Optical scanner and image forming apparatus

Abstract

To provide a compact optical scanner with a simple configuration.SOLUTION: An optical scanner includes: a deflector that deflects a first light flux to scan a first scanned surface in a main scanning direction; a first imaging optical system that guides the first light flux deflected by the deflector to the first scanned surface; a light receiving element that receives the first light flux deflected by the deflector without the first imaging optical system; a first optical element that guides the first light flux deflected by the deflector to the light receiving element; and a housing that holds the deflector, the first imaging optical system, the light receiving element, and the first optical element. The first optical element and the deflector are arranged inside and outside a first surface of the housing, respectively.SELECTED DRAWING: Figure 6

Description

[Technical field]

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

[0002] 2. Description of the Related Art Conventionally, optical scanning devices have been known that have been made smaller by devising an arrangement of optical elements for so-called synchronous detection, which controls the timing of writing on a surface to be scanned. Patent document 1 discloses an optical scanning device that is miniaturized by arranging a deflector, a light receiving element that receives a light beam for synchronous detection, and a synchronous detection optical element that guides the light beam to the light receiving element on opposite sides of a substrate provided on a predetermined main scanning cross section. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2005-62516 A Summary of the Invention [Problem to be solved by the invention]

[0004] In the optical scanning device disclosed in Patent Document 1, the synchronous detection optical element is attached to the rear side of the substrate, and therefore the configuration is complex such that it is difficult to access the synchronous detection optical element. SUMMARY OF THE PRESENT EMBODIMENT An object of the present invention is to provide an optical scanning device that is small in size and has a simple configuration. [Means for solving the problem]

[0005] The optical scanning device of the present invention comprises a deflector that deflects a first light beam to scan a first scanned surface in a main scanning direction, a first imaging optical system that guides the first light beam deflected by the deflector to the first scanned surface, a light receiving element that receives the first light beam deflected by the deflector without passing through the first imaging optical system, a first optical element that guides the first light beam deflected by the deflector to the light receiving element, and a housing that holds the deflector, the first imaging optical system, the light receiving element, and the first optical element, and is characterized in that the first optical element and the deflector are arranged on the outside and inside of the first surface of the housing, respectively. Effect of the Invention

[0006] According to the present invention, it is possible to provide a small-sized optical scanning device with a simple configuration. [Brief description of the drawings]

[0007] [Figure 1] 2 is a partial development view in a main scanning section of the optical scanning device according to the first embodiment. FIG. [Diagram 2] 3A and 3B are a partial development view and a partial sub-scanning sectional view of the optical scanning device according to the first embodiment. [Diagram 3] 2A and 2B are a partial development view in a main-scanning section and a partial sub-scanning section of the optical scanning device according to the first embodiment. [Figure 4] 3 is a sub-scanning sectional view of a first imaging optical element included in the optical scanning device according to the first embodiment. [Diagram 5] 2 is a partial main-scan sectional projection view of the optical scanning device according to the first embodiment. FIG. [Figure 6] FIG. 2 is a partially enlarged cross-sectional view of the optical scanning device according to the first embodiment. [Figure 7] 5A and 5B are diagrams showing image height dependences of the LSF depth center position in the main scanning direction and the LSF depth center position in the sub-scanning direction on each scanned surface in the optical scanning device according to the first embodiment. [Figure 8] 2A and 2B are a partial development view in a main-scanning section and a partial sub-scanning section of the optical scanning device according to the first embodiment. [Figure 9] 11A and 11B are a partial development view in a main-scanning section and a partial sub-scanning section of an optical scanning device according to a second embodiment. [Figure 10] 11A and 11B are a partial development view in a main-scanning section and a partial sub-scanning section of an optical scanning device according to a second embodiment. [Figure 11] 13A and 13B are diagrams showing the image height dependence of the LSF depth center position in the main scanning direction and the LSF depth center position in the sub-scanning direction on each scanned surface in the optical scanning device according to the second embodiment. [Figure 12] 13A and 13B are a partial development view in a main-scanning section and a partial sub-scanning section of an optical scanning device according to a third embodiment. [Figure 13] 13A and 13B are a partial development view in a main-scanning section and a partial sub-scanning section of an optical scanning device according to a third embodiment. [Figure 14] 13A and 13B are diagrams showing the image height dependence of the LSF depth center position in the main scanning direction and the LSF depth center position in the sub-scanning direction on each scanned surface in the optical scanning device according to the third embodiment. [Figure 15] 2 is a sub-scanning sectional view of a main part of the image forming apparatus according to the embodiment. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] Hereinafter, an 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 a scale different from the actual scale in order to facilitate understanding of the present embodiment.

[0009] 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 by the deflector), the sub-scanning direction is the direction parallel to the rotation axis of the deflector, the main scanning cross section is the cross section perpendicular to the sub-scanning direction, and the sub-scanning cross section is the cross section perpendicular to the main scanning direction. In the following description, the direction parallel to the optical axis of the imaging optical system is defined as the X direction, the main scanning direction as the Y direction, and the sub-scanning direction as the Z direction.

[0010] [First embodiment] 1(a) and (b) are partial developments in the main scanning section of an optical scanning device 1 according to the first embodiment. 2(a) and (b) are partial developments in the sub-scanning section of the optical scanning device 1 according to the first embodiment. FIG. 2(c) is a partial sub-scanning sectional view of the optical scanning device 1 according to the first embodiment.

[0011] Specifically, FIG. 1(a) and FIG. 2(a) show a first incident optical system 75a and a first imaging optical system 85a that guide a first light flux LA to a first scanned surface 100a. FIGS. 1(a) and 2(a) also show a fourth incident optical system 75d and a fourth imaging optical system 85d that guide a fourth light flux LD to a fourth scanned surface 100d.

[0012] Specifically, FIGS. 1(b) and 2(b) show a second incident optical system 75b and a second imaging optical system 85b that guide a second light flux LB to a second scanned surface 100b. FIGS. 1(b) and 2(b) also show a third incident optical system 75c and a third imaging optical system 85c that guide a third light flux LC to a third scanned surface 100c. The first reflective optical elements 70a, 70b, 70c, and 70d and the second reflective optical elements 90a and 90b are shown by dashed lines in Figures 1(a) and (b), and are omitted in Figures 2(a) and (b).

[0013] The optical scanning device 1 of this embodiment includes a housing 2 (holding member), first, second, third and fourth light sources 10a, 10b, 10c and 10d, and first, second, third and fourth incident 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.

[0014] The optical scanning device 1 according to this embodiment also includes first imaging optical elements 60a and 60b, and first reflecting optical elements 70a, 70b, 70c, and 70d. The optical scanning device 1 according to this embodiment also includes second imaging optical elements 80a, 80b, 80c and 80d, and second reflecting optical elements 90a and 90b (second optical elements).

[0015] The optical scanning device 1 according to this embodiment also includes a synchronous detection lens 200 (first optical element, refractive optical element), a synchronous detection slit 210, and a synchronous detection sensor 220 (light receiving element) (FIG. 3(a)). The optical scanning device 1 of this embodiment employs a so-called double-sided scanning system that scans first and second scanned surfaces 100a and 100b, and third and fourth scanned surfaces 100c and 100d, which are provided on different sides of the deflector 50 in the main scanning cross section.

[0016] The housing 2 has a box portion having an internal space in which each optical element provided in the optical scanning device 1 of this embodiment is arranged, and a lid portion that covers the internal space from the top of the box portion, and is configured to store and hold each optical element. Each of the first to fourth light sources 10a to 10d is a light source having two light emitting points, such as a semiconductor laser, etc. That is, the optical scanning device 1 according to this embodiment is provided with a total of eight light emitting points.

[0017] Furthermore, the first light source 10a and the second light source 10b are disposed at the same position in the main scanning cross section, but are disposed at different positions in the sub-scanning direction. Furthermore, the third light source 10c and the fourth light source 10d are disposed at the same position in the main scanning cross section, but are disposed at different positions in the sub-scanning direction.

