Optical scanner and image forming apparatus

Abstract

To provide an optical scanner that can sufficiently suppress an increase in astigmatism due to temperature rise.SOLUTION: An optical scanner according to the present invention comprises: a deflector that deflects a light beam from a light source and scans a scanning target surface in a main scanning direction; an incident optical system that is formed of an optical element having an incident surface and an emission surface, at least one of which is a diffraction surface, and guides the light beam from the light source to a deflection surface of the deflector; and an imaging optical system that guides the light beam deflected by the deflection surface to the scanning target surface. When the distance between a light emission surface of the light source and the incident surface of the optical element, and the distance between the emission surface of the optical element and an on-axis deflection point of the deflection surface, which are on an optical axis of the incident optical system, are defined as Df and Db, respectively, and the absolute value of a refractive power and the absolute value of a diffraction power on a main scanning cross section of the optical element are defined as |Prm| and|Pdm|, respectively, conditions of 0.20≤Df / Db≤0.40 and 1.00<|Pdm| / |Prm|≤1.50 are satisfied.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an optical scanning device, and more particularly to an optical scanning device that is suitable for use in image forming apparatuses such as laser beam printers (LBPs), digital copying machines, and multifunction printers. [Background technology]

[0002] 2. Description of the Related Art Conventionally, optical scanning devices have been known in which a diffractive surface is provided in addition to a refractive surface in an incident optical system, thereby suppressing degradation of optical performance due to temperature rise. Patent Document 1 discloses an optical scanning device that specifies the value of the ratio between the refractive power of the refractive surface and the diffractive power of the diffractive surface in order to suppress the shift of the image plane due to a temperature rise. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-115364 Summary of the Invention [Problem to be solved by the invention]

[0004] In the optical scanning device disclosed in Patent Document 1, the shift of the image plane in the sub-scanning cross section is not suppressed as much as the shift of the image plane in the main-scanning cross section when the temperature rises. That is, in the optical scanning device disclosed in Patent Document 1, the difference between the focus in the main scanning section and the focus in the sub-scanning section, that is, the increase in astigmatism due to temperature rise, is not sufficiently suppressed.

[0005] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide an optical scanning device that can sufficiently suppress an increase in astigmatism due to a rise in temperature. [Means for solving the problem]

[0006] The optical scanning device according to the present invention includes a deflector that deflects a first light beam from a first light source to scan a first scanned surface in a main scanning direction, a first incident optical system that includes a first optical section having at least one of an incident surface and an exit surface that is a diffractive surface and that guides the first light beam from the first light source to a first deflecting surface of the deflector, and a first imaging optical system that guides the first light beam deflected by the first deflecting surface to the first scanned surface, and the distance on the optical axis of the first incident optical system between the light emitting surface of the first light source and the incident surface of the first optical section and the distance between the exit surface of the first optical section and an on-axis deflection point of the first deflecting surface are respectively defined as D and D. f and D b , the absolute values ​​of the refractive power and the diffractive power in the main scanning cross section of the first optical unit are |P rm | and |P dm When | is set, 0.20≦D f / D b ≦0.40 1.00<|P dm | / |P rm |≦1.50 The present invention is characterized by satisfying the following conditions. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide an optical scanning device that can sufficiently suppress an increase in astigmatism due to a rise in temperature. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 2 is a schematic development view of a part of the optical scanning device according to the first embodiment in a main scanning cross section. [Figure 2] FIG. 2 is a schematic development view of a part of the optical scanning device according to the first embodiment in a sub-scanning cross section. [Figure 3] FIG. 2 is a schematic partial sub-scanning cross-sectional view of the optical scanning device according to the first embodiment. [Figure 4] 2A and 2B are a partial schematic development view in a main scanning section and a partial schematic sub-scanning section of the optical scanning device according to the first embodiment. [Figure 5] FIG. 2 is a partially enlarged schematic sub-scanning sectional view of the optical scanning device according to the first embodiment. [Figure 6]5A and 5B are diagrams showing the image height dependency of the amount of change in astigmatism in the optical scanning device according to the first embodiment. [Figure 7] FIG. 11 is a schematic development view of a part of an optical scanning device according to a second embodiment in a main scanning cross section. [Figure 8] FIG. 11 is a schematic development view of a part of an optical scanning device according to a second embodiment in a sub-scanning cross section. [Figure 9] FIG. 10 is a partial schematic sub-scanning cross-sectional view of an optical scanning device according to a second embodiment. [Figure 10] 10A and 10B are diagrams showing the image height dependency of the amount of change in astigmatism in the optical scanning device according to the second embodiment. [Figure 11] FIG. 11 is a schematic development view of a part of an optical scanning device according to a third embodiment in a main scanning cross section. [Figure 12] FIG. 11 is a schematic partial development view in sub-scanning section of an optical scanning device according to a third embodiment. [Figure 13] FIG. 10 is a partial schematic sub-scanning cross-sectional view of an optical scanning device according to a third embodiment. [Figure 14] 10A and 10B are diagrams showing the image height dependency of the amount of change in astigmatism in the optical scanning device according to the third embodiment. [Figure 15] 1 is a sub-scanning cross-sectional view of a main part of a color image forming apparatus according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] The optical scanning device according to the present embodiment will be described in detail below with reference to the accompanying drawings. Note that the drawings may be drawn to a scale different from the actual scale in order to facilitate understanding of the present embodiment. In the following description, the main scanning direction is the direction perpendicular to the rotation axis of the deflector and the optical axis of the imaging optical system (the direction in which the light beam is deflected and scanned by the deflector), and the sub-scanning direction is the direction parallel to the rotation axis of the deflector.

[0010] Furthermore, the main scanning section is a section perpendicular to the sub-scanning direction, and the sub-scanning section is a section perpendicular to the main scanning direction. In the following description, the main scanning direction is defined as the Y direction, the sub-scanning direction as the Z direction, and the direction perpendicular to the main scanning direction and the sub-scanning direction as the X direction.

[0011] [First embodiment] Conventionally, in order to reduce costs, various configurations have been proposed for optical scanning devices in which the incident optical system that guides the light beam from the light source to the deflector is formed using only a single optical element that has both refractive power and diffractive power, in order to suppress deterioration of optical performance due to temperature rise.

[0012] For example, an optical scanning device is known that suppresses deterioration of optical performance due to temperature rise of the light source by adjusting the optical performance of the incident optical system and the imaging optical system according to wavelengths determined based on the wavelengths immediately after the light source is turned on and when it has stabilized. However, in this optical scanning device, no consideration is given to a change in the shape of at least one optical element that may occur due to a temperature rise of the light source. Therefore, in this optical scanning device, the difference between the focus in the main scanning section and the focus in the sub-scanning section, that is, the increase in astigmatism, is not sufficiently suppressed.

[0013] Further, for example, an optical scanning device is known that specifies the ratio between the refractive power and the diffractive power of a single optical element forming the incident optical system in order to suppress shifts of the image plane due to changes in environmental temperature. However, in this optical scanning device, the shift amount in the main scanning section of the image plane is reduced to within 1 mm within a temperature change range of ±30°C, while the shift amount in the sub-scanning section of the image plane is allowed to be within 4 mm. Therefore, in this optical scanning device, the increase in astigmatism is not sufficiently suppressed.

[0014] As described above, conventionally proposed optical scanning devices having a configuration for suppressing the deterioration of optical performance due to temperature rise do not sufficiently suppress the increase in astigmatism. Therefore, the present embodiment aims to provide an optical scanning device in which the incident optical system is formed using only a single diffractive optical element and which can suppress an increase in astigmatism even when the ambient temperature changes due to an increase in the temperature of the light source.

[0015] 1(a) and (b) are partial schematic development views in the main scanning section of the optical scanning device 1 according to the first embodiment. 2(a) and 2(b) are partial schematic development views of the optical scanning device 1 according to the first embodiment in the sub-scanning cross section. FIG. 3 is a partial schematic sub-scan cross-sectional view of the optical scanning device 1 according to the first embodiment.

