with a single stage optical deflector 4 as shown in FIG.
That is, by applying the oblique incidence method to the optical scanning device 10, the height (in the sub-scanning direction) h of the polygon mirror of the optical deflector 4 is low, and the contact area with air is smaller than that of the two-stage. Therefore, power consumption due to the influence of windage is suppressed, and as a result, the optical writing device 100 can be driven with low power.

The light emitting unit 1 and the coupling lens 20 of the light source unit 2 that are semiconductor lasers may emit m light beams 3. The light source unit 2 illustrated in FIG. 1 is disposed so as to face the optical deflector 4.
That is, in FIG. 1, n light source portions 2 are arranged to face each other, and 2 n light source portions 2 are provided, and m × n light beams 3 face each other and enter the optical deflector 4. become.
When m = 1, it corresponds to the optical beam scanning apparatus 10 of the single beam system (see FIG. 2), and when m ≧ 2, it corresponds to the optical beam scanning apparatus 10 of the multi-beam system (see FIG. 3).
That is, m × n light beams 3 are respectively incident on the opposing reflecting surfaces of the optical deflector 4, and each scanning lens system is provided on 2n scanned surfaces 5 arranged so as to oppose the optical deflector 4. The image is formed by the scanning lens system 60 and the scanning lens system 61. The 2n scanned surfaces 5 are arranged so as to be aligned with the rotation center 40 of the optical deflector 4 in a substantially straight line 7. The arrangement shown in FIG. 1 can also be realized by the oblique incidence method shown in FIG.

In FIG. 2, a divergent light beam 3 emitted from the light emitting unit 1 which is a semiconductor laser of the light source unit 2 is coupled to a subsequent optical system by a coupling lens 20. The form of the light beam 3 converted by the coupling lens 20 is a weak divergent light beam 3.
When the light beam 3 transmitted through the coupling lens 20 of the light source unit 2 passes through the opening of the aperture 21, the peripheral part of the light beam is blocked and shaped, and enters the cylindrical lens 22 which is a line image imaging optical system. . The cylindrical lens 22 has a power-less direction in the main scanning direction and a positive power in the sub-scanning direction. The cylindrical lens 22 focuses the incident light beam 3 in the sub-scanning direction and A line image that is long in the main scanning direction is condensed near the deflecting reflection surface.

The light beam 3 reflected by the deflecting and reflecting surface of the optical deflector 4 is deflected at a constant angular velocity as the polygon mirror of the optical deflector 4 is rotated at a constant angular velocity, and one of the scanning lens system 6 constituting the scanning optical system. The light path is transmitted through the scanning lens, the optical path is bent by the bending mirror 111 of the image writing means 101, and the light is condensed as a light spot on the photoconductor of the photoconductive image carrier 211 forming the substance of the scanned surface 5, The surface to be scanned 5 is optically scanned.
Prior to the optical scanning of the image carrier 211 by the scanning light beam 31, the synchronous light beam 32 of the light beam 3 deflected by the optical deflector 4 is reflected by the mirror 80 and is condensed by the scanning lens 81 onto the light receiving element of the synchronous light receiving means 8. The Based on the output of the synchronous light receiving means 8, the write start timing of optical scanning is determined.

Each scanning lens system 60 and scanning lens system 61 of the scanning lens system 6 is an optical system that condenses the light beam 3 deflected by the optical deflector 4 as a light spot on the surface to be scanned 5, and is a single scanning. Consists of lenses (L, M). The scanning lenses (L, M) of the scanning lens system 6 are biconvex in both the main scanning direction and the sub-scanning direction. In this embodiment, the scanning lenses (L, M) of the scanning lens system 6 are This is an anamorphic optical system having a function of making the vicinity of the deflecting reflection surface and the photosensitive member of the image carrier 211 as the scanned surface 5 geometrically conjugate with respect to the sub-scanning direction.
In the embodiment of the optical scanning device 10, a constant curvature surface is used for one surface of the scanning lens (L, M) of the scanning lens system 6, and a special toric surface is used for the other surface. The change of the curvature in the cross section along the main scanning direction is asymmetric with respect to the optical axis.
A single beam type optical scanning device 10 shown in FIG. 2 couples a light beam 3 from a light source unit 2 to a subsequent optical system by a coupling lens 20, and couples the coupled light beam 3 of a line image imaging optical system. A cylindrical lens 22 forms an image as a long line image in the main scanning direction in the vicinity of the deflecting reflection surface of the optical deflector 4, deflects the optical deflector 4 at an equal angular velocity, and scans the scanning light beam 31 of the deflected light beam 3. The system 6 collects the light as a light spot on the image carrier 211 on the surface to be scanned 5 and optically scans the surface to be scanned 5.

