Optical scanning device and image forming apparatus

Abstract

The invention relates to an optical scanning device and an image forming apparatus. The optical scanner includes: a deflector that deflects a beam from a light source to scan a surface to be scanned in a main scanning direction; and a first element closest to the surface to be scanned and guiding a beam to the surface to be scanned, in which a thickness of the first element in an optical axis direction in a main scanning cross section varies in a main scanning direction, the first element including an optical surface to which a normal on the main scanning cross section is inclined, a normal inclination amount varies in the main scanning direction, in a region on one side of the optical surface with respect to the optical axis in the main scanning direction, a position in the main scanning direction at which the distance in the optical axis direction between both ends of the effective region of the optical surface in the sub-scanning direction is maximum in the sub-scanning cross-section; a position in the main scanning direction at which the thickness of the first element in the optical axis direction is maximum in the main scanning cross-section; and the maximum image height in the main scanning direction on the surface to be scanned is appropriately set.

Description

Technical Field

[0001] The present disclosure relates to an optical scanning device and is particularly suitable for an image forming device such as a laser beam printer (LBP), a digital copier, or a multifunction printer (MFP). Background Art

[0002] Conventionally, in order to miniaturize an optical scanning apparatus for a color image forming apparatus, an optical system (sub-scanning oblique incidence system) has been adopted in which a plurality of light beams emitted from a plurality of light sources are obliquely incident on a deflector in a sub-scanning cross section.

[0003] Japanese Patent Application Laid-Open No. 2010-140011 discloses a technique for correcting curvature of a scanning line and wavefront aberration in a sub-scanning oblique-incidence system by setting an optical surface of an image forming optical element as a sagittal line tilt changing surface. Summary of the Invention

[0004] According to an embodiment of the present disclosure, an optical scanning device is provided, comprising: a deflector that deflects a light beam from a light source to scan a scanned surface in a main scanning direction; and an optical system comprising at least one optical element that guides the light beam from the deflector to the scanned surface, wherein the at least one optical element comprises a first optical element that is disposed closest to the scanned surface, wherein a thickness of the first optical element in an optical axis direction in a main scanning cross section varies in the main scanning direction, wherein the first optical element comprises an optical surface whose normal on the main scanning cross section is inclined relative to the main scanning cross section, wherein an amount of inclination of the normal of the optical surface varies in the main scanning direction, wherein in a region of the optical surface on one side relative to the optical axis in the main scanning direction, the following inequality is satisfied,

[0005] 0.0≤|y |Δs|max1 -y dmax1 | / W1≤0.1

[0006] where y |Δs|max1 represents the position relative to the optical axis in the main scanning direction where the distance between one end and the other end of the effective area in the sub-scanning direction of the optical surface in the optical axis direction is the largest, y dmax1 represents the position relative to the optical axis in the main scanning direction where the thickness of the first optical element in the optical axis direction in the main scanning cross section is maximum, and W1 represents the maximum image height in the main scanning direction on the scanned surface.

[0007] Further features of the present disclosure will become apparent from the following description of exemplary embodiments with reference to the attached drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1A is a sub-scanning cross-sectional view of the optical scanning device according to the first embodiment.

[0009] Figure 1B is a developed view in main scanning cross section of the optical scanning device according to the first embodiment.

[0010] Figure 1C is a developed view in a sub-scanning cross section of the optical scanning device according to the first embodiment.

[0011] Figure 2A is a diagram for explaining a sub-scan cross-sectional view of the image pickup lens according to the first embodiment.

[0012] Figure 2B : are diagrams for explaining aberrations |Δs|(y) and d(y) of the image pickup lens according to the first embodiment.

[0013] Figure 3A is a diagram illustrating |Δs|(y) of the image pickup lens according to the first embodiment.

[0014] Figure 3B is a diagram illustrating d(y) of the image pickup lens according to the first embodiment.

[0015] Figure 4 is a diagram illustrating field curvature of the optical scanning device according to the first embodiment.

[0016] Figure 5 is a diagram illustrating fθ characteristics of the optical scanning device according to the first embodiment.

[0017] Figure 6 is a diagram illustrating bending of a scanning line of the optical scanning device according to the first embodiment.

[0018] Figure 7 : is a diagram illustrating astigmatism in a 45-degree direction of the optical scanning device according to the first embodiment.

[0019] Figure 8 is a diagram illustrating an image plane illuminance distribution of the optical scanning device according to the first embodiment.

[0020] Figure 9A is a sub-scanning cross-sectional view of the optical scanning device according to the second embodiment.

[0021] Figure 9B is a developed view of a main scanning cross section of the optical scanning device according to the second embodiment.

[0022] Figure 9C is a developed view of a sub-scanning cross section of the optical scanning device according to the second embodiment.

[0023] Figure 10A is a diagram illustrating an image plane illuminance distribution of the optical scanning device according to the second embodiment.

[0024] Figure 10B is a diagram illustrating an image plane illuminance distribution of the optical scanning device according to the second embodiment.

[0025] Figure 10C is a diagram illustrating an image plane illuminance distribution of the optical scanning device according to the second embodiment.

[0026] Figure 10D is a diagram illustrating an image plane illuminance distribution of the optical scanning device according to the second embodiment.

[0027] Figure 11 It is a sub-scan cross-sectional view of the color image forming apparatus. DETAILED DESCRIPTION

[0028] Hereinafter, the optical scanning device according to the present embodiment will be described in detail with reference to the accompanying drawings. To facilitate understanding of the present embodiment, the following drawings may be drawn in a scale different from the actual scale.

[0029] In the following description, the main scanning direction (Y direction) is a direction perpendicular to the rotation axis (or oscillation axis) of the deflector and the optical axis (X direction) of the optical system (the direction in which the light beam is reflected by the rotating polygon mirror and deflected (deflected for scanning)). The sub-scanning direction (Z direction) is a direction parallel to the rotation axis (or oscillation axis) of the deflector. The main scanning cross section is a section perpendicular to the sub-scanning direction and including the optical axis. The sub-scanning transverse cross section is a section perpendicular to the main scanning direction.

[0030] The present disclosure relates to an optical scanning device, and particularly to an image forming device such as a laser beam printer (LBP), a digital copier, or a multifunction printer (MFP).