[0016] The optical scanning device 1 of this embodiment is configured to scan four scanned surfaces, including a first scanned surface 100a, a second scanned surface 100b, a third scanned surface 100c, and a fourth scanned surface 100d, as will be described in detail below. Of the first and second photosensitive drums 100a and 100b corresponding to the first and second scanned surfaces 100a and 100b, respectively, the second photosensitive drum 100b is arranged so as to be closer to the deflector 50 in the X direction than the first photosensitive drum 100a. Furthermore, of the third and fourth photosensitive drums 100c and 100d corresponding to the third and fourth scanned surfaces 100c and 100d, respectively, the third photosensitive drum 100c is arranged to be closer to the deflector 50 in the X direction than the fourth photosensitive drum 100d.

[0017] Specifically, Figures 1(a) and 2(a) respectively show a schematic main-scan cross-sectional development and a schematic sub-scan cross-sectional development of a first incident optical system 75a and a first imaging optical system 85a that guide a first light beam to a first scanned surface 100a. In addition, Figures 1(a) and 2(a) also show schematic developments in the main scanning section and the sub-scanning section of a fourth incident optical system 75d and a fourth imaging optical system 85d that guide the fourth light beam to the fourth scanned surface 100d.

[0018] Also, Figures 1(b) and 2(b) respectively show a schematic development view in the main scanning section and a schematic development view in the sub-scanning section of the second incident optical system 75b and the second imaging optical system 85b that guide the second light beam to the second scanned surface 100b. In addition, Figures 1(b) and 2(b) also show schematic developments in the main scanning section and the sub-scanning section of the third incident optical system 75c and the third imaging optical system 85c that guide the third light beam to the third scanned surface 100c, respectively. In addition, in Figures 1(a) and (b), the reflective optical elements 70a, 70b, 70c, 70d, 90a and 90b that reflect the first to fourth light beams deflected by the deflector 50 are shown by dashed lines, while in Figures 2(a) and (b), the reflective optical elements are not shown.

[0019] The optical scanning device 1 according to this embodiment includes first, second, third and fourth light sources 10a, 10b, 10c and 10d, and first, second, third and fourth optical elements 20a, 20b, 20c and 20d. The optical scanning device 1 of this embodiment also includes first, second, third and fourth sub-scanning apertures 30a, 30b, 30c and 30d, first, second, third and fourth main scanning apertures 40a, 40b, 40c and 40d, and a deflector 50. The optical scanning device 1 according to this embodiment also includes first imaging optical elements 60a and 60b, second imaging optical elements 80a, 80b, 80c and 80d, and reflecting optical elements 70a, 70b, 70c, 70d, 90a and 90b.

[0020] In the optical scanning device 1 according to this embodiment, the first incident optical system 75a that guides the first light flux from the first light source 10a to the first deflecting surface 50a of the deflector 50 is made up of the first optical element 20a. The second incident optical system 75b, which guides the second light beam from the second light source 10b to the first deflecting surface 50a of the deflector 50, is made up of a second optical element 20b. Furthermore, a third incident optical system 75c that guides the third light flux from the third light source 10c to the second deflecting surface 50b of the deflector 50 is made up of a third optical element 20c. Furthermore, a fourth incident optical system 75d that guides the fourth light flux from the fourth light source 10d to the second deflecting surface 50b of the deflector 50 is made up of a fourth optical element 20d.

[0021] In the optical scanning device 1 according to this embodiment, the upper optical part 60au of the first imaging optical element 60a and the second imaging optical element 80a form a first imaging optical system 85a. In addition, a second imaging optical system 85b is formed by the lower optical part 60al of the first imaging optical element 60a and the second imaging optical element 80b, and a third imaging optical system 85c is formed by the upper optical part 60bu of the first imaging optical element 60b and the second imaging optical element 80c. Furthermore, the lower optical part 60bl of the first imaging optical element 60b and the second imaging optical element 80d form a fourth imaging optical system 85d.

[0022] Each of the first to fourth light sources 10a to 10d is formed by a semiconductor laser having a plurality of light emitting points. The number of light emitting points provided in each of the first to fourth light sources 10a to 10d may be one.

[0023] Furthermore, the first light source 10a and the second light source 10b are arranged at the same position in the main scanning cross section, but are arranged at different positions in the sub-scanning direction. The third light source 10c and the fourth light source 10d are arranged at the same position in the main scanning cross section, but are arranged at different positions in the sub-scanning direction.

[0024] The first to fourth optical elements 20a to 20d are anamorphic lenses having different powers between the main scanning cross section and the sub-scanning cross section, respectively. The first to fourth optical elements 20a to 20d convert the first to fourth light beams emitted from the first to fourth light sources into parallel light beams in the main scanning cross section, and condense the light in the sub-scanning cross section, respectively. It should be noted that the parallel light beam here 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.

[0025] In addition, in the optical scanning device 1 of this embodiment, the first and second optical elements 20a and 20b are integrally formed with each other (see Figure 4(b)), and the third and fourth optical elements 20c and 20d are integrally formed with each other. That is, the first and second optical elements 20a and 20b form different optical portions (first optical portion and second optical portion) of a single (common) optical element. Moreover, the third and fourth optical elements 20c and 20d form different optical sections (third optical section and fourth optical section) of a single (common) optical element.

[0026] The first to fourth sub-scanning apertures 30a to 30d each have a rectangular opening and regulate the beam width in the sub-scanning direction of the first to fourth beams that have passed through the first to fourth optical elements 20a to 20d. That is, the first to fourth sub-scanning apertures 30a to 30d are provided between the first to fourth optical elements 20a to 20d and the deflector 50 in the first to fourth incident optical systems 75a to 75d, respectively.

[0027] In other words, the first to fourth sub-scanning diaphragms 30a to 30d are provided downstream of the first to fourth optical elements 20a to 20d in the first to fourth incident optical systems 75a to 75d, respectively. The first to fourth main scanning apertures 40a to 40d each have a rectangular opening and regulate the beam width in the main scanning direction of the first to fourth light beams that have passed through the first to fourth sub-scanning apertures 30a to 30d.

[0028] The deflector 50 is formed by a polygon mirror (rotating polygonal mirror) having four reflecting surfaces, and is configured to rotate at a constant speed in the direction of the arrow in Figures 1(a) and (b) by a driving means (not shown) such as a motor. The first imaging optical elements 60a and 60b and the second imaging optical elements 80a to 80d are each formed by an fθ lens (scanning lens) having fθ characteristics. Each of the reflective optical elements 70a, 70b, 70c, 70d, 90a and 90b is formed by a long mirror that does not have the power to reflect a predetermined light beam deflected by the deflector 50 and thereby bend the optical path of the predetermined light beam in the sub-scanning direction.

[0029] The first to fourth optical elements 20a to 20d, the first imaging optical elements 60a and 60b, and the second imaging optical elements 80a to 80d are each made of a plastic molded lens formed by injection molding a resin material. However, the present invention is not limited to this, and glass molded lenses may also be used. In addition, since molded lenses are easy to form aspherical shapes and are suitable for mass production, the use of plastic molded lenses as described above can improve productivity and optical performance.

[0030] Furthermore, as the reflecting optical elements 70a, 70b, 70c, 70d, 90a and 90b, general elongated glass on which a mirror surface is formed is used. However, the present invention is not limited to this, and components formed by injection molding a plastic material and having a mirror surface formed thereon, or components formed from a metal material such as aluminum and having a mirror finish may also be used. Furthermore, the reflecting surfaces of the reflecting optical elements 70a, 70b, 70c, 70d, 90a and 90b have a planar shape without power, but are not limited to this and may have a curved shape such as a spherical surface.

