JP2017191143A - Optical scanner and image forming apparatus including the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical scanner that is compact and can achieve accurate synchronization detection, and an image forming apparatus.SOLUTION: An optical scanner comprises: a deflector 10 that deflects a light beam and optically scans a scanning target surface 17 in a main scanning direction; an imaging optical system 20 that guides the light beam deflected by the deflector 10 to the scanning target surface 17; a light receiving part 13 that receives the light beam deflected by the deflector 10 and creates a signal; and a refraction optical element 11 that refracts a principal ray of the light beam deflected by the deflector 10 in a direction separated from the imaging optical system 20 in a main scanning cross section and guides the principal ray to a light receiving surface of the light receiving part 13. The optical scanner satisfies the condition L×cosθ≤Ls.SELECTED DRAWING: Figure 1

Description

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

  As an optical scanning device provided in an image forming apparatus, a light beam emitted from a light source is deflected by a deflector, and the deflected light beam is guided to a scanned surface by an imaging optical system, thereby moving the scanned surface in the main scanning direction. What scans light is known. In such an optical scanning device, in order to optically scan the surface to be scanned with high accuracy, the light beam deflected by the deflector is synchronously detected to determine the scanning start position in the main scanning direction on the surface to be scanned. A synchronization detector is required.

  Patent Document 1 describes a configuration in which an off-axis light beam before being incident on the imaging optical system after being deflected by a deflector is guided to a synchronization detection unit by being reflected by a mirror. According to this configuration, since the light beam from the deflector can be guided to the synchronization detection unit without passing through the end of the imaging optical system, the deflector and the imaging optical system are arranged in the main scanning section. It becomes possible to reduce the size.

JP 2009-145569 A

  However, in the configuration described in Patent Document 1, when the mirror posture deviates from the design value due to an arrangement error or environmental variation (temperature change), the arrival position of the light beam reflected by the mirror deviates significantly from the design position. End up. In this case, highly accurate synchronization detection cannot be performed, and a good image may not be obtained.

  An object of the present invention is to provide an optical scanning device and an image forming apparatus that are small and can realize highly accurate synchronous detection.

In order to achieve the above object, an optical scanning device according to one aspect of the present invention includes a deflector that deflects a light beam and optically scans a surface to be scanned in a main scanning direction, and the light beam deflected by the deflector. An imaging optical system that guides light to a surface to be scanned, a light receiving unit that receives a light beam deflected by the deflector and generates a signal, and a principal ray of the light beam deflected by the deflector within the main scanning section. A refracting optical element that refracts in a direction away from the imaging optical system and guides the light to the light receiving surface of the light receiving unit, and from the deflection surface of the deflector within the main scanning section, The distance to the incident surface is L _BD , the angle formed between the principal ray of the light beam incident on the refractive optical element when going to the center of the light receiving surface and the optical axis of the imaging optical system is θ _BD , from the deflection surface To the optical surface closest to the deflection surface of the imaging optical system When the distance Ls, _and, and satisfies the _{L BD} × _{cosθ BD} ≦ Ls following condition.

  According to the present invention, it is possible to provide an optical scanning device and an image forming apparatus that are small and can realize highly accurate synchronization detection.

1 is a main scanning sectional view of an optical scanning device according to Embodiment 1 of the present invention. 1 is a sub-scan sectional view of an optical scanning device according to Embodiment 1 of the present invention. The figure which shows arrangement | positioning of each light emission point of the light source which concerns on Example 1 of this invention. FIG. 3 is a main scanning sectional view of the synchronization detection unit according to the first embodiment of the invention. FIG. 9 is a main scanning sectional view of a synchronization detection unit according to a second embodiment of the present invention. FIG. 6 is a main scanning sectional view of a synchronization detection unit according to a third embodiment of the present invention. The figure which shows the magnification chromatic aberration on the light-receiving surface which concerns on each Example of this invention. 1 is a sub-scanning sectional view of an image forming apparatus according to an embodiment of the present invention.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. Each drawing may be drawn on a different scale for convenience. Moreover, in each drawing, the same reference number is attached | subjected about the same member and the overlapping description is abbreviate | omitted.

  In the following description, the main scanning direction is a direction perpendicular to the rotation axis of a deflector described later and the optical axis direction of the optical system, and the sub-scanning direction is a direction parallel to the rotation axis of the deflector. It is. The main scanning section is a section that includes the optical axis of the optical system and is parallel to the main scanning direction (cross section perpendicular to the sub scanning direction). The sub scanning section is a section that is parallel to the sub scanning direction (main scanning). Cross section perpendicular to the direction). That is, each direction and each cross section may be different for each optical system.

[Example 1]
Hereinafter, the optical scanning device according to the first embodiment of the present invention will be described in detail.

(Optical scanning device)
1 and 2 are schematic views of a main part of an optical scanning device 100 according to Embodiment 1 of the present invention. FIG. 1 is a main scanning sectional view (XY sectional view), and FIG. 2 is a sub-scanning sectional view (ZX section). Figure). The optical scanning device 100 according to the present embodiment includes a light source 1, a deflector 10, an imaging optical system 20, a synchronization detection unit (BD optical system) 30, an incident optical system 40, a light amount detection unit 50, A reflective optical system 60. In FIG. 1, the optical path is developed by omitting the reflection optical system 60, and in FIG. 2, members other than those arranged in the optical path from the deflection surface 10 to the scanned surface 17 are omitted.