[0031] Conventionally, in order to miniaturize optical scanning devices for color image forming apparatuses, an optical system (sub-scanning oblique-incidence system) has been adopted in which multiple light beams emitted from multiple light sources are obliquely incident on a deflector in a sub-scanning cross section. Japanese Patent Application Laid-Open No. 2010-140011 discloses a technology for correcting the curvature of the scan line and wavefront aberration in the sub-scanning oblique-incidence system by providing an optical surface of an image forming optical element with a sagittal tilt changing surface.

[0032] However, when the sagittal line tilt is used to change the surface as in Japanese Patent Application Laid-Open No. 2010-140011, the thickness of the image forming optical element in the optical axis direction in the sub-scanning cross section becomes uneven in the sub-scanning direction. Therefore, when the amount of birefringence in the sub-scanning cross section of the image forming optical element changes in the sub-scanning direction, causing the position of the light beam passing through the image forming optical element to fluctuate in the sub-scanning direction due to arrangement errors, etc., optical performance deteriorates.

[0033] An advantage of some aspects of the embodiments is that an optical scanning device with excellent optical performance is provided.

[0034] [First embodiment]

[0035] Figure 1A 、 Figure 1B and Figure 1C 1 and 2 are respectively a sub-scanning portion cross-sectional view, a developed view in a main scanning portion cross-sectional view, and a developed view in a sub-scanning portion cross-sectional view of the optical scanning device 100 according to the first embodiment.

[0036] The optical scanning device 100 of the present embodiment includes a light source 1A, an incident optical system LA, a deflector 5 , an image forming optical system SA (first optical system), and a reflection mirror (reflective optical element) M1 .

[0037] The optical scanning device 100 according to the present embodiment uses a so-called sub-scanning oblique-incidence optical system in which the light beam RA is deflected by the deflector 5 to scan the scanned surface 8A and is obliquely incident on the deflector 5 in the sub-scanning direction.

[0038] As the light source 1A, a semiconductor laser or the like is used. The number of light emitting points of the light source 1A may be one or more.

[0039] The incident optical system LA includes an anamorphic lens 2A, a sub-scanning aperture stop 3A, and a main-scanning aperture stop 4A.

[0040] The anamorphic lens 2A converts the light beam RA emitted from the light source 1A into a parallel beam in the main scanning cross section and converges the parallel beam in the sub-scanning direction. Here, the parallel beam includes not only an exact parallel beam but also a substantially parallel beam such as a weakly diverging beam or a weakly converging beam. A collimating lens or a cylindrical lens may be used instead of the anamorphic lens 2A.

[0041] Sub-scanning aperture stop 3A limits the diameter of light beam RA having passed through anamorphic lens 2A in the sub-scanning direction. Similarly, main-scanning aperture stop 4A limits the beam diameter of light beam RA having passed through sub-scanning aperture stop 3A in the main-scanning direction.

[0042] The deflector 5 is rotated in the direction of arrow A in the figure by a driving unit such as a motor (not shown), so that the deflector 5 deflects the incident light beam RA and scans the scanned surface 8A in the direction of arrow B in the figure. The deflector 5 is composed of, for example, a polygonal mirror.

[0043] In the image forming optical system SA, the deflected light beam RA deflected and reflected by the deflecting surface 5A of the deflector 5 passes through the image forming lenses (optical elements) 6A and 7A and is then reflected by the reflecting mirror M1 to be guided to the scanned surface 8A. The image forming optical system SA includes the image forming lens 7A (first optical element) as an optical element disposed at a position closest to the scanned surface 8A on the optical path of the deflected light beam RA deflected and reflected by the deflecting surface 5A.

[0044] The reflecting mirror M1 is a component for reflecting a light beam, and an evaporation mirror or the like is used as the reflecting mirror M1. In addition, the effect of the present embodiment is not limited to the number of reflecting mirrors, and the number of reflecting mirrors can be changed appropriately.

[0045] Here, C0 in the figure is the deflection point (on-axis deflection point) at which the principal ray of the on-axis light beam is deflected, and P0 is a plane (reference plane) that passes through the deflection point C0 and is perpendicular to the rotation axis of the deflector 5. The light beam RA incident on the deflection surface 5a is deflected at the deflection point C0 in the sub-scan cross section so as to intersect with the main-scan cross section. Hereinafter, the length of the optical path from the deflection point C0 to each scanned surface is referred to as the optical path length of each image forming optical system.

[0046] Next, the specifications, optical arrangement, and optical surface shape of the optical scanning device 100 according to this embodiment are shown in Tables 1 to 3 below. Table 1 shows the specifications and lens arrangement of the incident optical system LA and the image forming optical system SA, while Tables 2 and 3 show the optical surface shapes of the incident optical system LA and the image forming optical system SA. It should be noted that the column "Optical arrangement" in Table 1 shows the coordinates of the reflection point on each reflector of the light beam RA directed toward the center (on-axis image height) of the image in the main scanning direction on the scanned surface 8A.

[0047] In Tables 1 and 2, the optical axis direction when the intersection of each optical surface and the optical axis is defined as the origin, the axis orthogonal to the optical axis in the main scanning cross section, and the axis orthogonal to the optical axis in the sub-scanning cross section are defined as the x-axis, y-axis, and z-axis, respectively. Here, the direction of light travel corresponds to the positive x side of the x-axis, and the light source side relative to the optical axis corresponds to the positive y side of the y-axis. In Table 3, "Ex" means "×10 -x ”.

[0048] [Table 1]

[0049]

[0050] [Table 2]

[0051]

[0052] [Table 3]

[0053]

[0054] Although temperature compensation is performed by forming a diffraction surface on the incident surface of the anamorphic lens 2A, the effect of this embodiment is not limited to this configuration. The incident surface of the anamorphic lens 2A is a rotationally asymmetric diffraction surface, and the phase function Φ of the diffraction grating is expressed by the following equation (1),

[0055]

[0056] Here, k = 1. In addition, λ is a wavelength, and it is assumed here that λ is 790 nm.

[0057] The image forming lenses 6A and 7A according to the present embodiment are optical elements made of resin, and the meridian shape of each optical surface (the shape of the optical surface in the main scanning cross section) is an aspherical shape that can be expressed as a function up to the tenth order of the position x in the optical axis direction relative to the position y in the main scanning direction, as expressed by Expression (2),

[0058]

[0059] Wherein R represents the meridian curvature radius, K represents the eccentricity, and Bi (i=1, 2, . . . , 10) is the aspheric coefficient.