[0031] The first light beam emitted from the first light source 10a is converted into a parallel light beam in the main scanning cross section by the first optical element 20a, and is condensed in the sub-scanning cross section. The first light beam that passes through the first optical element 20a is shaped by the first sub-scanning aperture 30a and the first main-scanning aperture 40a, and then focused in the sub-scanning direction near the first deflecting surface 50a of the deflector 50, thereby forming a long line image in the main-scanning direction. The first incident optical system 75a causes the first light flux from the first light source 10a to be obliquely incident on the first deflecting surface 50a of the deflector 50 in the sub-scanning cross section.

[0032] In addition, the first light beam deflected by the first deflection surface 50a of the deflector 50 is focused onto the first scanned surface 100a by the upper optical part 60au of the first imaging optical element 60a and the second imaging optical element 80a to form a spot. The first light beam deflected by the first deflecting surface 50a of the deflector 50 is reflected in the sub-scanning direction by the reflecting optical element 70a when being guided to the first surface to be scanned 100a.

[0033] The second light beam emitted from the second light source 10b is converted into a parallel light beam in the main scanning cross section by the second optical element 20b, and is condensed in the sub-scanning cross section. The second light beam that passes through the second optical element 20b is shaped by the second sub-scanning aperture 30b and the second main-scanning aperture 40b, and then focused in the sub-scanning direction near the first deflection surface 50a of the deflector 50, thereby forming a long line image in the main-scanning direction. The second incident optical system 75b causes the second light flux from the second light source 10b to be obliquely incident on the first deflecting surface 50a of the deflector 50 in the sub-scanning cross section.

[0034] In addition, the second light beam deflected by the first deflection surface 50a of the deflector 50 is focused onto the second scanned surface 100b by the lower optical part 60al of the first imaging optical element 60a and the second imaging optical element 80b to form a spot. The second light beam deflected by the first deflecting surface 50a of the deflector 50 is reflected in the sub-scanning direction by the reflecting optical elements 70b and 90a when guided to the second surface to be scanned 100b.

[0035] By rotating the deflector 50 in the direction of the arrow in Figures 1(a) and (b), the first and second light beams scan the first and second scanned surfaces 100a and 100b at a uniform speed in the main scanning direction. This allows image recording on the first and second scan surfaces 100a and 100b.

[0036] As shown in Figures 1(a) and (b), the optical scanning device 1 of this embodiment employs a double-sided scanning system that scans the first to fourth scanned surfaces 100a to 100d located on both sides of the deflector 50. The third incident optical system 75c and the third imaging optical system 85c have optically equivalent configurations to the second incident optical system 75b and the second imaging optical system 85b, respectively.

[0037] The fourth incident optical system 75d and the fourth imaging optical system 85d have optically equivalent configurations to the first incident optical system 75a and the first imaging optical system 85a, respectively. Therefore, a description of the configuration for guiding the third light flux to the third scanned surface 100c by the third incident optical system 75c and the third imaging optical system 85c will be omitted here. Furthermore, a description of the configuration for guiding the fourth light flux to the fourth scanned surface 100d by the fourth incident optical system 75d and the fourth imaging optical system 85d will also be omitted.

[0038] Furthermore, in the optical scanning device 1 according to this embodiment, in order to align the scanning lines formed on the first to fourth surfaces to be scanned 100a to 100d with each other, it is necessary to synchronize the timings at which each scan is started with each other. Therefore, in the optical scanning device 1 according to this embodiment, a part of the first light beam deflected by the first deflecting surface 50a of the deflector 50 is made incident on a synchronization detection sensor (not shown).

[0039] Then, the light emission timings of the first to fourth light sources 10a to 10d are determined using the (BD signal) acquired by the synchronization detection sensor. As a result, by synchronizing the timings at which each scan is started on each of the first to fourth surfaces to be scanned 100a to 100d, the formed scanning lines can be aligned with each other.

[0040] Next, the specifications of the optical scanning device 1 according to this embodiment, and the refractive index and coordinates of each optical surface are shown in Tables 1 and 2 below, respectively. The shapes of the optical surfaces in the first incident optical system 75a and the first imaging optical system 85a, and the shapes of the optical surfaces in the second incident optical system 75b and the second imaging optical system 85b are shown in Tables 3 and 4 below, respectively. It should be noted that Table 2 only shows the first incident optical system 75a and the first imaging optical system 85a, and the second incident optical system 75b and the second imaging optical system 85b.

[0041] [Table 1]

[0042] [Table 2]

[0043] [Table 3]

[0044] [Table 4]

[0045] 4(a) and (b) respectively show a partially schematic main-scan cross-sectional view and a partially schematic sub-scan cross-sectional view for explaining some of the parameters shown in Table 1 in the optical scanning device 1 according to this embodiment. In FIG. 4B, the broken line indicates the main scanning cross section including the center of the deflector 50.

[0046] The incident surfaces of the first to fourth optical elements 20a to 20d provided in the optical scanning device 1 according to this embodiment are formed as diffractive surfaces on which diffraction gratings are formed. In the first to fourth optical elements 20a to 20d, a diffractive surface may be formed on the exit surface instead of the entrance surface, or a diffractive surface may be formed on both the entrance surface and the exit surface. Specifically, the first to fourth optical elements 20a to 20d can be formed by injection molding using a resin material, for example.

[0047] The optical scanning device 1 according to this embodiment employs a so-called temperature compensation optical system that compensates for changes in refractive power due to environmental fluctuations with changes in diffracted power due to changes in the wavelength of the semiconductor laser. More specifically, the diffractive surfaces formed on the first to fourth optical elements 20a to 20d are defined by a phase function φ as expressed in the following equation (1).

[0048]

number

[0049] In the formula (1), M is the diffraction order, and specifically, in the optical scanning device 1 according to this embodiment, first-order diffracted light is used, that is, M is 1. Furthermore, λ is the design wavelength, and specifically, in the optical scanning device 1 according to this embodiment, λ is 790 nm.

[0050] In addition, the meridional shapes of the entrance and exit surfaces of the first imaging optical elements 60a and 60b and the second imaging optical elements 80a to 80d provided in the optical scanning device 1 of this embodiment have aspherical shapes represented by polynomial functions up to the tenth order. Specifically, for each of the entrance and exit surfaces of the first imaging optical elements 60a and 60b and the second imaging optical elements 80a to 80d, the intersection with the optical axis (i.e., the surface vertex) is set as the origin, and the direction parallel to the optical axis is set as the X-axis.

[0051] In addition, an axis perpendicular to the optical axis in the main scanning section is defined as the Y axis, and an axis perpendicular to the optical axis in the sub-scanning section is defined as the Z axis. In this case, the shapes (meridional shapes) of the entrance and exit surfaces of the first imaging optical elements 60a and 60b and the second imaging optical elements 80a to 80d in the main scanning cross section are expressed by the following formula (2).

[0052]

number

[0053] In equation (2), R is the radius of curvature (generatrix radius of curvature) in the main scanning section, K is the eccentricity, B3, B4, B5, B6, B7, B8, B9 and B 10 is the aspherical coefficient. The shapes (sagittal shapes) of the entrance and exit surfaces of the first imaging optical elements 60a and 60b and the second imaging optical elements 80a to 80d in the sub-scan cross section are expressed by the following formula (3).

[0054]

number

[0055] In equation (3), S is the sagittal shape defined in the cross section perpendicular to the main scanning cross section, including the normal to the generatrix at each position on the generatrix, m j_i indicates the aspherical coefficient. Furthermore, r' is the radius of curvature (sagittal radius of curvature) in the sub-scanning cross section at a position spaced apart from the optical axis by Y in the main scanning direction, and is specifically expressed by the following equation (4).