The optical scanning device 10 shown in FIG. 3 is of a multi-beam type. In order to avoid complications, the same symbols as those in the single beam system in FIG.
The light emitting unit 1 of the light source unit 2 is a semiconductor laser array 11 in which four light emitting units ch1 to ch4 are arranged in a line at equal intervals. Here, an embodiment arranged in the sub-scanning direction is shown. Of course, the light emitting source array direction of the semiconductor laser array 11 may be tilted with respect to the sub-scanning direction.
The four light beams 3 emitted from the four light sources ch1 to ch4 are divergent light beams 3 in which the major axis direction of the elliptical far field pattern is directed to the main scanning direction. The ring lens 20 is coupled to the subsequent optical system.
The form of each coupled light beam 3 can be a weak divergent light beam 3, a weakly convergent light beam 3, or a parallel light beam 3 depending on the optical characteristics of the subsequent optical system.

The four light beams 3 transmitted through the coupling lens 20 are shaped by an aperture 21 and focused in the sub-scanning direction by the action of a cylindrical lens 22 which is a common line image forming optical system. In the vicinity of the deflecting and reflecting surface of a certain polygon mirror, the images are separated from each other in the sub-scanning direction as line images that are long in the main scanning direction.
The four light beams 3 deflected at a constant angular velocity by the deflecting reflecting surface of the optical deflector 4 pass through one lens (L, M) forming the scanning lens system 6 and are bent by the folding mirror 111 of the image writing means 101. The light path is bent and condensed as four light spots separated in the sub-scanning direction on the photosensitive member of the image carrier 211 forming the substance of the scanned surface 5, and 4 of the image carrier 211 on the scanned surface 5. Two scanning lines are optically scanned simultaneously.
Prior to optical scanning of the image carrier 211 by the scanning light beam 31, one synchronous light beam 32 of the light beam 3 deflected by the optical deflector 4 is reflected by the mirror 80 and collected by the scanning lens 81 on the light receiving element of the synchronous light receiving means 8. To be lighted. Based on the output of the synchronous light receiving means 8, the timing of starting the writing of the optical scanning of each of the four light beams 3 is determined.

The scanning optical system of the scanning lens system 6 is an optical system that condenses the four light beams 3 simultaneously deflected by the optical deflector 4 as four light spots on the surface to be scanned 5, and is a single scanning lens. (L, M).
As in the embodiment of the optical scanning device 10 shown in FIG. 2, a constant curvature surface is employed on one surface of the scanning lens (L, M) of the scanning lens system 6 and a special toric surface is employed on the other surface. The change along the main scanning direction of the curvature in the sub-scan section of the special toric surface is asymmetric with respect to the optical axis.
The multi-beam optical scanning device 10 shown in FIG. 3 couples a plurality of light beams 3 from a plurality of light emitting sources ch1 to ch4 of a light source unit 2 to a subsequent optical system by a common coupling lens 20, A plurality of light beams 3 that are long in the main scanning direction and separated in the sub-scanning direction in the vicinity of the deflection reflection surface of the optical deflector 4 by the cylindrical lens 22 of the common line-image imaging optical system. An image is formed and simultaneously deflected at a constant angular velocity by the optical deflector 4, and the scanning light beam 31 of the deflected light beam 3 is formed on the image carrier 211 on the surface to be scanned 5 by the common scanning lens system 6 in the sub-scanning direction. This is a multi-beam method in which light is condensed as one or more separated light spots, and one or more scanning lines are simultaneously scanned by these one or more light spots. And the monolithic semiconductor laser array 11 in which the light emission parts ch1-ch4 of the light source part 2 were arranged in 1 row is used, and it is excellent in the stability with respect to attachment. Regarding implementation, the light source unit 2 having the plurality of light emitting units 1 is not limited to the monolithic semiconductor laser array 11 alone.

