Optical scanner and image formation device

Abstract

To provide a small optical scanner.SOLUTION: An optical scanner comprises: a deflector including a common deflection surface for deflecting first and second light fluxes and scanning each of first and second scanned surfaces in a main scanning direction; and first and second optical systems guiding the first and second light fluxes deflected by the deflection surface to the first and second scanned surfaces. The first optical system includes a first refractive element, a second refractive element and a first reflective element arranged in order from the deflection surface toward the first scanned surface. The second optical system includes a third refractive element, a second reflective element, a fourth refractive element and a third reflective element arranged in order from the deflection surface toward the second scanned surface. At least one of the first and third refractive elements includes an optical surface in which a normal line on a bus line in a sub-scanning cross section is nonparallel to an optical axis.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an optical scanning device, and is particularly suitable for image forming devices such as a laser beam printer (LBP), a digital copier, and a multi-function printer (MFP).

Background Art

[0002] In recent years, in order to achieve miniaturization, an optical scanning device has been known which is configured to deflect a plurality of light beams emitted from a plurality of light sources by one (common) deflector and scan a plurality of scanned surfaces through a plurality of imaging optical systems.

[0003] In such an optical scanning device, in order to avoid interference between optical elements provided in the imaging optical system and to further miniaturize, Patent Document 1 discloses an optical scanning device in which the optical path lengths of the respective imaging optical systems are made different from each other.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, as disclosed in Patent Document 1, if the optical path lengths of the respective imaging optical systems are made different from each other, the distance between the scanned surfaces increases, and the entire device becomes large-sized.

[0006] Therefore, an object of the present invention is to provide a compact optical scanning device.

Means for Solving the Problems

[0007] To achieve the above object, as one aspect of the present invention, an optical scanning device includes a deflector that deflects first and second light beams to scan respective first and second scanned surfaces in a main scanning direction, the deflector including a common deflection surface, and first and second optical systems that guide the first and second light beams deflected by the deflection surface to the first and second scanned surfaces. The first optical system has a first refractive element, a second refractive element, and a first reflective element arranged in order from the side of the deflection surface toward the side of the first scanned surface. The second optical system has a third refractive element, a second reflective element, a fourth refractive element, and a third reflective element arranged in order from the side of the deflection surface toward the side of the second scanned surface. At least one of the first and third refractive elements includes an optical surface whose normal on the generatrix in the sub-scanning cross section is non-parallel to the optical axis.

Advantages of the Invention

[0008] According to the present invention, a small-sized optical scanning device can be provided.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Embodiments for Carrying Out the Invention

[0010] Hereinafter, the optical scanning device according to the present embodiment will be described in detail with reference to the accompanying drawings. Note that the drawings shown below may be drawn at scales different from the actual ones in order to facilitate understanding of the present embodiment.

[0011] In the following description, the main scanning direction (Y direction) is a direction perpendicular to the rotation axis (or swing axis) of the deflector and the optical axis of the optical system (the direction in which the light beam is deflected and scanned (deflection scanning) by the rotating polygon mirror). The sub-scanning direction (Z direction) is a direction parallel to the rotation axis (or swing axis) of the deflector. The main scanning cross-section is a cross-section including the optical axis and perpendicular to the sub-scanning direction. The sub-scanning cross-section is a cross-section perpendicular to the main scanning direction.

[0012] [First Embodiment] FIG. 1(a) is a sub-scanning cross-sectional view of a main part of the optical scanning device 100 according to the first embodiment. FIGS. 1(b) and 1(c) are optical path development views in the main scanning cross-section of the main part of the optical scanning device 100 according to the first embodiment. FIG. 1(d) is an optical path development view in the sub-scanning cross-section of the main part of the optical scanning device 100 according to the first embodiment.

[0013] The optical scanning device 100 of the present embodiment includes a light source 1A (first light source) and 1B (second light source), incident optical systems LA and LB, a deflector 5, imaging optical systems SA (first optical system) and SB (second optical system), and mirrors (reflective elements) M1, M2, and M3.

[0014] The optical scanning device 100 of the present embodiment deflects and scans two light beams RA (first light beam) and RB (second light beam) by one deflector 5, and scans corresponding scanned surfaces 8A (first scanned surface) and 8B (second scanned surface). A so-called sub-scanning oblique incidence optical system is used in which one deflector 5 is shared by a plurality of light beams and the light beam is incident on the deflector obliquely from the sub-scanning direction. The advantage of the sub-scanning oblique incidence optical system is that it enables separation of the deflected and reflected light beams without increasing the size of the deflector surface in the sub-scanning direction.

