JP2015176126A - Optical scanning device and image formation device including the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical scanning device that can highly accurately detect intensity of a light ray emitted by a light source without inducing increase in size of a device nor high costs thereof.SOLUTION: An optical scanning device 100 according to the present invention comprises: a light source 10a; a first lens 12 on which a light ray emitted from the light source 10a is incident; a light ray separation element 14b that separates a light ray from the first lens 12 into a transmission light ray Lt and a reflection light ray Ls; a mirror 19 that reflects the reflection light ray; a deflector 15 that deflects the transmission light ray Lt so that the transmission light ray Lt scans on a scanned surface 18; an image formation optical system 16 that converges the deflected light ray deflected by the deflector 15 on the scanned surface 18; and a light reception unit 10b that receives the reflection light ray Ls reflected on the mirror 19 via the first lens 12.

Description

  The present invention relates to an optical scanning device, and is particularly suitable for an image forming apparatus such as a laser beam printer, a digital copying machine, or a multifunction printer.

  In recent years, there has been known an optical scanning device that employs a light source having a plurality of light emitting points and scans a photosensitive drum with a multi-beam emitted from the light source to improve the image recording speed and the image recording density. As a light source having a plurality of light emitting points, a surface emitting laser (VCSEL) has attracted attention.

In an optical scanning device, automatic light intensity control (APC: Automatic Power Control) is performed by detecting a part of a light beam emitted from a light source by a light amount detecting means.
In Patent Document 1, an aperture and a parallel plate glass having an optical axis inclined with respect to the optical axis of the coupling lens are arranged behind the coupling lens, and converted into substantially parallel light by the coupling lens. The multi-beam is regularly reflected by the parallel flat glass. Then, the light separated and reflected by the parallel flat glass is passed through the aperture, again converted from the substantially parallel light to the convergent light by the coupling lens, and incident on the light amount detection means arranged near the condensing position. APC is performed.
Patent Document 2 discloses a method of performing APC using a light beam deflected and reflected in the vicinity of the end of the deflecting surface of an optical deflector that is not used for image recording.

JP 2007-241240 A JP 2011-123240 A

In an optical scanning device using a surface emitting laser as a light source, generally about 32 to 64 light emitting units are arranged at regular intervals in the main scanning direction and the sub scanning direction. Therefore, there is a possibility that the arrival position of each light beam emitted from the light emitting portions at both ends in the main scanning direction and incident on the deflecting surface of the optical deflector is greatly separated. As a result, the print quality may be deteriorated due to density unevenness as the photosensitive drum surface is decentered in the optical axis direction.
Further, when APC is performed in an optical scanning device using a surface emitting laser, the light amount of the light beam detected by the light amount detecting means, the light amount of the light beam actually output from the light source, and the actual surface of the photosensitive drum. It is desired that the amount of light beam to be directed can be correlated with high accuracy.

In the optical scanning device disclosed in Patent Document 1, it is necessary to increase an angle Δθ formed by the optical axis of the coupling lens and the optical axis of the parallel plate glass in order to separate the light source and the light amount detection means. Further, in order to reduce the density unevenness, in order to associate the light amount of the light beam detected by the light amount detection unit with the light amount of the light beam actually directed to the photosensitive drum surface with high accuracy, a parallel flat glass as a light beam separation unit, Apertures need to be integrated. Furthermore, as described above, in order to suppress the separation of the arrival positions of the light beams that are emitted from the light emitting portions at both ends in the main scanning direction and are incident on the deflecting surface of the optical deflector, the light beam width in the main scanning direction is set to It is desirable to provide a limiting aperture in the vicinity of the optical deflector.
However, when the angle Δθ is increased, the aperture is integrated with the parallel plate glass, and the parallel plate glass is installed in the vicinity of the optical deflector, the light separated and reflected by the parallel plate glass can be incident again on the coupling lens. Have difficulty. Moreover, the enlargement of an apparatus will also be invited.
Therefore, in the optical scanning device disclosed in Patent Document 1, it is difficult to perform high-precision APC without causing an increase in size and cost.

  In addition, in the optical scanning device disclosed in Patent Document 2, APC is performed using a light beam deflected and reflected in the vicinity of the end of the deflecting surface of the optical deflector. Since the influence of dirt attached by the wind flow of the optical deflector is significant, there is a possibility that APC cannot be performed with high accuracy.

  SUMMARY An advantage of some aspects of the invention is that it provides an optical scanning device that can detect the intensity of a light beam emitted from a light source with high accuracy without increasing the size and cost of the device.

  Therefore, an optical scanning device according to the present invention includes a light source, a first lens on which a light beam emitted from the light source is incident, a light beam separation element that separates the light beam from the first lens into a transmitted light beam and a reflected light beam, and a reflected light beam. A reflecting mirror; a deflector that deflects the transmitted light beam so that the transmitted light beam scans the scanned surface; an imaging optical system that focuses the light beam deflected by the deflector on the scanned surface; And a light receiving unit that receives the reflected light flux through the first lens.