[0060] The image forming lenses 6A and 7A according to the present embodiment are optical elements made of a resin material, but are not limited to optical elements made of only resin and may contain components other than resin, such as inorganic microparticles (the main component of which may be resin). It is preferable but not necessary that the image forming lenses 6A and 7A be made of a resin material. The image forming lenses 6A and 7A may be made of a glass material as needed.

[0061] Furthermore, in this specification, a meridian refers to a shape in a main scanning cross section of an optical element.

[0062] The shape of the sagittal line shape of each of the optical surfaces of the image forming lenses 6A and 7A according to this embodiment (the shape of the optical surface in the sub-scan cross section at arbitrary image height (y) and z) is an aspherical shape, which is expressed by the following expression (3).

[0063]

[0064] Where S represents the sagittal line shape defined in the sub-scan cross section at each position on the meridian, and m i,j (i = 1, 2, ..., 10 and j = 1) represents the aspheric coefficient. The term composed of the first-order function of z is a term that gives the amount of tilt in the sagittal direction (sagittal tilt). Here, sagittal tilt is the deviation of the normal line on the main scanning cross section of the optical surface.

[0065] The sagittal curvature radius r' is the curvature radius in the sub-scan cross section, and changes continuously according to the y coordinate of the optical surface as described in the following equation (4),

[0066]

[0067] Wherein r represents the curvature radius (sagittal curvature radius) in the sub-scanning cross section on the optical axis, and Ei (i=1, 2, . . . , 10) represents the coefficient of change of the sagittal line.

[0068] Next, the effects of the optical scanning device 100 according to the present embodiment will be described.

[0069] In the optical scanning device 100 according to the present embodiment, a sub-scanning oblique-incidence optical system is adopted, and it is necessary to correct the curvature of the scanning line and the difference in the amount of wavefront aberration in the azimuth angle ±45 degrees (astigmatism in the 45-degree direction) generated by the sub-scanning oblique-incidence optical system. Therefore, as shown in Tables 2 and 3, the incident surface and the exit surface of the image forming lens (first image forming optical element) 7A according to the present embodiment include aspheric coefficients m i,1 (≠0), so that correction is performed on the sagittal line inclination change surface in which the sagittal line inclination amount changes in the main scanning direction (y-axis direction).

[0070] Note that, in this specification, a sagittal line tilt changing surface is an optical surface in which the amount of sagittal line tilt changes from an on-axis position to an off-axis position.

[0071] The incident surface and the exit surface of the image forming lens 7A according to the present embodiment are formed in shapes in the sub-scan cross section by sagittal line inclination changing surfaces that are tilted in directions different from each other with respect to a plane perpendicular to the optical axis.

[0072] When using a sagittal line tilt changing surface, the curvature of the scan line can be corrected by appropriately setting the sagittal line tilt at each beam passing position and controlling the irradiation position on the scanned surface 8A. Similarly, by setting the inclination of the optical surface according to the inclination of the incident wavefront, astigmatism in the 45-degree direction can be corrected. In other words, by configuring both the incident and exit surfaces as sagittal line tilt changing surfaces, both the curvature of the scan line and astigmatism in the 45-degree direction can be satisfactorily corrected.

[0073] However, as a result of correcting the curvature of the scanning line and the astigmatism in the 45-degree direction, when the sagittal line of the incident surface is inclined and the sagittal line of the exit surface is inclined as shown in FIG. Figure 2A , when shown with mutually different symbols, the image forming lens 7A has a shape with uneven thickness in the optical axis direction in the sub-scan cross section (uneven thickness shape). When a lens having such an uneven thickness shape is molded by injection molding, the amount of birefringence is generally different in the sub-scan direction. Then, because the birefringence fluctuates when the passing position of the light beam passing through the image forming lens 7A fluctuates in the sub-scan direction due to an assembly error of the image forming lens 7A, etc., the optical performance also fluctuates and deteriorates. When a laser is used for the light source 1A, the polarization state of the light beam RA changes due to the birefringence, and the reflectivity of the light beam also changes due to the polarization reflection characteristics of the reflector M1, and as a result, unevenness of the amount of light on the scanned surface 8A occurs.

[0074] Therefore, when the position y in the main scanning direction on the optical surface is divided into a positive area (y ≥ 0, an area on one side) and a negative area (y < 0, an area on the opposite side), the optical surface of the image forming lens 7A according to the present embodiment satisfies the inequality (5) in at least one area, 0.0 ≤ |y |Δs|max -y dmaxl | / W≤0.1…(5)

[0075] where y |Δs|max represents y (position relative to the optical axis in the main scanning direction) at which |Δs|(y) is maximized when |Δs|(y) is the interval in the optical axis direction (the absolute value of the difference in position) between one end and the other end in the sub-scanning direction of the effective area of the optical surface in the sub-scanning cross section at position y in the main scanning direction on the optical surface, y dmax represents the position y (position relative to the optical axis in the main scanning direction) where the thickness (d(y)) in the optical axis direction of the image forming lens on the meridian line at the position y in the main scanning direction becomes the largest, and w represents the maximum image height in the main scanning direction on the scanned surface (the outermost off-axis image height).

[0076] More specifically, in a region on one side relative to the optical axis in the main scanning direction of the sagittal line inclination change surface, the following inequality is satisfied,

[0077] 0.0≤|y |Δs|max1 -y dmax1 | / W1≤0.1

[0078] where y |Δs|max1 The position y in the main scanning direction relative to the optical axis where the distance between one end and the other end of the effective area of the sagittal line tilt change surface in the sub-scanning cross section in the optical axis direction is the largest, dmax1 represents the position relative to the optical axis in the main scanning direction where the thickness of the image forming lens 7A in the optical axis direction in the main scanning cross section is the largest, and W1 represents the maximum image height on one side in the main scanning direction on the scanned surface.