  The light source 1 is a semiconductor laser as a multi-beam light source having a plurality of light emitting points. As shown in FIG. 3, the light source 1 according to the present invention has a surface emission having 32 light emitting points LD1 to LD32 which are arranged apart from each other in the main scanning direction (Y direction) and the sub scanning direction (Z direction). Laser (VCSEL). The light emitting points according to the present embodiment are arranged (one-dimensional arrangement) on a straight line inclined by an angle α with respect to the main scanning direction, but two-dimensional arrangement may be adopted as necessary. Good. As described above, by using the multi-beam light source, it is possible to realize high-speed and high-definition optical scanning.

  The incident optical system 40 is an optical system for guiding the light beam emitted from the light source 1 to the deflecting surface 10a of the deflector 10, and includes a first diaphragm 2, a collimator lens 3, a spherical lens 4, and a cylindrical lens. 5, a second diaphragm 6, and a prism 7.

  The first stop 2 is a sub-scanning stop that limits the width of the light beam in the sub-scanning direction. By disposing the first diaphragm 2 in the vicinity of the collimator lens 3, the exit pupil position in the sub-scan section of the entire system of the optical scanning device 100 can be set in the vicinity of the imaging lens 20b described later. Thus, each of the principal rays emitted from each light emitting point can be configured to pass through substantially the same position in the sub-scanning direction in the vicinity of the imaging lens 20b.

  The collimator lens 3 is a bonded lens formed by bonding a convex lens and a concave lens made of glass to each other, and the spherical lens 4 is a convex spherical lens made of glass. By the collimator lens 3 and the spherical lens 4, divergent light beams emitted from the respective light emitting points can be converted into substantially parallel light beams, and the diameters of the respective light beams on the scanned surface 17 can be made uniform. The cylindrical lens 5 is a lens having power only in the sub-scanning section, condenses the light beam that has passed through the spherical lens 4 in the sub-scanning section, and forms a line image that is long in the main scanning direction on the deflection surface 10a. Yes. The collimator lens 3 and the cylindrical lens 5 may be integrated into one lens.

  The second diaphragm 6 is a main scanning diaphragm that limits the width of the light beam in the main scanning direction. By disposing the second diaphragm 6 in the vicinity of the deflection surface 10a, the principal rays of the light beams from the respective light emitting points can be brought close to each other on the deflection surface 10a. It becomes possible to reduce vertical line fluctuations.

  The prism 7 is a branching optical element for branching the light flux from the light source 1 into a transmitted light flux directed to the deflecting surface 10a of the deflector 10 and a reflected light flux directed to the light amount detection unit 50 described later. Specifically, the prism 7 is a wedge-shaped wedge prism in which the surface normal of the entrance surface and the surface normal of the exit surface at the principal ray passage position form an angle of 4 ° in the main scanning section. is there. The second diaphragm 6 is disposed on the incident surface of the prism 7.

  The light quantity detection unit 50 includes an imaging lens 8 that collects the reflected light beam reflected by the incident surface of the prism 7, and a light quantity detection sensor 9 that receives the light beam from the imaging lens 8. The prism 7 is configured so that the light beam reflected by the exit surface does not enter the light amount detection unit 50. By feeding back the detection signal output from the light amount detection sensor 9 to the drive circuit of the light source 1, the intensity of the light beam emitted from the light source 1 can be automatically controlled (auto power control: APC). As a result, the output of the light source 1 (the amount of emitted light) can be controlled to be always equal to the design value, so that stable image formation can be performed regardless of temperature changes.

  The deflector 10 is a polygon mirror (rotating polygonal mirror) having five deflecting surfaces 10a, and is rotated at a constant speed in the direction of arrow A in FIG. 1 by driving means (not shown) such as a motor. The deflector 10 deflects the light beam guided by the incident optical system 40 at each deflecting surface 10a, and optically scans the effective scanning area on the scanned surface 17 at a constant speed in the main scanning direction. The number of deflection surfaces 10a can be selected as appropriate. Further, as the deflector 10, a oscillating mirror that oscillates at a constant speed around the oscillating shaft may be employed.

  The imaging optical system 20 is an fθ optical system having a condensing function and fθ characteristics, and includes two imaging lenses (imaging optical elements). The first imaging lens 20a is a plano-convex spherical lens made of glass, and the second imaging lens 20b is an anamorphic lens having a non-arc-shaped lens surface (optical surface) in the main scanning section. In this embodiment, the imaging optical system 20 is configured by two imaging lenses, but a configuration including one imaging lens or three or more imaging lenses may be adopted as necessary.

  In addition, the imaging optical system 20 forms a spot image of each light emitting point by condensing the light beam (scanning light beam) deflected by the deflector 10 onto the surface to be scanned 17. Further, the imaging optical system 20 performs surface tilt correction of the deflection surface 10a by making the deflection surface 10a and the scanned surface 17 in a conjugate relationship in the sub-scan section.