[0056]

number

[0057] In equation (4), r is the radius of curvature of the sagittal line on the optical axis, E1, E2, E3, E4, E5, E6, E7, E8, E9 and E 10 is the sagittal variation coefficient. In the optical scanning device 1 according to this embodiment, the surface shapes of the entrance and exit surfaces of the first imaging optical elements 60a and 60b and the second imaging optical elements 80a to 80d are defined by the functions expressed in the above-mentioned respective definition equations. However, the scope of the invention is not limited by this definition.

[0058] As also shown in FIG. 3, the first and second light beams deflected by the first deflecting surface 50a of the deflector 50 each pass through a common first imaging optical element 60a. On the other hand, as shown in Table 3, the exit surface of the first imaging optical element 60a is defined by different aspherical coefficients in the areas through which the first and second light beams pass, i.e., has different aspherical shapes. In other words, the first imaging optical element 60a is an optical element in which the upper optical portion 60au and the lower optical portion 60al are integrally formed so that the shapes of the exit surfaces are different between the upper and lower sides in the sub-scanning direction.

[0059] FIG. 5 is a schematic sub-scan cross-sectional view of the first imaging optical element 60a provided in the optical scanning device 1 according to this embodiment. As shown in Figure 5, the first imaging optical element 60a has an upper optical section 60au located on the side opposite the scanned surface, and a lower optical section 60al located on the side of the scanned surface, on either side of a center line indicated by a dashed line passing through the vertices of the incident surface and the exit surface in the sub-scanning cross section.

[0060] The upper optical portion 60au and the lower optical portion 60al are defined by the aspherical coefficients shown in Tables 3 and 4, respectively. This makes it possible to efficiently focus the first and second light beams deflected by the first deflecting surface 50a of the deflector 50 onto the first and second surfaces to be scanned 100a and 100b, respectively.

[0061] Next, the influence of temperature rise on the optical performance of the optical scanning device 1 according to this embodiment will be described. The semiconductor lasers used in the first to fourth light sources 10a to 10d generate heat by themselves when turned on, causing a temperature rise and changing the environmental temperature. The temperature rise of the semiconductor laser and the resulting change in the environmental temperature have the following three main effects on the optical performance.

[0062] The first effect is a change in the wavelength of each of the semiconductor lasers forming the first to fourth light sources 10a to 10d, which is called mode hopping. Generally, the oscillation wavelength of a semiconductor laser increases with increasing temperature. The amount of change in the oscillation wavelength per unit temperature varies depending on the type of laser element used and individual differences. Specifically, the first to fourth light sources 10a to 10d can be semiconductor lasers having a typical characteristic value in which the wavelength λ changes by 0.26 nm when the temperature T changes by 1 degree, i.e., a change of dλ / dT=0.26 (nm / degree).

[0063] The second effect is that the ambient temperature rises as the temperature of the semiconductor laser rises, causing a change in the refractive index of an optical element disposed in the vicinity of the semiconductor laser. Specifically, in the optical scanning device 1 according to this embodiment, the refractive indexes of the first to fourth optical elements 20a to 20d arranged in the vicinity of the first to fourth light sources 10a to 10d change, respectively.

[0064] Generally, the refractive index of a resin material decreases when the temperature is increased, but the amount of change in the refractive index per unit temperature varies depending on the type of resin material used and individual differences. Specifically, the first to fourth optical elements 20a to 20d have a general characteristic value in which the refractive index n changes by only 1 degree when the temperature T changes by only 1 degree. -5 That is, dn / dT=-9.5×10 -5 The thickness of the resin material can be changed by 1 / degree.

[0065] The third effect is that the ambient temperature rises as the temperature of the semiconductor laser rises, causing the shapes of the first to fourth optical elements 20a to 20b arranged in close proximity to the first to fourth light sources 10a to 10d to change. Generally, optical elements made of resin materials expand when heated, reducing the power of the optical surface of the optical element, while the coefficient of thermal expansion per unit temperature of the optical element varies depending on the type of resin material used and individual differences. Specifically, the first to fourth optical elements 20a to 20d can be formed from a resin material having a thermal expansion coefficient that is a general characteristic value of isotropic expansion of 0.008% when the temperature rises by just 1 degree.

[0066] In the optical scanning device 1 according to this embodiment, the first to fourth optical elements 20a to 20d are formed in consideration of the above three influences, thereby suppressing an increase in astigmatism when the environmental temperature rises. Specifically, the optical scanning device 1 according to this embodiment employs a temperature compensation optical system that uses diffraction power.

[0067] More specifically, when the environmental temperature rises, the refractive indexes of the first to fourth optical elements 20a to 20d decrease and the elements expand. At this time, the focal points of the first to fourth optical elements 20a to 20d are shifted so as to be farther away from the first to fourth light sources 10a to 10d, respectively.

[0068] On the other hand, in the optical scanning device 1 according to this embodiment, the oscillation wavelength becomes longer as the temperature of each of the first to fourth light sources 10a to 10d increases. At this time, the focal points of the first to fourth optical elements 20a to 20d are shifted closer to the first to fourth light sources 10a to 10d, respectively, depending on the diffraction power of each of the first to fourth optical elements 20a to 20d.

[0069] That is, in the optical scanning device 1 according to this embodiment, the above two shifts can be cancelled out by appropriately setting the diffraction power of each of the first to fourth optical elements 20a to 20d. In reality, the amount of change in focus due to the above-mentioned changes in refractive index and shape varies depending on the power distribution in the entire optical scanning device 1 of this embodiment and the power distribution in each optical surface, but is generally proportional to the overall system magnification of the optical scanning device 1 of this embodiment.

[0070] Here, the overall system magnification of the optical scanning device 1 according to this embodiment means the composite magnification of the incident optical system and the imaging optical system, in other words, the composite magnification (composite lateral magnification) of each optical element provided in each of the incident optical system and the imaging optical system. Therefore, in the optical scanning device 1 according to this embodiment, the diffraction power of each of the first to fourth optical elements 20a to 20d is set based on the overall system magnification.

[0071] This makes it possible to effectively suppress an increase in astigmatism by adjusting the amount of focus shift in the main scanning cross section and the sub-scanning cross section when the temperature of each of the first to fourth optical elements 20a to 20d increases. The characteristics of the semiconductor lasers forming the first to fourth light sources 10a to 10d and the first to fourth optical elements 20a to 20d that occur with temperature rise are not limited to those described above, and other characteristics may also be taken into consideration.

[0072] Figure 6(a) shows the image height dependence of the change in focus in the main scanning section, and the change in focus and astigmatism in the sub-scanning section on the first scanned surface 100a when the temperature is raised by 25 degrees in the optical scanning device 1 of this embodiment. Figure 6(b) also shows the image height dependence of the change in focus in the main scanning section, and the change in focus and astigmatism in the sub-scanning section on the second scanned surface 100b when the temperature is raised by 25 degrees in the optical scanning device 1 of this embodiment.

[0073] Here, the astigmatism is calculated as a value obtained by subtracting the amount of change in focus in the main scanning section from the amount of change in focus in the sub-scanning section. The magnitude of the change is positive in the direction in which the focus moves away from the corresponding light source (rear focus), and negative in the direction in which the focus moves closer to the corresponding light source (front focus). Regarding the size of the image height, the side on which the first to fourth light sources 10a to 10d are arranged relative to the optical axis of the first to fourth imaging optical systems 85a to 85d is positive, and the side opposite to the side on which the first to fourth light sources 10a to 10d are arranged is negative.

[0074] The focal position is calculated from the center position of the area where the LSF width is equal to or smaller than a predetermined size (slice level) when defocusing is performed in a direction parallel to the optical axis of the corresponding imaging optical system near the corresponding scanned surface. The LSF width in the main scanning direction refers to the width when the light quantity profile obtained by integrating the spot profile in the sub-scanning direction at each image height is sliced ​​at a position 13.5% of its maximum value.

[0075] The LSF width in the sub-scanning direction refers to the width when the light quantity profile obtained by integrating the spot profile in the main scanning direction at each image height is sliced ​​at a position 13.5% of its maximum value. In the optical scanning device 1 according to this embodiment, the slice level is set to 120 μm over the entire image height range in both the main scanning direction and the sub-scanning direction.