[0015] As the light sources 1A and 1B, semiconductor lasers or the like are used. Note that the number of light emitting points of the light sources 1A and 1B may be one or more.

[0016] The incident optical systems LA and LB include anamorphic lenses 2A and 2B as refractive elements, sub-scanning aperture stops 3A and 3B, and main-scanning aperture stops 4A and 4B.

[0017] The anamorphic lenses 2A and 2B convert the light beams RA and RB emitted from the light sources 1A and 1B into parallel light beams within the main-scanning cross-section and condense them in the sub-scanning direction. Here, the parallel light beam includes not only a strictly parallel light beam but also a substantially parallel light beam such as a weakly divergent light beam or a weakly convergent light beam. Further, a collimator lens and a cylinder lens may be used instead of the anamorphic lens.

[0018] The sub-scanning aperture stops 3A and 3B respectively limit the beam diameters of the light beams RA and RB in the sub-scanning direction that have passed through the anamorphic lenses 2A and 2B. Similarly, the main-scanning aperture stops 4A and 4B respectively limit the beam diameters of the light beams RA and RB in the main-scanning direction that have passed through the anamorphic lenses 2A and 2B.

[0019] The deflector 5 rotates in the direction of arrow A in the figure by a driving means such as a motor (not shown), so that the deflector 5 deflects the incident light beams LA and LB and scans the scanned surfaces 8A and 8B in the direction of arrow B in the figure. Note that the deflector 5 is composed of, for example, a polygon mirror or the like.

[0020] In the imaging optical system SA, the deflected light beam RA deflected and reflected by the deflection surface 5A of the deflector 5 passes through a lens 6A (first refractive element, first optical part) and a lens 7A (second refractive element), which are parts of the multi-stage lens, and is then reflected back by a mirror (first reflecting element) M1 and guided to the surface to be scanned 8A. Also, in the imaging optical system SB, the deflected light beam RB deflected and reflected by the deflection surface 5A of the deflector 5 passes through a lens 6B (third refractive element, second optical part), which is a part of the multi-stage lens, is then reflected back by a mirror (second reflecting element) M2, passes through a lens 7B (fourth refractive element), and is then reflected back by a mirror (third reflecting element) M3 and guided to the surface to be scanned 8B.

[0021] The mirrors M1, M2, and M3 are means (reflecting elements) for reflecting the light beam, and a vapor deposition mirror or the like is used. Note that instead of the mirrors M1, M2, and M3, an optical element such as a lens or a prism having a reflecting surface may be used as the reflecting element. Also, instead of each lens, a prism or the like may be used as the refractive element.

[0022] Here, C0 in the figure is the incident point (deflection point) of the principal ray of the light beam (axial light beam) reaching the axial image height on the surface to be scanned on the deflection surface when the principal ray is deflected, and will be referred to as the axial deflection point hereinafter. P0 is a plane (reference plane) passing through the deflection point C0 and perpendicular to the rotation axis of the deflector 5. The light beams RA and RB incident on the common deflection surface 5A intersect and are deflected at the deflection point C0 within the sub-scanning cross-section.

[0023] Hereinafter, the length of the optical path from the deflection point C0 to each surface to be scanned is defined as the optical path length of each imaging optical system.

[0024] Next, the specifications, optical arrangements, and lens surface shapes of the optical scanning device 100 according to this embodiment are shown in Tables 1 to 4 below. Here, Table 1 shows the specifications and lens arrangements of the incident optical system LA and the imaging optical system SA, and Table 2 shows the lens surface shapes of the incident optical system LA and the imaging optical system SA. Further, Table 3 shows the specifications and lens arrangements of the incident optical system LB and the imaging optical system SB, and Table 4 shows the lens surface shapes of the incident optical system LB and the imaging optical system SB. In the columns of the optical arrangements in Tables 1 and 3, the coordinates of the reflection points of the light beams RA and RB at each mirror toward the image center (axial image height) in the main scanning direction on the surface to be scanned are shown.

[0025] In Tables 2 and 4, when the intersection of each lens surface and the optical axis is taken as the origin, the optical axis direction, 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 respectively the x-axis, the y-axis, and the z-axis. However, the x-axis is in the +x direction of the light propagation direction, and the y-axis is in the +y direction on the light source side with respect to the optical axis. Also, in Tables 2 and 4, "E-x" means "×10-x".

[0026] [Table 1]

[0027] [Table 2]

[0028] [Table 3]

[0029] [Table 4]

[0030] Temperature compensation is performed by providing a diffractive surface on the incident surface side of the anamorphic lenses 2A, 2B, 2C, and 2D. However, the effects of this embodiment are not limited to this configuration. The incident surfaces of the anamorphic lenses 2A and 2B are rotationally asymmetric diffractive surfaces, and the phase function Φ of the diffraction grating is represented by the following equation.