  In the first imaging lens 20a according to the present embodiment, the lens surface (incident surface) on the deflector 10 side is a flat surface, and the lens surface (exit surface) on the scanned surface 17 side is in the main scanning section. And a circular arc shape in both the sub-scan section. On the other hand, the shape of each lens surface of the second imaging lens 20b in the main scanning section is represented by the following equation.

Here, the intersection of each lens surface and the optical axis is the origin, the optical axis is the X axis, the axis orthogonal to the optical axis in the main scanning section is the Y axis, and the axis orthogonal to the optical axis in the sub-scanning section is Z. The axis. R is a radius of curvature, K, B ₄ , B ₆ , B ₈ , and B ₁₀ are aspherical coefficients, the suffix s of each coefficient is the scanning start side, and e is the scanning end side. In the present embodiment, since the aspherical coefficients coincide on the scanning start side and the scanning end side, the shape of each lens surface in the main scanning section is symmetric with respect to the optical axis.

  In addition, the shape of each lens surface of the second imaging lens 20b in the sub-scan section is expressed by the following equation.

Here, r ′ is the radius of curvature in the sub-scan section, r is the radius of curvature on the axis in the sub-scan section, Mi is the aspheric coefficient, D ₂ , D ₄ , D ₆ , D ₈ , D ₁₀ are Curvature change coefficient, the subscript s of each curvature change coefficient indicates the scanning start side, and e indicates the scanning end side. In the sub-scan section, each lens surface of the second imaging lens 20b has an arc shape, and the curvature of each lens surface continuously changes from the scanning start side to the scanning end side.

  The reflection optical system 60 includes two folding mirrors (reflection optical elements). As shown in FIG. 2, the scanning light beam that has passed through the imaging optical system 20 is sequentially reflected by the first folding mirror 60 a and the second folding mirror 60 b, and guided to the scanned surface 17 through the dust-proof glass 16. Is done. In this way, by folding the optical path with the reflection optical system 60, the size of the optical scanning device 100 in the X direction can be reduced.

  Table 1 shows numerical values related to the optical scanning device 100 according to the present embodiment. In Table 1, the incident angle in each cross section indicates the incident angle when the light beam from the incident optical system 40 enters the deflecting surface 10a, and the focal length of the imaging optical system 20 is a value on the optical axis. Is shown. The rotation center coordinates of the deflector 10 are shown with the intersection (on-axis deflection point) between the deflection surface 10a and the principal ray having an image height of 0 (on-axis) as the origin. The rotation angle of the deflector 10 indicates an angle when deflecting the most off-axis light beam when the angle when deflecting the axial light beam is 0 °. In Table 1, d indicates the surface separation, and N indicates the refractive index.

(Synchronization detector)
FIG. 4 is an enlarged view of the synchronization detection unit 30 shown in FIG. The synchronization detection unit 30 includes a wedge prism 11 as a refractive optical element, a BD lens (light condensing element) 12, and a BD sensor (light receiving unit) 13. The wedge prism 11 is a wedge-shaped optical element in which the surface normal of the incident surface and the surface normal of the output surface are not parallel to each other in the main scanning section. Specifically, in the present embodiment, the surface normal of the entrance surface and the surface normal of the exit surface form an angle of 4 ° in the main scanning section. The BD lens 12 is an anamorphic lens including an anamorphic surface made of resin and having different powers in the main scanning section and the sub-scanning section.

  Table 2 shows numerical values related to the synchronization detection unit 30 according to the present embodiment.

  As shown in FIG. 1, the deflecting surface 10 a of the deflector 10 rotates in the direction of arrow A, so that the light beam deflected by the deflecting surface 10 a passes through the scanning surface 17 via the imaging optical system 20. It enters the synchronization detection unit 30 before scanning. At this time, the principal ray of the light beam (BD light beam) incident on the synchronization detection unit 30 is refracted by the wedge prism 11 in a direction away from the imaging optical system 20 in the main scanning section. In addition, since the wedge prism 11 which concerns on a present Example is the shape same as the prism 7 in the incident optical system 40, each can be manufactured with the same metal mold | die.

  The principal ray and other rays of the BD light beam refracted by the wedge prism 11 are condensed on the light receiving surface 13a of the BD sensor 13 by the BD lens 12 in the main scanning section. The BD sensor 13 generates a BD signal (synchronization detection signal) at the timing when the BD light beam is received, and outputs it to a synchronization control unit (not shown). The synchronization control unit determines a scanning start position (writing position) in the main scanning direction on the scanning surface 17 based on the BD signal, and controls the light emission timing (writing timing) of each light emitting point of the light source 1.

  As described above, according to the optical scanning device 100 according to the present embodiment, the imaging optical system 20 is reduced in size in the main scanning direction by adopting a configuration in which the BD light beam does not pass through the end of the imaging optical system 20. be able to. Even when the deflection surface 10a is small (the deflection angle is small), the wedge prism 11 refracts the principal ray of the BD light beam to avoid interference between the imaging optical system 20 and its holding member and the BD light beam. Therefore, the deflector 10 can be downsized.

  In this embodiment, the wedge prism 11 as a refractive optical element is employed to guide the BD light beam to the BD sensor 13 without using a mirror (reflection optical element). In general, the positional variation of the light beam caused by deformation due to mirror placement error or environmental variation is larger than the positional variation of the light beam caused by deformation due to refractive optical element placement or environmental variation. Therefore, according to the optical scanning device 100 according to the present embodiment, compared with the case where a mirror is provided in the synchronization detection unit 30, the occurrence of a shift in synchronization detection timing due to an arrangement error, environmental variation, and the like is suppressed. High-precision synchronization detection can be realized.

