JP2010072237A - Optical scanner and image forming apparatus - Google Patents

Abstract

By using an optical element that changes the scanning position in the sub-scanning direction when the temperature changes, an optical scanning device that can perform high-quality writing with little color shift is realized.
Light sources 1a and 1b for emitting a light beam, a deflector 5 for deflecting a light beam from the light source, a scanned surface 7 scanned with the light beam from the deflector, and light emitted from the light source. First optical systems 2a and 2b for converting the light beam to be in a desired condensing state, and deflecting the light beam converted by the first optical system by forming an image in a sub-scanning direction perpendicular to the scanning direction of the deflector An incident optical system having a second optical system 4 that forms a long line image in the main scanning direction in the vicinity of the scanner, and scanning lenses L1 and L2 that scan and image a plurality of scanned surfaces with the light beams deflected by the deflector An optical scanning apparatus that includes a third optical system including a deflecting scan for scanning a surface to be scanned, and that changes a scanning position on the surface to be scanned so as to reduce a change in color shift in the sub-scanning direction when the environmental temperature changes. An element is provided.
[Selection] Figure 1

Description

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

In recent years, colorization of image forming apparatuses such as laser printers and digital copying machines has been progressing rapidly. For this reason, it is more desirable that the optical scanning device used in these devices is capable of forming a plurality of scanning lines on a plurality of photoconductors at the same time in accordance with the user's needs for high-speed image formation.
Several methods are conceivable as methods satisfying such needs. For example, four photosensitive members corresponding to cyan (C), magenta (M), yellow (Y), and black (K) are used as recording materials. There are tandem color image forming apparatuses arranged along a conveyance belt or an intermediate transfer member.
However, in the tandem image forming apparatus, improvement of image quality stability against environmental changes is a major issue.
Therefore, as an effective technique for this problem, there are a technique using a temperature correcting lens and a technique using a diffractive optical element.

Here, as an example of the temperature correction lens, Patent Document 1 (Japanese Patent Laid-Open No. 2003-5111) and Patent Document 2 (Japanese Patent Laid-Open No. 2002-214556) disclose scanning having a temperature correction lens in the second optical system. An optical system is disclosed.
For example, there is a conventional technique of Patent Document 1 as an optical scanning device that compensates for characteristic fluctuations caused by temperature fluctuations by having a resin lens having negative power in an incident optical system.
Further, as an optical scanning device that compensates for characteristic fluctuations caused by temperature fluctuations by having a diffractive optical element in which an elliptical multi-step diffraction surface is formed in an incident optical system, Patent Document 3 (Japanese Patent Laid-Open No. 2008-033251), etc. There is.

  Although these conventional techniques compensate well for temperature changes, there is a problem that the second optical system becomes large because it is difficult to optically shorten the lens interval. In addition, since the second optical system has power only in the sub-scanning direction, it is not preferable to change the convergence state coupled by the first optical system. Therefore, high accuracy is required for the shape accuracy of the temperature correction lens in the main scanning direction.

  Next, as an example of a diffractive optical element, the diffractive optical element can be regarded as an optical element having negative dispersion, and has a diffractive power that cancels an imaging position shift due to an oscillation wavelength change and a shape change due to an environmental temperature change. By providing the above, it is possible to compensate the temperature of the entire scanning optical system and improve the image quality stability.

Patent Document 4 (Japanese Patent Application Laid-Open No. 2007-241182) discloses an optical scanning device in which a multi-step diffractive surface is introduced into a collimating lens (first optical system) to compensate for an imaging position variation caused by a temperature variation. Has been.
However, since the collimating lens having a multi-step diffractive surface is made of resin, the linear expansion coefficient of the collimating lens itself is as large as “7.0 × 10E-5”. In addition, since the fluctuation due to the wavelength change is proportional to the diffraction power of the diffractive optical element, it becomes weak against the wavelength change and cannot cope with multi-beam.

Patent Document 5 (Japanese Patent Laid-Open No. 2002-221681) discloses a scanning optical device in which a diffractive surface is provided on a scanning lens. By changing the diffraction power in the sub-scanning direction from on-axis to off-axis, the F-number in the sub-scanning direction is aligned within the image range to achieve high-definition printing. The focus change is compensated.
However, there is no compensation for scanning position deviation and color deviation, and it is difficult to use as a tandem optical scanning device.

Next, the temperature change of the optical box (housing) will be described.
In the optical scanning device, the entire scanning optical system except for the photosensitive member as the surface to be scanned is usually arranged in one optical box. When the environmental temperature rises, the optical box is fastened to the structure of the image forming apparatus in several places, the linear expansion coefficient of the material of the structure and the optical box is different, or a partial temperature gradient occurs. As a result, the optical box is not simply expanded but twisted or twisted.
In this case, since the relative positional relationship of the optical elements in the optical box also changes, the scanning position on the photoconductor changes. A change in scanning position on the photosensitive member is likely to cause a color shift in a tandem color image forming apparatus.