[0079] Furthermore, in a region on the opposite side to the one side with respect to the optical axis in the main scanning direction of the sagittal line inclination change surface, the following inequality is satisfied,

[0080] 0.0≤|y |Δs|max2 -y dmax2 | / W2≤0.1

[0081] where y |Δs|max2 The position y in the main scanning direction relative to the optical axis where the distance between one end and the other end of the effective area of the sagittal line tilt change surface in the sub-scanning cross section in the optical axis direction is the largest, dmax2 represents the position relative to the optical axis in the main scanning direction where the thickness of the image forming lens 7A in the optical axis direction in the main scanning cross section is maximum, and W2 represents the maximum image height on the opposite side in the main scanning direction on the scanned surface.

[0082] Here, W = 163 mm (the scanning width on the scanned surface is 326 mm). |Δs|max and y dmax exist Figure 2B Shown in.

[0083] Note that the optical surface effective area is the area on the optical surface of the optical element through which the light beam passes by design (light beam utilization area), and is also an area appropriately set to take into account variations in the light beam's passing position due to manufacturing errors, assembly errors, etc. of the optical element. Here, while the width of the light beam utilization area in the sub-scanning direction is 3 mm (±1.5 mm from the optical axis), the width of the optical surface effective area in the sub-scanning direction is set to 6 mm (±3 mm from the optical axis).

[0084] In the optical scanning device 100 of this embodiment, inequality (5) is satisfied, and the sagittal line tilt changing surface is designed so that the y position where |Δs|(y) of the optical surface is large and the y position where the thickness in the optical axis direction on the meridian is large are close to each other in the y direction. By satisfying inequality (5), the thickness in the optical axis direction on the meridian is made thick to form a thickness deviation shape by reducing the sagittal line tilt of the thickness deviation ratio, and the difference in the amount of birefringence generated in the sub-scanning direction is reduced. Here, the thickness deviation ratio is the ratio of the maximum thickness to the minimum thickness in the optical axis direction of the optical element. As a result, changes in optical performance due to birefringence can be suppressed, and degradation of optical performance can be suppressed, while satisfactorily correcting the curvature of the scanning line and astigmatism in the 45-degree direction by using the sagittal line tilt changing surface.

[0085] If inequality (5) is not satisfied, the thickness deviation ratio becomes large and the difference in the amount of birefringence generated in the sub-scanning direction becomes large, so that fluctuation in optical performance due to assembly error becomes large and optical performance deteriorates.

[0086] It is more preferable that inequality (5a) is satisfied.

[0087] 0.0≤|y |Δs|max -y dmax | / W≤0.05…(5a)

[0088] Furthermore, when the position y in the main scanning direction is divided into a positive region and a negative region, it is more preferable that the inequality (5) or the inequality (5a) is satisfied in both regions.

[0089] In addition, it is more preferable that both the incident surface and the exit surface of the image forming lens 7A satisfy Inequality (5) or Inequality (5a).

[0090] In addition, the optical surface of the image forming lens 7A according to this embodiment satisfies inequality (6) in at least one of the positive area where the position y in the main scanning direction on the optical surface is positive (y≥0) and the negative area where the position y in the main scanning direction on the optical surface is negative (y<0).

[0091] 0.0≤|y |Δs|max -y dmax | / x|y max |≤0.12…(6)

[0092] Here, y max The y position of the end portion in the main scanning direction of the effective area of the optical surface of the image forming lens 7A (the position relative to the optical axis in the main scanning direction) is indicated.

[0093] More specifically, in a region on one side relative to the optical axis in the main scanning direction of the sagittal line inclination change surface, the following inequality is satisfied,

[0094] 0.0≤|y |Δs|max1 -y dmax1 | / |y max1 |≤0.12

[0095] where y |Δs|max1 The position y in the main scanning direction relative to the optical axis where the distance between one end and the other end of the effective area of the sagittal line tilt change surface in the sub-scanning cross section in the optical axis direction is the largest, dmax1 represents the position relative to the optical axis in the main scanning direction where the thickness of the image forming lens 7A in the optical axis direction is the largest in the main scanning cross section, and y max1 The sagittal line inclination change surface indicates the position of an end portion on one side in the main scanning direction of the effective area with respect to the optical axis in the main scanning direction.

[0096] Furthermore, in a region on the opposite side to the one side with respect to the optical axis in the main scanning direction of the sagittal line inclination change surface, the following inequality is satisfied,

[0097] 0.0≤|y |Δs|max2 -y dmax2 | / |y max2 |≤0.12

[0098] where y |Δs|max2 The position y in the main scanning direction relative to the optical axis where the distance between one end and the other end in the sub-scanning direction of the effective area of the sagittal line tilt change surface in the sub-scanning cross section is the largest in the optical axis direction is represented. dmax2 represents the position relative to the optical axis in the main scanning direction where the thickness of the image forming lens 7A in the optical axis direction is the largest in the main scanning cross section, and y max2 Indicates the positions of the ends of the effective area of the sagittal line inclination changing surface on the opposite sides in the main scanning direction relative to the optical axis in the main scanning direction.

[0099] Here, y max = 90 mm (the width of the effective area of the optical surface in the main scanning direction is 180 mm). The width of the light beam use area in the main scanning direction is 170 mm (within the range of ±85 mm from the optical axis position).

[0100] If the value is outside the upper or lower limit of inequality (6), the thickness deviation ratio is large and the difference in the amount of birefringence generated in the sub-scanning direction is large, so that the fluctuation of optical performance due to assembly error is large and the optical performance is degraded.

[0101] It is more preferable that inequality (6a) described below is satisfied.

[0102] 0.0≤|y |Δs|max -y dmax | / |y max |≤0.09…(6a)

[0103] In addition, it is more preferable that inequality (6b) described below is satisfied.

[0104] 0.0≤|y |Δs|max -y dmax | / |y max |≤0.06…(6b)

[0105] Furthermore, when the position y in the main scanning direction is divided into a positive region and a negative region, it is more preferable that the inequality (6), (6a), or (6b) is satisfied in both regions.

[0106] While the above description has been given of a sagittal line tilt-changing surface for correcting the curvature of the scan line and astigmatism in the 45-degree direction that occurs when employing a sub-scanning oblique-incidence optical system, this embodiment is not limited to the sub-scanning oblique-incidence optical system and can be applied to any image-forming optical system that includes a sagittal line tilt-changing surface. For example, in a so-called deflecting surface-incidence optical system in which a light beam is incident perpendicularly to the rotation axis of the deflector in the sub-scan cross section, ghost images are generated by reflection on the optical surface of the image-forming lens. This embodiment can also be applied to a configuration in which the ghost optical path is controlled so that the ghost images do not reach the scanned surface by providing at least one of the optical surfaces of the image-forming lens as a sagittal line tilt-changing surface.