Here, in the main scanning section, the distance from the deflecting surface 10a to the wedge prism 11 is L _BD , and the angle between the principal ray of the BD light beam incident on the wedge prism 11 and the optical axis of the imaging optical system 20 is θ _BD. The distance from the deflecting surface 10a to the imaging optical system 20 is Ls. However, the distance _{L BD} indicates the distance from the deflecting surface 10a to the incident surface of the wedge prism 11, the distance Ls is the optical surface closest to the deflection surface 10a of the imaging optical system 20 from the deflection surface 10a (first sintering The distance to the incident surface) of the image lens 20a is shown. Further, the angle θ _BD indicates an angle when the principal ray of the BD light beam is directed toward the center of the light receiving surface 13a. At this time, the optical scanning device 100 according to the present embodiment satisfies the following conditional expression (1).
L _BD × cos θ _BD ≦ Ls (1)

By satisfying conditional expression (1), the principal ray can be refracted by the wedge prism 11 before the BD light beam deflected by the deflector 10 enters the imaging optical system 20. Thereby, even when an inexpensive deflector 10 having a smaller deflection surface 10a is employed, it is possible to avoid interference between the imaging optical system 20 and its holding member and the BD light beam. When the conditional expression (1) is not satisfied, the wedge prism 11 is disposed between the imaging optical system 20 and the surface to be scanned 17, so that the principal ray of the BD light beam is refracted by the wedge prism 11. The effect will not be obtained. In this embodiment, L _BD = 90 mm, θ _BD = 48 °, and Ls = 90 mm, so that L _BD × cos θ _BD = 60.2 <90.

Further, when the maximum scanning field angle of the deflector 10 corresponding to the effective scanning area on the scanned surface 17 is θ _max , it is desirable to satisfy the following conditional expression (2).
1.1 <θ _BD / θ _max <1.5 (2)

By satisfying the conditional expression (2), the deflection angle θ _BD of the BD light beam can be reduced to approach the maximum scanning field angle θ _max, and thus the deflection surface 10a can be reduced in size. Further, since the distance in the main scanning direction between the area for deflecting the scanning light beam and the area for deflecting the BD light beam on the deflection surface 10a can be reduced, even if the surface accuracy of the deflection surface 10a is low, a detection error is generated. It is possible to suppress the occurrence of jitter and the like. In this example, θ _max = 39.12 ° and θ _BD / θ _max = 1.23, which satisfies the conditional expression (2).

Further, θ _s is the angle formed between the principal ray incident on the extreme end of the incident surface of the first imaging lens 20a and the optical axis of the imaging optical system 20, and the optical axis of the incident optical system 40 and the imaging optical system. When the angle formed by the 20 optical axes is θ _i , the following conditional expression (3) is preferably satisfied. However, the endmost part of the incident surface of the first imaging lens 20a here is the endmost part on the BD sensor 13 side (light source 1 side).
θ _s <θ _BD <(θ _i −θ _s ) / 2 (3)

  If the lower limit of conditional expression (3) is not reached, there is a possibility that the scanning light beam toward the end of the effective scanning area on the scanned surface 17 and the wedge prism 11 interfere with each other. If the upper limit of conditional expression (3) is exceeded, there is a possibility that the BD light beam and the second diaphragm 6 interfere with each other.

  In the wedge prism 11, the angle formed by the surface normals of the entrance surface and the exit surface at the pass position of the principal ray of the BD light beam in the main scanning section is preferably 2 ° or more and 10 ° or less. If the angle is less than 2 °, there is a possibility that the effect of refracting the principal ray of the BD light beam may not be sufficiently obtained. The possibility of becoming large arises.

  The BD lens 12 according to the present embodiment focuses on the light receiving surface 13a of the BD sensor 13 in the main scanning section, but does not intentionally focus on the light receiving surface 13a in the sub scanning section (so as to be a rear pin). )doing. Thereby, it is possible to avoid erroneous detection when dirt, dust, or the like adheres on the light receiving surface 13a.

  Each optical surface of the BD lens 12 is decentered by 3 mm in the direction away from the imaging optical system 20 with respect to the optical axis of the synchronization detection unit 30. As a result, the BD light beam from the wedge prism 11 can be further separated from the imaging optical system 20, and the image forming lens 20a and its holding member and the BD light beam can be made less likely to interfere with each other. As shown in FIG. 4, in this embodiment, the light beam is emitted at a position 5.7 mm below the light collecting position 14 where the wedge prism 11 is not disposed and the BD lens 12 is not decentered. It can be condensed.

  Note that the oscillation wavelengths of the plurality of light emitting points in the light source 1 may differ from each other due to manufacturing errors or the like. For this reason, when each of the light beams from a plurality of light emitting points is individually detected synchronously, there is a possibility that a detection timing shift occurs for each light emitting point. Therefore, in this embodiment, by detecting only the light beam from one light emitting point and performing the synchronous control of each light emitting point based on the obtained BD signal, the detection timing shift for each light emitting point is reduced. Reduced.