The spot diameter of the light spot is defined by 1 / e ² intensity in the line spread function of the light intensity distribution in the light spot on the scanned surface 5.
The line spread function uses the center coordinates of the light spot formed on the surface to be scanned 5 as a reference and the coordinates in the main scanning direction and the sub-scanning direction: Y, Z, and the light intensity distribution of the light spot: f (Y, Z). When defined, the line spread function in the Z direction: LSZ is defined by LSZ (Z) = ∫f (Y, Z) dY (integration is performed for the full width of the light spot in the Y direction), and the line spread function in the Y direction : LSY is defined by LSY (Y) = ∫f (Y, Z) dZ (integration is performed for the entire width of the light spot in the Z direction).
These line spread functions: LSZ (Z), LSY (Y) are generally of a Gaussian distribution type, and the spot diameters in the Y direction and Z direction are determined by the line spread functions: LSZ (Z), LSY (Y ) Is given by the width in the Y and Z directions of the region that is 1 / e ² or more of the maximum value.
The spot diameter defined above by the line spread function can be easily measured by scanning the light spot at a constant speed with a slit, receiving the light passing through the slit with a photodetector, and integrating the amount of light received. There are also commercially available devices for performing such measurements.

Specific examples will be given below. The shape or the like of the scanning lens surface of the scanning lens system 6 shown in the embodiment is based on the following expression.
For the non-arc shape in the main scanning section, the paraxial radius of curvature in the main scanning section: R, the distance in the main scanning direction from the optical axis: Y, the conic constant: K, the higher order coefficients: A ₁ , A ₂ , A ₃ , A ₄ , A ₅ , A ₆ .
(1) X = (Y ² / R) / [1 + √ {1- (1 + K) (Y / R) ² }] + A ₁ Y ₁ + A ₂ Y ₂ + A ₃ Y ₃ + A ₄ Y ₄ + A ₅ Y ₅ + A ₆ Y ₆ + ...
In the formula (1), when one or more of odd-numbered coefficients A ₁ , A ₃ , A ₅ ,... Is not 0, an asymmetric shape is formed in the main scanning direction.

Regarding the curvature in the sub-scanning section, when the curvature in the sub-scanning section (the reciprocal of the radius of curvature) changes in the main scanning direction (coordinate with the optical axis position as the origin: Y), the curvature in the sub-scanning section: C (Y) is represented by the following formula (2). r (0) represents the radius of curvature on the optical axis in the sub-scan section, and B ₁ , B ₂ ... represent higher order coefficients.
(2) C (Y) = {1 / r (0)} + B ₁ Y ₁ + B ₂ Y ₂ + B ₃ Y ₃ + B ₄ Y ₄ + B ₅ Y ₅ + B ₆ Y ₆ +
In equation (2), when one or more of odd-order coefficients of Y: B ₁ , B ₃ , B ₅ ,... Is not 0, the change in the radius of curvature in the sub-scanning section is asymmetric in the main scanning direction. When the coefficients of Y: B ₁ , B ₂ , B ₃ ,... Are all 0, a constant curvature surface is obtained.
The analytical expression of the special toric surface is not limited to the above-described ones, and various types are possible, and the surface shape in the present invention is not limited to the expression by the above formula.

In Example 1, the wavelength of the light emitting unit 1 of the light source unit 2 is 780 nm, the focal length of the coupling lens 20 is 15 mm, and the coupling action is a diverging action. The natural condensing point (the condensing position when the divergent light beam 3 emitted from the coupling lens 20 is back-tracked) is −1256.179 mm from the incident surface of the coupling lens 20 toward the scanned surface 5 side. In position. The focal length of the cylindrical lens 22 in the sub-scanning direction is 41.00 mm.
The number of deflecting and reflecting surfaces of the polygon mirror of the optical polarizer 4 is 6; the inscribed circle radius is 13 mm; and the angle formed by the incident angle of the light beam 3 from the light source unit 2 side and the normal of the scanned surface 5 is 68. Degree.
The data of the optical system between the polygon mirror of the optical polarizer 4 and the surface to be scanned 5 is shown in the chart of FIG. The radius of curvature is represented by “R” for the main scanning direction, “r” for the sub scanning direction, and the refractive index by “n”. In the following data, “R, r” is a paraxial radius of curvature.