[0107] Figure 3A and Figure 3B Δs|(y) and d(y) on the optical surface of the image forming lens 7A according to the present embodiment are shown respectively. |Δs|max 、y dmax 、y max 、W、|y |Δs|max -y dmax |、|y |Δs|max -y dmax | / W and |y |Δs|max -y dmax | / |y max The numerical values of | are shown in Table 4. As shown in Table 4, the image forming lens 7A according to the present embodiment satisfies inequality (5) in both the region where the position y in the main scanning direction is positive (y ≥ 0) and the region where the position y in the main scanning direction is negative (y < 0) on both the incident surface and the exit surface.

[0108] In addition, as shown in Table 4, the image forming lens 7A according to this embodiment satisfies inequality (6) in both the region where the position y in the main scanning direction is positive (y≥0) and the region where the position y in the main scanning direction is negative (y<0).

[0109] In addition, as shown in Table 4, |y |Δs|max -y dmax The value of | is approximately 11 mm at most.

[0110] [Table 4]

[0111]

[0112] As shown in Table 4, the maximum value of the interval in the optical axis direction between one end and the other end in the sub-scan direction of the effective area of the sagittal line inclination change surface in the sub-scan cross section |Δs| (y |Δs|max )(mm) satisfies inequality (7).

[0113] 0.2≤|Δs|(y |Δs|max )≤1.2……(7)

[0114] If the value falls below the lower limit of inequality (7), the absolute value of the sagittal line inclination amount is small, which makes it impossible to fully correct the curvature of the scanning line and the astigmatism in the 45-degree direction, thereby deteriorating the optical performance. On the other hand, when the value exceeds the upper limit of inequality (7), the absolute value of the sagittal line inclination is large and the thickness deviation ratio is large, so that the change amount of birefringence in the sub-scanning direction is large and the optical performance is deteriorated.

[0115] Furthermore, it is more preferable that the following inequality (7a) is satisfied.

[0116] 0.23≤|Δs|(y |Δs|max )≤1.15……(7a)

[0117] As shown in Table 3, the exit surface of the image forming lens (second imaging optical element) 6A according to this embodiment is configured as a sagittal line tilt changing surface. The sagittal line tilt changing surface can change the angle of the emitted light beam RA in the main scanning direction, and the curvature of the scan line on the incident surface of the image forming lens 7A, which is generated in the sub-scanning oblique-incidence optical system, is corrected. By performing correction so that the scan line on the incident surface of the image forming lens 7A passes near the meridian, the influence of birefringence fluctuation in the sub-scanning direction caused by the sagittal line tilt changing surface of the image forming lens 7A can be reduced, and degradation of optical performance can be reduced.

[0118] Next, the optical performance of the optical scanning device 100 according to the present embodiment will be described.

[0119] Figure 4 1 is a diagram showing the curvature of field in the main scanning direction and the sub-scanning direction of the optical scanning device 100 according to the present embodiment. Figure 4 As shown in , in the optical scanning device 100 according to the present embodiment, the field curvature in the main scanning direction and the sub-scanning direction is corrected satisfactorily.

[0120] Figure 5 : is a graph showing the fθ characteristic dy of the optical scanning device 100 according to the present embodiment. The fθ characteristic dy indicates the difference obtained by subtracting the ideal image height from the position where the light beam actually reaches. Figure 5 As shown in , it can be seen that, in the optical scanning device 100 according to the present embodiment, the fθ characteristic dy is corrected satisfactorily.

[0121] Figure 6 The figure shows the image height dependency of the curvature dz of the scanning line on the scanned surface 8A of the optical scanning device 100 according to this embodiment. Here, the curvature dz of the scanning line means the difference between the image forming position in the sub-scanning direction at each image height on the scanned surface 8A and the image forming position in the sub-scanning direction at the axial image height. Figure 6 As shown in , in the optical scanning device 100 according to the present embodiment, it can be seen that the bending of the scanning line is corrected satisfactorily.

[0122] Figure 7 FIG. 2 shows the difference in the wavefront aberration amount in the azimuth angle ±45° direction (astigmatism in the 45-degree direction) of the optical scanning device 100 according to this embodiment. Figure 7 As shown in , it can be seen that the optical scanning device 100 according to the present embodiment satisfactorily corrects astigmatism in the 45-degree direction.

[0123] Figure 8 The image height dependency (image plane illuminance distribution) of the amount of light on the scanned surface 8A of the optical scanning device 100 according to the present embodiment is shown. Here, normalization is performed so that the amount of light at an image height of 0 mm is set to 1. Furthermore, the image plane illuminance distribution is shown when the image forming lens 7A according to the present embodiment is shifted by ±0.0 mm, +0.5 mm, and -0.5 mm in the sub-scanning direction.

[0124] like Figure 8As shown in , variations in the image plane illumination relative to variations along the optical axis are within ±10%, and variations in the amount of light on scanned surface 8A are substantially suppressed. To further suppress fluctuations in the amount of light on scanned surface 8A, an electrical correction unit can be used to adjust the amount of light from light source 1A based on a pre-measured image plane illumination distribution. Furthermore, in the optical scanning device 100 according to this embodiment, even if the light beam RA passing through image forming lens 7A fluctuates by ±0.5 mm due to assembly errors, etc., the fluctuation in the image plane illumination at each image height is a maximum of 0.02 or less, and changes in the image plane illumination distribution are substantially minimized.

[0125] When using the aforementioned electrical correction unit, if the image plane illumination distribution varies significantly for each optical scanning device, a correction coefficient for correcting the light intensity must be applied individually to each optical scanning device. However, this complexity increases the manufacturing cost of the optical scanning device. Alternatively, even if a uniform correction coefficient is applied, the correction residual of the image plane illumination distribution becomes large. In the optical scanning device 100 according to this embodiment, because variations in the image plane illumination distribution due to assembly errors, etc., are substantially reduced, even when the electrical correction unit uses a uniform correction coefficient to correct the image plane illumination distribution, the correction residual can be reduced, and a simple electrical correction unit can be used.