[0031]

Equation

[0032] k is the diffraction order, and here k = 1. Also, λ is the wavelength, and here λ = 790 nm.

[0033] The generatrix shape (the shape of the lens surface in the main scanning cross-section) of each lens surface of the lenses 6A and 6B and the lenses 7A and 7B according to this embodiment is an aspherical shape that can be represented as a function up to the 10th order as shown in the following equation.

[0034]

Equation

[0035] Here, when the intersection of each lens surface and the optical axis is taken as the origin, the optical axis direction, 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. However, the x-axis is in the +x direction of the light propagation direction, and the y-axis is in the +y direction on the light source side with respect to the optical axis. Also, R is the generatrix curvature radius, K is the eccentricity, and Bi (i = 1, 2,..., 10) are aspherical coefficients.

[0036] Also, the fillet shape (the shape of the lens surface in the sub-scanning cross-section at an arbitrary image height S) of each lens surface of the lenses 6A and 6B and the lenses 7A and 7B according to this embodiment is an aspherical shape as shown in the following equation.

[0037]

Equation

[0038] Here, S is a sub-ray shape defined in a plane perpendicular to the main scanning cross-section and including the normal line of the bus bar at each position in the bus bar direction, and m i,j (i = 1, 2,..., 10 and j = 1) are aspherical coefficients. The term consisting of a first-order function of Z is a term that gives the tilt amount in the sub-ray direction.

[0039] Also, the sub-ray radius of curvature r' continuously changes as follows according to the Y coordinate of the lens surface.

[0040] [Number]

[0041] Here, r is the sub-ray radius of curvature on the optical axis, and Ei (i = 1, 2,..., 10) are sub-ray change coefficients.

[0042] Next, the effects of the optical scanning device 100 according to the present embodiment will be described.

[0043] In the optical scanning device 100 according to the present embodiment, as shown in Table 2 and Table 4, the exit surfaces of the lenses 6A and 6B are set as surfaces with an aspherical coefficient m i,1 ≠0 (sub-ray tilt surface). The sub-ray tilt surface indicates an optical surface in which the normal line on the bus bar in the sub-scanning cross-section including the optical axis is inclined with respect to the optical axis (non-parallel to the optical axis). Here, the bus bar refers to the intersection line of the optical surface and the main scanning cross-section. Since y = 0 on the optical axis, the sub-ray tilt amount (the inclination of the normal line on the bus bar with respect to the optical axis) in the sub-scanning cross-section including the optical axis is m 0,1 represented by. Also, m 2,1It has aspherical coefficients and is a sub-ray tilt surface (sub-ray tilt change surface) where the sub-ray tilt amount of each optical surface changes according to the position y in the main scanning direction. By changing the sub-ray tilt amount, the angle in the sub-scanning cross-section of the light beam after passing through the sub-ray tilt surface can be changed. Compared with a conventional lens that does not use a sub-ray tilt surface, the angles of the light beams RA and RB after passing through the lenses 6A and 6B according to this embodiment from the reference plane in the sub-scanning cross-section can be increased. As a result, while avoiding interference between the mirror M2 and the light beam RA, the mirror M2 can be arranged closer to the lenses 6A and 6B, achieving miniaturization of the optical scanning device 100.

[0044] Here, if the incident surfaces and the exit surfaces of the lenses 6A and 6B are not sub-ray tilt surfaces, interference will occur between the mirror M2 and the light beam RA. As shown in FIG. 2(b), to avoid interference and arrange them, it is necessary to move the mirror M2 in a direction away from the lenses 6A and 6B. As a result, the optical scanning device 100 becomes larger. Furthermore, when the mirror is moved, the interval in the sub-scanning cross-section between the deflector 5 and the surface to be scanned 8A becomes wider, and when mounted on an image forming apparatus, the image forming apparatus becomes larger.

[0045] Note that it is not necessary to make all of the incident surfaces and the exit surfaces of the lenses 6A and 6B sub-ray tilt surfaces. The above-described effects can be obtained if at least one of these four optical surfaces is a sub-ray tilt surface. However, it is preferable to make the exit surfaces of the lenses 6A and 6B sub-ray tilt surfaces, and it is more preferable to make both the incident surfaces and the exit surfaces of the lenses 6A and 6B sub-ray tilt surfaces. Also, it is desirable that the incident surfaces of the lenses 6A and 6B have the same shape as each other in the effective region. This makes it possible to facilitate the manufacture of each lens.