Next, the oblique incidence optical system will be described.
As a low-cost scanning optical system suitable for the tandem method, there is an “oblique incident optical system” that makes a light beam incident on a polygon mirror at an angle within a sub-scanning section.
In this oblique incidence optical system, since the light beam is incident on the deflection surface at an angle within the sub-scan section, a polygon mirror with a thin polygon mirror and a low cost can be used.
However, the oblique incidence optical system has a problem that scanning line bending occurs. Further, the oblique incidence optical system has a problem that the scanning line curve changes due to a change in the environmental temperature. If the scanning line curve changes, it is observed as a color shift between stations and image quality deteriorates, which is a big problem.
For example, Patent Document 6 (Japanese Patent Application Laid-Open No. 2007-010868) discloses an example in which scanning line bending is corrected using a special tilt eccentric surface having no power in the sub-scanning direction and having only a tilt. However, there is no mention of the change in scanning line bending due to the temperature change.

JP 2003-5111 A JP 2002-214556 A JP 2008-033251 A JP 2007-241182 A JP 2002-221681 A JP 2007-010868 A

The present invention has been made in view of the above circumstances, and by using an optical element that changes the scanning position in the sub-scanning direction so as to reduce color misregistration when temperature changes, high-quality writing with little color misregistration is performed. It is a first object of the present invention to provide an optical scanning device that can be used.
Further, the present invention provides an optical scanning device that takes into account the environment, such as downsizing of the optical deflector and reduction of power consumption due to a reduction in the rotational speed of the rotary polygon mirror that is an optical deflector using multi-beams. The second object is to realize an image forming apparatus capable of achieving the above object.

In order to achieve the above object, the present invention employs the following solutions.
The first means of the present invention includes a plurality of light source units that emit a light beam, a deflector that deflects the light beam from the light source unit, and a plurality of scanned surfaces that are scanned by the light beam from the deflector. A first optical system that converts a light beam emitted from the light source unit into a desired condensing state, and a light beam converted by the first optical system in a scanning direction of the deflector (hereinafter referred to as main scanning). An incident optical system having a second optical system that forms an image in the sub-scanning direction perpendicular to the direction) and forms a long line image in the main scanning direction in the vicinity of the deflector, and is deflected by the deflector A third optical system including a scanning lens for imaging and scanning a light beam on a plurality of scanned surfaces, and an optical scanning device that deflects and scans the scanned surface. Change the scanning position on the scanned surface to reduce the change. Characterized in that it has an optical element that.

According to a second means of the present invention, in the optical scanning device of the first means, the optical element has a diffractive surface having no power at least in the sub-scanning direction in a room temperature environment.
According to a third means of the present invention, in the optical scanning device of the first or second means, the light beam incident on the deflector is deflected at an angle in a sub-scanning direction with respect to a main scanning section. It is incident on the vessel.

According to a fourth means of the present invention, in the optical scanning device of any one of the first to third means, the optical element is included in the first optical system.
According to a fifth means of the present invention, in the optical scanning device of any one of the first to third means, the optical element is included in the third optical system.

According to a sixth means of the present invention, in the optical scanning device according to any one of the first to fifth means, the diffractive surface of the optical element has a symmetric shape in the sub-scanning section.
According to a seventh means of the present invention, in the optical scanning device according to any one of the first to sixth means, the light source section has a plurality of light emitting points and is simultaneously formed by the same deflection surface of the deflector. A single scanning surface is deflected and scanned.

An eighth means of the present invention is an image forming apparatus, and the optical scanning device of any one of the first to sixth means or the multi-beam optical scanning device of the seventh means is written on the image carrier. It is characterized by being used as an insertion means.
According to a ninth means of the present invention, in the image forming apparatus of the eighth means, the image carrier is a photoconductive photosensitive member, and the plurality of photosensitive members are along the recording material conveying means or the intermediate transfer member. It is characterized by being attached together.

The optical scanning device of the first means has an optical element that changes the scanning position on the surface to be scanned so as to reduce the change in color shift in the sub-scanning direction when the environmental temperature changes, so that the color changes when the environmental temperature changes. Since the change in deviation can be reduced, it is possible to provide an optical scanning device that is more robust against environmental temperature changes.
In the optical scanning device of the second means, in addition to the configuration and effect of the first means, the optical element has a diffractive surface having no power at least in the sub-scanning direction in a room temperature environment, thereby By using a multi-step diffractive surface in which the power and the power of the refracting part are offset, it becomes difficult to be affected by the relative decentration of the entrance surface and the exit surface, so that it can be manufactured at low cost.
In the optical scanning device of the third means, in addition to the configuration and effect of the first or second means, the light beam incident on the deflector has an angle in the sub-scanning direction with respect to the main scanning section. Since the light enters the deflector, the diffractive surface can reduce the variation in the scanning line bending characteristic of the temperature characteristic peculiar to the oblique incidence, and thus the color shift can be reduced.