  According to the present invention, it is possible to provide an optical scanning device that can detect the intensity of a light beam emitted from a light source with high accuracy without increasing the size and cost of the device.

1 is a schematic diagram of a main scanning section of an optical scanning device according to a first embodiment of the present invention. The figure which showed the structure of the surface emitting laser array in a light source. (A) is sectional drawing of a main scanning stop and a wedge prism, (b) is a front view of a main scanning stop and a wedge prism. The figure which showed a mode that the chief ray radiate | emitted from the light emission point was condensed on a to-be-scanned surface. The front view of an APC sensor. The main scanning cross-sectional schematic diagram of the optical scanning device which concerns on 2nd Embodiment of this invention. The perspective view of the parallel plate glass as a light beam separation means. The perspective view of a separation reflection main scanning stop. 1 is a schematic diagram of a color image forming apparatus including an optical scanning device according to the present invention.

  Hereinafter, an optical scanning device according to the present invention will be described with reference to the drawings. It should be noted that the drawings shown below may be drawn at a scale different from the actual scale so that the present invention can be easily understood.

  FIG. 1 is a schematic diagram of a main scanning section of an optical scanning device 100 according to the first embodiment of the present invention.

  Here, the sub-scanning direction (Z direction) is a direction parallel to the rotation axis of the polygon mirror 15, and the main scanning direction (Y direction) is perpendicular to the optical axis direction (X direction) and the sub-scanning direction. Direction. The main scanning section is a section including the optical axis direction and the main scanning direction, and can also be referred to as a section having the sub scanning direction as a normal line. Further, the sub-scan section is a section including the optical axis direction and the sub-scan direction. It should be noted that the optical axis direction is defined for each optical element. That is, the main scanning direction is also defined for each optical element. Further, the main scanning direction in elements other than the optical element is defined as a direction orthogonal to the surface normal direction and the sub-scanning direction of the element.

  The optical scanning device 100 includes a light source 10a, an APC sensor 10b as a light receiving unit, a sub-scanning diaphragm 11, a collimator lens (first lens) 12, a cylinder lens (second lens) 13, a main scanning diaphragm 14a, and a light beam separation element. A wedge prism 14b is provided. The optical scanning device 100 also includes a polygon mirror 15 as a deflector, a first scanning lens 16a, a second scanning lens 16b, a dustproof glass 17, a surface to be scanned (photosensitive drum surface) 18, and an APC mirror 19. .

  The detailed configuration such as the arrangement and shape of each optical element provided in the optical scanning device 100 is shown in Table 1 below.

In Table 1, “ ^EX ” indicates “× 10 ^−X ”, and the definition of the surface of the collimator lens 12 will be described later.

  The light source 10a is a surface emitting laser array (VCSEL) having a plurality of light emitting units arranged with a constant interval in the main scanning direction and the sub scanning direction.

The configuration of the surface emitting laser array in the light source 10a is shown in FIG. As shown in FIG. 2, in the light source 10a, 64 light emitting points LD1 to LD64 are two-dimensionally arranged. LD1 and LD2 are adjacent light emitting portions, and are arranged at an interval of Pm = 50 μm in the main scanning direction and Ps = 6 μm in the sub-scanning direction. Similarly, LD3 to LD32 are arranged at intervals of Pm = 50 μm in the main scanning direction and Ps = 6 μm in the main scanning direction from the adjacent light emitting units, and therefore, LD1 to LD32 are equally spaced on a straight line. It is arranged. The LD 33 is separated from the LD 32 by Ps in the sub scanning direction, and is disposed at the same position as the LD 1 in the main scanning direction. Similarly to LD1 to LD32, LD33 to LD64 are arranged on a straight line at equal intervals (Pm = 50 μm, Ps = 6 μm) in the main scanning direction and the sub-scanning direction, respectively.
In this way, by arranging LD1 to LD64 at a constant interval Ps in the sub-scanning direction, light beams emitted from a plurality of light emitting points can be condensed at a constant interval in the sub-scanning direction on the surface to be scanned. In addition, as long as each light emission point is arranged at a fixed interval in the sub-scanning direction, an arrangement other than the arrangement according to the present embodiment may be used.

  The sub-scanning aperture 11 is provided to limit the beam width in the sub-scanning direction of the light beam emitted from the light source 10a.

  The collimator lens 12 is provided to convert the light beam that has passed through the sub-scanning diaphragm 11 into a substantially parallel light beam. Here, the substantially parallel light beam includes a weak convergent light beam to a weak divergent light beam, and is not limited to a perfect parallel light beam.