In the above, X and Y represent the surface numbers; the distance between the vertices in i to i + 1 in the optical axis direction and the main scanning direction. For example, X = 31.5 and Y = 0.49 on the surface number 0 (deflection reflection surface) are the scanning lens (L of the scanning lens system 6 with respect to the deflection reflection point position (reflection position giving image height: 0). , M) means that the apex of the incident surface (surface number: 1) is 31.5 mm apart in the optical axis direction (X direction) and 0.49 mm in the main scanning direction (Y direction). X = 13.5 in the surface number: 1 gives the thickness on the optical axis of the scanning lens (L, M) of the scanning lens system 6.
The incident surface (surface number: i = 1) is a constant curvature surface, and the shape in the main scanning section is a non-arc shape represented by the above equation (2). The coefficients of this surface in the main scanning direction are listed in the chart of FIG.
The exit surface (surface number: i = 2) is a special surface, and the shape in the main scanning section is a non-arc shape symmetric with respect to the optical axis. The coefficients of the main scanning direction and the sub-scanning direction of this surface are listed in the chart of FIG. The lateral magnification β ₂ in the sub-scanning direction at the center image height of the scanning optical system of the example is β ₂ = −4.17.
In FIG. 4 (a), the solid line represents the sub-scanning field curvature, the broken line represents the main scanning field curvature, and the constant velocity characteristic in FIG. 4 (b) represents the linearity and the broken line represents the fθ characteristic. Show. The main scanning direction is 0.945 mm / 216 mm, the sub-scanning direction is 2.049 mm / 216 mm, and the linearity is 1.287% / 216 mm. Both field curvature and constant velocity characteristics are corrected extremely well.

The depth curve of the spot diameter for each image height of the light spot in the embodiment (spot diameter variation with respect to defocusing of the light spot) is shown in FIG. 5A for the main scanning direction and FIG. 5B for the sub-scanning direction. Show. In the embodiment, a spot diameter defined by 1 / e ² intensity of the line spread function is intended to be about 70 μm. As shown in the figure, the main scanning and sub-scanning directions have good depth, and the tolerance for the positional accuracy of the surface to be scanned 5 is high.
In the embodiment, the scanning lenses (L, M) forming the scanning lens system 6 are made of a plastic material, but of course, a glass material may be used. In order to further reduce the beam spot diameter, the sub-scanning direction may be a non-arc shape.
Further, it is possible to correct aberration more preferably by decentering the scanning lens system 6. In the embodiment, the scanning lens (L, M) is 0.50 with respect to the normal line of the surface to be scanned 5. The above-mentioned good performance is realized by tilting the angle.

While realizing the compact optical scanning device 10 that satisfies the optical performance as described above, the synchronous light flux 32 shown in FIG. 1 does not pass through the scanning lenses (L, M) of the scanning lens systems 6, 60, 61. Even if the scanning lenses (L, M) of the scanning lens systems 6, 60, 61 are deformed due to temperature fluctuation or the like, the positional deviation of the light spot formed by the synchronous light beam 32 does not occur.
In the optical scanning device 10 that is rotationally symmetric with respect to the optical deflector 4 in the present invention, the synchronous light flux 32 of each scanning optical system and the synchronous detection position of the synchronous light receiving means 8 are also arranged symmetrically. For this reason, when the synchronizing light flux 32 passes through the scanning lens system 6, the writing position of the scanning line changes when the temperature changes. In FIG. 1, the writing positions are shifted in the opposite directions. Here, the positional deviation deviation between the two scanning optical systems facing each other, that is, the color deviation, is obtained by adding the positional deviations in the main scanning direction generated in each scanning optical system. As described above, if the synchronizing light beam 32 does not pass through the scanning lens system 6, the writing position of the scanning line does not change with respect to temperature fluctuations, so color misregistration is the main scanning direction inherent to each scanning optical system. It is given only by the difference in displacement.
In the optical scanning device 10 of this embodiment, the color shift between the scanning optical systems facing each other due to a temperature variation of + 20 ° C. is 445 μm when the synchronous light beam 32 passes through the scanning lens system 6, but the synchronous light beam 32. Is 73 μm when the lens does not pass through the scanning lens system 6. Color misregistration is a deviation in positional deviation in the main scanning direction between scanning optical systems.
Accordingly, it is clear that the effect of reducing the color misregistration is improved by not allowing the synchronizing light beam 32 to pass through the scanning lens system 6.

In the second embodiment, the oblique incidence method shown in FIG. 6 can be applied to the optical scanning device 10. However, it is necessary to apply a special surface shape to the scanning lens system 6 in order to reduce scanning line bending and wavefront aberration caused by application of this method. As for the special surface shape, a special surface such as a surface having a different eccentric angle (tilt amount) in the lens lateral direction (sub-scanning direction) according to the lens height in the lens longitudinal direction (main scanning direction) is used. There is a need.
The surface shape of the special 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 paraxial radius of curvature in the main scanning section, which is a flat section parallel to the main scanning direction, including the optical axis, is RY, the distance from the optical axis in the main scanning direction is Y, the higher order coefficients are A, B, C, D,. Let RZ be the paraxial radius of curvature in the sub-scan section that is orthogonal to the main scan section.