In the optical scanning device of the fourth means, in addition to the configuration and effect of any one of the first to third means, the optical element is included in the first optical system, so that the temperature change before entering the deflector. Can be corrected.
Further, in the optical scanning device of the fifth means, in addition to the configuration and effect of any one of the first to third means, the third optical system has the optical element, so that different correction effects for each image height. Therefore, it is possible to reduce the bending of the scanning line.

In the optical scanning device of the sixth means, in addition to the configuration and effect of any one of the first to fifth means, the diffractive surface of the optical element is symmetrical with respect to the sub-scanning direction, so Common use is possible, and cost can be further reduced.
Further, in the optical scanning device of the seventh means, in addition to the configuration and effect of any one of the first to sixth means, the light source section has a plurality of light emitting points and is simultaneously formed by the same deflection surface of the deflector. By deflecting and scanning a single surface to be scanned, it is possible to increase the speed and density by using a laser diode array (LDA) type multi-beam, and to reduce the environmental load by reducing the rotation of the polygon mirror. .

  In the image forming apparatus of the eighth and ninth means, the optical scanning device of any one of the first to sixth means, or the multi-beam optical scanning device of the seventh means is written to the image carrier. As a result, it is possible to realize an image forming apparatus that is sufficiently small and can ensure high-quality image reproducibility.

Hereinafter, the configuration, operation, and effects of the present invention will be described in detail with reference to the drawings.
FIG. 2 is a main scanning sectional view showing a configuration example of a scanning optical system of a commonly used optical scanning device. The scanning optical system includes a light source unit 1 that emits a light beam, and a light source unit 1 A deflector 5 that deflects the light beam, a scanned surface 7 that is scanned with the light beam from the deflector 5, and a first optical system 2 that converts the light beam emitted from the light source unit 1 into a desired condensing state. Then, the light beam converted by the first optical system 2 is imaged in the sub-scanning direction perpendicular to the scanning direction of the deflector 5 (referred to as the main scanning direction), and a line image long in the main scanning direction near the deflector. And an incident optical system having a second optical system 4 for imaging, and a third optical system including scanning lenses L1 and L2 for imaging and scanning the light beam deflected by the deflector 5 on the scanned surface 7. The scanning surface 7 is deflected and scanned.

  A semiconductor laser (LD) is usually used for the light source unit 1, and a coupling lens is used for the first optical system 2. Further, the light beam converted into substantially parallel light by the coupling lens 2 is imaged in the sub-scanning direction perpendicular to the scanning direction (referred to as main scanning direction) of the deflector 5 and is long in the main scanning direction near the deflector. A cylindrical lens is used as the second optical system 4 that forms a line image. Further, as the deflector 5, a rotating polygon mirror that rotates a polygonal polygon mirror at a constant speed by a polygon motor is used. An aperture 3 is provided between the coupling lens 2 and the cylindrical lens 4, and an optical path folding mirror M is provided between the cylindrical lens 4 and the deflector 5 as necessary.

  A constant-speed scanning lens such as an fθ lens is used for the first scanning lens L1 constituting the third optical system, and a lens for field curvature and aberration correction is used for the second scanning lens L2. Further, what forms the surface to be scanned is a photosensitive surface of a photosensitive medium such as a photoconductive photosensitive member. In addition, between the 2nd scanning lens L2 and the to-be-scanned surface 7, there exists a light beam emission part of the optical housing which is not shown in figure, and the dust-proof glass G is provided in this emission part.

In the optical scanning apparatus configured as shown in FIG. 2, since there is one light source unit 1, the light beam is incident perpendicular to the rotation axis of the deflector (rotating polygon mirror) 5 (that is, the light beam is (Because it is perpendicularly incident on the deflecting surface of the polygon mirror within the sub-scan section), there is almost no problem of bending of the scanning line. However, a plurality of light sources are used in correspondence with the tandem image forming apparatus, and the light beam is converted to a polygon. In the case of the “oblique incidence optical system” in which the mirror is incident at an angle within the sub-scanning section, as described above, the oblique incidence optical system is configured to change the angle of the light beam to the deflection surface within the sub-scanning section. There is a problem in that the scanning line is bent because it is incident. Further, the oblique incidence optical system has a problem that the scanning line curve changes due to a change in the environmental temperature. When the scan line curve changes, color misalignment is observed between stations, and image quality deteriorates.
Therefore, the present invention realizes an optical scanning device that can perform high-quality writing with little color misregistration by using an optical element that changes the scanning position in the sub-scanning direction so as to reduce color misregistration when temperature changes. To do. Specific examples will be described below.