The surface of the collimator lens 12 according to the present embodiment has an aspherical shape. This is because the light beam incident on the APC sensor 10b is incident with a finite field angle of about 5 ° to 30 ° with respect to the optical axis of the collimator lens 12, as shown in FIG. Therefore, for example, when the light source 10a and the APC sensor 10b are arranged on the same substrate 10c as in the present embodiment, the collimator lens 12 is installed at such a distance that the light beam emitted from the light source 10a becomes substantially parallel light. ing. As a result, the light beam incident on the APC sensor 10b is collected in front of the APC sensor 10b due to field curvature. When this amount of field curvature increases, the spot diameter in the main scanning direction of the light beam on the APC sensor 10b increases, and in particular, a part of the light beam from the end light source such as the LD1 may overflow from the APC sensor 10b. is there. As a result, it is considered that the laser emission intensity cannot be accurately controlled. Therefore, by making the collimator lens 12 an aspherical shape, the light beams emitted from all the light emitting points are surely incident on the APC sensor 10b.
Here, the aspheric shape of the collimator lens 12 is as follows when R is a radius of curvature, h is a distance from the center of the surface, k is a conic constant, and Ci (i = 1... N) is an aspheric coefficient. (1).

  Specific values used in this embodiment are shown in Table 1.

  The cylinder lens 13 has power in the sub-scan section, and the light beam converted into substantially parallel light by the collimator lens 12 is condensed in the sub-scan section in the vicinity of the deflecting surface 15a of the polygon mirror 15 to perform main scan. It is provided for converting into convergent light that forms a line image in the cross section. The sub-scanning section is a plane that is perpendicular to the direction in which the transmitted light beam separated by the wedge prism 14b by the polygon mirror 15 scans the surface to be scanned 18 and includes the optical axis.

  The main scanning stop 14 a is provided to limit the beam width in the main scanning direction of the light beam that has passed through the cylinder lens 13.

  The wedge prism 14b is provided to separate the light beam that has passed through the main scanning diaphragm 14a into a light beam (transmitted light beam) incident on the scanned surface 18 and a light beam (reflected light beam) incident on the APC sensor 10b. Of the surface of the wedge prism 14b on the light source means 10a side (first surface) and the surface on the polygon mirror 15 side (second surface), an antireflection coating is applied only to the second surface.

FIGS. 3A and 3B are a sectional view and a front view of the main scanning stop 14a and the wedge prism 14b, respectively. The main scanning stop 14a is disposed so as to contact the first surface of the wedge prism 14b. In FIG. 3A, the incident light beam Li to the main scanning stop 14a and the reflected light beam Ls generated by the wedge prism 14b are indicated by straight lines and dotted lines, respectively.
In the present embodiment, in order to perform light beam separation on the first surface of the wedge prism 14b, the main scanning stop 14a is disposed closer to the light source 10a than the wedge prism 14b. When the light beam separation is performed on the second surface of the wedge prism 14b, the main scanning stop 14a may be installed behind the wedge prism 14b.

  The opening of the main scanning stop 14a is chamfered at the end surface in the main scanning direction. This chamfering is performed at such an angle that the reflected light beam generated by the wedge prism 14b is not vignetted. Even if the far field pattern (FFP) of each light beam from the light source 10a fluctuates due to a temperature rise or the like because the chamfer and the main scanning stop 14a are in contact with the first surface of the wedge prism 14b, The light quantity ratio of the reflected light beam can be kept almost constant. Therefore, more stable light amount detection can be performed.

  In the present embodiment, the main scanning stop 14a is installed at a position 27.5 mm from the deflection surface 15a of the polygon mirror 15. As described above, the main scanning stop 14a is installed as close as possible to the deflection surface 15a of the polygon mirror 15, so that the light beams emitted from the respective light emitting points of the light source 10a are separated from each other in the main scanning direction on the deflection surface 15a. The amount is reduced. As a result, for example, when the position of the surface to be scanned fluctuates due to operating heat, vibration, or the like of the image forming apparatus main body, the difference amount of the printing position deviation in the main scanning direction of each light emitting point is reduced. Degradation of image quality due to the like can be reduced.

  The reason for this will be described with reference to FIG. 4A and 4B show principal rays (light rays passing through the center of the stop) L1, L16.5, and L32 emitted from both end light-emitting points LD1 and LD32 and the virtual central light-emitting point LD16.5. FIG. 8 is a diagram showing how light is focused on the scanned surface 18.

In an ideal design, as shown in FIG. 4A, the light beams L1, L16.5, and L32 reach the center position Y = 0 in the main scanning direction (Y direction) on the scanned surface 18. As described above, the deflection angle of the deflecting surface 15a is phase-matched for each light emitting point. However, FIG. 4A shows only the deflection surface 15a when the phase adjustment is performed on the light beam L16.5.
In FIG. 4B, the scanning surface 18 is decentered by ΔX in the optical axis direction (X direction) from the position (dotted line) in FIG. 4A due to some reason such as operating heat or vibration of the image forming apparatus main body. A state of moving to a position (straight line) is shown.