[0046] The lenses 6A and 6B according to this embodiment are multi-stage lenses arranged in the sub-scanning direction and integrally formed with each other. By doing so, the lenses can be shared by a plurality of light beams RA and RB, thereby reducing the number of lenses and achieving miniaturization and cost reduction of the optical scanning device 100. However, the lenses 6A and 6B may be separate from each other as necessary.

[0047] In the multi-stage lens of the present embodiment, at least one of the incident surface and the exit surface of the lenses 6A and 6B has a lens surface shape that is asymmetric in the sub-scanning direction with respect to the reference plane P0, and the upper shape and the lower shape with respect to the reference plane P0 are different.

[0048] In the present embodiment, the aspherical coefficient m1 0,1 and m3 0,1 which are the sub-ray tilt amounts on the axis (y = 0) of the exit surfaces of the lenses 6A and 6B satisfy the following conditional expression (1). m1 0,1 / m3 0,1 <0 (1)

[0049] The conditional expression (1) indicates that the value of the aspherical coefficient m1 0,1 of the exit surface of the first refractive element is smaller than the value of the aspherical coefficient m3 0,1 of the exit surface of the third refractive element. When the conditional expression (1) is satisfied, the signs of the aspherical coefficients m10,1 and m30,1 are different from each other, and the directions of the sub-ray tilt amounts on the axis are different from each other. As a result, the angles from the reference plane in the sub-scanning cross-section of the light fluxes RA and RB after passing through the lenses 6A and 6B can be increased, and the mirror M2 can be arranged closer to the lenses 6A and 6B, achieving miniaturization of the optical scanning device 100. When the upper limit of the conditional expression (1) is exceeded, the directions of the sub-ray tilt amounts on the axis become the same, and the mirror M2 and the light flux RA interfere with each other.

[0050] Furthermore, it is more preferable to satisfy the conditional expression (1a). 0.01 < m1 0,1 / m3 0,1 <100 (1a)

[0051] If the conditional expression (1a) is not satisfied, the difference in the sub-ray tilt amounts of the lenses 6A and 6B becomes large, the difference in the optical performance in the imaging optical systems SA and SB becomes large, and the color shift deteriorates when the optical scanning device 100 is used in an image forming device.

[0052] Furthermore, it is more preferable to satisfy the conditional expression (1b). 0.1 < m1 0,1 / m3 0,1 <10 (1b)

[0053] As shown in Table 2 and Table 4, the aspherical coefficients m1 0,1 , m3 0,1 on the optical axis (y = 0) of the exit surfaces of the lenses 6A and 6B according to this embodiment are -2.1236E-02 and 7.6609E-02, respectively, and satisfy the conditional expressions (1), (1a), and (1b).

[0054] In the optical scanning device 100 of this embodiment, when the distances (optical distances) on the optical axis from the deflection point C0 to the lenses 7A and 7B are L1 and L2, respectively, the following conditional expression (2) is satisfied. In this embodiment, "optical" means "in the state when the optical path is developed". L1 / L2 ≠ 1 (2)

[0055] The conditional expression (2) indicates that the distances on the optical axis from the on-axis deflection point to the second and fourth refractive elements (to their respective incident surfaces) are different from each other. By satisfying the conditional expression (2), the lenses 7A and 7B are arranged such that the optical positions from the deflection point C0 to the respective lenses 7A and 7B are different from each other, increasing the degree of freedom in arrangement and achieving miniaturization of the optical scanning device 100 while avoiding interference.

[0056] Also, in the optical scanning device 100 of this embodiment, the following conditional expression (3) is satisfied. L1 / L2 < 1 (3)

[0057] Conditional expression (3) indicates that the distance L1 on the optical axis from the on-axis deflection point to the second refractive element is shorter than the distance L2 on the optical axis from the on-axis deflection point to the fourth refractive element. In the imaging optical systems SA and SB according to the present embodiment, the imaging optical system SA has fewer mirrors than the imaging optical system SB, and there are fewer arrangement restrictions on lenses and mirrors. Therefore, in order to satisfy the conditional expression (3), the lens 7A is arranged closer to the deflection point C0 compared to the lens 7B. As a result, the size of the lens 7A in the main scanning direction can be made smaller compared to the lens 7B, achieving miniaturization of the optical scanning device 100. Further, by reducing the size of the lens 7A in the main scanning direction, deformation of the lens shape of the solid nozzle can be reduced, and image degradation can be suppressed.

[0058] It is more preferable to satisfy the conditional expression (3a). 0.5 < L1 / L2 < 1.0 (3a)

[0059] When the lower limit of the conditional expression (3a) is exceeded, the optical distances L1 and L2 on the optical axis from the deflection point C0 to the lenses 7A and 7B increase, the difference in optical performance between the imaging optical systems SA and SB increases, and color shift deteriorates when the optical scanning device 100 is used in an image forming apparatus.