  Here, among the light beams emitted from a plurality of light emitting points, the light beam that is most difficult to be placed at the end of the deflection surface 10a is a light beam emitted from the light emitting point LD32 arranged at the end shown in FIG. . Therefore, in this embodiment, by selecting the light emitting point LD32 as the detection target, it is possible to stabilize the light amount reaching the BD sensor 13 while miniaturizing the deflection surface 10a. Further, in this embodiment, instead of placing a slit at the light condensing position of the BD lens 12, the edge of the light receiving surface 13a of the BD sensor 13 is used as a knife edge, thereby reducing the number of parts and manufacturing errors of the slit. And a decrease in detection accuracy due to an arrangement error is suppressed. However, you may use a slit as needed.

(Conjugate point adjustment)
In this embodiment, the deflection surface 10a and the scanned surface 17 are conjugated in the sub-scan section, but when the oscillation wavelength of the light source 1 is changed, the conjugate relationship is broken. Therefore, when there is variation in the oscillation wavelength of each light emitting point of the light source 1, when the deflection surface 10a is tilted, the spacing in the sub-scanning direction between the scanning lines formed on the scanned surface 17 by each light flux Variation (pitch unevenness) occurs.

  In order to reduce such pitch unevenness, axial chromatic aberration in the sub-scan section of the imaging optical system 20 may be corrected. However, for this purpose, a plurality of glass lenses and diffractive optical elements are required, and the cost is reduced. Is undesirably raised. Therefore, in this embodiment, the deviation amount of the conjugate point position between the deflection surface 10a and the surface to be scanned 17 in the sub-scanning direction is measured. Then, as shown in FIG. 2, the occurrence of pitch unevenness is suppressed by adjusting the optical path length from the deflecting surface 10a to the scanned surface 17 by moving the folding mirror 60b based on the deviation amount. .

  In addition to the change in the oscillation wavelength, pitch unevenness also occurs due to an arrangement error of the imaging lens and the folding mirror. For example, when the imaging lens and the folding mirror are arranged while being tilted, the amount of deviation of the conjugate point differs between the scanning start side and the scanning end side. Therefore, it is desirable that the position of the folding mirror 60b can be adjusted independently on the scanning start side and the scanning end side.

  In this embodiment, a feed screw is provided on each of the scanning start side and the scanning end side of the folding mirror 60b, whereby the position of the folding mirror 60b is adjusted, and the change in the oscillation wavelength and the arrangement error of each member are reduced. It is possible to suppress the occurrence of pitch unevenness due to both. In this embodiment, since the light beam traveling toward the synchronization detection unit 30 does not pass through the folding mirror 60b, even if the adjustment is performed, there is no influence on the synchronization detection.

  As described above, according to the optical scanning device 100 according to the present embodiment, by using the refractive optical element, the BD light beam from the deflector 10 is received by other members without using the reflective optical element. The light can be guided to the surface 13a. This makes it possible to suppress a change in the arrival position of the BD light beam on the light receiving surface 13a caused by an arrangement error, environmental fluctuation, and the like as compared with the case where a reflective optical element is used. Accurate synchronization detection can be realized.

[Example 2]
Hereinafter, the optical scanning device according to the second embodiment of the present invention will be described in detail. Since the optical scanning device according to the present embodiment is the same as the configuration of the optical scanning device 100 according to the first embodiment except for the synchronization detection unit, the description thereof is omitted.

  FIG. 5 is a cross-sectional view of a main part of the synchronization detection unit 32 according to the present embodiment. The synchronization detection unit 32 according to the present embodiment is different from the synchronization detection unit 30 according to the first embodiment in that a wedge prism and a BD lens are integrated. Specifically, the synchronization detection unit 32 includes one BD lens 18 as a refractive optical element, and the BD lens 18 has the functions of both the wedge prism 11 and the BD lens 12 according to the first embodiment. Yes. That is, the BD lens 18 condenses the light beam deflected by the deflector 10 on the light receiving surface 13a of the BD sensor 13 while refracting the light beam deflected by the deflector 10 in the direction away from the imaging optical system 20 in the main scanning section.

  Table 3 shows numerical values related to the synchronization detection unit 32 according to the present embodiment.

  Similar to the BD lens 12 according to the first embodiment, the BD lens 18 is an anamorphic lens made of resin. The BD lens 18 focuses on the light receiving surface 13a in the main scanning section, and focuses on the light receiving surface 13a in the sub-scanning section. I try not to match. However, each lens surface of the BD lens 18 has a shape obtained by cutting out a part of the reference lens surface having the radius of curvature shown in Table 3. The normal line at the surface vertex (not shown) of each reference lens surface forms an angle of 8 ° in the main scanning section. Thus, by providing the BD lens 18 with the function of a wedge prism, the number of parts constituting the synchronization detection unit 32 can be reduced.

In this embodiment, the distance L _BD = 93 mm from the deflecting surface 10a to the BD lens 18 and the values of θ _BD and Ls are the same as those in the first embodiment, and therefore L _BD × cos θ _BD = 62.2 <90. Conditional expression (1) is satisfied. Moreover, since the value of θ _max is the same as that of the first embodiment, the conditional expression (2) is satisfied. As shown in FIG. 5, in this embodiment, the light beam can be condensed at a position 5.3 mm below the light beam condensing position 14 when the BD lens 18 is not disposed.