[Example 1]
The first embodiment of the optical scanning device of the present invention will be described with reference to FIG. The basic configuration of the scanning optical system of the optical scanning apparatus of this embodiment is substantially the same as that shown in FIG. 2, but a plurality of light source sections are provided to form an oblique incidence optical system.
In FIG. 1, a divergent light beam emitted from a semiconductor laser (LD) as a light source of the light source units 1a and 1b is transferred to a subsequent optical system in a first optical system 2a and 2b having a coupling lens and a diffractive optical element. It is converted into a suitable luminous flux form. The form of the light beam converted by the first optical systems 2a and 2b can be a parallel light beam, or a weak divergent or weakly convergent light beam.
The coupling lenses of the first optical systems 2a and 2b can be adjusted in the optical axis direction, the main scanning corresponding direction, and the sub-scanning corresponding direction, and are adjusted to the “desired light beam form” by the adjustment.

The diffractive optical elements provided in the first optical systems 2a and 2b are arranged closer to the deflector 5 than the coupling lens. In this embodiment, the diffractive optical element is provided with a multi-step diffractive surface shape to correct the temperature change.
In the illustrated example, two light source units 1a and 1b are provided, and LD arrays each having two light emitting points are used. That is, one scanned surface 7 can be scanned simultaneously with four beams. Each LD array 1a, 1b rotates about 57 degrees around the optical axis and scans at a pitch corresponding to a resolution of 600 dpi. The two LD arrays 1a, 1b correspond to a resolution of 1200 dpi on the surface to be scanned. Scanning at the pitch.
Further, the coupling lens and the diffractive optical element of the first optical systems 2a and 2b are both held by the same member.

A light beam from the coupling lens of the first optical system 2a, 2b is reduced in diameter by the aperture 3, condensed in the sub-scanning direction by the cylindrical lens 4, and a rotating polygon mirror (deflector) 5 that rotates the polygon mirror. Are incident in the state of a line image long in the main scanning direction. The light beam reflected by the deflecting reflecting surface is deflected at a constant angular velocity along with the constant speed rotation of the polygon mirror, passes through the first scanning lens L1 and the second scanning lens L2 as the third optical system, and is scanned. 7 is condensed. As a result, the deflected light beam forms a light spot on the surface to be scanned, and optical scanning of the surface to be scanned 7 is performed. In the present embodiment, the two scanning lenses L1 and L2 of the third optical system are both made of resin. The resin scanning lens has a large shrinkage / expansion when the environmental temperature fluctuates as compared with the glass scanning lens, but is low in cost because it can be injection-molded and has a high degree of freedom in optical surface shape.
In FIG. 1, M is an optical path folding mirror, G1 is a soundproof glass provided in a light beam entrance / exit part of a deflector housing (not shown), and G2 is provided in a light beam exit part of the optical housing. It is dust-proof glass.

Next, the multi-step diffraction surface (MS surface) of the diffractive optical element will be described.
The element shape (actual shape) of the diffractive surface of the diffractive optical element can be represented by the sum of the substrate shape and the diffractive shape, as shown in FIGS.
As shown in FIG. 3, the multi-step diffractive surface of the present invention causes refraction because the refractive power and the diffractive power do not cancel each other at the time of temperature change. It is designed to cancel out “diffraction power”, which is a substantially non-power surface. For this reason, it is possible to loosen the placement accuracy of the optical element as compared with a lens having power on both sides, and it can be expected to produce an effect that can be manufactured at a lower cost by assembling by a simpler method.

  By the way, if the diffractive surface is formed by folding the surface shape of the refracting surface with an appropriate step and pitch, the pitch gradually decreases toward the periphery of the lens. Production is difficult. However, if a diffractive surface is created by combining the first surface and the second surface having opposite powers, the folded portion on the diffractive surface becomes obtuse, which is advantageous for mold manufacture. In particular, when the surface shape of the diffractive surface is a multi-step shape as in this embodiment, the angle of the folded portion becomes a right angle, a step-like shape symmetrical to the optical axis, and the convenience in mold manufacture is further increased. improves.

When the temperature rises, the optical elements constituting the scanning optical system expand. Therefore, the diffractive optical element having the MS surface also expands. Moreover, the reverse behavior is exhibited when the temperature drops.
Due to the expansion of the optical element, the canceling relationship between the refracting surface and the diffractive surface is lost, and as shown in FIG. 3, the MS surface when the temperature rises causes a refracting action. At this time, it is possible to provide a desired function by appropriately setting the power.

Next, an optical element that changes the scanning position in the sub-scanning direction so as to reduce the color shift when the temperature changes may be disposed in the third optical system. Here, an example of the MS surface disposed on the second scanning lens L2 as a diffractive optical element will be described.
In this embodiment, a multi-step (MS) diffraction surface is provided on the exit surface of the second scanning lens L2.