[0076] As shown in Figures 6(a) and (b), when the temperature is raised by 25 degrees, the amount of change in focus in the main scanning section and the amount of change in focus in the sub-scanning section are approximately the same for the first and second scanned surfaces 100a and 100b, respectively. Furthermore, when the temperature is raised by 25 degrees, the change in astigmatism is within 1 mm across all image heights for the first and second scanned surfaces 100a and 100b, respectively, which shows that the increase in astigmatism is effectively suppressed.

[0077] Next, each conditional expression in the optical scanning device 1 according to this embodiment will be described. First, the distance between the light emitting surfaces of the first to fourth light sources 10a to 10d and the incident surfaces of the first to fourth optical elements 20a to 20d on the optical axes of the first to fourth incident optical systems 75a to 75d is defined as D f Let's say. Here, the light-emitting surfaces of the first to fourth light sources 10a to 10d are surfaces on which at least one light-emitting point is arranged in the first to fourth light sources 10a to 10d and which are perpendicular to the optical axes of the first to fourth incident optical systems 75a to 75d. In other words, the light-emitting surfaces of the first to fourth light sources 10a to 10d are planes that include at least one light-emitting point in the first to fourth light sources 10a to 10d and are perpendicular to the optical axes of the first to fourth incident optical systems 75a to 75d.

[0078] The distance between the exit surfaces of the first and second optical elements 20a and 20b on the optical axes of the first and second incident optical systems 75a and 75b and the on-axis deflection point of the first deflecting surface 50a of the deflector 50 is defined as D b Let's say. Similarly, the distance between the exit surfaces of the third and fourth optical elements 20c and 20d on the optical axes of the third and fourth incident optical systems 75c and 75d and the on-axis deflection point of the second deflection surface 50b of the deflector 50 is also D b Let us assume that: Here, the light beam deflected by the deflector 50 so as to scan the axial image height on a predetermined scanned surface is referred to as the axial light beam, and the deflection point of the chief ray of the axial light beam on a predetermined deflection surface of the deflector 50 is referred to as the axial deflection point.

[0079] The absolute values ​​of the refractive power and the diffractive power of the first to fourth optical elements 20a to 20d in the main scanning cross section are |P rm | and |P dm |Let's say. At this time, in the optical scanning device 1 according to this embodiment, the following conditional expressions (5) and (6) are satisfied.

[0080]

number

number

[0081] Here, conditional expression (5) is a condition that is necessary for the optical scanning device 1 according to this embodiment to satisfy conditional expression (6) and thereby sufficiently suppress an increase in astigmatism. If the upper limit of conditional expression (6) is exceeded, the cancellation of the focus shift due to the diffraction power when the temperature rises in the main scanning cross section becomes too large, making it difficult to sufficiently suppress the increase in astigmatism, which is undesirable.

[0082] On the other hand, if the value is below the lower limit of conditional expression (6), the cancellation of the focus shift caused by the diffraction power when the temperature rises in the main scanning cross section becomes too small, making it difficult to sufficiently suppress the increase in astigmatism, which is not preferable. In the optical scanning device 1 according to this embodiment, it is preferable that the following conditional expression (6a) be fulfilled instead of the conditional expression (6).

[0083]

number

[0084] In the optical scanning device 1 according to this embodiment, it is more preferable that the following conditional expression (6b) be fulfilled instead of the conditional expression (6a).

[0085]

number

[0086] In the optical scanning device 1 according to this embodiment, D f / D b =33.59 / 125.11=0.268, so conditional expression (5) is satisfied. Furthermore, in Table 1, in the first to fourth optical elements 20a to 20d, |P dm | / |P rm Since it can be determined that |=|0.0157| / |0.0142|=1.106, the conditional expressions (6), (6a) and (6b) are satisfied.

[0087] Next, the absolute values ​​of the overall system magnification in the main scanning section and the sub-scanning section of the optical scanning device 1 according to this embodiment are |β m | and |β s |Let's say. In this case, it is preferable that the optical scanning device 1 according to this embodiment fulfills the following conditional expression (7). In other words, in the optical scanning device 1 according to this embodiment, it is preferable that the absolute value of the total system magnification in the main scanning cross section is larger than the absolute value of the total system magnification in the sub-scanning cross section.

[0088]

number

[0089] If the value is below the lower limit of condition (7), the amount of focus shift in the sub-scan section when the temperature rises becomes too large, making it difficult to sufficiently suppress an increase in astigmatism, which is undesirable. In the optical scanning device 1 according to this embodiment, it is more preferable that the following conditional expression (7a) be fulfilled instead of the conditional expression (7).

[0090]

number

[0091] If the upper limit of conditional expression (7a) is exceeded, the amount of focus shift in the main scanning section when the temperature rises becomes too large, making it difficult to sufficiently suppress an increase in astigmatism, which is undesirable. Furthermore, in the optical scanning device 1 according to this embodiment, it is even more preferable that the following conditional expression (7b) be fulfilled instead of conditional expression (7a).

[0092]

number

[0093] In the optical scanning device 1 according to this embodiment, |β m | / |β s The result is |=|-6.55| / |5.30|=1.236. Furthermore, for the second and third scanned surfaces 100b and 100c, |β m | / |β s The result is |=|-6.66| / |5.30|=1.257. Therefore, in the optical scanning device 1 according to this embodiment, the conditional expressions (7), (7a), and (7b) are satisfied for the first to fourth surfaces to be scanned 100a to 100d.

[0094] Next, the absolute values ​​of the refractive power and the diffractive power in the sub-scan section of the first to fourth optical elements 20a to 20d provided in the optical scanning device 1 according to this embodiment are respectively expressed as |P rs | and |P ds |Let's say. In this case, it is preferable that the optical scanning device 1 according to this embodiment fulfills the following conditional expression (8). In other words, in the optical scanning device 1 according to this embodiment, it is preferable that the absolute value of the refractive power in the sub-scanning cross section of the first to fourth optical elements 20a to 20d is greater than the absolute value of the diffractive power in the sub-scanning cross section.

[0095]

number

[0096] If the upper limit of conditional expression (8) is exceeded, the cancellation of the focus shift due to the diffraction power when the temperature rises in the sub-scanning cross section becomes too large, making it difficult to sufficiently suppress the increase in astigmatism, which is undesirable. In the optical scanning device 1 according to this embodiment, it is more preferable that the following conditional expression (8a) be fulfilled instead of the conditional expression (8).

[0097]

number

[0098] If the lower limit of conditional expression (8a) is not reached, the cancellation of the focus shift caused by the diffraction power when the temperature rises in the sub-scanning cross section becomes too small, making it difficult to sufficiently suppress the increase in astigmatism, which is undesirable. Furthermore, in the optical scanning device 1 according to this embodiment, it is even more preferable that the following conditional expression (8b) be fulfilled instead of conditional expression (8a).

[0099]

number

[0100] In the optical scanning device 1 according to this embodiment, it is clear from Table 1 that |P ds | / |P rs |=|0.0173| / |0.0202|=0.856, so that the conditional expressions (8), (8a) and (8b) are satisfied.

[0101] Next, the distance between the axial deflection point on the first deflecting surface 50a on the optical axis of the first and second imaging optical systems 85a and 85b and the first and second scanned surfaces 100a and 100b is defined as T c Let's say. Similarly, the distance between the axial deflection point on the second deflecting surface 50b on the optical axis of the third and fourth imaging optical systems 85c and 85d and the third and fourth scanned surfaces 100c and 100d is also T c Let us assume that:

[0102] Furthermore, the angle that the traveling direction of the first and second light beams toward the most off-axis image heights of the first and second scanned surfaces 100a and 100b when deflected by the first deflecting surface 50a in the main scanning cross section makes with the optical axis of the first and second imaging optical systems 85a and 85b is defined as θ. Similarly, the angle that the direction of travel of the third and fourth light beams toward the most off-axis image heights of the third and fourth scanned surfaces 100c and 100d when deflected by the second deflecting surface 50b in the main scanning cross section makes with the optical axis of the third and fourth imaging optical systems 85c and 85d is also θ. In this case, it is preferable that the optical scanning device 1 according to this embodiment fulfills the following conditional expression (9).