  As described above, according to the optical scanning device according to the present embodiment, it is possible to realize downsizing and high-precision synchronization detection with fewer parts than the optical scanning device according to the first embodiment.

[Example 3]
Hereinafter, an optical scanning device according to a third embodiment of the present invention will be described in detail. Since the optical scanning device according to the present embodiment is the same as the configuration of the optical scanning device according to the first embodiment except for the synchronization detection unit, description thereof will be omitted.

  FIG. 6 is a cross-sectional view of a main part of the synchronization detection unit 33 according to the present embodiment. Similar to the synchronization detection unit 32 according to the second example, the synchronization detection unit 33 according to the present example includes one BD lens 19 having the functions of both the wedge prism 11 and the BD lens 12 according to the first example. ing. Unlike the BD lens 18 according to the second embodiment, the BD lens 19 includes a diffraction surface provided with a diffraction grating.

  Table 4 shows numerical values related to the synchronization detection unit 33 according to the present embodiment.

  Similar to the BD lens 18 according to the second embodiment, the BD lens 19 according to the present embodiment has an angle of 8 ° with respect to the normal line of each of the reference lens surfaces of the entrance surface and the exit surface in the main scanning section. This is a wedge prism-shaped anamorphic lens. Also in this embodiment, as in the second embodiment, the conditional expressions (1) and (2) are satisfied. As shown in FIG. 6, in this embodiment, the light beam can be condensed at a position 5.3 mm below the light beam condensing position 14 when the BD lens 19 is not disposed. The exit surface of the BD lens 19 is a blazed diffractive surface represented by the following optical path difference function.

Here, m is the diffraction order, λ is the oscillation wavelength of the light source 1, and E _{1 to} E ₁₀ and F _{0 to} F ₁₀ are phase coefficients. By providing the BD lens 19 with a diffractive surface, it is possible to correct lateral chromatic aberration and to reduce the synchronization detection timing shift caused by the change in the oscillation wavelength of the light source 1 due to the environmental change (temperature change). In addition, instead of providing a diffractive surface, it is also possible to correct lateral chromatic aberration using a prism or the like. However, in this case, since the degree of freedom of arrangement of each member is reduced due to an increase in the number of parts, this embodiment It is desirable to employ a diffractive surface as shown in FIG.

In this embodiment, the diffraction order m = 1, and the phase coefficient of the diffractive surface is determined so as to cancel the lateral chromatic aberration generated on the refracting surface of the BD lens 19. Specifically, the diffraction grating is designed using only the first-order y coefficient (E ₁ and F ₁ ), and the grating pitch is constant at 246 μm. This facilitates the processing of the mold when forming the diffractive surface and the release of the diffractive surface from the mold, and as a result, the manufacture of the diffractive surface can be facilitated.

  FIG. 7 is a diagram showing chromatic aberration of magnification on the light receiving surface 13a according to each of the above-described embodiments. In FIG. 7, the vertical axis indicates the imaging position shift in the main scanning direction on the light receiving surface 13 a, and the horizontal axis indicates the oscillation wavelength of the light source 1. As shown in FIG. 7, in this embodiment, it is possible to suppress the occurrence of image formation position shift when the oscillation wavelength of the light source 1 changes.

The imaging position shift in the main scanning direction on the light receiving surface 13 a is δY, the focal lengths in the main scanning section of the imaging optical system 20 and the synchronization detection unit 33 are f and f _BD , respectively, and the resolution of the optical scanning device 100. Is DPI, it is desirable to satisfy the following conditional expression (3).
(F / f _BD ) × δY ≦ (25.4 / DPI) / 2 (3)

In the left side of the conditional expression (3), the imaging position deviation δY on the light receiving surface 13a is enlarged on the scanned surface 17 in accordance with the ratio of the focal length of the imaging optical system 20 to the focal length of the synchronization detector 33. It shows that. By satisfying conditional expression (3), it is possible to suppress the enlarged image formation position shift on the scanned surface 17 to ½ or less of the dot (pixel) pitch determined by the print resolution DPI. It becomes possible to obtain a simple image. When conditional expression (3) is modified, the following conditional expression (4) is obtained.
δY ≦ (25.4 / DPI) / 2 × (f _BD / f) (4)

In this embodiment, f = 250 (mm), f _BD = 76.8 (mm), DPI = 2400 (dpi), and (25.4 / 2400) / 2 × (76.8 / 250) = 1.63 (μm). Therefore, it is desirable to set the upper limit value of the imaging position deviation δY on the light receiving surface 13a to 1.63 (μm) and to determine the allowable amount of change in the oscillation wavelength of the light source 1 accordingly.

  At this time, as shown in FIG. 7, in the present embodiment, the chromatic aberration of magnification of the synchronization detection unit 33 is reduced using a diffraction surface, so that the light source 1 of the light source 1 is compared with the first and second embodiments. The allowable amount of change in oscillation wavelength is increased. Thereby, an inexpensive laser having a large variation in oscillation wavelength between light emitting points, an edge emitting laser having a large change in oscillation wavelength due to environmental change (temperature change), and the like can be used as the light source 1.