Since the multi-step diffractive surface is formed so that the diffractive power and the refractive power change while canceling in the sub-scanning direction, the multi-step diffractive surface has a linear diffractive structure.
Further, as shown in FIG. 5, the refractive power due to the substrate shape can be made into the MS surface by making it a parabolic shape that cancels out the diffraction power. Specifically, the paraxial radius of curvature is −3000.
The diffraction power can be expressed by a phase function. When the distance from the optical axis in the sub-scanning direction on the surface perpendicular to the optical axis is Z, the phase function φ (Z) of the first surface is expressed by the following equation (1). Note that a point on the optical axis is R = 0.
φ (Z) = Cz2 · Z ² (1)
Here, at the design wavelength of 780 nm, Cz2 = −8.733E−05 and the step difference is 1.489 μm.

In the present embodiment, as shown in FIG. 5, since the substrate shape is a parabolic shape symmetrical in the sub-scanning section, the MS surface is also symmetric in the sub-scanning section.
By doing so, both scanning lenses can be made common when obliquely incident on the deflecting reflecting surface of the deflector 5 from above and below the main scanning section. For this reason, since the types of lenses necessary for the tandem image forming apparatus can be reduced, the cost can be reduced.
Further, by using such an MS surface, a change in scanning line bending due to a change in environmental temperature is reduced.

Next, based on FIG. 6 and FIG. 7, the reduction of the scanning line bending due to the environmental change by the MS surface provided in the scanning lens will be described.
In the oblique incidence optical system, as shown in FIG. 7A, since the sag amount of the polygon mirror is different for each image height, it is known to enter the second scanning lens L2 with an arcuate locus in the sub-scanning direction. (FIG. 7B).
The light beam does not pass through the main scanning section of the second scanning lens L2 due to the trajectory bent in the sub-scanning direction. For this reason, the influence of expansion and contraction of the scanning lens L2 varies depending on the image height when the temperature changes, and even if it is designed so that there is no scanning line bending at room temperature, the scanning line bending changes due to the temperature change. (Graph on the left side of FIG. 6 (without diffractive surface)).
However, in this embodiment, since the MS surface as shown in FIG. 5 is provided in the second scanning lens L2, as shown in the graph on the right side of FIG. The change in bending can be reduced.
The scanning line bending at room temperature (25 ° C.) is adjusted by an adjusting unit (not shown) so as to bend by pressing the second scanning lens L2 in the sub-scanning direction and to have a desired scanning line characteristic. .

In this embodiment, it is also possible to use an MS surface in which the substrate shape is a plane inclined in the sub-scan section as shown in FIG. In this case, since the direction of the die machining step does not reverse, it is not necessary to reverse the tool. Further, the surface accuracy is also advantageous.
Further, in this embodiment, the angle formed by the annular surface and the adjacent back cut surface is configured to be an obtuse angle in the cross section including the reference axis. Specifically, the back cut surface for generating the above-described step between the annular surfaces with respect to the reference axis direction has a width of about 6 μm in the height direction, and the angle formed by the annular surface and the back cut surface is It is set to 165 °.

The diffractive optical element of this embodiment is processed by molding. By adopting a configuration having such an obtuse angle, a sufficient draft is provided, and the mold can be easily removed from the mold, so that the moldability is improved.
More preferably, the following conditional expression should be satisfied.
135 ° <θ <170 °
Here, θ represents an angle formed by the annular surface and the back cut surface.

[Example 2]
A second embodiment of the optical scanning device of the present invention will be described with reference to FIG. The basic configuration of the scanning optical system of this embodiment is substantially the same as that shown in FIG. 1, but in this embodiment, an MS surface that changes the scanning position in the sub-scanning direction due to environmental temperature changes is provided on the optical system before the deflector. The diffractive optical elements H1 and H2 are disposed. Specifically, as shown in FIG. 4, an MS surface is used in which the substrate shape is a plane inclined in the sub-scanning direction.

Here, when the incident angle to the polygon mirror of the deflector 5 changes from a predetermined angle as shown in FIG. 9B due to the deformation of the optical housing that occurs when the temperature changes as shown in FIG. The incident position in the sub-scanning direction is shifted on the (photosensitive member) 7 and color shift occurs.
Therefore, as shown in FIGS. 8, 9A and 9C, the diffractive optical elements H1 and H2 having MS surfaces set so that the incident angle to the polygon mirror does not change when the temperature changes are arranged in front of the deflector 5. By introducing it into the first optical system, it is possible to provide a high-quality scanning optical system free from sub-scanning position shift and color shift between photoconductors.

[Example 3]
Next, in the optical scanning device according to the present invention described in the first and second embodiments, the light source units 1a and 1b are, for example, a semiconductor laser array (LDA) having a plurality of light emitting points, or a single light emitting point. Alternatively, a multi-beam light source device using a plurality of light sources having a plurality of light emitting points may be used, and a plurality of light beams may be simultaneously scanned on the surface to be scanned (photosensitive member surface). By doing so, it is possible to configure an optical scanning device and an image forming apparatus that are increased in speed and density, and even when such an optical scanning device and an image forming apparatus are configured, the same effects as described above are obtained. The effect of can be obtained.