[0126] As described above, in the optical scanning device 100 according to the present embodiment, fluctuations in optical performance due to birefringence are suppressed and degradation of optical performance is reduced, while bending of scanning lines and astigmatism in the 45-degree direction are satisfactorily corrected.

[0127] [Second embodiment]

[0128] Hereinafter, an optical scanning device 200 according to a second embodiment of the present disclosure will be described.

[0129] Figure 9A is a partial sub-scanning cross-sectional view of the optical scanning device 200 according to the second embodiment. Figure 9B is a partial main-scan cross-sectional development diagram of the optical scanning device 200 according to the second embodiment. Figure 9C FIG. 2 is a partial sub-scanning cross-sectional development diagram of the optical scanning device 200 according to the second embodiment.

[0130] The optical scanning device 200 according to the present embodiment is different from the optical scanning device 100 according to the first embodiment in that four scanned surfaces 8A, 8B, 8C, and 8D can be scanned simultaneously by a common deflector 5 .

[0131] The optical scanning device 200 according to the present embodiment includes light sources 1A, 1B, 1C, and 1D, incident optical systems LA, LB, LC, and LD, a deflector 5, image forming optical systems SA, SB, SC, and SD, and reflecting mirrors M1, M2, M3, M'1, M'2, and M'3.

[0132] In the same manner as the light source 1A according to the first embodiment, for each of the light sources 1A, 1B, 1C, and 1D, a semiconductor laser or the like is used. The number of light emission points of the light sources 1A, 1B, 1C, and 1D may be one or more.

[0133] Each of the incident optical systems LA, LB, LC, and LD in this embodiment has the same configuration and optical function as the incident optical system LA according to the first embodiment, except that the combinations of oblique incident angles in the main scanning direction and the sub-scanning direction are different. Components such as optical elements and apertures may be integrated between adjacent optical systems. For example, the main scanning aperture stop 4A and the main scanning aperture stop 4B may be integrated to form a single aperture stop having a single aperture.

[0134] The light beams RA and RB emitted from the light source 1A (first light source) and the light source 1B (second light source) are incident on the deflection surface 5a of the deflector 5 via the incident optical system LA (first incident optical system) and the incident optical system LB (second incident optical system). The light beams RC and RD emitted from the light sources 1C and 1D are incident on the deflection surface 5b of the deflector 5 via the incident optical systems LC and LD. At this time, the deflection surface 5a on which the light beams RA and RB from the light sources 1A and 1B are incident and the deflection surface 5b on which the light beams RC and RD from the light sources 1C and 1D are incident at the same time are different from each other.

[0135] The incident optical systems LA and LB are arranged so that their optical axes are tilted relative to the main scanning cross section so that the light beams RA and RB are obliquely incident on the deflection surface 5a in the sub-scanning cross section. Thus, the optical paths of the light beams RA and RB can be separated and guided to the corresponding scanned surfaces 8A and 8B. In this embodiment, in order to make the optical performance in each optical path equal, the absolute values of the oblique incidence angles of the optical axes of the incident optical systems LA and LB relative to the main scanning cross section are equal to each other, and their signs are different from each other. However, it is necessary to satisfy at least one of the absolute values of the optical axes being equal to each other and the signs of the deflection angles of the optical axes being different from each other, and as needed, the absolute values can be different from each other or the signs can be equal to each other. The same applies to the incident optical systems LC and LD.

[0136] Each of the image forming lenses 6A and 6B is an image forming lens similar to the image forming lens 6A according to the first embodiment. Each of the image forming lenses 7A and 7B is an image forming lens similar to the image forming lens 7A according to the first embodiment. Each of the exit surfaces of the image forming lenses 6A and 6B is a multi-stage toric surface composed of two toric surfaces arranged in the sub-scanning direction. The image forming lens 6A and the image forming lens 7A constitute the image forming optical system SA, and the image forming lens 6B and the image forming lens 7B constitute the image forming optical system SB. The image forming optical systems SC and SD have the same configuration as the image forming optical systems SA and SB.

[0137] The reflecting mirror M1 is disposed between the image forming lens 7A and the scanned surface 8A, the reflecting mirror M2 is disposed between the image forming lens 6B and the image forming lens 7B, and the reflecting mirror M3 is disposed between the image forming lens 7B and the scanned surface 8B. The light beam RA emitted from the light source 1A and deflected by the deflecting surface 5a is guided to the scanned surface (first scanned surface) 8A via the image forming lens 6A, the image forming lens 7A, and the reflecting mirror M1 in sequence.

[0138] Light beam RB emitted from light source 1B and deflected by deflection surface 5a is guided to scanned surface (second scanned surface) 8B via image forming lens 6B, mirror M2, image forming lens 7B, and mirror M3 in sequence. Mirrors M'1, M'2, and M'3 are similarly arranged, and light beam RD emitted from light source 1D and deflected by deflection surface 5b is guided to scanned surface 8D via image forming lens 6D, image forming lens 7D, and mirror M'1 in sequence. Light beam RC emitted from light source 1C and deflected by deflection surface 5b is guided to scanned surface 8C via image forming lens 6C, mirror M'2, image forming lens 7C, and mirror M'3 in sequence.

[0139] Here, on each of the two sides of the deflector 5, the light path reaching the scanned surfaces 8A and 8D spatially (physically) disposed on the side away from the deflector 5 is referred to as the "external light path", and the light path reaching the scanned surfaces 8B and 8C spatially disposed on the side close to the deflector 5 is referred to as the "inner light path". At this time, only one reflector is disposed in the external light path, and two reflectors are disposed in the internal light path. In this way, by making the number of reflective elements different between the external light path and the internal light path, it is possible to avoid interference between each optical element and the light path while matching the light path length in all light paths, and to achieve easy manufacturing. However, the number of reflectors is not limited to this, and can be appropriately determined according to the spacing between the scanned surfaces, the arrangement of the image forming elements, etc.

[0140] The specification values, optical arrangement, and optical surface shape of the optical scanning device 200 according to the present embodiment are shown in Tables 5 to 11 below. Here, Tables 5 to 9 show the specification values and lens arrangement of the incident optical systems LA to LD and the image forming optical systems SA to SD, and Tables 10 and 11 show the optical surface shapes of the incident optical systems LA to LD and the image forming optical systems SA to SD.