[0103]

number

[0104] If the upper limit value of conditional expression (9) is exceeded, the size of the first to fourth incident optical systems 75a to 75d becomes too large, which is undesirable because it increases the magnification of the first to fourth incident optical systems 75a to 75d in the sub-scanning cross section, and ultimately the magnification of the entire system in the sub-scanning cross section. On the other hand, if the lower limit of conditional expression (9) is not reached, the size of the first to fourth imaging optical systems 85a to 85d will be too small, which will result in the size of the first to fourth incident optical systems 75a to 75d becoming small, i.e., the overall lengths of the first to fourth incident optical systems 75a to 75d becoming short. In this case, the first to fourth optical elements 20a to 20d may be affected by heat generated by the deflector 50, which is not preferable.

[0105] In the optical scanning device 1 according to this embodiment, it is more preferable that the following conditional expression (9a) be fulfilled instead of the conditional expression (9).

[0106]

number

[0107] In the optical scanning device 1 according to this embodiment, the first to fourth imaging optical systems 85a to 85d are shown in Table 1. c × tan θ=233×tan(0.79)=235.154, so that conditional expressions (9) and (9a) are satisfied.

[0108] As described above, in the optical scanning device 1 of this embodiment, the first to fourth incident optical systems 75a to 75d that guide the first to fourth light beams from the first to fourth light sources 10a to 10d to the deflector 50 are each composed of the first to fourth optical elements 20a to 20d having diffractive surfaces. In such an incident optical system, the conditional expressions (5) and (6) are satisfied, so that the increase in astigmatism due to the temperature rise in the optical scanning device 1 according to this embodiment can be sufficiently suppressed.

[0109] The above configuration can also be applied to an optical scanning device that scans a single surface to be scanned. Furthermore, the first and second optical elements 20a and 20b may be provided separately from each other, and the third and fourth optical elements 20c and 20d may be provided separately from each other.

[0110] [Second embodiment] 7(a) and (b) are partial schematic development views in the main scanning cross section of the optical scanning device 2 according to the second embodiment. 8(a) and (b) are partial schematic development views in the sub-scanning cross section of the optical scanning device 2 according to the second embodiment.

[0111] FIG. 9 is a partial schematic sub-scan cross-sectional view of an optical scanning device 2 according to the second embodiment. The optical scanning device 2 of this embodiment has the same configuration as the optical scanning device 1 of the first embodiment except for the various numerical values, so the same components are given the same reference numerals and their explanations are omitted.

[0112] The specifications of the optical scanning device 2 according to this embodiment, and the refractive index and coordinates of each optical surface are shown in Tables 5 and 6 below, respectively. The shapes of the optical surfaces in the first incident optical system 75a and the first imaging optical system 85a, and the shapes of the optical surfaces in the second incident optical system 75b and the second imaging optical system 85b are shown in Tables 7 and 8 below, respectively. It should be noted that Table 6 only shows the first incident optical system 75a and the first imaging optical system 85a, and the second incident optical system 75b and the second imaging optical system 85b.

[0113] [Table 5]

[0114] [Table 6]

[0115] [Table 7]

[0116] [Table 8]

[0117] Figure 10(a) shows the image height dependence of the change in focus in the main scanning section, and the change in focus and astigmatism in the sub-scanning section on the first scanned surface 100a when the temperature is raised by 25 degrees in the optical scanning device 2 of this embodiment. Figure 10(b) also shows the image height dependence of the change in focus in the main scanning section, and the change in focus and astigmatism in the sub-scanning section on the second scanned surface 100b when the temperature is raised by 25 degrees in the optical scanning device 2 of this embodiment.

[0118] As shown in Figures 10(a) and (b), when the temperature is raised by 25 degrees, the amount of change in focus in the main scanning section and the amount of change in focus in the sub-scanning section are approximately the same for the first and second scanned surfaces 100a and 100b, respectively. Furthermore, when the temperature is raised by 25 degrees, the change in astigmatism is within 1 mm across all image heights for the first and second scanned surfaces 100a and 100b, respectively, which shows that the increase in astigmatism is effectively suppressed.

[0119] In the optical scanning device 2 according to this embodiment, D f / D b =33.59 / 125.11=0.268, so conditional expression (5) is satisfied. In the optical scanning device 2 according to this embodiment, it is clear from Table 5 that |P dm | / |P rm Since |=|0.0154| / |0.0145|=1.062, the conditional expressions (6), (6a) and (6b) are satisfied.

[0120] In the optical scanning device 2 according to this embodiment, |β m | / |β s The result is |=|-6.50| / |5.34|=1.217. Furthermore, for the second and third scanned surfaces 100b and 100c, |β m | / |β s The result is |=|-6.56| / |5.30|=1.238. Therefore, in the optical scanning device 2 according to this embodiment, the conditional expressions (7), (7a), and (7b) are satisfied for the first to fourth surfaces to be scanned 100a to 100d.

[0121] In the optical scanning device 2 according to this embodiment, it is clear from Table 5 that |P ds | / |P rs |=|0.0173| / |0.0202|=0.856, so that the conditional expressions (8), (8a) and (8b) are satisfied. In the optical scanning device 2 according to this embodiment, the first to fourth imaging optical systems 85a to 85d are shown in Table 5. c× tan θ=233×tan(0.79)=235.154, so that conditional expressions (9) and (9a) are satisfied.

[0122] As described above, in the optical scanning device 2 of this embodiment, the first to fourth incident optical systems 75a to 75d that guide the first to fourth light beams from the first to fourth light sources 10a to 10d to the deflector 50 are each composed of the first to fourth optical elements 20a to 20d having diffractive surfaces. In such an incident optical system, the conditional expressions (5) and (6) are satisfied, so that the increase in astigmatism due to the temperature rise in the optical scanning device 2 according to this embodiment can be sufficiently suppressed.

[0123] [Third embodiment] 11(a) and 11(b) are partial schematic development views in the main scanning cross section of the optical scanning device 3 according to the third embodiment. 12(a) and 12(b) are partial schematic development views of the optical scanning device 3 according to the third embodiment in the sub-scanning cross section.

[0124] FIG. 13 is a partial schematic sub-scan cross-sectional view of an optical scanning device 3 according to a third embodiment. The optical scanning device 3 of this embodiment has the same configuration as the optical scanning device 1 of the first embodiment except for the various numerical values, so the same components are given the same reference numerals and their explanations are omitted.

[0125] The specifications of the optical scanning device 3 according to this embodiment, and the refractive index and coordinates of each optical surface are shown in Tables 9 and 10 below, respectively. The shapes of the optical surfaces in the first incident optical system 75a and the first imaging optical system 85a, and the shapes of the optical surfaces in the second incident optical system 75b and the second imaging optical system 85b are shown in Tables 11 and 12 below, respectively. Table 10 shows only the first incident optical system 75a and the first imaging optical system 85a, and the second incident optical system 75b and the second imaging optical system 85b.

[0126] [Table 9]

[0127] [Table 10]

[0128] [Table 11]

[0129] [Table 12]

[0130] Figure 14(a) shows the image height dependence of the change in focus in the main scanning section, and the change in focus and astigmatism in the sub-scanning section on the first scanned surface 100a when the temperature is raised by 25 degrees in the optical scanning device 3 of this embodiment. Figure 14(b) also shows the image height dependence of the change in focus in the main scanning section, and the change in focus and astigmatism in the sub-scanning section on the second scanned surface 100b when the temperature is raised by 25 degrees in the optical scanning device 3 of this embodiment.