Here, FIG. 10 shows a configuration example of a light source unit constituting the multi-beam light source device.
FIG. 10A shows a first configuration example of the light source unit. In FIG. 10A, the semiconductor lasers 403 and 404 are individually fitted in fitting holes 405-1 and 405-2 (not shown) formed on the back side of the base member 405, respectively. The fitting holes 405-1 and 405-2 are inclined at a predetermined angle in the main scanning direction, in the embodiment, about 1.5 °, and the semiconductor lasers 403 and 404 fitted in the fitting holes are also main. It is inclined about 1.5 ° in the scanning direction. The semiconductor lasers 403 and 404 have notches formed in the cylindrical heat sink portions 403-1 and 404-1, and the protrusions 406-1 and 407-1 formed in the center round holes of the pressing members 406 and 407 are provided. The alignment direction of the light emitting sources is adjusted by matching the notch portion of the heat sink portion. The holding members 406 and 407 are fixed to the base member 405 with screws 412 from the back side thereof, so that the semiconductor lasers 403 and 404 are fixed to the base member 405. Further, the collimating lenses 408 and 409 are adjusted in the optical axis direction along the outer circumferences of the semicircular mounting guide surfaces 405-4 and 405-5 of the base member 405, and the diverging beam emitted from the light emitting point is generated. Positioned and bonded so as to be a parallel light beam.

  In the above-described embodiment, since the light beams from the respective semiconductor lasers are set so as to intersect within the main scanning plane, the fitting holes 405-1 and 405-2 and the semicircular mounting guide are disposed along the light beam direction. The surfaces 405-4 and 405-5 are formed to be inclined. By engaging the cylindrical engagement portion 405-3 of the base member 405 with the holder member 410 and passing the screw 413 through the through hole 410-2 and screwing into the screw holes 405-6 and 405-7, the base member Reference numeral 405 denotes a light source unit that is fixed to the holder member 410.

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

  FIG. 10B shows a second configuration example of the light source unit. In FIG. 10B, each light beam from the semiconductor laser 703 having four light emitting sources is configured to be combined using beam combining means. Reference numeral 706 denotes a pressing member, 705 denotes a base member, 708 denotes a collimating lens, and 710 denotes a holder member. In this embodiment, there is one semiconductor laser 703 as a light source, and the number of pressing members 706 corresponding to this is different from the configuration example shown in FIG. Are the same.

  FIG. 10C shows a configuration similar to the example shown in FIG. 10B, in which the light beams from the semiconductor laser array 801 having four light emitting sources are combined using the beam combining means 802. An example is shown. Since the basic components are the same as those shown in FIGS. 10A and 10B, description thereof is omitted here.

[Example 4]
Next, an embodiment of an image forming apparatus using the optical scanning device according to the present invention will be described with reference to FIG.
In this embodiment, the optical scanning device according to the present invention is applied to a tandem type full color laser printer. In FIG. 11, a conveying belt 17 for conveying a recording material (for example, transfer paper) S fed from a paper feeding cassette 13 disposed in the horizontal direction is provided on the lower side in the apparatus. A yellow (Y) photosensitive member 7Y, a magenta (M) photosensitive member 7M, a cyan (C) photosensitive member 7C, and a black (K) photosensitive member 7K are transferred onto the transfer belt 17. S is arranged at equal intervals in order from the upstream side in the transport direction to the downstream side. Hereinafter, subscripts Y, M, C, and K are appropriately added to the reference numerals for distinction. These photoreceptors 7Y, 7M, 7C, and 7K are all formed to have the same diameter, and process members that perform each process according to the electrophotographic process are sequentially arranged around the photoreceptors. Taking the photoconductor 7Y as an example, a charging charger 8Y, an optical scanning optical system 6Y of the optical scanning device 9, a developing device 10Y, a transfer charger 11Y, a cleaning device 12Y, and the like are sequentially arranged. The same applies to the other photoconductors 7M, 7C, and 7K.

  In this embodiment, the surfaces of the photoconductors 7Y, 7M, 7C, and 7K are used as scanning surfaces (or irradiated surfaces) that are set for the respective colors, and the respective photoconductors 7Y, 7M, 7C, and 7K are provided. On the other hand, the optical scanning optical systems 6Y, 6M, 6C, and 6K of the optical scanning device 9 are provided in a one-to-one correspondence relationship. However, the deflector 5 and the first scanning lens L1 on the side close to the deflector 5 are commonly used by the four optical scanning optical systems 6Y, 6M, 6C, and 6K, and the photosensitive member (scanned surface) 7Y. , 7M, 7C, 7K, the second scanning lens L2 on the side is provided in each optical system. It should be noted that illustration of a pre-deflector optical system such as a plurality of light source units, coupling lenses, apertures, and cylindrical lenses is omitted.