  Further, in the present embodiment, unlike the first and second embodiments, all the light beams emitted from the light emitting points LD1 to LD32 in the light source 1 are detected by the synchronization detection unit 33. This eliminates the need to calculate the light emission timing of each light emission point based on one BD signal as in the first and second embodiments, and reduces the capacity of the memory for holding the data of each light emission timing. Therefore, the cost of the synchronization control unit can be reduced.

  As described above, according to the optical scanning device according to the present embodiment, the allowable amount of the change in the oscillation wavelength of the light source 1 can be made larger than that of the optical scanning device according to the second embodiment, and high printing accuracy can be realized with an inexpensive configuration. it can.

[Image forming apparatus]
FIG. 8 is a schematic diagram (ZX cross-sectional view) of a main part of the image forming apparatus 80 according to the embodiment of the present invention. The image forming apparatus 80 includes four optical scanning devices according to any of the first to third embodiments described above, and records image information on the photosensitive surfaces (scanned surfaces) of the four photosensitive drums (photosensitive members) in parallel. This is a tandem type color image forming apparatus.

  The image forming apparatus 80 includes a printer controller 83, optical scanning devices 101, 102, 103, 104, photosensitive drums 201, 202, 203, 204, developing devices 301, 302, 303, 304, a conveyance belt 81, And a fixing device 84. Here, the optical scanning devices 101 to 104 are arranged so that the sub-scanning direction coincides with the Z direction that is the rotation direction of each of the photosensitive drums 201 to 204.

  As shown in FIG. 8, R (red), G (green), and B (blue) color signals are output from an external device 82 such as a personal computer. Each color signal is converted into image data (dot data) of Y (yellow), M (magenta), C (cyan), and K (black) by the printer controller 83 and input to the optical scanning devices 101-104. The printer controller 83 controls not only the signal conversion described above but also each part of the image forming apparatus 80 such as a motor described later.

  Each of the optical scanning devices 101 to 104 causes the photosensitive surfaces of the photosensitive drums 201 to 204 as image carriers to move in the main scanning direction (Y) by the light beams 401, 402, 403, and 404 modulated according to each image data. Direction). Each of the photosensitive drums 201 to 204 is rotated clockwise by a motor (not shown), and along with this rotation, each photosensitive surface moves in the sub-scanning direction (Z direction) with respect to the light beams 401 to 404. By exposing each photosensitive surface charged by a charging roller (not shown) with each of the light beams 401 to 404, an electrostatic latent image is formed on each photosensitive surface.

  Thereafter, the electrostatic latent images of the respective colors formed on the photosensitive surfaces of the photosensitive drums 201 to 204 are developed as toner images of the respective colors by the developing units 301 to 304, respectively. Then, the toner images of the respective colors are multiplexed and transferred onto the transfer material conveyed by the conveying belt 81 by a transfer device (not shown), and then fixed by the fixing device 84. One full color image is formed by the above process.

  The image forming apparatus 80 employs a configuration including four optical scanning devices that optically scan one surface to be scanned with one deflector as shown in the first to third embodiments. It is not limited. For example, a configuration including one optical scanning device that optically scans four scanned surfaces using one deflector, or a configuration including two optical scanning devices that optically scan two scanned surfaces using one deflector. It may be adopted. In addition, a color digital copying machine may be configured by connecting a color image reading apparatus including a line sensor such as a CCD sensor or a CMOS sensor to the image forming apparatus 80 as an external device 82.

[Modification]
The preferred embodiments and examples of the present invention have been described above, but the present invention is not limited to these embodiments and examples, and various combinations, modifications, and changes can be made within the scope of the gist.

  For example, in each embodiment, one scanned surface is optically scanned with a light beam from one light source. However, the present invention is not limited thereto, and a plurality of scanned surfaces are optically scanned with light beams from a plurality of light sources. May be adopted. At this time, a configuration in which a plurality of light beams are simultaneously deflected by a plurality of deflection surfaces of the deflector may be employed. In each optical path from the deflection surface to the plurality of scanned surfaces, the imaging lenses may be individually arranged, or the imaging lenses may be integrated and shared by the optical paths. Note that the number, material, and shape of the imaging lens may be appropriately changed according to the configuration of the optical scanning device.

  As shown in FIG. 1, the synchronization detection unit according to each embodiment is disposed on the same side as the light source with respect to the optical axis of the imaging optical system (scanning upstream side of the imaging optical system). However, it may be arranged on the side opposite to the light source (on the downstream side of the imaging optical system) as necessary. However, since the detection error can be reduced if synchronous detection is performed immediately before the light beam deflected by the deflector enters the imaging optical system, that is, immediately before writing on the scanning surface, imaging is performed. More preferably, the synchronization detection unit is disposed upstream of the optical system.

  In each of the embodiments, the synchronization control unit that controls the light emission timing of the light source based on the BD signal from the synchronization detection unit may be arranged inside the optical scanning device, or outside the optical scanning device and in the image. It may be arranged inside the forming apparatus. In addition, the control unit may be shared by the light amount detection unit and the synchronization detection unit, and both the light amount control and the light emission timing control of the light source may be performed by one control unit.