[0060] It is more preferable to satisfy the conditional expression (3b). 0.8 < L1 / L2 < 0.9 (3b)

[0061] As shown in Tables 1 and 3, the optical distances L1 and L2 on the optical axis from the deflection point C0 to the lenses 7A and 7B according to the present embodiment are 103.5 mm and 122 mm, respectively, satisfying the conditional expressions (2), (3), (3a), and (3b).

[0062] As described above, in the optical scanning device 100 according to the present embodiment, by arranging each lens and mirror so as to satisfy the above relationships, miniaturization of the optical scanning device 100 can be achieved while avoiding an increase in the distance between photoreceptors of the mounted image forming apparatus.

[0063] [Second Embodiment] FIG. 3(a) is a sub-scanning cross-sectional view of a main part of the optical scanning device 200 according to the second embodiment. FIGS. 3(b) and 3(c) are optical path development views in the main scanning cross-section of the main part of the optical scanning device 200 according to the second embodiment. FIG. 3(d) is an optical path development view in the sub-scanning cross-section of the main part of the optical scanning device 200 according to the second embodiment.

[0064] The optical scanning device 200 according to the present embodiment includes light sources 1A (first light source), 1B (second light source), 1C (third light source), and 1D (fourth light source), incident optical systems LA, LB, LC, and LD, a deflector 5, imaging optical systems SA (first imaging optical system), SB (second imaging optical system), SC (third imaging optical system), and SD (fourth imaging optical system), and folding mirrors M1, M2, M3, M'1, M'2, and M'3.

[0065] Note that, in the optical scanning device 200 according to the present embodiment, the light sources 1A and 1B, the incident optical systems LA and LB, the deflector 5, the imaging optical systems SA and SB, and the mirrors M1, M2, and M3 have the same configuration as those of the optical scanning device 100 according to the first embodiment. Therefore, the description of the same members is omitted.

[0066] As the light sources 1A, 1B, 1C, and 1D, semiconductor lasers or the like are used. Note that the number of light emitting points of the light sources 1A, 1B, 1C, and 1D may be one or more.

[0067] The incident optical systems LA and LB in the present embodiment have the same configuration and optical action as the incident optical systems LA and LB according to the first embodiment. Also, in the incident optical systems LC and LD in the present embodiment, they have the same configuration and optical action as the imaging optical systems SA and SB in the present embodiment.

[0068] In the optical scanning device 200 according to this embodiment, imaging optical systems SA and SB and imaging optical systems SC and SD are arranged with a single deflector 5 interposed therebetween. Four light beams RA (first light beam), RB (second light beam), RC (third light beam), and RD (fourth light beam) are deflected and scanned by a single deflector 5, and corresponding scanned surfaces 8A (first scanned surface), 8B (second scanned surface), 8C (third scanned surface), and 8D (fourth scanned surface) are scanned. A so-called sub-scanning oblique incidence optical system is used in which a single deflector 5 is shared by a plurality of light beams and the light beams are incident obliquely from the sub-scanning direction with respect to the deflector. The advantage of the sub-scanning oblique incidence optical system is that it enables separation of the deflected and reflected light beams without increasing the size of the deflector surface in the sub-scanning direction of the optical deflector.

[0069] In the imaging optical system SA, the deflected light beam RA deflected and reflected by the deflection surface 5A of the deflector 5, which is a deflecting means, passes through lenses 6A (first optical element) and 7A (second optical element), is then folded by a folding mirror M1, and is guided to the scanned surface 8A. Also, in the imaging optical system SB, the deflected light beam RB deflected and reflected by the deflection surface 5A of the deflector 5 passes through a lens 6B (third optical element), is folded by a mirror M2, passes through a lens 7B (fourth optical element), and then is folded by a mirror M3 and reaches the scanned surface 8B.

[0070] Also in the imaging optical system SD (SC), the same optical path routing as in the imaging optical system SA (SB) is performed in the same manner. The deflected light beam RD deflected and reflected by the deflection surface 5'A of the deflector 5 passes through lenses 6D (seventh optical element) and 7D (eighth optical element), is then folded by a folding mirror M'1, and is guided to the scanned surface 8D. Also, the deflected light beam RC deflected and reflected by the deflection surface 5'A of the deflector 5 passes through a lens 6C (fifth optical element), is folded by a folding mirror M'2, passes through a lens 7C (sixth optical element), and is then folded by a folding mirror M'3 and is guided to the scanned surface 8C.