[0018] The first to fourth incident optical elements 20a to 20d are anamorphic lenses having different refractive powers in the main scanning section and the sub-scanning section, respectively. The first to fourth incident optical elements 20a to 20d convert the first to fourth light beams LA to LD emitted from the first to fourth light sources 10a to 10d into parallel beams in the main scanning direction, respectively. Note that the parallel beam here includes not only a strictly parallel beam but also an approximately parallel beam such as a weakly divergent beam or a weakly convergent beam. The first to fourth incident optical elements 20a to 20d respectively condense the first to fourth light beams LA to LD emitted from the first to fourth light sources 10a to 10d toward the deflector 50 in the sub-scanning direction.

[0019] The first to fourth sub-scanning apertures 30a to 30d each have a rectangular opening and limit the beam diameter in the sub-scanning direction of the first to fourth light beams LA to LD that pass through the first to fourth incident optical elements 20a to 20d. The first to fourth main scanning apertures 40a to 40d each have a rectangular opening and limit the beam diameter in the main scanning direction of the first to fourth light beams LA to LD that pass through the first to fourth sub-scanning apertures 30a to 30d.

[0020] The deflector 50 is a polygon mirror (rotating polygonal mirror) having four deflection surfaces, and is rotated at a constant speed in the direction of the arrows shown in FIGS. 1(a) and (b) by a driving means such as a motor (not shown). The first imaging optical elements 60a and 60b and the second imaging optical elements 80a to 80d are each an fθ lens (scanning lens) having fθ characteristics.

[0021] The first imaging optical element 60a and the second imaging optical element 80a focus (guide) the first light beam LA deflected by the deflector 50 onto a scanning area (image forming area) of the first scanned surface 100a, thereby forming a spot image on the scanning area. In addition, the first imaging optical element 60a and the second imaging optical element 80b focus (guide) the second light beam LB deflected by the deflector 50 onto the scanning area of ​​the second scanned surface 100b, thereby forming a spot image on the scanning area.

[0022] In addition, the first imaging optical element 60b and the second imaging optical element 80c focus (guide) the third light beam LC deflected by the deflector 50 onto the scanning area of ​​the third scanned surface 100c, thereby forming a spot image on the scanning area. In addition, the first imaging optical element 60b and the second imaging optical element 80d focus (guide) the fourth light beam LD deflected by the deflector 50 onto the scanning area of ​​the fourth scanned surface 100d, thereby forming a spot image on the scanning area. The first reflective optical elements 70a to 70d and the second reflective optical elements 90a and 90b are long mirrors without refractive power that bend the optical paths of the first to fourth light beams LA to LD deflected by the deflector 50 in the sub-scanning cross section.

[0023] The first to fourth incident optical elements 20a to 20d, 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 are each a molded lens formed by injection molding of a plastic material. However, the present invention is not limited to this, and these may be molded lenses formed by injection molding a glass material. In the optical scanning device 1 according to this embodiment, it is easy to form an optical surface having an aspheric shape, and by using a molded lens that is suitable for mass production, it is possible to improve productivity and optical performance.

[0024] In addition, the first reflective optical elements 70a to 70d and the second reflective optical elements 90a and 90b provided in the optical scanning device 1 of this embodiment are long mirrors formed by depositing a reflective surface on a typical long piece of glass, but are not limited to this. That is, these may be long mirrors formed by forming a reflective surface on a member formed by injection molding a plastic material, or by performing mirror finishing on a metal member such as aluminum. In addition, in the optical scanning device 1 according to this embodiment, the reflecting surfaces of these are formed in a planar shape without refractive power, but are not limited to this and may be formed in a curved shape such as a spherical surface.

[0025] The first and second light beams LA and LB emitted from the first and second light sources 10a and 10b are converted into approximately parallel light beams in the main scanning cross section by the first and second incident optical elements 20a and 20b, and are condensed in the sub-scanning cross section. The first and second light beams LA and LB, which pass through the first and second incident optical elements 20a and 20b, pass through the first and second sub-scanning apertures 30a and 30b and the first and second main-scanning apertures 40a and 40b, and are then guided to the first deflection surface 50a of the deflector 50. As a result, the first and second light beams LA and LB have limited beam diameters in the main scanning direction and the sub-scanning direction, and are focused in the sub-scanning direction so as to form a long line image in the main scanning direction near the first deflection surface 50a of the deflector 50.

[0026] The third and fourth light beams LC and LD emitted from the third and fourth light sources 10c and 10d are converted into approximately parallel light beams in the main scanning cross section by the third and fourth incident optical elements 20c and 20d, and are condensed in the sub-scanning cross section. The third and fourth light beams LC and LD that pass through the third and fourth incident optical elements 20c and 20d pass through the third and fourth sub-scanning apertures 30c and 30d and the third and fourth main-scanning apertures 40c and 40d, and are then guided to the second deflection surface 50b of the deflector 50. As a result, the third and fourth light beams LC and LD are limited in light beam diameter in the main scanning direction and the sub-scanning direction, and are focused in the sub-scanning direction so as to form a long line image in the main scanning direction near the second deflection surface 50b of the deflector 50.

[0027] In the optical scanning device 1 of this embodiment, the first and second light beams LA and LB emitted from the first and second light sources 10a and 10b, respectively, are obliquely incident on the first deflection surface 50a of the deflector 50 at different angles relative to the main scanning section in the sub-scanning section. Specifically, the first and second light beams LA and LB are obliquely incident on the first deflecting surface 50a of the deflector 50 at angles of −0.05 radians and +0.05 radians with respect to the main scanning cross section, respectively.

[0028] Further, the third and fourth light beams LC and LD emitted from the third and fourth light sources 10c and 10d, respectively, are obliquely incident on the second deflecting surface 50b of the deflector 50 at different angles in the sub-scanning section with respect to the main-scanning section. Specifically, the third and fourth light beams LC and LD are obliquely incident on the second deflecting surface 50b of the deflector 50 at angles of −0.05 radians and +0.05 radians with respect to the main scanning cross section, respectively.

[0029] Next, the first and second light beams LA and LB deflected by the first deflection surface 50a of the deflector 50 are focused onto the first and second scanned surfaces 100a and 100b by the first imaging optical element 60a and the second imaging optical elements 80a and 80b. In addition, the third and fourth light beams LC and LD deflected by the second deflection surface 50b of the deflector 50 are focused on the third and fourth scanned surfaces 100c and 100d by the first imaging optical element 60b and the second imaging optical elements 80c and 80d.

[0030] As the deflector 50 rotates, the first to fourth light beams LA to LD optically scan the first to fourth scanned surfaces 100a to 100d in the main scanning direction at a uniform speed, thereby enabling image recording on the first to fourth scanned surfaces 100a to 100d. In the optical scanning device 1 according to this embodiment, a first incident optical system 75a is formed by the first incident optical element 20a, the first sub-scanning aperture 30a, and the first main-scanning aperture 40a.

[0031] The second incident optical element 20b, the second sub-scanning aperture 30b, and the second main scanning aperture 40b form a second incident optical system 75b. The third incident optical element 20c, the third sub-scanning aperture 30c, and the third main scanning aperture 40c form a third incident optical system 75c. Furthermore, the fourth incident optical element 20d, the fourth sub-scanning aperture 30d, and the fourth main-scanning aperture 40d form a fourth incident optical system 75d.

[0032] In addition, in the optical scanning device 1 of this embodiment, a first imaging optical system 85a is formed by the first imaging optical element 60a and the second imaging optical element 80a, and a second imaging optical system 85b is formed by the first imaging optical element 60a and the second imaging optical element 80b. Furthermore, the first imaging optical element 60b and the second imaging optical element 80c form a third imaging optical system 85c, and the first imaging optical element 60b and the second imaging optical element 80d form a fourth imaging optical system 85d.