  The conveying belt 17 is supported by a driving roller 18 and a driven roller 19 and rotated in the direction of the arrow in the figure. Around the periphery thereof, a registration roller 16 and a belt charging charger 20 are positioned upstream of the photoreceptor 7Y. And a belt separation charger 21, a belt neutralization charger 22, a belt cleaning device 23, and the like are provided in this order so as to be positioned downstream of the photoreceptor 7K in the rotation direction of the belt 17. A fixing device 24 including a heating roller 24 a and a pressure roller 24 b is provided downstream of the belt separation charger 21 in the transfer paper conveyance direction, and is connected to a paper discharge tray 26 by a paper discharge roller 25.

  In the laser printer having such a schematic configuration, for example, in the full color mode (multiple color mode), each of the photoconductors 7Y, 7M, 7C, and 7K is charged by the chargers 8Y, 8M, 8C, and 8K, Light beams from the optical scanning optical systems 6Y, 6M, 6C, and 6K of the optical scanning device 9 based on the image signals of the colors Y, M, C, and K for the photoreceptors 7Y, 7M, 7C, and 7K. By scanning, an electrostatic latent image corresponding to each color signal is formed on the surface of each photoconductor. These electrostatic latent images are developed with toners of respective colors Y, M, C, and K by the corresponding developing devices 10Y, 10M, 10C, and 10K to form toner images. The transfer paper S in the paper feed cassette 13 is fed by the paper feed roller 14 and the transport roller 15 in synchronization with this image forming process, and is sent out to the transport belt 17 by the registration roller 16. The transfer sheet S fed to the conveyor belt 17 is electrostatically attracted to the conveyor belt 17 by the action of the belt charger 20 and is conveyed toward the photoreceptors 7Y, 7M, 7C, 7K. , 7M, 7C, and 7K are sequentially transferred onto the transfer paper S so that they are superimposed, and a full-color image is formed on the transfer paper S. The transfer sheet S on which the full-color image has been transferred is separated from the transport belt 17 by the belt separation charger 21 and transported to the fixing device 24. After the full-color image is fixed on the transfer paper S by the fixing device 34, the discharge roller 25 As a result, the sheet is discharged to the discharge tray 26.

  By using the optical scanning optical systems 6Y, 6M, 6C, and 6K of the image forming apparatus as the optical scanning apparatus according to Example 1 or Example 2 described above, high-quality image reproducibility can be achieved while being sufficiently small. An image forming apparatus that can be secured can be realized. The explanation is supplemented below.

As described above, there is an “oblique incidence optical system” as a low-cost scanning optical system of an optical scanning apparatus suitable for the tandem method. In this oblique incidence optical system, as shown in FIG. 11, the height of the deflector (polygon mirror) 5 can be suppressed low.
On the other hand, since the sag amount of the polygon mirror differs for each image height, there is a problem (problem (1)) in which the second scanning lens L2 is incident in an arcuate locus in the sub-scanning direction and the scanning line is bent. . The second scanning lens L2 is designed to suppress the scanning line bending, but as described above, there is a problem that the suppression of the scanning line bending becomes ineffective due to the fluctuation of the environmental temperature (problem (2)). .

The present invention addresses the problem (2) and provides a solution to the problem. The scanning position in the sub-scanning direction described in the first and second embodiments so that the color shift is reduced when the temperature changes. By using an optical element that changes the color, an optical scanning device that can perform high-quality writing with little color shift is realized.
As an example, as described in the first embodiment, the second scanning lens L2 has a multi-step (MS) diffraction surface. FIG. 12 shows an example of the shape of the scanning lens according to the present invention, where (a) is a sectional view of the scanning lens and (b) is a perspective view of the scanning lens.

Here, due to the above problem (1), the locus of the light beam incident on the scanning lens L2 is bent as shown in FIG.
For this reason, as the image height becomes higher, it shifts greatly in the sub-scanning direction. Then, as shown in FIG. 14, the incident light flux (incident light flux at a high image height position) incident with a large deviation in the sub-scanning direction due to the curvature of the exit surface is larger than the incident light flux at an image height of 0. Refracted.

Hereinafter, the above problem (2) will be considered with reference to the explanatory diagram of FIG.
As shown in FIG. 15A, when the temperature of a normal scanning lens becomes high, the scanning lens expands and the refractive power decreases. Therefore, it becomes difficult to suppress the bending of the scanning line.
On the other hand, in the case of the present invention, as shown in FIG. 15B, the refractive power of the lens surface on the exit surface side is weakened due to expansion at high temperatures.
However, the multi-step surface on the incident side is subject to temperature fluctuations,
Refractive power> Diffraction power, and the decrease in refractive power on the exit slope is compensated.
Thereby, even if temperature fluctuation occurs in the oblique incidence optical system, it is possible to suppress scanning line bending.