但し、Cm＝1/RY、Cs(Y)＝1/RZとする。
(Ｆ0+Ｆ1・Y+Ｆ2・Y²+Ｆ3・Y³+Ｆ4・Y⁴+・・)Zは、チルト量を表す部分であり、チルト量を持たないとき、F0、F1、F2、・・・は全て０である。F1、F2、・・・が０で無いとき、チルト量は、主走査方向に変化することになる。

However, Cm = 1 / RY and Cs (Y) = 1 / RZ.
(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, ·・ ・ Are all zero. When F1, F2,... Are not 0, the tilt amount changes in the main scanning direction.

As for the third embodiment, the form of the first embodiment can be applied to an optical writing device 100 including a plurality of optical scanning devices 10. FIG. 8 shows a schematic diagram when two optical scanning devices 10 are stacked in the sub-scanning direction with the rotation axis 41 of the optical deflector 4 in common.
The optical writing device 100 capable of writing images of four or more colors is realized by one optical polarizer 4. At this time, in order to reduce the difference in the writing range of the scanning optical systems on both sides of the optical deflector 4, a method of making the reflection points of the upper and lower light beams 3 different can be applied.
FIG. 9 shows a schematic diagram when two optical scanning devices 10 are arranged in parallel with the main scanning plane being a plane perpendicular to the rotation axis 41 of the optical deflector 4 being the same. It can be seen that this arrangement can reduce the number of folding mirrors 111 and 112 of the image writing means 101 required to construct a tandem type image forming apparatus. The reduction in the number of bending mirrors 111 and 112 is a reduction in factors that cause disturbance in the optical performance on the scanned surface 5. Further, with respect to the photosensitive drum of the image carrier 211 that is the surface to be scanned 5, the distance between the two optical scanning devices 10 compared to the arrangement in the case where the rotation shaft 41 of the optical deflector 4 is shared and overlapped in the sub-scanning direction. Therefore, it becomes easy to lay out the photosensitive drum of the image carrier 211 having a large diameter, and a long life can be realized.

In FIG. 10, an image forming apparatus 200 that forms a recorded image on a recording medium includes the optical scanning device 10 according to any one of claims 1 to 13 and the optical scanning device 10 according to any one of claims 14 to 19. The laser printer includes the optical writing device 100 described above and an image forming unit 201 that forms a recorded image on a recording sheet of a recording medium (P) by the optical scanning device 10 or the optical writing device 100.
The image forming unit 201 has a photoconductive photosensitive drum formed in a cylindrical shape as the photosensitive image carrier 211. Around the image carrier 211, a charging roller as a charging unit 212, a developing unit 213, a transfer roller as a transfer unit 216, and a cleaning unit 215 are arranged. A corona charger can be used as the charging means 212.
An optical scanning device 10 or an optical writing device 100 that performs optical scanning with a scanning light beam 31 of a laser beam is provided, and exposure by optical writing is performed between the charging unit 212 and the developing unit 213.

Further, a fixing device 217, a paper feed cassette 220, a registration roller pair 222, a paper feed roller 221, a conveyance path 214, a paper discharge roller pair 218, a paper discharge tray 219, and the like are arranged at predetermined positions.
When forming a recorded image on the recording medium (P), the image carrier 211, which is a photoconductive photoconductor, is rotated at a constant speed in the clockwise direction of the arrow (A) in the figure, and the surface is charged. Uniformly charged by the means 212 and exposed by optical writing of the scanning light beam 31 of the optical scanning device 10, an electrostatic latent image is formed. The formed electrostatic latent image is a so-called negative latent image, and the image portion is exposed.
This electrostatic latent image is reversely developed by the developing means 213, and a toner image is formed on the image carrier 211. The paper feed cassette 220 storing the recording medium (P) of the recording medium feeding unit 202 is detachable from the main body of the image forming apparatus 200, and in the state of being mounted as shown, the stored recording medium ( The uppermost sheet of (P) is fed by the sheet feeding roller 221, and the fed recording medium (P) is fed by the registration roller pair 222 at the leading end.
The registration roller pair 222 feeds the recording medium (P) to the transfer unit in time with the toner image on the image carrier 211 moving to the transfer position.

The recording medium (P) fed in is superposed on the toner image at the transfer portion, and the toner image is electrostatically transferred by the action of the transfer means 216. The recording medium (P) to which the toner image is transferred is sent to the fixing device 217, where the toner image is fixed in the fixing device 217, passes through the conveyance path 214, and is discharged onto the discharge tray 219 by the discharge roller pair 218. The
The surface of the image carrier 211 after the toner image is transferred is cleaned by the cleaning unit 215, and residual toner, paper dust, and the like are removed.
Therefore, by using the optical scanning device 10, it is possible to provide an image forming apparatus 200 that forms a very good high quality image.