[0033] 3(a) and (b) respectively show a partial main-scanning sectional development view and a partial sub-scanning sectional view of the optical scanning device 1 according to this embodiment. Specifically, FIG. 3(a) shows a synchronous detection optical system 95 in addition to the first and second incident optical systems 75a and 75b and the first and second imaging optical systems 85a and 85b provided in the optical scanning device 1 of this embodiment.

[0034] In addition, first and second imaging optical systems 85a and 85b, and a synchronous detection optical system 95 are shown in FIG. Please note that in FIG. 3(b), in order to clearly show the synchronous detection optical system 95, the first imaging optical element 60a is omitted, and the first and second light beams LA and LB are shown by dashed lines.

[0035] Consider a direction (first direction) parallel to a straight line passing through a first intersection point of the optical axes of the first scanned surface 100a and the first imaging optical system 85a and a second intersection point of the optical axes of the second scanned surface 100b and the second imaging optical system 85b. At this time, as shown in FIG. 3(b), the second surface to be scanned 100b is disposed between the deflector 50 and the first surface to be scanned 100a in the said direction.

[0036] In the optical scanning device 1 of this embodiment, in order to align the scanning lines formed on the first to fourth scanned surfaces 100a to 100d with each other, the write timings for starting optical scanning on each of the first to fourth scanned surfaces 100a to 100d are synchronized with each other. In the optical scanning device 1 according to this embodiment, a synchronization detection optical system 95 and a synchronization detection sensor 220 are provided to perform such synchronization.

[0037] Specifically, the first light beam LA deflected in a predetermined direction by the first deflection surface 50a of the deflector 50 is focused in the main scanning direction by the synchronization detection lens 200 and guided to the synchronization detection sensor 220 provided on the substrate 230 (see also Figures 5 and 6). In other words, the synchronization detection sensor 220 receives the first light beam LA deflected by the first deflecting surface 50a of the deflector 50 without passing through the first imaging optical system 85a.

[0038] As described above, by using the synchronization detection lens 200 to collect the first light beam LA in the main scanning direction near the synchronization detection slit 210, the waveform received by the synchronization detection sensor 220 can be made steep. Therefore, it is possible to improve the accuracy of synchronization in the optical scanning device 1 according to this embodiment.

[0039] A control unit (not shown) determines the light emission timing of each of the first to fourth light sources 10a to 10d using a synchronization signal (Beam Detection (BD) signal) obtained based on the signal output from the synchronization detection sensor 220. In the optical scanning device 1 according to this embodiment, the synchronous detection lens 200 and the synchronous detection slit 210 form a synchronous detection optical system 95.

[0040] Next, the specifications of the optical scanning device 1 according to this embodiment, the refractive index and coordinates of each optical element, and the shape of the optical surface of each optical element are shown in the following Tables 1, 2, 3-1, 3-2, and 3-3. In Tables 2, 3-1, 3-2 and 3-3, only the first and second incident optical systems 75a and 75b, the first and second imaging optical systems 85a and 85b, and the synchronous detection optical system 95 are shown. That is, in Tables 2, 3-1, 3-2, and 3-3, the third and fourth incident optical systems 75c and 75d and the third and fourth imaging optical systems 85c and 85d are omitted.

[0041] [Table 1]

[0042] [Table 2]

[0043] [Table 3-1] [Table 3-2] [Table 3-3]

[0044] In addition, the entrance surfaces of the first to fourth entrance optical elements 20a to 20d provided in the optical scanning device 1 of this embodiment are diffractive surfaces on which a diffraction grating is formed, and each of them is formed by injection molding using a plastic material as described above. For this reason, a so-called temperature compensation optical system is adopted in which the change in the refractive power of the first to fourth incident optical elements 20a to 20d due to environmental fluctuations is compensated for by the change in the diffractive power of the diffractive surface associated with the change in wavelength of the first to fourth light beams LA to LD in the first to fourth light sources 10a to 10d. Specifically, the diffractive surface formed on the entrance surface of each of the first to fourth entrance optical elements 20a to 20d is defined by a phase function as expressed by the following formula (1).

number

[0045] In equation (1), φ is the phase function, M is the diffraction order, and λ is the design wavelength. Since the optical scanning device 1 according to this embodiment uses first-order diffracted light, M is 1 and λ is 790 nm.

[0046] In addition, the shapes (general line shapes) of the entrance surfaces 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 in the main scanning cross section have aspheric shapes expressed by a 10th order polynomial function. Specifically, the points of intersection (surface vertices) between the optical axis and the optical surfaces of the first imaging optical elements 60a and 60b and the second imaging optical elements 80a to 80d are set as the origin.

[0047] The optical axis of each optical surface is defined as the X-axis, the axis perpendicular to the optical axis in the main-scanning section is defined as the Y-axis, and the axis perpendicular to the optical axis in the sub-scanning section is defined as the Z-axis. In this case, the aspheric shapes of the entrance surfaces 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).

number

[0048] In formula (2), R is the radius of curvature in the main scanning section (generatrix radius of curvature), K is the eccentricity, Bi are the aspheric coefficients. The shapes (sagittal shapes) of the entrance surfaces and exit surfaces of the first imaging optical elements 60a and 60b and the second imaging optical elements 80a to 80d in the sub-scanning cross section are expressed by the following formula (3).

number

[0049] In formula (3), S is the shape (sagittal shape) in a cross section perpendicular to the main scanning cross section, including the normal to the generatrix at a given position in the main scanning direction, and M ij are the aspheric coefficients. Further, the radius of curvature (sagittal radius of curvature) r′ in the sub-scanning cross section at a position spaced apart by Y from the optical axis in the main scanning direction is expressed by the following formula (4).

number

[0050] In equation (4), r is the radius of curvature of the sagittal line on the optical axis, E i is the sagittal variation coefficient. In addition, in the first imaging optical elements 60a and 60b and the second imaging optical elements 80a to 80d provided in the optical scanning device 1 in this embodiment, the shapes of the optical surfaces are defined by the functions expressed in the above equations (1) to (4), but they may be defined by other functions without being limited to these.

[0051] As described above, in the optical scanning device 1 of this embodiment, the first and second light beams LA and LB pass through a common first imaging optical element 60a, and the third and fourth light beams LC and LD pass through a common first imaging optical element 60b. Specifically, as shown in FIGS. 2(a) to 2(c), the first and second light beams LA and LB pass through an upper portion 60au and a lower portion 60al, respectively, of the first imaging optical element 60a in the sub-scanning direction.

[0052] Moreover, the third and fourth light beams LC and LD pass through the upper and lower portions, respectively, of the first imaging optical element 60b in the sub-scanning direction. The upper and lower portions in the sub-scanning direction referred to here can also be referred to as the opposite sides of the scanned surface in the sub-scanning direction, that is, the anti-scanned surface side portion and the scanned surface side portion, respectively.

[0053] As shown in Tables 3-1 and 3-2, the shape of the exit surface of the first imaging optical element 60a is defined to be different between the upper portion 60au through which the first light beam LA passes and the lower portion 60al through which the second light beam LB passes. That is, while the first imaging optical element 60a is a single optical element, it is formed as a multi-stage structure in which the shape of the exit surface differs between an upper portion 60au and a lower portion 60al in the sub-scanning direction, and the first imaging optical element 60b has a similar configuration.

[0054] FIG. 4 shows a sub-scanning sectional view of a first imaging optical element 60a provided in the optical scanning device 1 according to this embodiment. As shown in FIG. 4, the first imaging optical element 60a has an upper portion 60au through which the first light beam LA passes, and a lower portion 60al through which the second light beam LB passes, on either side of a center line indicated by a dashed line in the sub-scanning direction.