[0131] As shown in Figures 14(a) and (b), when the temperature is raised by 25 degrees, the amount of change in focus in the main scanning section and the amount of change in focus in the sub-scanning section are approximately the same for the first and second scanned surfaces 100a and 100b, respectively. Furthermore, when the temperature is raised by 25 degrees, the change in astigmatism is within 1 mm across all image heights for the first and second scanned surfaces 100a and 100b, respectively, which shows that the increase in astigmatism is effectively suppressed.

[0132] In the optical scanning device 3 according to this embodiment, as shown in Table 9, the first to fourth incident optical systems 75a to 75d have D f / D b=43.57 / 115.13=0.378, so conditional expression (5) is satisfied. In the optical scanning device 3 according to this embodiment, it is clear from Table 9 that |P dm | / |P rm |=0.0125 / 0.0107=1.168, so that the conditional expressions (6), (6a) and (6b) are satisfied.

[0133] In addition, in the optical scanning device 3 according to this embodiment, |β m | / |β s The result is |=|-5.06| / |3.70|=1.368. Furthermore, for the second and third scanned surfaces 100b and 100c, |β m | / |β s The result is |=|-5.14| / |3.79|=1.356. Therefore, in the optical scanning device 3 according to this embodiment, the conditional expressions (7) and (7a) are satisfied for the first to fourth surfaces to be scanned 100a to 100d.

[0134] In the optical scanning device 3 according to this embodiment, it is clear from Table 9 that |P ds | / |P rs Since it can be determined that |=|0.0150| / |0.0166|=0.903, the conditional expressions (8), (8a) and (8b) are satisfied. In the optical scanning device 3 according to this embodiment, T c × tan θ=233×tan(0.79)=235.154, so that conditional expressions (9) and (9a) are satisfied.

[0135] As described above, in the optical scanning device 3 of this embodiment, the first to fourth incident optical systems 75a to 75d that guide the first to fourth light beams from the first to fourth light sources 10a to 10d to the deflector 50 are each composed of the first to fourth optical elements 20a to 20d having diffractive surfaces. In such an incident optical system, the conditional expressions (5) and (6) are satisfied, so that the increase in astigmatism due to the temperature rise in the optical scanning device 3 according to this embodiment can be sufficiently suppressed.

[0136] Moreover, the values ​​of the respective conditional expressions in the optical scanning devices according to the first to third embodiments are shown in Table 13 below.

[0137] [Table 13]

[0138] [Image forming equipment] FIG. 15 is a sub-scanning cross-sectional view of a main part of an image forming apparatus 93 including an optical scanning device 4 according to any one of the first to third embodiments.

[0139] The image forming apparatus 93 is a 4-in-1 type color image forming apparatus that uses a single optical scanning device 4 according to any one of the first to third embodiments to record image information on the photosensitive surfaces of four photosensitive drums, each of which is an image carrier. Specifically, the image forming apparatus 93 includes the optical scanning device 4 according to any one of the first to third embodiments, photosensitive drums 111, 112, 113 and 114, developing units 121, 122, 123 and 124, and a conveyor belt 141. The image forming apparatus 93 also includes a printer controller 143 and a fixing unit 145 .

[0140] As shown in FIG. 15, an image forming apparatus 93 receives R (red), G (green), and B (blue) color signals output from an external device 142 such as a personal computer. The input color signals are then converted by a printer controller 143 provided in the image forming device 93 into image data (dot data) for C (cyan), M (magenta), Y (yellow), and B (black).

[0141] Next, each converted image data is input to the optical scanning device 4. Then, light beams 131, 132, 133, and 134 modulated in accordance with each image data are emitted from the optical scanning device 4, and the emitted light beams 131 to 134 scan the photosensitive surfaces of the photosensitive drums 111, 112, 113, and 114 in the main scanning direction, respectively. Furthermore, charging rollers (not shown) that uniformly charge the surfaces of the photosensitive drums 111 to 114 are provided so as to come into contact with the surfaces. Then, light beams 131 to 134 are irradiated from the optical scanning device 4 onto the surfaces of the photosensitive drums 111 to 114 charged by the charging rollers.

[0142] As described above, the light beams 131 to 134 are modulated based on image data for each color, and electrostatic latent images are formed on the surfaces of the photosensitive drums 111 to 114 by irradiating the light beams 131 to 134. The formed electrostatic latent images are developed into toner images by developing units 121, 122, 123, and 124 arranged in contact with the photosensitive drums 111 to 114.

[0143] The toner images developed by the developing devices 121 to 124 are transferred in multiple layers onto a sheet of paper (transfer receiving material) (not shown) conveyed on a conveyor belt 141 by transfer rollers (transfer devices) (not shown) arranged opposite the photosensitive drums 111 to 114. In this way, one full-color image is formed. The paper onto which the unfixed toner image has been transferred as described above is further transported to a fixing device 145 provided behind the photosensitive drums 111 to 114 (on the left side in FIG. 15).

[0144] The fixing unit 145 is formed by a fixing roller having a fixing heater (not shown) therein, and a pressure roller disposed so as to be in pressure contact with the fixing roller. The paper conveyed from the transfer section is heated and pressed by the pressure contact portion between the fixing roller and the pressure roller, thereby fixing the unfixed toner image on the paper. Furthermore, a paper discharge roller (not shown) is disposed behind the fixing roller, and the paper discharge roller discharges the paper on which the fixed image has been fixed to the outside of the image forming apparatus 93 .

[0145] In the image forming device 93, the optical scanning device 4 records image signals (image information) on the photosensitive surfaces of the photosensitive drums 111 to 114 corresponding to each of the colors C (cyan), M (magenta), Y (yellow), and B (black), thereby enabling color images to be printed at high speed. The external device 142 may be, for example, a color image reading device equipped with a CCD sensor. In this case, the color image reading device and the image forming device 93 form a color digital copying machine.

[0146] 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 present invention.