In FIG. 11, an image forming apparatus 300 for forming a color recording image on a recording medium is the optical scanning apparatus 10 according to any one of claims 1 to 13 or any one of claims 14 to 19. And the image forming unit for forming a color recording image for synthesizing a color image or a multicolor image on the recording medium (P) by the optical scanning device 10 or the optical writing device 100. 301 is provided.
The image forming apparatus 300 includes a plurality of image carriers (yellow) 211 (Y), an image carrier (magenta) 211 (M), an image carrier (cyan) 211 (C), and an image carrier (black) 211 ( Tandem color that has a photosensitive drum corresponding to each color of yellow (Y), magenta (M), cyan (C), and black (Bk) of Bk) to obtain a color image or a multicolor image synthetically An example of the machine is shown.
An optical writing device 100 in which two scanning devices 10 having the same main scanning plane which is a plane perpendicular to the rotation axis 41 of the optical deflector 4 are arranged in parallel is mounted on yellow (Y) and magenta (M). , Cyan (C), and black (Bk). Scanning light flux (yellow, magenta, cyan, blank) 31 (Y) of the light beam from the optical writing device 100 corresponding to each color of yellow (Y), magenta (M), cyan (C), and black (Bk) , M, C, and Bk) are the image carrier (yellow) 211 (Y), the image carrier (magenta) 211 (M), the image carrier (cyan) 211 (C), and the image carrier (black) 211. Irradiate (Bk) to form an electrostatic latent image.

In the image forming apparatus 300, the optical writing device 100 is mounted on the upper part of the image forming unit 301, and the image forming unit 301 is held on the upper part of the recording medium feeding unit 202.
The image forming unit 301 has an intermediate transfer belt 203 as an intermediate transfer body of a recording medium, and an image carrier (yellow) 211 (Y) along the direction of the arrow (B) in the movement direction thereof. Image forming stations including an image carrier (magenta) 211 (M), an image carrier (cyan) 211 (C), and an image carrier (black) 211 (Bk) are arranged in parallel. In each image forming station having an image carrier (yellow) 211 (Y), an image carrier (magenta) 211 (M), an image carrier (cyan) 211 (C), and an image carrier (black) 211 (Bk) Yellow (Y), magenta (M), cyan (C), and black (Bk) toner images are formed.

  The image forming station for forming a yellow (Y) toner image will be described as a representative. Around the photosensitive drum of the image carrier (yellow) 211 (Y), there is an image carrier (yellow) 211 (Y). The electrostatic latent image formed by the charging means (yellow) 212 (Y) for uniformly charging the surface and the scanning light beam (yellow) 31 (Y) from the optical writing device 100 is attached to the electrostatic latent image and is clearly visible. Developing means (yellow) 213 (Y) for forming an image, transfer means provided inside the intermediate transfer belt 203 for primary transfer of the toner image on the image carrier (yellow) 211 (Y) to the intermediate transfer belt 203 Cleaning means (yellow) 215 (Y) for scraping off toner remaining on (yellow) 216 (Y) and image carrier (yellow) 211 (Y) is disposed. Since the other image forming stations have the same configuration, they are distinguished by adding European characters for each color, and description thereof is omitted.

The intermediate transfer belt 203 is supported around the three rollers 230, 231, and 232, and is rotated counterclockwise in the direction of the arrow (B) shown in the figure.
The yellow (Y), magenta (M), cyan (C), and black (Bk) toner images are sequentially transferred onto the intermediate transfer belt 203 at the appropriate timing, and are superimposed to form a color toner image.
The recording papers of the recording medium (P) are fed one by one from the paper feeding cassette 221 of the recording medium feeding unit 202 in order from the uppermost one by the paper feeding roller 221, and in the sub-scanning direction by the registration roller pair 222. It is sent out to a secondary transfer roller 204 as a secondary transfer means at the transfer portion in accordance with the recording start timing.

The superimposed color toner images on the intermediate transfer belt 203 are collectively transferred onto a recording medium (P) by a secondary transfer roller 204 as a secondary transfer unit at a transfer portion. The recording medium (P) to which the color toner recording image has been transferred is sent to a fixing device 217 having a fixing roller and a pressure roller, where the color toner recording image is fixed.
The recording medium (P) that has been fixed is discharged from the conveying path 214 to a discharge tray 219 formed on the upper surface of the main body of the image forming apparatus 300 by the discharge roller pair 218 and stacked.
Accordingly, the scanning lens system 6 is not specially processed, and the optical scanning is performed by synchronous detection that is not affected by disturbances such as temperature fluctuations, so that writing can be performed in a compact and low-quality manner to form a color image and a multicolor image. It is possible to provide the image forming apparatus 300 including the optical scanning device 10 with low cost and low driving power or the optical writing device 100 including the optical scanning device 10.