[0055] The upper portion 60au and the lower portion 60al of the first imaging optical element 60a each have an exit surface formed in the shape shown in Tables 3-1 and 3-2. This makes it possible to efficiently collect both the first and second light beams LA and LB emitted from the first and second light sources 10a and 10b, respectively, by the first imaging optical element 60a.

[0056] Next, the return of the optical paths of the first to fourth light beams LA to LD by the first reflecting optical elements 70a to 70d and the second reflecting optical elements 90a and 90b in the optical scanning device 1 according to this embodiment will be described. The optical paths of the second and third light beams LB and LC guided to the second and third scanned surfaces 100b and 100c, which are located inside the first and fourth scanned surfaces 100a and 100d in the optical axis direction, are folded back by two reflective optical elements as shown in Figure 2(c).

[0057] This allows the optical paths and optical path lengths of the first and fourth light beams LA and LD guided to the first and fourth scanned surfaces 100a and 100d to be aligned with the optical paths and optical path lengths of the second and third light beams LB and LC guided to the second and third scanned surfaces 100b and 100c. Therefore, in the optical scanning device 1 according to this embodiment, it is possible to reduce the size of the housing 2 in the sub-scanning direction by using the minimum number of reflective optical elements required.

[0058] Next, the arrangement of the synchronous detection optical system 95 in the optical scanning device 1 according to this embodiment will be described. As described above, in the optical scanning device 1 of this embodiment, synchronization is achieved between the first to fourth light sources 10a to 10d by receiving a portion of the first light beam LA emitted from the first light source 10a by the synchronization detection sensor 220.

[0059] Here, the first light source 10a corresponds to the first scanned surface 100a, which is disposed relatively on the outer side in the X direction, among the first to fourth scanned surfaces 100a and 100b. In other words, the optical scanning device 1 of this embodiment is configured to perform synchronous detection using a light beam emitted from a light source other than the light source corresponding to a scanned surface that is located relatively inward in the optical axis direction among a plurality of scanned surfaces.

[0060] In other words, in the optical scanning device 1 of this embodiment, separate optical paths are provided for the second and third light beams LB and LC on the inside in the optical axis direction where multiple reflections occur as described above, and the first light beam LA on the outside in the optical axis direction where synchronous detection is performed. As a result, as shown in FIG. 3B, the second reflecting optical element 90a for folding back the optical path of the second light beam LB on the inside in the optical axis direction is disposed below the deflector 50 in the sub-scanning direction.

[0061] On the other hand, a synchronous detection lens 200 provided in a synchronous detection optical path along which a part of the first light flux LA deflected by the deflector 50 travels is disposed above the deflector 50 in the sub-scanning direction. Therefore, it is possible to dispose the second reflecting optical element 90a and the synchronization detection lens 200 apart from each other in the sub-scanning direction.

[0062] Next, the distances between the first to fourth scanned surfaces 100a to 100d in the optical scanning device 1 according to this embodiment will be described. As shown in FIG. 2(c), the distance DP between adjacent photosensitive drums among the first to fourth photosensitive drums 100a to 100d that form the first to fourth scanned surfaces 100a to 100d, respectively, is a parameter that is directly related to the size of the housing 2 in the optical axis direction.

[0063] That is, the shorter the distance DP between the adjacent photosensitive drums, the more compact the housing 2 becomes in the optical axis direction, which is advantageous for products such as image forming apparatuses in which the optical scanning device 1 according to this embodiment is mounted. Specifically, DP is the distance between the first intersection of the optical axes of the first scanned surface 100a and the first imaging optical system 85a and the second intersection of the optical axes of the second scanned surface 100b and the second imaging optical system 85b.

[0064] When the scanning width on the first and second scanned surfaces 100a and 100b is W, it is preferable that the optical scanning device 1 according to this embodiment satisfies the following conditional expression (5). 0.25≦DP / W≦0.30 (5) In the optical scanning device 1 of this embodiment, the scanning width W in the main scanning direction is 326 mm so as to be compatible with A3 size printing paper, while the distance DP between adjacent photosensitive drums is 83 mm (DP / W=0.25), thereby achieving a compact housing 2.

[0065] On the other hand, in the optical scanning device 1 according to this embodiment, the distance DP between the adjacent photosensitive drums is shortened, so that care must be taken with respect to the arrangement of the optical elements. Specifically, in order to reduce the size of the housing 2 in the optical axis direction, it is necessary to arrange each optical element housed in the housing 2 in the center of the housing 2, that is, close to the deflector 50.

[0066] FIG. 5 is a partial projection view of the optical scanning device 1 according to this embodiment in the main scanning section. Specifically, FIG. 5 shows the optical path of the first light beam LA between the first light source 10a and the synchronization detection sensor 220, and the optical path of the second light beam LB between the second light source 10b and the second scanned surface 100b.

[0067] As shown in Figure 5, when an attempt is made to reduce the distance DP between adjacent photosensitive drums in the optical scanning device 1 of this embodiment, the synchronization detection lens 200 and one longitudinal end of the second reflective optical element 90a are positioned close to or partially overlapping each other in the main scanning cross section. Each of the reflective optical elements provided in the optical scanning device 1 according to this embodiment is supported by abutting both ends in the longitudinal direction against support portions (not shown) formed on the housing 2. That is, in the optical scanning device 1 according to this embodiment, the synchronous detection lens 200 and a support portion that supports one end portion in the longitudinal direction of the second reflecting optical element 90a are adjacent to or partially overlap each other in the main scanning cross section.

[0068] As shown in FIG. 2(c), in the optical scanning device 1 according to this embodiment, the housing 2 has a box portion formed in a U-shape in the sub-scanning cross section. Then, each optical element is loaded into the internal space of the box portion from the open lower side of the housing 2 in the sub-scanning direction, and each optical element is supported by each support portion formed in the housing 2, and then the internal space is covered by a lid portion not shown.

[0069] When loading each optical element from the lower side in the sub-scanning direction which is open to the housing 2 in this manner, it is extremely difficult to support each optical element by the support portion at each of multiple positions which are the same in the main scanning cross section but different from each other in the sub-scanning direction. In other words, when shortening the distance DP between adjacent photosensitive drums in the optical scanning device 1 of this embodiment, it is difficult to arrange the synchronization detection lens 200 and the second reflective optical element 90a on the same side of the bottom surface 2a (first surface) of the housing 2. In other words, it is difficult to dispose both the synchronous detection lens 200 and the second reflecting optical element 90a inside the bottom surface 2a of the housing 2 in the optical scanning device 1 according to this embodiment.

[0070] Therefore, in the optical scanning device 1 of this embodiment, a configuration is adopted in which the synchronization detection lens 200 is arranged in an area on the opposite side of the bottom surface 2a of the housing 2 from the area in which the deflector 50 and the second reflective optical element 90a are arranged. In other words, in the optical scanning device 1 according to this embodiment, the synchronization detection lens 200 and the deflector 50 are disposed on one side and the other side of the bottom surface 2a of the housing 2, respectively.

[0071] In other words, in the optical scanning device 1 according to this embodiment, the synchronization detection lens 200 and the deflector 50 are disposed on the outer side and the inner side of the bottom surface 2a of the housing 2, respectively. Figure 6 shows an enlarged view of a portion of the optical scanning device 1 according to this embodiment in cross section 6A perpendicular to the main scanning cross section shown in Figure 5, and specifically shows an enlarged view of the vicinity of the synchronization detection lens 200 in cross section 6A.

[0072] As shown in FIG. 6, in the optical scanning device 1 according to this embodiment, the synchronization detection lens 200 is disposed on the opposite side of the bottom surface 2a of the housing 2 from the deflector 50, i.e., on the outside of the bottom surface 2a of the housing 2. More specifically, in the optical scanning device 1 according to this embodiment, the synchronization detection lens 200 is disposed in a recess formed in the bottom surface 2 a of the housing 2 .