As shown in FIG. 4A, each of the principal rays L1, L16.5, and L32 passes through the center of the main scanning stop 14a and is incident on the deflection surface 15a. Therefore, if the main scanning stop 14a is closer to the deflecting surface 15a, the field angle difference between the main rays L1 and L32 and the optical path length from the main scanning stop 14a to the deflecting surface 15a are reduced, and as a result, the deflecting surface 15a. The separation amount of each light emitting point in the main scanning direction is reduced.
On the deflection surface 15a, the principal rays L1, L16.5, and L32 from the respective light emitting points deflected and reflected at positions separated in the main scanning direction are respectively in the main scanning direction of the first scanning lens 16a and the second scanning lens 16b. Incident at different positions. Therefore, when the principal rays L1, L16.5, and L32 reach the center position Y = 0 of the scanned surface 18, L16.5 does not have an exit angle of view from the scanning lens, but L1 and L32 are It has a finite exit angle of view.

Next, referring to FIG. 4B, the scanned surface 18 is eccentric in the optical axis direction by ΔX. ΔX is, for example, an amount of about 50 μm to several times that amount. Due to this eccentricity, the arrival positions of the principal rays L1 and L32 on the scanned surface 18 are separated by ΔY. ΔY is, for example, about 3 μm to 10 μm. Due to the occurrence of ΔY, a deviation occurs in the arrival position of the light beam from each light emitting point in the main scanning direction. As a result, a moire appears in the image, and the print quality deteriorates.
From the above, it is preferable to install the main scanning stop 14a as close to the deflection surface 15a as possible.

  The polygon mirror 15 is rotated at a constant speed counterclockwise by a driving means (polygon motor) (not shown), and deflects and scans the light beam incident on the deflection surface 15a.

The scanning lens system 16 as an imaging optical system is composed of a first scanning lens 16a and a second scanning lens 16b. The first scanning lens 16a and the second scanning lens 16b are each made of resin or glass. The first scanning lens 16 a and the second scanning lens 16 b collect the light beams deflected by the polygon mirror 15 at desired positions on the scanned surface 18.
In addition, the scanning lens system 16 compensates for surface tilt of the deflection surface 15a by making a conjugate relationship between the deflection surface 15a of the polygon mirror 15 and the scanned surface 18 in the sub-scan section.
Further, in the scanning lens system 16, in order to obtain good aberration characteristics such as a field curvature characteristic and an fθ characteristic, the following aspherical expression (2) in the main scanning direction and the following non-spherical expression in the sub-scanning direction are used. The spherical formula (3) is used.

  Here, R is the radius of curvature in the main scanning direction, Y is the position in the main scanning direction on the scanning lens, X is the position in the optical axis direction of the surface at each Y, Ky is the conic constant, B2i (i = 1... N) Indicates the aspheric coefficient in the main scanning direction. Further, r is a radius of curvature in the sub-scanning direction, E2i (i = 1... N) is an aspherical coefficient in the sub-scanning direction, and r ′ is a radius of curvature in the sub-scanning direction at the position Y in the main scanning direction. .

  The dustproof glass 17 is provided in order to prevent dust from entering the inside of the optical scanning device 100.

  On the surface to be scanned 18, light beams emitted from the respective light emitting points of the light source 10 a are condensed at a desired position based on the image information by the scanning lens system 16.

The APC mirror 19 deflects and reflects the light beam Ls separated and reflected by the first surface of the wedge prism 14b. Further, the separated reflected light beam from the second surface of the wedge prism 14b is suppressed to a low light amount by the antireflection coating on the second surface. In addition, since there is an angle difference between the surface normals of the first surface and the second surface, the incident angle to the APC mirror 19 differs between the light beam reflected by the first surface and the light beam reflected by the second surface. The influence of ghost light or the like on the sensor 10b is reduced.
The APC mirror 19 is installed at a position and an angle such that the separated reflected light beam Ls deflected and reflected by the APC mirror 19 passes through the collimator lens 12 and enters the vicinity of the center of the APC sensor 10b.
Specifically, the incident field angle θin of the separated reflected light beam of the principal ray L16.5 emitted from the virtual central light emitting point LD16.5 with respect to the collimator lens 12 is 20 deg. It has become. At this time, the focal length fcol at the reference radius of curvature of the collimator lens 12 is 60 mm. Therefore, from the center of the light source 10a (intersection of the optical axis of the light source 10a and the collimator lens 12) Y _LD16.5 = fcol × tan (θin) = 60 × tan (20 °) = 21.84 mm
The virtual central ray L16.5 is condensed at a position spaced apart in the main scanning direction.
Further, since the adjacent light emitting points are arranged at an interval of Pm = 50 μm in the main scanning direction, the end light emitting points LD1 and LD32 of the light source 10a are respectively θ _{LD32− with} respect to the virtual central ray L16.5. _LD16.5 = θ _LD16.5−LD1 = tan ⁻¹ (0.775 / 60) = 0.74 °
Only has an angle of view in the main scanning direction. Therefore, the chief rays L1 and L32 are condensed at positions separated from the center of the light source 10a by Y _LD1 = 22.72 mm and Y _LD32 = 20.96 mm, respectively, in the main scanning direction.
As described above, the separated reflected light beam is incident on the collimator lens 12 with a certain angle of view to be separated from the center of the light source 10a and the main scanning direction of the APC sensor 10b. The light flux that has passed has a curvature of field. Therefore, the separated reflected light beam does not spread too much in the main scanning direction at the position of the APC sensor 10b.
θin <θin_max (= 30 °)
It is necessary to install the APC mirror 19 so that
Further, θin <30 ° is preferable because the light source 10a and the APC sensor 10b can be installed so as not to be separated from each other, and the optical scanning device 100 can be further downsized.