1 is a main scanning sectional view of a scanning optical system of an optical scanning device showing a first embodiment of the present invention. It is a main scanning sectional view showing a structural example of a scanning optical system of a commonly used optical scanning device. It is explanatory drawing of the change of refraction by a multistep diffraction surface and a temperature change. It is a figure which shows the example of a board | substrate shape and the shape of a multistep diffraction surface. It is a figure which shows another example of a substrate shape and another shape of a multistep diffraction surface. It is explanatory drawing of the scanning line curve change by environmental temperature change, and the reduction effect by a diffraction surface. It is explanatory drawing of the scanning line bending of an oblique incidence optical system. It is a main scanning sectional view of the scanning optical system of the optical scanning device showing the second embodiment of the present invention. It is explanatory drawing which shows typically the mode of the subscanning position shift generation | occurrence | production by the deformation | transformation of the optical housing which generate | occur | produces at the time of a temperature change. It is a figure which shows the structural example of the light source unit which comprises a multi-beam light source device. 1 is a schematic configuration diagram showing an embodiment of an image forming apparatus using an optical scanning device according to the present invention. 1A and 1B show an example of a scanning lens shape according to the present invention, in which FIG. 1A is a cross-sectional view of a scanning lens, and FIG. It is a figure which shows the locus | trajectory of the light ray which injects into a scanning lens when a scanning line curve generate | occur | produces. It is a figure which shows the difference in refraction by the position of the image height of the light beam which entered the scanning lens. It is explanatory drawing of the effect at the time of providing a multistep diffraction surface in a scanning lens.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1a, 1b: Light source part 2a, 2b: Coupling lens 3: Aperture 4: Cylindrical lens 5: Deflector (rotating polygon mirror)
6Y, 6M, 6C, 6K: optical scanning optical system 7: surface to be scanned (photosensitive member)
7Y, 7M, 7C, 7K: photoconductor (scanned surface)
8Y, 8M, 8C, 8K: Charger charger 9: Optical scanning device 10Y, 10M, 10C, 10K: Developing device 11Y, 11M, 11C, 11K: Transfer charger 12Y, 12M, 12C, 12K: Cleaning device 13: Paper feed cassette 14: Paper feeding roller 15: Conveying roller 16: Registration roller 17: Conveying belt 18: Drive roller 19: Driven roller 20: Belt charging charger 21: Belt separation charger 22: Charge eliminating charger 23: Belt cleaning device 24: Fixing device 25: Paper discharge roller 26: Paper discharge tray H1, H2: Diffractive optical element L1: First scanning lens L2: Second scanning lens G1: Soundproof glass G2: Dustproof glass M: Folding mirror S: Transfer paper (recording material)

Claims (9)

A plurality of light source units for emitting a light beam;
A deflector for deflecting a light beam from the light source unit;
A plurality of scanned surfaces scanned with a light beam from the deflector;
A first optical system that converts a light beam emitted from the light source unit into a desired condensing state, and a light beam converted by the first optical system is converted into a scanning direction of the deflector (hereinafter referred to as a main scanning direction). An incident optical system having a second optical system that forms an image in the sub-scanning direction perpendicular to the main scanning direction in the vicinity of the deflector,
A third optical system including a scanning lens for imaging and scanning the light beam deflected by the deflector on a plurality of scanned surfaces;
In the optical scanning device that deflects and scans the surface to be scanned,
An optical scanning device comprising: an optical element that changes a scanning position on the surface to be scanned so as to reduce a change in color shift in the sub-scanning direction when an environmental temperature changes. The optical scanning device according to claim 1,
The optical element has a diffractive surface having no power at least in the sub-scanning direction in a room temperature environment. The optical scanning device according to claim 1 or 2,
The optical scanning device according to claim 1, wherein the light beam incident on the deflector is incident on the deflector at an angle in a sub-scanning direction with respect to a main scanning section. In the optical scanning device according to any one of claims 1 to 3,
An optical scanning device having the optical element in the first optical system. In the optical scanning device according to any one of claims 1 to 3,
An optical scanning device having the optical element in the third optical system. In the optical scanning device according to any one of claims 1 to 5,
The diffractive surface of the optical element has a symmetric shape in the sub-scan section. In the optical scanning device according to any one of claims 1 to 6,
A multi-beam optical scanning apparatus having a plurality of light emitting points in the light source unit, and simultaneously deflecting and scanning a single surface to be scanned by the same deflecting surface of the deflector.   An image forming apparatus using the optical scanning device according to any one of claims 1 to 6 or the multi-beam optical scanning device according to claim 7 as writing means for an image carrier. The image forming apparatus according to claim 8.
The image forming apparatus, wherein the image carrier is a photoconductive photoconductor, and a plurality of photoconductors are provided along a recording material conveying unit or an intermediate transfer body.

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