[0073] In other words, the bottom surface 2a of the housing 2 provided in the optical scanning device 1 according to this embodiment has a concave shape around the area where the synchronization detection lens 200 is arranged. In other words, the shape of the bottom surface 2a of the housing 2 provided in the optical scanning device 1 according to this embodiment is not flat. On the other hand, the second reflective optical element 90a is arranged on the same side of the bottom surface 2a of the housing 2 as the deflector 50, that is, inside the bottom surface 2a of the housing 2, in other words, in the internal space within the box portion of the housing 2.

[0074] As a result, even if the support portion of the synchronization detection lens 200 and the support portion of the second reflective optical element 90a overlap each other in the main scanning cross section, they can be inserted from opposite sides in the sub-scanning direction and abutted against the support portions, making it possible to position them without physical interference. Furthermore, by isolating the area in which the synchronous detection lens 200 is arranged and the area in which the deflector 50 is arranged by the bottom surface 2a of the housing 2, the impact of temperature rise and dust caused by the rotation of the deflector 50 on the synchronous detection lens 200 can be mitigated.

[0075] Therefore, in the optical scanning device 1 according to this embodiment, it is possible to suppress a decrease in the synchronization detection performance. In the optical scanning device 1 of this embodiment, by adopting the above configuration and devising a method of mounting the synchronous detection lens 200, it is possible to achieve both a reduction in the distance DP between adjacent photosensitive drums and the mounting of the synchronous detection optical system 95.

[0076] In addition, in the optical scanning device 1 of this embodiment, as shown in FIG. 6, the synchronization detection sensor 220 is arranged on the outside of the side surface 2b (second surface) of the housing 2, and the synchronization detection slit 210 is formed integrally with the side surface 2b of the housing 2, i.e., within the side surface 2b of the housing 2.

[0077] As shown in Figure 6, the first light beam LA deflected in a predetermined direction by the deflector 50 passes through an opening formed in a predetermined wall surface of the recess in the bottom surface 2a of the housing 2, and is emitted to the outside of the bottom surface 2a of the housing 2, and then enters the synchronization detection lens 200. Then, the first light flux LA having passed through the synchronous detection lens 200 passes through a synchronous detection slit 210 and is incident on a synchronous detection sensor 220 .

[0078] Next, the shapes of the second imaging optical elements 80a to 80d provided in the optical scanning device 1 according to this embodiment will be described. As described above, the second imaging optical element 80a that guides the first light beam LA to the first scanned surface 100a and the second imaging optical element 80b that guides the second light beam LB to the second scanned surface 100b have different shapes and are arranged in optically asymmetric positions relative to each other.

[0079] That is, in the optical scanning device 1 according to this embodiment, the second imaging optical elements 80a to 80d are formed in different shapes from one another. This makes it possible to suitably focus the first to fourth light beams LA to LD guided by the first to fourth imaging optical systems 85a to 85d, respectively, on the first to fourth scanned surfaces 100a to 100d. However, the present invention is not limited to this. For example, the second imaging optical elements 80a and 80b may be formed to have the same shape and arranged at positions optically symmetrical to each other, and the effect of this embodiment can be obtained.

[0080] 7(a) and (b) respectively show the image height dependence of the main scanning direction LSF (Line Spread Function) depth center position and the sub-scanning direction LSF depth center position on each scanned surface in the optical scanning device 1 according to this embodiment. Note that the main scanning direction LSF depth center position and the sub-scanning direction LSF depth center position referred to here respectively refer to the center positions of an area where the LSF widths in the main scanning direction and sub-scanning direction are equal to or less than the slice level when defocused in the optical axis direction near a specified scanned surface.

[0081] 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. In addition, the LSF width in the main scanning direction and the LSF width in the sub-scanning direction respectively refer to the widths when the light quantity profile obtained by integrating the spot profile at each image height in the sub-scanning direction and the main scanning direction is sliced ​​at a position that is 13.5% of the maximum value. As shown in Figures 7(a) and (b), both the main scanning direction LSF depth center position and the sub-scanning direction LSF depth center position are within ±1 mm over the entire image height, which shows that the optical scanning device 1 of this embodiment achieves good imaging performance.

[0082] 8(a) and (b) respectively show a partial development view in the main-scanning section and a partial sub-scanning section for explaining each conditional expression in the optical scanning device 1 according to this embodiment. First, the angle (acute angle) between the optical axis of the first incident optical system 75a and the optical axis of the first imaging optical system 85a when projected in the main scanning section is defined as θ im (radians).

[0083] At this time, in the optical scanning device 1 according to this embodiment, it is preferable that the following conditional expression (6) be satisfied. 1.00<θ im <1.50 ···(6)

[0084] If the upper limit of conditional expression (6) is exceeded, vignetting in the deflector 50 is likely to occur, and if the position of the first light source 10a is shifted to suppress the vignetting, the optical performance is likely to deteriorate. On the other hand, if the lower limit of conditional expression (6) is exceeded, the first incident optical system 75a and the first imaging optical system 85a will tend to interfere with each other.

[0085] In the optical scanning device 1 according to this embodiment, it is more preferable that the following conditional formula (6a) be satisfied. 1.20<θ im <1.50 (6a) As shown in Table 1, in the optical scanning device 1 according to this embodiment, θ im is 1.36, and conditional expressions (6) and (6a) are satisfied.

[0086] The angle (acute angle) between the optical axis of the synchronous detection optical system 95 and the optical axis of the first imaging optical system 85a when projected in the main scanning section is defined as θ bd (radians). At this time, in the optical scanning device 1 according to this embodiment, it is preferable that the following conditional expression (7) be satisfied. 0.80<θ bd / θ im <0.95 ···(7)

[0087] If the upper limit of conditional expression (7) is exceeded, the synchronous detection optical system 95 will be too close to the first incident optical system 75a. Therefore, the first light beam LA guided by the synchronous detection optical system 95 and the first light beam LA guided by the first incident optical system 75a tend to interfere with each other.

[0088] On the other hand, if the lower limit of conditional expression (7) is not reached, the synchronous detection optical system 95 will be too close to the first imaging optical system 85a. Therefore, the first light beam LA guided by the synchronous detection optical system 95 and the first light beam LA guided by the first imaging optical system 85a tend to interfere with each other.

[0089] In the optical scanning device 1 according to this embodiment, it is more preferable that the following conditional formula (7a) be satisfied. 0.84<θ bd / θ im <0.95 (7a) As shown in Table 1, in the optical scanning device 1 according to this embodiment, θ bd / θ im is 0.91, and conditional expressions (7) and (7a) are satisfied.

[0090] The distance on the optical axis of the synchronous detection optical system 95 between the deflection point on the first deflection surface 50a of the principal ray of the first light beam LA, which is deflected in a predetermined direction by the deflector 50 so as to reach the synchronous detection sensor 220, and the synchronous detection sensor 220 is defined as D. bd Let us assume that. The focal length of the synchronous detection lens 200 in the main scanning section is F bd In this case, in the optical scanning device 1 according to this embodiment, it is preferable that the following conditional expression (8) is satisfied. 0.30 <F bd / D bd <0.70 ···(8)

[0091] If the upper limit of the condition (8) is exceeded, the synchronous detection lens 200 will be too close to the deflector 50 . Therefore, the first light beam LA guided by the synchronous detection optical system 95 is likely to interfere with the first light beam LA guided by the first incident optical system 75a and the first light beam LA guided by the first imaging optical system 85a. On the other hand, if the lower limit of the conditional expression (8) is exceeded, the focal length F bd If becomes too short, the optical sensitivity increases.

[0092] In the optical scanning device 1 according to this embodiment, it is more preferable that the following conditional formula (8a) be satisfied. 0.30 <F bd / D bd <0.50 (8a) As shown in Table 1, in the optical scanning device 1 according to this embodiment, F bd / D bd is 0.37, and conditional expressions (8) and (8a) are satisfied.