[0071] The imaging optical systems SA and SB in this embodiment have the same configuration and optical actions as the imaging optical systems SA and SB according to the first embodiment. Also, in the imaging optical systems SC and SD in this embodiment, they have the same configuration and optical actions as the imaging optical systems SA and SB in this embodiment.

[0072] Next, the specifications, optical arrangements, and lens surface shapes of the optical scanning device 200 according to this embodiment are shown in Tables 5 to 8 below. Here, Table 5 shows the specifications and lens arrangements of the incident optical systems LA (LD) and the imaging optical systems SA (SD), and Table 6 shows the lens surface shapes of the incident optical systems LA (LD) and the imaging optical systems SA (SD). Also, Table 7 shows the specifications and lens arrangements of the incident optical systems LB (LC) and the imaging optical systems SB (SC), and Table 8 shows the lens surface shapes of the incident optical systems LB (LC) and the imaging optical systems SB (SC). In the columns of the optical arrangements in Tables 5 and 7, the coordinates of the reflection points of the light beams RA (RD), RB (RC) at each mirror toward the image center (axial image height) in the main scanning direction on the surface to be scanned are shown.

[0073] In Tables 6 and 8, when the intersection of each lens surface and the optical axis is taken as the origin, the optical axis direction, 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 respectively the x-axis, y-axis, and z-axis. However, the x-axis is in the +x direction of the light propagation direction, and the y-axis is in the +y direction on the light source side with respect to the optical axis. Also, in Tables 6 and 8, "E-x" means "×10 -x ".

[0074]

Table 5

[0075]

Table 6

[0076]

Table 7

[0077]

Table 8

[0078] Next, the effects of the optical scanning device 200 according to the present embodiment will be described.

[0079] In the imaging optical systems SA, SB, SC, and SD according to the present embodiment, since the configurations and optical actions of the imaging optical systems SA and SB and the imaging optical systems SC and SD are the same as each other, the effects will be described below with respect to the imaging optical systems SA and SB.

[0080] In the optical scanning device 200 according to the present embodiment, as shown in Table 6 and Table 8, the exit surfaces of the lenses 6A and 6B are sub-ray tilt surfaces with an aspheric coefficient m i,j ≠0.

[0081] Compared with a conventional lens that does not use a sub-ray tilt surface, the angles of the light beams RA and RB passing through the lenses 6A and 6B in the sub-scanning cross-section with respect to the reference plane can be increased. As a result, while avoiding interference with the light beam RA, the mirror M2 can be arranged closer to the lenses 6A and 6B, achieving miniaturization of the optical scanning device 200.

[0082] The lenses 6A and 6B according to the present embodiment are multi-stage lenses arranged in the sub-scanning direction, with their respective incident surfaces and exit surfaces integrally formed. By doing so, the lenses can be shared by a plurality of light beams RA and RB, thereby reducing the number of lenses and achieving miniaturization and cost reduction of the optical scanning device 200.

[0083] In the multi-stage lens of the present embodiment, at least one of the incident surfaces and the exit surfaces of the lenses 6A and 6B has a lens surface shape that is asymmetric in the sub-scanning direction with respect to the reference plane P0, and the shape on the upper side and the shape on the lower side with respect to the reference plane P0 are different.

[0084] As shown in Tables 6 and 8, the aspherical coefficients m1 0,1 , m3 0,1 are -3.9283E-02 and 1.1363E-01, respectively, and satisfy the conditional expressions (1), (1a), and (1b). As a result, for the same reasons described in the first embodiment, miniaturization of the optical scanning device 200 is achieved.

[0085] As shown in Tables 5 and 7, the optical distances L1 and L2 on the optical axis from the deflection point C0 to the lenses 7A and 7B according to the present embodiment are 100.8 mm and 122 mm, respectively, and satisfy the conditional expressions (2), (3), (3a), and (3b). As a result, for the same reasons described in the first embodiment, miniaturization of the optical scanning device 200 is achieved.

[0086] As described above, in the optical scanning device 200 according to the present embodiment, by arranging each lens and mirror so as to satisfy the above-described relationships, it is possible to achieve miniaturization of the optical scanning device 200 while avoiding an increase in the distance between the photoreceptors of the image forming apparatus to be mounted.

[0087] Although the preferred embodiments have been described above, the present invention is not limited to these embodiments, and various modifications and changes are possible within the scope of the gist thereof.

[0088] [Image forming apparatus] FIG. 4 shows a main part sub-scanning cross-sectional view of a color image forming apparatus 90 on which an optical scanning device 100 according to any of the embodiments is mounted.