The APC sensor 10b is provided so as to detect the light quantity of the separated reflected light beam that has been deflected and reflected by the APC mirror 19 and passed through the collimator lens 12. The APC sensor 10b and the light source 10a are provided on the same substrate 10c. However, the present invention is not limited to this, and each may be provided on a separate substrate. In that case, it is not particularly necessary to consider field curvature or the like.
From the above calculation, the APC sensor 10b is disposed at a position spaced 21.84 mm away from the center position of the light source 10a in the main scanning direction. That is, the separated reflected light beam of the virtual central light beam L16.5 emitted from the virtual light emitting point LD16.5 of the light source 10a is arranged so as to reach the center of the APC sensor 10b. In consideration of the package size of the light source 10a and the package size of the APC sensor 10b, the elements can be arranged on the same substrate as long as they are separated by 15 mm or more.
Therefore, it is desirable that the distance Y (= fcol × tan (θin)) between the light source 10a and the APC sensor 10b satisfies the following conditional expression (4).
Y1 <Y <Y2 (4)

Here, Y1 is 15 mm, Y2 is
fcol × tan (θin_max) = 60 × tan (30 °) = 34.64 mm
It is.
In this embodiment, since the separation amount is 21.84 mm, Expression (4) is satisfied, and each element (light emitting element and APC sensor) can be arranged on the same substrate.

FIG. 5 shows a front view of the APC sensor 10b. The APC sensor 10b includes a light receiving unit 10d and a package unit 10e. The light receiving unit 10d uses a square photodiode whose sensor size in the main scanning direction and the sub-scanning direction is a × a = 3 mm × 3 mm. Yes. Further, the maximum separation amount in the main scanning direction of the marginal rays of the separated reflected light beams from the LD1 and LD32 on the APC sensor 10b is d = 2.2 mm with the sensor center symmetrical. Therefore, light rays from all the light emitting points are incident on the light receiving portion 10d of the APC sensor 10b without being vignetted by the package portion 10e or the like.
Further, the separated reflected light beams from the respective light emitting points incident on the APC sensor 10b are almost condensed in the main scanning section, but pass through the cylinder lens 13 in the sub-scanning section and pass through the reference curvature of the collimator lens 12. Since the light is once condensed in the vicinity of the focal length at the radius, it is not condensed. Therefore, even when a foreign object adheres to the light receiving portion 10d of the APC sensor 10b, the influence of a decrease in the amount of light due to the foreign object can be reduced, and APC can be performed with high accuracy. The amount of light at each light emitting point of the light source 10a is determined according to the amount of light received by the APC sensor 10b.

  As described above, in the optical scanning device 100 according to the present embodiment, the light beams emitted from all the light emitting points of the light source 10 a are separated and reflected on the first surface of the wedge prism 14 b and deflected and reflected by the APC mirror 19. Then, the light enters the collimator lens 12 with a finite field angle and enters the light receiving portion 10d of the APC sensor 10b without vignetting. Further, since the light beam incident on the APC sensor 10b is not condensed in the sub-scanning section, it is strong against foreign matter adhesion on the APC sensor 10b, and APC can be performed with high accuracy. In addition, by appropriately setting the position and angle of the APC mirror 19, it is sufficient to arrange the light source 10a and the APC sensor 10b on the same substrate 10c, and the substrate 10c does not become large, and the optical scanning device 100 is small. It is possible to arrange them at a separation distance that can be reduced. Further, since the collimator lens 12 also serves as a condenser lens for the APC sensor 10b, the number of parts of the optical scanning device 100 is reduced and the cost is reduced.

  FIG. 6 shows a schematic diagram of a main scanning section of an optical scanning device 200 according to the second embodiment of the present invention. In addition, about the optical scanning device 200 which concerns on this embodiment, only a different element from the optical scanning device 100 which concerns on 1st Embodiment is demonstrated, and description is abbreviate | omitted regarding the same component.