[0093] In addition, a direction parallel to a straight line passing through a first intersection point of the optical axes of the first scanned surface 100a and the first imaging optical system 85a and a second intersection point of the optical axes of the second scanned surface 100b and the second imaging optical system 85b is defined. The distance between the rotation center of the deflector 50 in that direction and the center of the entrance surface of the synchronous detection lens 200 is X bd Let us assume that. In addition, the distance between the rotation center of the deflector 50 in the direction and the center of the incidence surface of a predetermined optical element that is disposed closest to the deflector 50 among the imaging optical elements and reflecting optical elements provided on the optical paths of the first and second light beams LA and LB is defined as X. m Let us assume that.

[0094] At this time, in the optical scanning device 1 according to this embodiment, it is preferable that the following conditional expression (9) be satisfied. 0.60 <X m / X bd <1.50 ···(9)

[0095] If the upper limit value of conditional expression (9) is exceeded, the imaging optical elements and reflective optical elements arranged on the optical paths of the first and second light beams LA and LB will be too far away from the deflector 50, making it difficult to shorten the distance DP between the first and second photosensitive drums 100a and 100b. On the other hand, if the lower limit of conditional expression (9) is not reached, certain optical elements included in the imaging optical elements and reflective optical elements arranged on the optical paths of the first and second light beams LA and LB will be too close to the deflector 50, which may cause the housing 2 to become large in the sub-scanning direction. Furthermore, if the lower limit of conditional formula (9) is not reached, the specified optical element and the imaging optical element and the reflective optical element through which the third and fourth light beams LC and LD pass, which are provided on the opposite side of the deflector 50, are likely to interfere with each other.

[0096] In the optical scanning device 1 according to this embodiment, it is more preferable that the following conditional formula (9a) be satisfied. 0.70 <X m / X bd <1.20 ···(9a)

[0097] In the optical scanning device 1 of this embodiment, among the imaging optical elements and reflective optical elements provided on the optical paths of the first and second light beams LA and LB, the optical element arranged closest to the deflector 50 is the second reflective optical element 90a. Therefore, as shown in Table 1, m / X bd is 0.84, and conditional expressions (9) and (9a) are satisfied.

[0098] As described above, in the optical scanning device 1 according to this embodiment, the deflector 50 and the synchronization detection lens 200 are provided on opposite sides of the bottom surface 2a of the housing 2. This makes it possible to reduce the size of the optical scanning device 1 according to this embodiment in the directions perpendicular to the main scanning direction and the sub-scanning direction, that is, in the optical axis directions of the first to fourth imaging optical systems 85a to 85d.

[0099] [Second embodiment] Figures 9(a) and (b) respectively show a partial development view in the main-scanning section (corresponding to Figures 1(a) and (b)) and a partial sub-scanning section (corresponding to Figure 2(c)) of the optical scanning device 201 according to the second embodiment. In addition, Figures 10(a) and (b) respectively show a partial development view in the main-scanning section (corresponding to Figure 3(a)) and a partial sub-scanning section (corresponding to Figure 3(b)) of the optical scanning device 201 according to the second embodiment. The optical scanning device 201 according to this embodiment has the same configuration as the optical scanning device 1 according to the first embodiment except for various different numerical values, so the same components are given the same reference numerals and descriptions thereof are omitted.

[0100] The specification values ​​of the optical scanning device 201 according to this embodiment, the refractive index and coordinates of each optical element, and the shape of the optical surface of each optical element are shown in the following Tables 4, 5, 6-1, 6-2, and 6-3. In Tables 5, 6-1, 6-2 and 6-3, only the first and second incident optical systems 75a and 75b, the first and second imaging optical systems 85a and 85b, and the synchronous detection optical system 95 are shown. That is, in Tables 5, 6-1, 6-2, and 6-3, the third and fourth incident optical systems 75c and 75d and the third and fourth imaging optical systems 85c and 85d are omitted.

[0101] [Table 4]

[0102] [Table 5]

[0103] [Table 6-1] [Table 6-2] [Table 6-3]

[0104] 11A and 11B respectively show the image height dependence of the LSF depth center position in the main scanning direction and the LSF depth center position in the sub-scanning direction on each scanned surface in the optical scanning device 201 according to this embodiment. As shown in Figures 11(a) and (b), both the main scanning direction LSF depth center position and the sub-scanning direction LSF depth center position are within ±1 mm over the entire image height, which shows that the optical scanning device 201 of this embodiment achieves good imaging performance.

[0105] In addition, in the optical scanning device 201 according to this embodiment, DP / W is calculated to be 0.25, and conditional expression (5) is satisfied. Also, θ im is 1.36, so that conditional expressions (6) and (6a) are satisfied. Also, θ bd / θ im is found to be 0.88, and conditional expressions (7) and (7a) are satisfied. Also F bd / D bd is calculated as 0.32, and conditional expressions (8) and (8a) are satisfied. Also X m / X bd is found to be 0.77, and conditional expressions (9) and (9a) are satisfied.

[0106] As described above, in the optical scanning device 201 according to this embodiment, the deflector 50 and the synchronization detection lens 200 are provided on opposite sides of the bottom surface 2a of the housing 2. This makes it possible to reduce the size of the optical scanning device 201 according to this embodiment in the directions perpendicular to the main scanning direction and the sub-scanning direction, that is, in the optical axis directions of the first to fourth imaging optical systems 85a to 85d.

[0107] [Third embodiment] Figures 12(a) and (b) respectively show a partial development view in the main-scanning section (corresponding to Figures 1(a) and (b)) and a partial sub-scanning section (corresponding to Figure 2(c)) of an optical scanning device 301 according to the third embodiment. In addition, Figures 13(a) and (b) respectively show a partial development view in the main-scanning section (corresponding to Figure 3(a)) and a partial sub-scanning section (corresponding to Figure 3(b)) of the optical scanning device 301 according to the third embodiment. The optical scanning device 301 according to this embodiment has the same configuration as the optical scanning device 1 according to the first embodiment except for various different numerical values, so the same components are given the same reference numerals and descriptions thereof are omitted.

[0108] The specification values ​​of the optical scanning device 301 according to this embodiment, the refractive index and coordinates of each optical element, and the shape of the optical surface of each optical element are shown in the following Tables 7, 8, 9-1, 9-2, and 9-3. In Tables 8, 9-1, 9-2 and 9-3, only the first and second incident optical systems 75a and 75b, the first and second imaging optical systems 85a and 85b and the synchronous detection optical system 95 are shown. That is, in Tables 8, 9-1, 9-2, and 9-3, the third and fourth incident optical systems 75c and 75d and the third and fourth imaging optical systems 85c and 85d are omitted.

[0109] [Table 7]

[0110] [Table 8]

[0111] [Table 9-1] [Table 9-2] [Table 9-3]

[0112] 14A and 14B respectively show the image height dependence of the LSF depth center position in the main scanning direction and the LSF depth center position in the sub-scanning direction on each scanned surface in the optical scanning device 301 according to this embodiment. As shown in Figures 14(a) and (b), both the main scanning direction LSF depth center position and the sub-scanning direction LSF depth center position are within ±1 mm over the entire image height, which shows that the optical scanning device 301 of this embodiment achieves good imaging performance.

[0113] In addition, in the optical scanning device 301 according to this embodiment, DP / W is calculated to be 0.28, which satisfies the conditional expression (5). Also, θ im is 1.48, so that conditional expressions (6) and (6a) are satisfied. Also, θ bd / θ im is found to be 0.85, and conditional expressions (7) and (7a) are satisfied. Also F bd / D bd is found to be 0.46, and conditional expressions (8) and (8a) are satisfied. Also X m / X bd is calculated to be 1.00, and conditional expressions (9) and (9a) are satisfied.