[0147] The disclosure of this embodiment includes the following configuration. (Configuration 1) A deflector that deflects a first light beam from a first light source to scan a first scanned surface in a main scanning direction, a first incident optical system that includes a first optical section having at least one of an incident surface and an exit surface that is a diffractive surface and that guides the first light beam from the first light source to the first deflection surface of the deflector, and a first imaging optical system that guides the first light beam deflected by the first deflection surface to the first scanned surface, and the distance on the optical axis of the first incident optical system between the light emitting surface of the first light source and the incident surface of the first optical section and the distance between the exit surface of the first optical section and the on-axis deflection point of the first deflection surface are respectively defined as D. f and D b , the absolute values ​​of the refractive power and the diffractive power in the main scanning cross section of the first optical unit are |P rm | and |P dm |, 0.20≦D f / D b ≦0.40 and 1.00<|P dm | / |P rm An optical scanning device characterized by satisfying the condition |≦1.50. (Configuration 2) An optical scanning device according to configuration 1, characterized in that the absolute value of the combined magnification of the first incident optical system and the first imaging optical system in the main scanning section is greater than the absolute value of the combined magnification of the first incident optical system and the first imaging optical system in the sub-scanning section. (Configuration 3) The optical scanning device according to configuration 1 or 2, wherein, in the sub-scan section, the absolute value of the refractive power of the first optical unit is greater than the absolute value of the diffractive power of the first optical unit. (Configuration 4) The distance between the axial deflection point on the optical axis of the first imaging optical system and the first scanned surface is defined as T c In the main scanning section, when the angle formed by the traveling direction of the first light beam directed toward the most off-axis image height of the first scanned surface immediately after being deflected by the first deflecting surface and the optical axis of the first imaging optical system is θ, 200≦T c 4. The optical scanning device according to any one of configurations 1 to 3, wherein the condition: ×tanθ≦300 is satisfied. (Configuration 5) The optical scanning device according to any one of configurations 1 to 4, further comprising a first light source including a plurality of light emitting points. (Configuration 6) An optical scanning device according to any one of configurations 1 to 5, characterized in that it comprises a second optical section in which at least one of the entrance surface and exit surface is a diffractive surface, and is provided with a second entrance optical system that guides a second light beam from a second light source to a first deflection surface, and a second imaging optical system that guides the second light beam deflected by the first deflection surface to a second scanned surface, and the deflector deflects the second light beam from the second light source to scan the second scanned surface in the main scanning direction. (Configuration 7) The optical scanning device according to configuration 6, wherein the first and second optical sections are provided in a single optical element. (Configuration 8) An optical scanning device according to configuration 6 or 7, comprising third and fourth incident optical systems that guide the third and fourth light beams from the third and fourth light sources to a second deflection surface of a deflector, and third and fourth imaging optical systems that guide the third and fourth light beams deflected by the second deflection surface to the third and fourth scanned surfaces, wherein the deflector deflects the third and fourth light beams from the third and fourth light sources to scan the third and fourth scanned surfaces in the main scanning direction, the third incident optical system comprising a third optical section in which at least one of the incident surface and the exit surface is a diffractive surface, and the fourth incident optical system comprising a fourth optical section in which at least one of the incident surface and the exit surface is a diffractive surface. (Configuration 9) The optical scanning device according to configuration 8, wherein the third and fourth optical sections are provided in a single optical element. (Configuration 10) An optical scanning device described in any one of configurations 1 to 9, characterized in that the first optical section converts the first light beam from the first light source into a parallel light beam in the main scanning cross section and focuses the light in the sub-scanning cross section. (Configuration 11) An optical scanning device described in any one of configurations 1 to 10, characterized in that the first incident optical system causes the first light beam from the first light source to be obliquely incident on the first deflection surface in the sub-scanning cross section. (Configuration 12) The absolute values ​​of the composite magnifications of the first incident optical system and the first imaging optical system in the main scanning section and the sub-scanning section are respectively |β m | and |β s When | is set, 1.00<|β m | / |β s 12. The optical scanning device according to any one of configurations 1 to 11, wherein the condition |≦1.40 is satisfied. (Configuration 13) The absolute values ​​of the refractive power and the diffractive power in the sub-scanning section of the first optical unit are |P rs | and |P ds When | is set, 0.80 ≦ |P ds | / |P rs 13. The optical scanning device according to any one of configurations 1 to 12, wherein the condition |<1.00 is satisfied. (Configuration 14) An image forming apparatus comprising an optical scanning device according to any one of configurations 1 to 13, a developing unit that develops an electrostatic latent image formed on a first scanned surface by the optical scanning device into a toner image, a transfer unit that transfers the developed toner image to a transfer material, and a fixing unit that fixes the transferred toner image to the transfer material. (Configuration 15) An image forming apparatus comprising: an optical scanning device according to any one of configurations 1 to 13; and a printer controller that converts a signal output from an external device into image data and inputs the image data to the optical scanning device. [Explanation of symbols]

[0148] 1 Optical scanning device 10a First light source 20a First optical element (first optical section) 50 Deflector 50a First deflection surface 75a First incident optical system 85a First imaging optical system 100a First scanned surface

Claims

1. a deflector that deflects a first light beam from a first light source to scan a first scanned surface in a main scanning direction; a first incident optical system including a first optical section having at least one of an incident surface and an exit surface that is a diffractive surface, and which guides the first light flux from the first light source to a first deflecting surface of the deflector; a first imaging optical system that guides the first light beam deflected by the first deflection surface to the first scanned surface, The distance between the light emitting surface of the first light source and the incident surface of the first optical unit, and the distance between the exit surface of the first optical unit and the on-axis deflection point of the first deflection surface, on the optical axis of the first incident optical system, are respectively defined as D ｆ and D ｂ , the absolute values ​​of the refractive power and the diffractive power in the main scanning cross section of the first optical unit are |P ｒｍ | and | P ｄｍ |When 0.20≦D ｆ / D ｂ ≦0.40 1.00<|P ｄｍ | / |P ｒｍ |≦1.50 An optical scanning device characterized by satisfying the following conditions.

2. 2. The optical scanning device according to claim 1, wherein the absolute value of the combined magnification of the first incident optical system and the first imaging optical system in the main scanning cross section is greater than the absolute value of the combined magnification of the first incident optical system and the first imaging optical system in the sub-scanning cross section.

3. 2. The optical scanning device according to claim 1, wherein, in the sub-scan section, the absolute value of the refractive power of said first optical unit is greater than the absolute value of the diffractive power of said first optical unit.

4. The distance between the axial deflection point on the optical axis of the first imaging optical system and the first scanned surface is defined as T ｃ In the main scanning cross section, when the traveling direction of the first light beam directed toward the most off-axis image height of the first scanned surface immediately after being deflected by the first deflecting surface is θ, the angle is made with respect to the optical axis of the first imaging optical system, 200≦T ｃ ×tanθ≦300 2. The optical scanning device according to claim 1, wherein the following conditions are satisfied:

5. 2. The optical scanning device according to claim 1, wherein the first light source includes a plurality of light-emitting points.

6. a second incident optical system including a second optical section having at least one of an incident surface and an exit surface that is a diffractive surface, and guiding a second light beam from a second light source to the first deflection surface; a second imaging optical system that guides the second light beam deflected by the first deflection surface to a second scanned surface, 2. The optical scanning device according to claim 1, wherein the deflector deflects the second light beam from the second light source to scan the second surface to be scanned in the main scanning direction.

7. 7. The optical scanning device according to claim 6, wherein the first and second optical sections are provided in a single optical element.

8. third and fourth incident optical systems that guide third and fourth light beams from third and fourth light sources to the second deflecting surface of the deflector; third and fourth imaging optical systems that guide the third and fourth light beams deflected by the second deflection surface to third and fourth scanned surfaces, the deflector deflects the third and fourth light beams from the third and fourth light sources to scan the third and fourth scanned surfaces in a main scanning direction; the third incident optical system includes a third optical section having at least one of an incident surface and an exit surface that is a diffractive surface; 7. The optical scanning device according to claim 6, wherein the fourth incident optical system comprises a fourth optical section in which at least one of the incident surface and the exit surface is a diffractive surface.

9. 9. The optical scanning device according to claim 8, wherein the third and fourth optical sections are provided in a single optical element.

10. 2. The optical scanning device according to claim 1, wherein the first optical section converts the first light beam from the first light source into a parallel light beam in a main scanning cross section and condenses the light beam in a sub-scanning cross section.

11. 2. The optical scanning device according to claim 1, wherein the first incident optical system makes the first light beam from the first light source obliquely incident on the first deflecting surface in the sub-scanning cross section.

12. The absolute values ​​of the composite magnifications of the first incident optical system and the first imaging optical system in the main scanning section and the sub-scanning section are |β ｍ | and |β ｓ |When １．００＜｜β ｍ ｜／｜β ｓ ｜≦１．４０ 2. The optical scanning device according to claim 1, wherein the following conditions are satisfied:

13. The absolute values ​​of the refractive power and the diffractive power in the sub-scanning cross section of the first optical unit are |P ｒｓ | and | P ｄｓ |When 0.80≦|P ｄｓ | / |P ｒｓ |<1.00 2. The optical scanning device according to claim 1, wherein the following conditions are satisfied:

14. 14. An image forming apparatus comprising: an optical scanning device according to claim 1; a developing unit that develops an electrostatic latent image formed on the first scanned surface by the optical scanning device into a toner image; a transfer unit that transfers the developed toner image to a transfer material; and a fixing unit that fixes the transferred toner image to the transfer material.

15. 14. An image forming apparatus comprising: the optical scanning device according to claim 1; and a printer controller that converts a signal output from an external device into image data and inputs the image data to the optical scanning device.

Images