The optical scanning device 200 includes a light source 10a, an APC sensor 10b, a sub-scanning diaphragm 11, a collimator lens (first lens) 12, a cylinder lens (third lens) 13, and a main scanning diaphragm 14a as a first optical system. . The optical scanning device 200 includes a wedge prism 14b, a first scanning lens 16a, a second scanning lens 16b, and a dustproof glass 17 as a first optical system.
The optical scanning device 200 includes a light source 20a, an APC sensor 20b, a sub-scanning diaphragm 21, a collimator lens (second lens) 22, a cylinder lens (fourth lens) 23, and a main scanning diaphragm 24a as a second optical system. ing. The optical scanning device 200 includes a wedge prism 24b, a first scanning lens 26a, a second scanning lens 26b, and a dustproof glass 27 as a second optical system.
The polygon mirror 15 as an optical deflector is shared by the first optical system and the second optical system.

  In the optical scanning device 200 according to the present embodiment, since the polygon mirror 15 is shared by the first optical system and the second optical system, the first scanned surface 18 and the second scanned surface are scanned by one polygon mirror 15. The surface 28 can be scanned (both sides scanning system), and cost reduction is realized.

In the optical scanning device 200 according to the present embodiment, by appropriately adjusting the angle of the wedge prism 14b, the light beam Ls1 (first reflected light beam) reflected and separated by the wedge prism 14b is a collimator of the second optical system. The light enters the lens 22 and is received by the APC sensor 20b. Similarly, by appropriately adjusting the angle of the wedge prism 24b, the light beam Ls2 (second reflected light beam) reflected and separated by the wedge prism 24b is incident on the collimator lens 12 of the first optical system, and the APC Light is received by the sensor 10b.
Thus, in the optical scanning device 200 according to the present embodiment, unlike the optical scanning device 100 according to the first embodiment, it is not necessary to provide an APC mirror by using a double-sided scanning system, thereby realizing cost reduction. doing.

Also in the optical scanning device 200 according to the present embodiment, the distance Y10 between the light source 10a and the APC sensor 10b is the principal ray of the light beam that is emitted from the central light emitting point of the light source 20a and reflected and separated by the wedge prism 24b. When the angle formed with the optical axis of the collimator lens 12 when entering the collimator lens 12 is θin1, and the focal length of the collimator lens 12 of the first optical system is fcol1,
Y10 = fcol1 × tan (θin1)
Y10 preferably satisfies the following conditional expression (5). The distance Y20 between the light source 20a and the APC sensor 20b is such that the principal ray of the light beam that is emitted from the central light emitting point of the light source 10a and reflected and separated by the wedge prism 14b is incident on the collimator lens 22. When the angle formed with the optical axis is θin2, and the focal length of the collimator lens 22 of the second optical system is fcol2,
Y20 = fcol2 × tan (θin2)
Y20 preferably satisfies the following conditional expression (6).

Y1 <Y10 <Y2 (5)
Y1 <Y20 <Y2 (6)

Here, fcol1 and fcol2 are 60 mm like the optical scanning device 100 according to the first embodiment. Further, θin1_max and θin2_max are 30 ° as in the optical scanning device 100 according to the first embodiment. Therefore, Y1 is 15 mm as in the optical scanning device 100 according to the first embodiment, and Y2 is
fcol1 × tan (θin1_max) = fcol2 × tan (θin2_max)
= 60 x tan (30 °)
= 34.64mm
It is.

  In the present invention, a wedge prism is used as the light beam separating means. However, if the light quantity of the separated reflected light beam generated by the surface other than the light separating surface is sufficiently small (particularly 1% or less) with respect to the light amount of the separated reflected light beam generated by the light separating surface, it is shown in FIG. Such parallel flat glass 14c may be used.

In the optical scanning device according to the present invention, the light beam separating means and the main scanning stop may be integrated in order to realize further cost reduction. For example, as shown in FIG. 8, it is possible to use a separate reflection main scanning stop 14d provided with a mirror surface portion 14e whose peripheral surface is mirror-finished. Thereby, the light beam separating means and the main scanning stop can be made the same member.
Here, the light quantity distribution on the same phase plane of the light beam generally has a Gaussian distribution as shown in FIG. Therefore, the separated reflected light beam received by the APC sensor uses the light beam separated and reflected by the mirror surface portion 14e, that is, the vicinity of the end of the far field pattern (FFP). For this reason, the amount of light may be lower than that of the light beam separated and reflected by the wedge prism. However, if the captured light quantity of the light beam emitted from the light source by the collimator lens is sufficiently large, a light quantity equivalent to the light beam reflected by the wedge prism can be obtained. Therefore, highly accurate APC can be performed.

  As mentioned above, although preferable embodiment of this invention was described, this invention is not limited to these embodiment, A various deformation | transformation and change are possible within the range of the summary.

  FIG. 9 is a schematic diagram of a color image forming apparatus 90 including an optical scanning device according to the present invention.