[0114] As described above, in the optical scanning device 301 according to this embodiment, the deflector 50 and the synchronization detection lens 200 are provided on opposite sides of the bottom surface 2a of the housing 2. This makes it possible to reduce the size of the optical scanning device 301 according to this embodiment in the directions perpendicular to the main scanning direction and the sub-scanning direction, that is, in the optical axis directions of the first to fourth imaging optical systems 85a to 85d.

[0115] The relationships between the various values ​​and the respective conditional expressions in the optical scanning devices according to the first to third embodiments are shown in Table 10 below.

[0116] [Table 10]

[0117] [Image forming equipment] FIG. 15 is a sub-scanning sectional view of a main part of an image forming apparatus 99 including an optical scanning device 1 according to any one of the first to third embodiments.

[0118] The image forming apparatus 99 is a tandem type color image forming apparatus in which the optical scanning device 1 according to any one of the first to third embodiments records image information on the surfaces of four photosensitive drums, each of which is an image carrier. The image forming apparatus 99 includes the optical scanning device 1 according to any one of the first to third embodiments, and first, second, third and fourth photosensitive drums 100a, 100b, 100c and 100d as image carriers. The image forming apparatus 99 also includes first, second, third and fourth developing units 15, 16, 17 and 18, a conveyor belt 91, a printer controller 93 and a fixing unit 94.

[0119] As shown in FIG. 15, an image forming apparatus 99 receives R (red), G (green), and B (blue) color signals output from an external device 92 such as a personal computer. The input color signals are then converted by a printer controller 93 within the device into image data (dot data) for each of C (cyan), M (magenta), Y (yellow), and K (black).

[0120] Next, each of the converted image data is input to the optical scanning device 1 according to any one of the first to third embodiments. Then, the photosensitive surfaces of the first to fourth photosensitive drums 100a to 100d are scanned in the main scanning direction by the first, second, third and fourth light beams LA, LB, LC and LD, respectively, which are modulated and emitted from the optical scanning device 1 according to each image data.

[0121] A charging roller (not shown) for uniformly charging the surface of each of the first to fourth photosensitive drums 100a to 100d is provided in contact with the surface. Then, the optical scanning device 1 irradiates the first to fourth light beams LA to LD onto the surfaces of the first to fourth photosensitive drums 100a to 100d that have been charged by the charging rollers.

[0122] As described above, the first to fourth light beams LA to LD are modulated based on image data for each color, and electrostatic latent images are formed on the surfaces of the first to fourth photosensitive drums 100a to 100d, respectively, by irradiating the first to fourth light beams LA to LD. The formed electrostatic latent images are then developed into toner images by first to fourth developing devices 15 to 18 arranged so as to come into contact with the first to fourth photosensitive drums 100a to 100d, respectively.

[0123] Next, the developed toner images are transferred in multiple layers onto a sheet of paper (transfer material) (not shown) conveyed on a conveyor belt 91 by transfer rollers (transfer devices) (not shown) arranged to face the first to fourth photosensitive drums 100a to 100d. As a result, a full-color image is formed on the sheet of paper. Then, the paper onto which the unfixed toner image has been transferred is further transported by the transport belt 91 to a fixing device 94 provided behind (on the left side in FIG. 15) the first to fourth photosensitive drums 100a to 100d.

[0124] The fixing unit 94 has a fixing roller having an internal fixing heater (not shown) and a pressure roller disposed so as to be in pressure contact with the fixing roller. The paper conveyed by the conveyor belt 91 is heated and pressed by the pressure contact portion between the fixing roller and the pressure roller, whereby the unfixed toner image on the paper is fixed. Furthermore, a paper discharge roller (not shown) is disposed behind the fixing unit 94 , and the paper discharge roller discharges the paper on which the fixed image has been fixed to the outside of the image forming apparatus 99 .

[0125] In the image forming apparatus 99, an image signal (image information) is recorded on the photosensitive surfaces of first to fourth photosensitive drums 100a to 100d, each of which corresponds to one of the colors C (cyan), M (magenta), Y (yellow), and K (black), by the optical scanning device 1. This makes it possible to print a color image at high speed.

[0126] The external device 92 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 99 form a color digital copying machine.

[0127] 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.

[0128] The disclosure of this embodiment includes the following configuration. (Configuration 1) An optical scanning device comprising: a deflector that deflects a first light beam to scan a first scanned surface in a main scanning direction; a first imaging optical system that guides the first light beam deflected by the deflector to the first scanned surface; a light receiving element that receives the first light beam deflected by the deflector without passing through the first imaging optical system; a first optical element that guides the first light beam deflected by the deflector to the light receiving element; and a housing that holds the deflector, the first imaging optical system, the light receiving element, and the first optical element, wherein the first optical element and the deflector are respectively arranged on the outside and inside of a first surface of the housing. (Configuration 2) An optical scanning device as described in configuration 1, further comprising a second imaging optical system that guides the second light beam deflected by the deflector to a second scanned surface, and the deflector deflects the second light beam to scan the second scanned surface in the main scanning direction. (Configuration 3) An optical scanning device according to configuration 2, characterized in that, when the distance between a first intersection point of the optical axis of the first scanned surface and the first imaging optical system and a second intersection point of the optical axis of the second scanned surface and the second imaging optical system is DP and the scanning width on the first and second scanned surfaces is W, the optical scanning device satisfies the condition 0.25≦DP / W≦0.30. (Configuration 4) In the optical scanning device according to configuration 2 or 3, the deflector deflects the first and second light beams by a first deflecting surface. (Configuration 5) An optical scanning device as described in configuration 4, characterized in that the second scanned surface is disposed between the deflector and the first scanned surface in a first direction parallel to a straight line passing through a first intersection of the optical axes of the first scanned surface and the first imaging optical system and a second intersection of the optical axes of the second scanned surface and the second imaging optical system. (Configuration 6) In the optical scanning device according to configuration 4 or 5, the first and second light beams are obliquely incident on the first deflecting surface of the deflector at different angles in the sub-scanning cross section with respect to the main-scanning cross section. (Configuration 7) A distance between the center of the deflector and the center of the entrance surface of the first optical element in a first direction parallel to a line passing through a first intersection point of the optical axes of the first scanned surface and the first imaging optical system and a second intersection point of the optical axes of the second scanned surface and the second imaging optical system is defined as X. bd The distance in the first direction between the center of the incidence surface of the second optical element disposed closest to the deflector among the optical elements provided on the optical paths of the first and second light beams deflected by the deflector is defined as X m When we set it to 0.60, <X m / X bd 7. The optical scanning device according to any one of configurations 4 to 6, wherein the optical scanning device satisfies the condition: (Configuration 8) An optical scanning device described in any one of configurations 1 to 7, characterized in that the housing includes a box portion having an internal space in which a deflector and a first imaging optical system are arranged, and a lid portion covering the internal space, and the first surface is a bottom surface of the box portion. (Configuration 9) An optical scanning device according to any one of configurations 1 to 8, wherein the first optical element is a refractive optical element that focuses the first light beam deflected by the deflector toward the light receiving element. (Configuration 10) The optical scanning device according to any one of configurations 1 to 9, further comprising a control unit that controls the timing of writing onto the first scanned surface based on a signal from the light receiving element. (Configuration 11) In the optical scanning device according to any one of configurations 1 to 10, the first surface has a recess in which the first optical element is disposed. (Configuration 12) An optical scanning device according to any one of configurations 1 to 11, wherein the light receiving element and the deflector are disposed on opposite sides of the second surface of the housing. (Configuration 13) An optical scanning device described in Configuration 12, characterized in that the housing includes a box portion having an internal space in which the deflector and the first imaging optical system are arranged, and a lid portion covering the internal space, and the second surface is a side surface of the box portion. (Configuration 14) The deflector deflects the first light beam by a first deflection surface, and defines a distance on the optical axis of the first optical element between the light receiving element and a deflection point on the first deflection surface of a principal ray of the first light beam deflected by the deflector toward the light receiving element as D. bd, the focal length of the first optical element in the main scanning section is F bd When this is done, the result is 0.30. <F bd / D bd 14. The optical scanning device according to any one of configurations 1 to 13, wherein the optical scanning device satisfies the condition: <0.70. (Configuration 15) A first incident optical system is provided that causes a first light beam to be incident on a deflector, and an angle formed between an optical axis of the first incident optical system and an optical axis of the first imaging optical system when projected onto a main scanning cross section is defined as θ im (radian), 1.00<θ im 15. The optical scanning device according to any one of claims 1 to 14, wherein the optical scanning device satisfies the condition: (Configuration 16) A first incident optical system is provided that causes a first light beam to be incident on a deflector, and an angle formed between an optical axis of the first incident optical system and an optical axis of the first imaging optical system when projected onto a main scanning cross section is defined as θ im The angle between the optical axis of the first optical element and the optical axis of the first imaging optical system is θ bd Then, 0.80<θ bd / θ im 16. The optical scanning device according to any one of configurations 1 to 15, wherein the condition of <0.95 is satisfied. (Structure 17) An optical scanning device described in any one of structures 1 to 16, comprising second, third and fourth imaging optical systems which guide the second, third and fourth light beams deflected by a deflector to the second, third and fourth scanned surfaces, the deflector deflects the second, third and fourth light beams to scan the second, third and fourth scanned surfaces in the main scanning direction, the first and second light beams are obliquely incident on a first deflection surface of the deflector at angles different from each other with respect to the main scanning cross section in the sub-scanning cross section, and the third and fourth light beams are obliquely incident on a second deflection surface of the deflector at angles different from each other with respect to the main scanning cross section in the sub-scanning cross section. (Configuration 18) An image forming apparatus comprising: an optical scanning device according to any one of configurations 1 to 17; a developing unit which develops an electrostatic latent image formed on a first scanned surface by the optical scanning device into a toner image; a transfer unit which transfers the developed toner image to a transfer material; and a fixing unit which fixes the transferred toner image to the transfer material. (Configuration 19) An image forming apparatus comprising: an optical scanning device according to any one of configurations 1 to 17; 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]