[0089] The image forming apparatus 90 is a tandem type color image forming apparatus that records image information on each photosensitive drum surface, which is an image carrier, using the optical scanning device 100.

[0090] The image forming apparatus 90 includes an optical scanning device 100, photosensitive drums (photoreceptors) 23, 24, 25, 26 as image carriers, and developing devices 15, 16, 17, 18. The image forming apparatus 90 also includes a conveyance belt 91, a printer controller 93, and a fixing device 94.

[0091] The image forming apparatus 90 receives R (red), G (green), and B (blue) color signals (code data) output from an external device 92 such as a personal computer.

[0092] The input color signals are converted by a printer controller 93 in the image forming apparatus 90 into respective C (cyan), M (magenta), Y (yellow), and K (black) image data (dot data).

[0093] Each of the converted image data is input into an optical scanning device 100. Then, from the optical scanning device 100, light beams 19, 20, 21, and 22 modulated according to the respective image data are emitted, and the photosensitive surfaces of photosensitive drums 23, 24, 25, and 26 are exposed by these light beams.

[0094] A charging roller (not shown) for uniformly charging the surfaces of the photosensitive drums 23, 24, 25, and 26 is provided so as to contact the surfaces. Then, the surfaces of the photosensitive drums 23, 24, 25, and 26 charged by the charging roller are irradiated with the light beams 19, 20, 21, and 22 by the optical scanning device 100.

[0095] As described above, the light beams 19, 20, 21, and 22 are modulated based on the color image data, and an electrostatic latent image is 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 image is developed as a toner image by developing devices 15, 16, 17, and 18 disposed so as to contact the photosensitive drums 23, 24, 25, and 26.

[0096] The toner image developed by the developing devices 15 to 18 is multi-transferred onto a sheet of paper (transfer material) (not shown) conveyed on a conveyance belt 91 by a transfer roller (transfer device) (not shown) disposed so as to face the photosensitive drums 23 to 26, and a single full-color image is formed.

[0097] As described above, the sheet on which the unfixed toner image has been transferred is further conveyed to the fixing device 94 behind (left side in FIG. 4) the photosensitive drums 23, 24, 25, 26. The fixing device 94 is composed of a fixing roller having a fixing heater (not shown) inside and a pressure roller disposed so as to be in pressure contact with the fixing roller. The sheet conveyed from the transfer section is heated while being pressed at the pressure contact section between the fixing roller and the pressure roller, whereby the unfixed toner image on the sheet is fixed. Further, a paper discharge roller (not shown) is disposed behind the fixing roller, and the paper discharge roller discharges the fixed sheet out of the image forming apparatus 90.

[0098] The color image forming apparatus 90 uses an optical scanning device 100 to record image signals (image information) on the photosensitive surfaces of the photosensitive drums 23, 24, 25, 26 corresponding to the respective colors of C, M, Y, and K, and prints color images at high speed.

[0099] As the external device 92, for example, a color image reading device equipped with a CCD sensor may be used. In this case, a color digital copying machine is configured by this color image reading device and the color image forming apparatus 90.

[0100] Note that the embodiments of the present invention include the following configurations.

[0101] (Configuration 1) A deflector including a common deflection surface that deflects the first and second light beams and scans each of the first and second scanned surfaces in the main scanning direction, and first and second optical systems that guide the first and second light beams deflected by the deflection surface to the first and second scanned surfaces, wherein the first optical system has a first refractive element, a second refractive element, and a first reflective element arranged in order from the side of the deflection surface toward the side of the first scanned surface, and the second optical system has a third refractive element, a second reflective element, a fourth refractive element, and a third reflective element arranged in order from the side of the deflection surface toward the side of the second scanned surface. The optical scanning device is characterized in that at least one of the first and third refractive elements includes an optical surface in a sub-scanning cross section including the optical axis, where the normal line on the generatrix is non-parallel to the optical axis.

[0102] (Configuration 2) The optical scanning device according to Configuration 1, wherein the first and third refractive elements are integrally formed with each other.

[0103] (Configuration 3) The optical scanning device according to Configuration 1 or 2, wherein the incident surfaces of the first and third refractive elements are the same shape as each other in the effective region.

[0104] (Configuration 4) The optical scanning device according to any one of Configurations 1 to 3, wherein the distances on the optical axis from the on-axis deflection point in the deflection plane to the second and fourth refractive elements are different from each other.

[0105] (Configuration 5) The optical scanning device according to Configuration 4, wherein the distance on the optical axis from the on-axis deflection point to the second refractive element is shorter than the distance on the optical axis from the on-axis deflection point to the fourth refractive element.