The color image forming apparatus 90 is a tandem type color image forming apparatus in which a plurality of optical scanning devices are arranged in parallel and image information is recorded on a photosensitive drum surface as an image carrier in parallel.
The color image forming apparatus 90 includes a printer controller 93, optical scanning devices 11, 12, 13 and 14, developing devices 15, 16, 17 and 18, photosensitive drums 23, 24, 25 and 26 as image carriers, and a conveyance belt 91. , A fixing device 94 and a paper cassette 95 are provided.

  In the color image forming apparatus 90, R (red), G (green), and B (blue) color signals (code data) are input to the printer controller 93 from an external device 92 such as a personal computer. These color signals are converted by the printer controller 93 into C (cyan), M (magenta), Y (yellow), and K (black) image data (dot data). These image data (image signals) are input to the optical scanning devices 11 to 14, respectively. Then, light beams 19 to 22 modulated according to each image data are emitted from the optical scanning devices 11 to 14, and the photosensitive surfaces of the photosensitive drums 23 to 26 are scanned in the main scanning direction.

  The photosensitive drums (photoconductors) 23 to 26 are rotated by a motor (not shown). With this rotation, the photosensitive surfaces of the photosensitive drums 23 to 26 move in the sub-scanning direction perpendicular to the main scanning direction with respect to the light beams 19 to 22. Above the photosensitive drums 23 to 26, a charging roller (not shown) for uniformly charging the surfaces of the photosensitive drums 23 to 26 is provided so as to contact the surfaces. The surfaces of the photosensitive drums 23 to 26 charged by the charging roller are irradiated with light beams 19 to 22 emitted from the optical scanning devices 11 to 14.

  As described above, the light beams 19 to 22 are modulated based on the image data, and an electrostatic latent image is formed on the surface of the photosensitive drums 23 to 26, that is, the photosensitive surface by irradiating the light beams 19 to 22. It is formed. The electrostatic latent image is developed into toner by developing units 15 to 18 arranged so as to come into contact with the photosensitive drums 23 to 26 further downstream in the rotation direction of the photosensitive drums 23 to 26 than the irradiation positions of the light beams 19 to 22. Developed as an image.

  The toner images developed by the developing units 15 to 18 are transferred onto a transfer material by a transfer roller (transfer unit) (not shown) disposed below the photosensitive drums 23 to 26 so as to face the photosensitive drums 23 to 26. The images are sequentially transferred onto a sheet of paper (not shown). The paper is stored in a paper cassette 95 in front of the photosensitive drums 23 to 26 (right side in FIG. 9), but can be fed manually. A paper feed roller (not shown) is provided at the end of the paper cassette 95, and the paper in the paper cassette 95 is sent to the transport belt 91 by the paper feed roller. Transport to 26.

  The sheet on which the unfixed toner image is transferred as described above is further conveyed to the fixing device 94 behind the photosensitive drums 23 to 26 (left side in FIG. 9). The fixing device 94 includes a fixing roller having a fixing heater (not shown) inside and a pressure roller disposed so as to be in pressure contact with the fixing roller. Then, the conveyed sheet is heated while being pressed by the press contact portion between the fixing roller and the pressure roller, thereby fixing the unfixed toner image on the sheet. Further, a paper discharge roller (not shown) is disposed behind the fixing device 94 and discharges the fixed paper to the outside of the image forming apparatus 90.

  In addition to the data conversion described above, the printer controller 93 is not only a motor that drives the photosensitive drums 23 to 26, but also each component in the image forming apparatus 90 and each of the optical scanning apparatuses 11 to 14. Control the polygon motor.

  Further, as the external device 92, for example, a color image reading device including a CCD sensor may be used. In this case, the color image reading apparatus and the color image forming apparatus 90 constitute a color digital copying machine.

10a Light source 10b APC sensor (light receiving part)
12 Collimator lens (first lens)
14b Wedge prism (beam separation element)
15 Polygon mirror (deflector)
16a First scanning lens (imaging optical system)
16b Second scanning lens (imaging optical system)
18 Scanned surface 100 Optical scanning device

Claims (22)