1 is a basic configuration diagram showing an optical arrangement in a main scanning section of an optical scanning device according to an embodiment of the present invention. 1 is a perspective view of a basic configuration of a single beam system of an optical scanning device according to an embodiment of the present invention or an optical writing device including the optical scanning device. 1 is a perspective view of a basic configuration of a multi-beam system of an optical scanning device according to an embodiment of the present invention or an optical writing device including the optical scanning device. It is a graph which shows the curvature of field (a) and constant velocity characteristic (b) of the optical scanning device concerning the embodiment of this invention. It is a graph which shows the depth curve (a) of the spot diameter of the main scanning direction of the optical scanning device concerning the embodiment of this invention, and the depth curve (b) of the spot diameter of a subscanning direction. 1 is a basic configuration diagram of an optical writing device including an oblique incidence type optical scanning device according to an embodiment of the present invention; FIG. It is a basic block diagram which gives a crossing angle to the optical scanning device concerning the embodiment of this invention, and changes the reflective point of the light beam of an upper-lower stage. 1 is a basic configuration diagram of an optical writing device including a plurality of optical scanning devices according to an embodiment of the present invention which are superposed in upper and lower stages. 1 is a basic configuration diagram of an optical writing device including a plurality of optical scanning devices according to an embodiment of the present invention arranged in parallel on the same main scanning plane. FIG. 1 is a basic configuration diagram of an image forming apparatus that includes an optical scanning device or an optical writing device according to an embodiment of the present invention and forms a recorded image on a recording medium. 1 is a basic configuration diagram of an image forming apparatus that includes a plurality of optical scanning devices or optical writing devices according to an embodiment of the present invention in parallel on the same main scanning plane to form a color recording image on a recording medium. It is. It is a graph which shows the data of the optical system which exists between the optical polarizer of the optical scanning device concerning the embodiment of this invention, and a to-be-scanned surface. It is a graph which shows each coefficient of the main scanning direction of the entrance plane (surface number: i = 1) of the optical scanning device concerning the embodiment of this invention. It is a graph which shows the coefficient of the main scanning direction and subscanning direction of the output surface (surface number: i = 2) of the optical scanning device concerning the embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Light emission part 2 Light source part 3 Light beam 4 Optical deflector 5 Scanning surface 6 Scanning lens system 7 Straight line 8 Synchronous light-receiving means 10 Optical scanning device 11 Semiconductor laser array 20 Coupling lens 21 Aperture 22 Cylindrical lens 31 (Y, M , C, Bk) Scanning light beam (yellow, magenta, cyan, blank)
32 Synchronous light beam 40 Rotation center 41 Rotation axis 50 Writing width center 60, 61 Scan lens system 80 Mirror 81 Scan lens 100 Optical writing device 101 Image writing means 111, 112 Bending mirror 200 Image forming device 201 Image forming unit 202 Covered Recording medium feeding unit 203 Intermediate transfer belt 204 Secondary transfer roller 211 (Y, M, C, Bk) Image carrier (yellow, magenta, cyan, blank)
212 (Y, M, C, Bk) Charging means (yellow, magenta, cyan, blank)
213 (Y, M, C, Bk) Developing means (yellow, magenta, cyan, blank)
214 Conveying path 215 (Y, M, C, Bk) Cleaning means (yellow, magenta, cyan, blank)
216 (Y, M, C, Bk) Transfer means (yellow, magenta, cyan, blank)
217 Fixing device 218 Paper discharge roller pair 219 Paper discharge tray 220 Paper feed cassette 221 Paper feed roller 222 Registration roller pair 230, 131, 132 Roller 300 Image forming apparatus 301 Image forming unit

Claims (21)