  In the first embodiment, the prism 7 in the incident optical system 40 and the wedge prism 11 in the synchronization detection unit 30 have the same shape, but those having different shapes are used as necessary. May be. For example, in the first embodiment, each optical surface of the wedge prism 11 is a flat surface, but each optical surface may have power as necessary. However, in order to make it possible to use the same mold and to facilitate manufacture, it is preferable to adopt the same shape as each prism, and it is more preferable to make each optical surface flat.

  Furthermore, at least one of the optical surfaces of the wedge prism 11 and the BD lens 12 according to the first embodiment may be a diffractive surface as in the third embodiment. Further, when the BD lens 12 is decentered, not only the shift decentering but also the shift decentering and / or tilt decentering may be performed. And the position of the wedge prism 11 in the synchronous detection part 30 should just satisfy | fill the said conditional expression (1), and may replace it with the position of the BD lens 12 as needed. In addition, in the optical path from the deflector 10 to the synchronization detection unit 30, a reflection optical element such as a mirror may not be disposed, and another refractive optical element may be provided as necessary.

DESCRIPTION OF SYMBOLS 10 Deflector 11 Refractive optical element 13 Light-receiving part 17 Surface to be scanned 20 Imaging optical system 100 Optical scanning device

Claims (21)

A deflector that deflects a light beam and optically scans the surface to be scanned in the main scanning direction;
An imaging optical system for guiding the light beam deflected by the deflector to the surface to be scanned;
A light receiving unit that receives a light beam deflected by the deflector and generates a signal;
A refracting optical element that refracts the principal ray of the light beam deflected by the deflector in a direction away from the imaging optical system in a main scanning section and guides it to the light receiving surface of the light receiving unit;
In the main scanning section, the distance from the deflecting surface of the deflector to the incident surface of the refractive optical element is L _BD , and the principal ray of the light beam incident on the refractive optical element when traveling toward the center of the light receiving surface and the concatenation. When the angle formed by the optical axis of the image optical system is θ _BD , and the distance from the deflection surface to the optical surface closest to the deflection surface of the imaging optical system is Ls,
L _BD × cos θ _BD ≦ Ls
An optical scanning device characterized by satisfying the following conditions. When the maximum scanning field angle of the deflector corresponding to the effective scanning area on the scanned surface is θ _max ,
1.1 <θ _BD / θ _max <1.5
The optical scanning device according to claim 1, wherein the following condition is satisfied.   3. The optical scanning according to claim 1, wherein in the refractive optical element, surface normals of an incident surface and an exit surface at a position where the principal ray passes are non-parallel to each other in a main scanning section. apparatus.   4. The optical scanning device according to claim 1, wherein the refractive optical element includes a refractive surface having power.   5. The optical scanning device according to claim 4, wherein the refractive optical element includes an anamorphic surface having different powers in the main scanning section and the sub-scanning section.   4. The optical scanning device according to claim 1, wherein an entrance surface and an exit surface of the refractive optical element are flat surfaces. 5.   The optical scanning device according to claim 6, further comprising a condensing element including a refractive surface having power.   The optical scanning device according to claim 7, wherein the condensing element includes an optical surface decentered in a direction away from the imaging optical system in a main scanning section.   The optical scanning device according to claim 7, wherein the condensing element includes a diffractive surface.   The optical scanning device according to claim 1, wherein the refractive optical element includes a diffractive surface.   11. The optical scanning device according to claim 1, wherein the refractive optical element is disposed on the same side as the light source with respect to the optical axis of the imaging optical system.   The optical scanning device according to claim 1, wherein the light receiving unit generates a signal for determining a write start position in the main scanning direction on the surface to be scanned.   The optical scanning device according to claim 1, further comprising a control unit that determines a writing position in the main scanning direction on the surface to be scanned based on the signal.   14. The optical scanning device according to claim 1, further comprising an incident optical system that guides a light beam from a light source to the deflector.   The optical scanning apparatus according to claim 14, wherein the incident optical system includes a branching optical element that transmits a light beam from the light source and guides the light beam to the deflector.   The optical scanning device according to claim 15, further comprising a light amount detection unit that receives a light beam reflected by an incident surface of the branch optical element and generates a signal for controlling a light emission amount of the light source.   16. The optical scanning device according to claim 14, wherein the refractive optical element and the branching optical element have the same shape. The angle formed between the principal ray of the light beam incident on the end of the optical surface closest to the deflection surface of the imaging optical system on the light receiving portion side and the optical axis of the imaging optical system is θ _s . When the angle formed by the optical axis of the image optical system and the optical axis of the incident optical system is θ _i ,
θ _s <θ _BD <(θ _i −θ _s ) / 2
The optical scanning device according to claim 14, wherein the following condition is satisfied.   The angle formed by the surface normals of the entrance surface and the exit surface at the pass position of the principal ray in the main scanning section of the refractive optical element is 2 ° or more and 10 ° or less. The optical scanning device according to any one of 18.   20. The optical scanning device according to claim 1, a developing device that develops an electrostatic latent image formed on the scanned surface by the optical scanning device as a toner image, and the developed toner An image forming apparatus comprising: a transfer device that transfers an image to a transfer material; and a fixing device that fixes the transferred toner image to the transfer material.   20. The optical scanning device according to claim 1, and a printer controller that converts a color signal output from an external device into image data and inputs the image data to the optical scanning device. Image forming apparatus.

Images