A light source;
A first lens on which a light beam emitted from the light source enters;
A light beam separating element for separating the light beam from the first lens into a transmitted light beam and a reflected light beam;
A mirror that reflects the reflected luminous flux;
A deflector for deflecting the transmitted light beam so that the transmitted light beam scans a surface to be scanned;
An imaging optical system for condensing the light beam deflected by the deflector onto the scanned surface;
A light receiving unit that receives the reflected light beam reflected by the mirror through the first lens;
An optical scanning device comprising:   The optical scanning device according to claim 1, wherein the light source and the light receiving unit are provided on the same substrate. A second lens having power in a sub-scan section perpendicular to a main scanning direction in which the transmitted light beam scans the surface to be scanned;
A diaphragm for limiting the beam width in the main scanning direction of the light beam that has passed through the second lens;
Further comprising
The optical scanning device according to claim 1, wherein the diaphragm is disposed between the second lens and the deflector. The light beam separating element includes a first surface facing the light source and a second surface facing the deflector,
The optical scanning device according to claim 3, wherein the diaphragm is in contact with the first surface of the light beam separating element. When the focal length of the first lens is fcol (mm) and the angle formed between the principal ray of the reflected light beam incident on the first lens and the optical axis of the first lens is θin (deg.),
15 <fcol × tan (θin) <34.64
5. The optical scanning device according to claim 1, wherein the following conditional expression is satisfied.   6. The optical scanning device according to claim 3, wherein the light beam separation element and the diaphragm are integrally formed.   7. The optical scanning device according to claim 1, wherein the light beam separation element is a wedge prism.   7. The optical scanning device according to claim 1, wherein the light beam separation element is a parallel plate glass.   The optical scanning device according to claim 1, wherein the first lens has an aspherical surface.   The optical scanning device according to claim 4, wherein the second surface of the light beam separating element is provided with an antireflection coating. First and second light sources;
First and second lenses on which light beams emitted from the first and second light sources respectively enter;
A first light beam separating element that separates a light beam that has passed through the first lens into a first transmitted light beam and a first reflected light beam;
A second light beam separating element for separating a light beam that has passed through the second lens into a second transmitted light beam and a second reflected light beam;
A deflector for deflecting the first and second transmitted light beams so that each of the first and second transmitted light beams scans the first and second scanned surfaces;
First and second imaging optical systems for condensing the first and second transmitted light beams deflected by the deflector on the first and second scanned surfaces, respectively.
A first light receiving portion for receiving the first reflected light flux through the second lens;
A second light receiving portion for receiving the second reflected light flux through the first lens;
An optical scanning device comprising:   The first light source and the second light receiving unit are provided on a first substrate, and the second light source and the first light receiving unit are provided on a second substrate. The optical scanning device according to claim 11. A third lens having power in a sub-scanning section perpendicular to a main scanning direction which is a direction in which the first transmitted light beam scans the first scanned surface by the deflector;
A fourth lens having power in a sub-scan section perpendicular to a main scanning direction, which is a direction in which the second transmitted light beam scans the second scanned surface by the deflector;
A first diaphragm for limiting a beam width in the main scanning direction of the light beam that has passed through the third lens;
A second diaphragm for limiting the beam width in the main scanning direction of the light beam that has passed through the fourth lens;
Further comprising
The first diaphragm is disposed between the third lens and the deflector, and the second diaphragm is disposed between the fourth lens and the deflector.
The optical scanning device according to claim 11, wherein the optical scanning device is characterized in that: Each of the first and second light beam separating elements includes a first surface facing the first and second light sources and a second surface facing the deflector;
The optical scanning device according to claim 13, wherein the first and second diaphragms are in contact with the first surfaces of the first and second light beam separation elements, respectively. The focal length of the first lens is fcol1 (mm), and the angle formed with the optical axis of the first lens when the principal ray of the second reflected light beam is incident on the first lens is θin1 (deg.). When the focal length of the second lens is fcol2 (mm), and the angle formed with the optical axis of the second lens when the principal ray of the first reflected light beam enters the second lens is θin2 (deg.). ,
15 <fcol1 × tan (θin1) <34.64
15 <fcol2 × tan (θin2) <34.64
The optical scanning device according to claim 12, wherein the following conditional expression is satisfied.   16. The first light beam separation element and the first diaphragm are integrally formed, and the second light beam separation element and the second diaphragm are formed integrally. The optical scanning device according to any one of the above.   17. The optical scanning device according to claim 11, wherein each of the first and second light beam separation elements is a wedge prism or a parallel plate glass.   The optical scanning device according to claim 11, wherein the first and third lenses have aspheric surfaces.   The optical scanning device according to claim 14, wherein an antireflection coating is applied to the second surfaces of the first and second light beam separating elements.   11. The optical scanning device according to claim 1, and a developing unit that develops, as a toner image, an electrostatic latent image formed on a photosensitive surface of a photosensitive member disposed on the surface to be scanned. An image forming apparatus comprising: a transfer device that transfers the developed toner image onto a transfer material; and a fixing device that fixes the transferred toner image onto the transfer material. An electrostatic latent image formed on the photosensitive surface of the optical scanning device according to any one of claims 11 to 19 and a plurality of photosensitive members arranged on the first and second scanned surfaces. A developing device for developing as a toner image;
An image forming apparatus comprising: a transfer device that transfers the developed toner image onto a transfer material; and a fixing device that fixes the transferred toner image onto the transfer material.   The image forming apparatus according to claim 20 or 21, further comprising a printer controller that converts code data input from an external device into an image signal and inputs the image signal to the optical scanning device.

Images