[0106] (Configuration 6) The optical scanning device according to any one of Configurations 1 to 5, wherein the exit surfaces of the first and third refractive elements are the optical surfaces.

[0107] (Configuration 7) For the exit surface of each of the first and third refractive elements, taking the intersection point with the optical axis as the origin, the axis parallel to the optical axis as the x-axis, the axis perpendicular to the optical axis in the main scanning cross section as the y-axis, the axis perpendicular to the optical axis in the sub-scanning cross section as the z-axis, the aspherical coefficient as m i,j , the radius of curvature in the sub-scanning cross section including the optical axis as r, the variation coefficient as Ei, and the shape S in the sub-scanning cross section of the exit surface of each of the first and third refractive elements as

[0108] [Number]

[0109]

Number

[0110] When expressed by the following formula, the value of the aspherical coefficient of the exit surface of the first refractive element is smaller than the value of the aspherical coefficient of the exit surface of the third refractive element. The optical scanning device according to any one of Configurations 1 to 6.

[0111] (Configuration 8) The inclination of the normal line with respect to the optical axis in the sub-scanning cross section changes in the main scanning direction. The optical scanning device according to any one of Configurations 1 to 7.

[0112] (Configuration 9) An image forming apparatus comprising: the optical scanning device according to any one of Configurations 1 to 8; and a developing device that develops an electrostatic latent image formed on a surface to be scanned by the optical scanning device into a toner image.

[0113] (Configuration 10) An image forming apparatus comprising: the optical scanning device according to any one of Configurations 1 to 8; and a printer controller that converts code data output from an external device into an image signal and inputs the image signal to the optical scanning device.

Explanation of Signs

[0114] SA First optical system SB Second optical system 5 Deflector 6A First refractive element 7A Second refractive element 6B Third refractive element 7B Fourth refractive element M1 First reflecting element M2 Second reflecting element M3 Third reflecting element 100 Optical scanning device

Claims

1. A deflector including a common deflection surface that deflects first and second light beams to scan respective first and second scanned surfaces in a main scanning direction; first and second optical systems that guide the first and second light beams deflected by the deflection surface to the first and second scanned surfaces; the first optical system having a first refractive element, a second refractive element, and a first reflective element arranged in order from the side of the deflection surface toward the side of the first scanned surface; the second optical system having a third refractive element, a second reflective element, a fourth refractive element, and a third reflective element arranged in order from the side of the deflection surface toward the side of the second scanned surface; at least one of the first and third refractive elements including an optical surface in which a normal line on a generatrix in a sub-scanning cross section including an optical axis is non-parallel to the optical axis; A light scanning device, wherein distances on the optical axis from an on-axis deflection point on the deflection surface to the second and fourth refractive elements are different from each other.

2. The light scanning device according to claim 1, wherein the first and third refractive elements are integrally formed with each other.

3. The light scanning device according to claim 1, wherein incident surfaces of the first and third refractive elements are the same in shape with each other in an effective region.

4. The light scanning device according to any one of claims 1 to 3, wherein an inclination of the normal line with respect to the optical axis in a sub-scanning cross section changes in a main scanning direction.

5. The light scanning device according to any one of claims 1 to 3, wherein a distance on the optical axis from the on-axis deflection point to the second refractive element is shorter than a distance on the optical axis from the on-axis deflection point to the fourth refractive element.

6. The light scanning device according to any one of claims 1 to 3, wherein exit surfaces of the first and third refractive elements are the optical surfaces.

7. For the exit surfaces of the first and third refractive elements respectively, taking the intersection point with the optical axis as the origin, the axis parallel to the optical axis as the x-axis, the axis perpendicular to the optical axis in the main scanning cross-section as the y-axis, the axis perpendicular to the optical axis in the sub-scanning cross-section as the z-axis, and the aspherical coefficient as m ｉ，ｊ , the radius of curvature in the sub-scanning cross-section including the optical axis as r, the change coefficient as Ei, and the shape S of the exit surface of each of the first and third refractive elements in the sub-scanning cross-section as 【Number 1】 【Number 2】 The light scanning device according to any one of claims 1 to 3, wherein when expressed by a certain formula, a value of an aspherical coefficient of an exit surface of the first refractive element is smaller than a value of an aspherical coefficient of an exit surface of the third refractive element.

8. An image forming apparatus, comprising: the light scanning device according to any one of claims 1 to 3; and a developing device that develops an electrostatic latent image formed on a scanned surface by the light scanning device into a toner image.

9. An image forming apparatus comprising: the optical scanning device according to any one of claims 1 to 3; and a printer controller that converts code data output from an external device into an image signal and inputs the image signal to the optical scanning device.

Images