  In an optical scanning device that optically scans a surface to be scanned along a main scanning direction with a plurality of light beams emitted from a light source, 2n (where n ≧ 1) light emitting units having m (where m ≧ 1) Corresponds to a light source unit, an optical deflector on which (m × n) light beams from each of the light source units are incident to face the rotation center, and 2n (where n ≧ 1) light source units. 2n (provided that n ≧ 1) scanned surfaces and 2n (provided that n ≧ 1) light beams of the light emitting section are arranged to face the optical deflector. ≧ 1) The scanning lens system that forms an image on each of the scanned surfaces, and the writing width center on the 2n (where n ≧ 1) scanned surfaces and the rotation center of the optical polarizer are in a straight line. Synchronously receiving the deflected light beam of the optical deflector as a synchronous light beam that determines the writing timing of the scanning light beam. Optical scanning apparatus comprising means.   The optical scanning device according to claim 1, wherein the light source unit includes a semiconductor laser array in which a plurality of the light emitting units are arranged in a line.   3. The optical scanning device according to claim 1, wherein the scanning optical system of the optical deflector has a function of optically scanning a light spot on the surface to be scanned at a constant speed in the main scanning direction. Optical scanning device.   4. The optical scanning device according to claim 1, wherein the scanning optical system of the optical deflector has a function of correcting surface tilt of the optical deflector in a sub-scanning direction. .   5. The optical scanning device according to claim 1, wherein the scanning lens system includes scanning lenses L <b> 1, L <b> 2 in order closer to the optical deflector of the scanning lens system including one or more scanning lenses L. ... Lj (j = 1.2, ...) and the light deflection of another scanning lens system comprising one or more scanning lenses M facing the scanning lens system with respect to the rotation center of the optical deflector The scanning lens Lj and the scanning lens Mj having the same shape are provided at any j of the scanning lenses M1, M2,... Mj (j = 1.2,. An optical scanning device.   6. The optical scanning device according to claim 1, wherein the scanning lens system includes an anamorphic surface.   7. The optical scanning device according to claim 1, wherein the scanning lens system includes a special toric surface in which at least one surface is a non-linear line connecting the center of curvature in the sub-scanning section in the main scanning section. An optical scanning device comprising:   8. The optical scanning device according to claim 7, wherein the scanning lens system includes a non-target change in the curvature in the sub-scan section of the special toric surface along the main scanning direction with respect to the optical axis of the scanning lens surface. An optical scanning device characterized by the above.   9. The optical scanning device according to claim 1, wherein the scanning lens system includes the scanning lens composed of a single lens. 10.   10. The optical scanning device according to claim 1, wherein the scanning lens system includes the scanning lens formed of a resin. 11.   11. The optical scanning device according to claim 1, wherein the scanning lens system includes at least one scanning lens having an optical axis that is inclined with respect to a normal line of a surface to be scanned. An optical scanning device characterized by the above.   12. The optical scanning device according to claim 1, wherein the synchronous light receiving unit includes a synchronous light beam that does not pass through the scanning lens system used for determination of writing timing.   13. The optical scanning device according to claim 1, wherein the light beam has an angle in a sub-scanning direction with respect to a normal line of a reflection surface of the optical deflector. .   14. An optical writing apparatus for forming an image by scanning a surface to be scanned along a main scanning direction with a plurality of light beams emitted from a light source, and the optical scanning apparatus according to any one of claims 1 to 13. An optical writing apparatus comprising image writing means for optically scanning the surface to be scanned by the optical scanning apparatus and writing an image.   15. The optical writing device according to claim 14, wherein a plurality of the optical scanning devices are provided in the sub scanning direction.   16. The optical writing device according to claim 15, wherein each of the optical scanning devices stacked in the sub-scanning direction includes the optical deflector having a common rotation axis.   17. The optical writing device according to claim 15, wherein each of the optical scanning devices stacked in the sub-scanning direction has different incident angles in the main scanning direction of upper and lower light beams incident on the same phase plane of the optical deflector. An optical writing device comprising:   18. The optical writing device according to claim 15, 16 or 17, wherein each of the optical scanning devices stacked in the sub-scanning direction is deflected in the main scanning direction of upper and lower light beams incident on the same phase plane of the optical deflector. An optical writing device comprising different reflection points.   15. The optical writing device according to claim 14, wherein the two optical scanning devices are arranged in parallel so that main scanning planes are the same.   The image forming apparatus for forming a recorded image on a recording medium, wherein the optical scanning device according to any one of claims 1 to 13 or the optical book according to any one of claims 14 to 19. And an image forming unit for forming a recorded image on a recording medium by the optical scanning device or the optical writing device.   The image forming apparatus for forming a color recording image on a recording medium, wherein the optical scanning device according to any one of claims 1 to 13 or the optical scanning device according to any one of claims 14 to 19. An image forming apparatus comprising: the optical writing device; and an image forming unit that forms a color recording image on a recording medium by the optical scanning device or the optical writing device.

Images