[0141] [Table 5]

[0142]

[0143] [Table 6]

[0144]

[0145] [Table 7]

[0146]

[0147] [Table 8]

[0148]

[0149] [Table 9]

[0150]

[0151] [Table 10]

[0152]

[0153] [Table 11]

[0154]

[0155] The incident surface and the exit surface of each of the image forming lenses 7A, 7B, 7C and 7D of this embodiment are formed in a shape in a sub-scan cross section by sagittal line tilt changing surfaces that are tilted in directions different from each other with respect to a plane perpendicular to the optical axis.

[0156] Next, the effects of the optical scanning device 200 according to the present embodiment will be described. In the optical scanning device 200 according to the present embodiment, |Δs|(y), d(y), y |Δs|max 、y dmax 、y max 、W、|y |Δs|max -y dmax |、|y |Δs|max -y dmax | / W and |y |Δs|max -y dmax | / y dmax, field curvature in the main scanning direction and the sub-scanning direction, fθ characteristic dy, curvature dz of the scanning line, and astigmatism in the 45-degree direction are the same as those in the optical scanning device 100 according to the first embodiment, and thus description thereof is omitted.

[0157] 10A to 10D The image height dependency (image plane illuminance distribution) of the light amount on the scanned surface of the optical scanning device 200 according to the present embodiment is shown. 10A to 10D The image plane illuminance distribution on the scanned surfaces 8A to 8D is shown. Here, normalization is performed so that the amount of light at the center image height in the main scanning direction on each scanned surface is set to 1. The image plane illuminance distribution when the image forming lenses 7A, 7B, 7C, and 7D according to this embodiment are moved by ±0.0 mm, +0.5 mm, and −0.5 mm in the sub-scanning direction is also shown.

[0158] like 10A to 10D As shown in , variations in the image plane illumination relative to variations along the optical axis are within ±10%, and variations in the amount of light on the scanned surface are substantially suppressed. Furthermore, to further suppress fluctuations in the amount of light on the scanned surface, an electrical correction unit can be used that adjusts the light intensity of the light source based on a pre-measured image plane illumination distribution. In the optical scanning device 200 according to this embodiment, even if the light beams passing through the image forming lenses 7A, 7B, 7C, and 7D fluctuate by ±0.5 mm due to assembly errors, etc., the fluctuation in the image plane illumination at each image height is a maximum of 0.01 or less, and changes in the image plane illumination distribution are substantially minimized.

[0159] [Image Forming Apparatus]

[0160] Figure 11 is a sub-scanning cross-sectional view of a main portion of the color image forming apparatus 90 on which the optical scanning apparatus 100 according to the first embodiment or the optical scanning apparatus 200 according to the second embodiment is mounted.

[0161] The color image forming apparatus 90 may adopt a configuration including four optical scanning devices 100 according to the first embodiment or a configuration including one optical scanning device 200 according to the second embodiment, and is a color image forming apparatus that records image information on the surface of each photosensitive drum serving as an image bearing member.

[0162] The color image forming apparatus 90 includes the optical scanning device 100 according to the first embodiment or the optical scanning device 200 according to the second embodiment, photosensitive drums (photosensitive members) 23, 24, 25, and 26 as image bearing members, and developing devices 15, 16, 17, and 18. The color image forming apparatus 90 includes a conveyor belt 91, a printer controller 93, and a fixing device 94.

[0163] Each color signal (code data) of R (red), G (green), and B (blue) output from an external device 92 such as a personal computer is input to the color image forming apparatus 90 .

[0164] The input color signal is converted into image data (dot data) of C (cyan), M (magenta), Y (yellow), and K (black) by the printer controller 93 in the color image forming apparatus 90 .

[0165] The converted image data is input to the optical scanning device 100 or 200. Light beams 19, 20, 21 and 22 modulated according to the image data are emitted from the optical scanning device 100 or 200, and the photosensitive surfaces of the photosensitive drums 23, 24, 25 and 26 are exposed by these light beams.

[0166] Charging rollers (not shown) for uniformly charging the surfaces of the photosensitive drums 23, 24, 25, and 26 are provided in contact with these surfaces. The surfaces of the photosensitive drums 23, 24, 25, and 26 charged by the charging rollers are irradiated with light beams 19, 20, 21, and 22 by the optical scanning device 100 or 200.

[0167] As described above, the light beams 19, 20, 21, and 22 are modulated based on the image data of each color, and electrostatic latent images are formed on the surfaces of the photosensitive drums 23, 24, 25, and 26 by irradiating the light beams 19, 20, 21, and 22. The formed electrostatic latent images are developed into toner images by the developing devices 15, 16, 17, and 18 disposed in contact with the photosensitive drums 23, 24, 25, and 26.

[0168] The colorant images developed by the developing devices 15 to 18 are multi-transferred onto a sheet (transfer material) (not shown) conveyed on a conveyor belt 91 by transfer rollers (transfer devices) (not shown) disposed facing the photosensitive drums 23 to 26, thereby forming a full-color image.

[0169] As described above, the sheet to which the unfixed toner image has been transferred is further conveyed behind the photosensitive drums 23, 24, 25, and 26 ( Figure 11 The fixing device 94 is shown on the left side of the image forming apparatus 90. The fixing device 94 includes a fixing roller having a fixing heater (not shown) therein and a pressure roller arranged in pressure contact with the fixing roller. The sheet conveyed from the transfer unit is heated while being pressed by the pressure contact portion between the fixing roller and the pressure roller, thereby fixing the unfixed toner image on the sheet. In addition, a discharge roller (not shown) is arranged behind the fixing roller, and the discharge roller discharges the fixed sheet to the outside of the color image forming apparatus 90.

[0170] The color image forming apparatus 90 records image signals (image information) on photosensitive surfaces of the photosensitive drums 23, 24, 25, and 26 corresponding to the respective colors of C, M, Y, and K using the optical scanning device 100 or 200, and prints a color image at a high speed.

[0171] As the external device 92, for example, a color image reading device including a CCD sensor can be used. In this case, the color image reading device and the color image forming device 90 constitute a color digital copying machine.

[0172] While the embodiments of the present invention have been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.