[0129] 1 Optical scanning device 2. Chassis 2a Bottom surface (first surface) 50 Deflector 85a First imaging optical system 100a: First scanned surface 200 Synchronous detection lens (first optical element) 220 Synchronous detection sensor (photodetector) LA First beam

Claims

1. a deflector that deflects the first light beam to scan the first scanned surface in a main scanning direction; a first imaging optical system that guides the first light beam deflected by the deflector to the first scanned surface; a light receiving element that receives the first light beam deflected by the deflector without passing through the first imaging optical system; a first optical element that guides the first light flux deflected by the deflector to the light receiving element; a housing that holds the deflector, the first imaging optical system, the light receiving element, and the first optical element, An optical scanning device, characterized in that the first optical element and the deflector are arranged on the outer side and the inner side, respectively, of a first surface of the housing.

2. a second imaging optical system that guides the second light beam deflected by the deflector to a second scanned surface; 2. The optical scanning device according to claim 1, wherein the deflector deflects the second light beam to scan the second surface to be scanned in a main scanning direction.

3. When a distance between a first intersection point of the optical axis of the first scanned surface and the first imaging optical system and a second intersection point of the optical axis of the second scanned surface and the second imaging optical system is defined as DP and a scanning width on the first and second scanned surfaces is defined as W, 0.25≦DP / W≦0.30 3. The optical scanning device according to claim 2, wherein the following condition is satisfied:

4. 3. The optical scanning device according to claim 2, wherein the deflector deflects the first and second light beams by a first deflecting surface.

5. The optical scanning device described in claim 4, characterized in that the second scanned surface is arranged between the deflector and the first scanned surface in a first direction parallel to a straight line passing through a first intersection of the first scanned surface and the optical axis of the first imaging optical system, and a second intersection of the second scanned surface and the optical axis of the second imaging optical system.

6. 5. The optical scanning device according to claim 4, wherein the first and second light beams are obliquely incident on the first deflecting surface of the deflector at angles different from each other in the sub-scanning cross section with respect to the main-scanning cross section.

7. The distance between the center of the deflector and the center of the entrance surface of the first optical element in a first direction parallel to a line passing through a first intersection point of the optical axes of the first scanned surface and the first imaging optical system and a second intersection point of the optical axes of the second scanned surface and the second imaging optical system is defined as X. ｂｄ The distance in the first direction between the center of the deflector and the center of the incidence surface of a second optical element that is disposed closest to the deflector among the optical elements provided on the optical paths of the first and second light beams deflected by the deflector is defined as X ｍ When 0.60<X ｍ / X ｂｄ <1.50 5. The optical scanning device according to claim 4, which satisfies the following conditions:

8. the housing includes a box portion having an internal space in which the deflector and the first imaging optical system are disposed, and a lid portion covering the internal space, 2. The optical scanning device according to claim 1, wherein the first surface is a bottom surface of the box portion.

9. 2. The optical scanning device according to claim 1, wherein the first optical element is a refractive optical element that condenses the first light beam deflected by the deflector toward the light receiving element.

10. 2. The optical scanning device according to claim 1, further comprising a control unit that controls a writing start timing on the first scanned surface based on a signal from the light receiving element.

11. 2. The optical scanning device according to claim 1, wherein the first surface has a recess in which the first optical element is disposed.

12. 2. The optical scanning device according to claim 1, wherein the light receiving element and the deflector are disposed on opposite sides of the second surface of the housing.

13. the housing includes a box portion having an internal space in which the deflector and the first imaging optical system are disposed, and a lid portion covering the internal space, 13. The optical scanning device according to claim 12, wherein the second surface is a side surface of the box portion.

14. The deflector deflects the first light beam by a first deflection surface, The distance on the optical axis of the first optical element between the light receiving element and a deflection point on the first deflection surface of the principal ray of the first light beam deflected by the deflector toward the light receiving element is defined as D. ｂｄ , the focal length of the first optical element in the main scanning section is F ｂｄ When 0.30<F ｂｄ / D ｂｄ <0.70 2. The optical scanning device according to claim 1, wherein the following conditions are satisfied:

15. a first incident optical system that causes the first light flux to be incident on the deflector; The angle between the optical axis of the first incident optical system and the optical axis of the first imaging optical system when projected onto the main scanning section is θ ｉｍ (radian), 1.000<θ ｉｍ <1.50 2. The optical scanning device according to claim 1, wherein the following conditions are satisfied:

16. a first incident optical system that causes the first light flux to be incident on the deflector; The angle between the optical axis of the first incident optical system and the optical axis of the first imaging optical system when projected onto the main scanning section is θ ｉｍ The angle between the optical axis of the first optical element and the optical axis of the first imaging optical system is θ ｂｄ When 0.80<θ ｂｄ / i ｉｍ <0.95 2. The optical scanning device according to claim 1, wherein the following conditions are satisfied:

17. a second, third, and fourth imaging optical system for guiding the second, third, and fourth light beams deflected by the deflector to second, third, and fourth scanned surfaces, the deflector deflects the second, third, and fourth light beams to scan the second, third, and fourth scanned surfaces in a main scanning direction; the first and second light beams are obliquely incident on a first deflecting surface of the deflector at angles different from each other in a sub-scanning cross section with respect to a main-scanning cross section, 2. The optical scanning device according to claim 1, wherein the third and fourth light beams are obliquely incident on the second deflecting surface of the deflector at mutually different angles in the sub-scanning cross section with respect to the main-scanning cross section.

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

19. 18. An image forming apparatus comprising: the optical scanning device according to claim 1; and a printer controller for converting a signal output from an external device into image data and inputting the image data to the optical scanning device.

Images