Claims

1. An optical scanning device, comprising: a deflector that deflects the light beam from the light source to scan the scanned surface in a main scanning direction; as well as an optical system comprising at least one optical element that directs the light beam from the deflector to the scanned surface, wherein the at least one optical element comprises a first optical element, the first optical element being disposed closest to the scanned surface, wherein the thickness of the first optical element in the optical axis direction in the main scanning cross section changes in the main scanning direction, wherein the first optical element comprises an optical surface, a normal line of the optical surface on the main scanning cross section is inclined relative to the main scanning cross section, wherein an amount of inclination of the normal to the optical surface changes in the main scanning direction, wherein in a region on one side relative to the optical axis in the main scanning direction of the optical surface, the following inequality is satisfied, 0.0≤|y| Δs|max1 -and dmax1 | / W1≤0.1 where y |Δs|max1 represents the position relative to the optical axis in the main scanning direction where the distance between one end and the other end of the effective area in the sub-scanning direction of the optical surface in the optical axis direction is the largest, y dmax1 represents the position relative to the optical axis in the main scanning direction where the thickness of the first optical element in the optical axis direction in the main scanning cross section is maximum, and W1 represents the maximum image height in the main scanning direction on the scanned surface.

2. The optical scanning device according to claim 1 , wherein in a region of the optical surface opposite to the one side with respect to the optical axis in the main scanning direction, the following inequality is satisfied, 0.0≤|y| Δs|max2 -and dmax2 | / W2≤0.1 where y |Δs|max2 represents a position relative to the optical axis in the main scanning direction where the distance between one end and the other end of the effective area of the optical surface in the sub-scanning direction in the optical axis direction is the largest, y dmax2 W2 represents the position relative to the optical axis in the main scanning direction where the thickness of the first optical element in the optical axis direction in the main scanning cross section is maximum, and W3 represents the maximum image height in the main scanning direction on the scanned surface.

3. An optical scanning device comprising: a deflector that deflects the light beam from the light source to scan the scanned surface in a main scanning direction; and an optical system comprising at least one optical element that directs the light beam from the deflector to the scanned surface, wherein the at least one optical element comprises a first optical element disposed closest to the scanned surface and made of a resin material, wherein the thickness of the first optical element in the optical axis direction in the main scanning cross section changes in the main scanning direction, wherein the first optical element comprises an optical surface, a normal line of the optical surface on the main scanning cross section is inclined relative to the main scanning cross section, wherein an amount of inclination of the normal to the optical surface changes in the main scanning direction, wherein in a region on one side relative to the optical axis in the main scanning direction of the optical surface, the following inequality is satisfied, 0.0≤|y |Δs|max1 -and dmax1 | / |and max1 |≤0.12 where y |Δs|max1 represents the position relative to the optical axis in the main scanning direction where the distance between one end and the other end of the effective area of the optical surface in the sub-scanning direction in the optical axis direction is the largest, y dmax1 represents the position relative to the optical axis in the main scanning direction where the thickness of the first optical element in the optical axis direction is the largest in the main scanning cross section, and y max1 The position of the end portion of the effective area in the main scanning direction of the optical surface relative to the optical axis in the main scanning direction is indicated.

4. The optical scanning device according to claim 3 , wherein in an area of the optical surface opposite to the one side with respect to the optical axis in the main scanning direction, the following inequality is satisfied: when the position of the end portion of the effective area of the optical surface in the main scanning direction with respect to the optical axis in the main scanning direction is defined as ymax1, the position with respect to the optical axis in the main scanning direction at which the interval in the optical axis direction between one end and the other end of the effective area of the optical surface in the sub-scanning direction becomes maximum is ydΔsdmax2, and the position with respect to the optical axis in the main scanning direction at which the thickness of the first optical element in the main scanning cross section in the optical axis direction becomes maximum is ydmax2, 0.0≤|y |Δs|max2 -and dmax2 | / |and max2 |≤0.12 where y |Δs|max2 represents a position relative to the optical axis in the main scanning direction where the distance between one end and the other end of the effective area in the sub-scanning direction of the optical surface in the optical axis direction is the largest, y dmax2 represents the position relative to the optical axis in the main scanning direction where the thickness of the first optical element in the optical axis direction is the largest in the main scanning cross section, and y max2 The position of the end portion of the effective area of the optical surface in the main scanning direction relative to the optical axis in the main scanning direction is indicated. 5 . The optical scanning device according to claim 1 , wherein an incident surface and an exit surface of the first optical element are the optical surfaces. 6 . The optical scanning device according to claim 5 , wherein the incident surface and the exit surface are skewed in directions different from each other in shapes in a sub-scan cross section with respect to a plane perpendicular to the optical axis.

7. The optical scanning device according to claim 1, wherein the optical surface satisfies the following inequality, 0.2≤|Δs|(and |Δs|max )≤1.2 where |Δs|(y |Δs|max ) represents the maximum value in mm of an interval in the optical axis direction between one end and the other end of the effective area of the optical surface in the sub-scanning direction. 8 . The optical scanning device according to claim 1 , comprising an incident optical system configured to make the light beam from the light source obliquely incident on the deflector in a sub-scanning cross section.

9. The optical scanning device according to claim 1 , wherein the at least one optical element comprises a second optical element disposed closer to the deflector than the first optical element in the optical path of the light beam, At least one of the incident surface or the exit surface of the second optical element is the optical surface. 10 . The optical scanning device according to claim 1 , wherein the deflector deflects the light beams from the first light source and the second light source to scan the first scanned surface and the second scanned surface in a main scanning direction.

11. The optical scanning device according to claim 10, comprising a first incident optical system and a second incident optical system, wherein the first incident optical system and the second incident optical system cause the light beams from the first light source and the second light source to be obliquely incident on the deflector at different angles from each other in the sub-scanning cross section.

12. The optical scanning device according to claim 11, wherein the first incident optical system and the second incident optical system cause the light beams from the first light source and the second light source to be obliquely incident on the deflector from sides different from each other with respect to the main scanning cross section including the deflector.

13. An image forming apparatus comprising: The optical scanning device according to any one of claims 1 to 12; a developing device that develops the electrostatic latent image formed on the scanned surface by the optical scanning device into a toner image; and a transferring device that transfers the developed toner image to a transfer material; and a fixing device that fixes the transferred toner image to the transfer material.

14. An image forming apparatus comprising: The optical scanning device according to any one of claims 1 to 12; and a printer controller configured to convert code data output from an external device into an image signal and input the image signal to the optical scanning device.

Images