Optical Scanning Device

Abstract

To provide a compact optical scanning device that employs the UFS method. [Solution] The optical scanning device of the present invention comprises a deflector that deflects a light beam from a light source to scan a surface to be scanned in a main scanning direction, and a first optical system that guides the light beam deflected by the deflector to the surface to be scanned, and is characterized in that, in the main scanning cross section, the width of the light beam immediately before it is incident on the first deflection surface of the deflector is smaller than the width of the first deflection surface, and when the first deflection surface is at a first angle in the main scanning cross section, only a portion of the light beam incident on the deflector is deflected by the first deflection surface and reaches the surface to be scanned.

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 and multifunction printers that employ an electrophotographic process. [Background technology]

[0002] 2. Description of the Related Art Conventionally, optical scanning devices have been used as exposure devices mounted in image forming apparatuses such as laser beam printers that use an electrophotographic process. Optical scanning devices can be classified into under-filled scanning (UFS) and over-filled scanning (OFS) types depending on the relationship between the size of the incident light beam incident on the deflector and the size of the deflection surface.

[0003] Specifically, in the UFS method, the width of the incident light beam incident on the deflector in the main scanning cross section is smaller than the width of the deflection surface of the deflector, whereas in the OFS method, the width of the incident light beam incident on the deflector in the main scanning cross section is larger than the width of the deflection surface of the deflector. Patent Document 1 discloses an optical scanning device that employs the UFS method. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-92129 Summary of the Invention [Problem to be solved by the invention]

[0005] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a compact optical scanning device that employs the UFS method. [Means for solving the problem]

[0006] The optical scanning device of the present invention comprises a deflector that deflects a light beam from a light source to scan a surface to be scanned in a main scanning direction, and a first optical system that guides the light beam deflected by the deflector to the surface to be scanned, and is characterized in that, in the main scanning cross section, the width of the light beam immediately before it is incident on the first deflection surface of the deflector is smaller than the width of the first deflection surface, and when the first deflection surface is at a first angle in the main scanning cross section, only a portion of the light beam incident on the deflector is deflected by the first deflection surface and reaches the surface to be scanned. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide a compact optical scanning device that employs the UFS method. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 2 is a main scanning sectional view of the optical scanning device according to the first embodiment. [Figure 2] FIG. 2 is a partially enlarged main-scan sectional view of the optical scanning device according to the first embodiment. [Figure 3] 5A and 5B are diagrams showing the angle dependency of the beam width of a light beam in the optical scanning device according to the first embodiment. [Figure 4] 10A and 10B are main-scanning cross-sectional views of an optical scanning device according to a second embodiment, and a diagram showing the angle dependency of the beam width of a light beam. [Figure 5] 11A and 11B are main-scanning cross-sectional views of an optical scanning device according to a third embodiment, and a diagram showing the angle dependency of the light beam width of a light beam. [Figure 6] 10A and 10B are main-scanning cross-sectional views of an optical scanning device according to a fourth embodiment, and a diagram showing the angle dependency of the beam width of a light beam. [Figure 7] 13A and 13B are main-scanning cross-sectional views of an optical scanning device according to a fifth embodiment, and a diagram showing the angle dependency of the light beam width of a light beam. [Figure 8] FIG. 11 is a partially enlarged main-scan sectional view of an optical scanning device according to a fifth embodiment. [Figure 9] 13A and 13B are main-scanning cross-sectional views of an optical scanning device according to a sixth embodiment, and a diagram showing the angle dependency of the beam width of a light beam. [Figure 10] 13A and 13B are main-scanning cross-sectional views of an optical scanning device according to a seventh embodiment, and a diagram showing the angle dependency of the beam width of a light beam. [Figure 11] 13A and 13B are main-scanning cross-sectional views of an optical scanning device according to an eighth embodiment, and a diagram showing the angle dependency of the beam width of a light beam. [Figure 12] 13A and 13B are main-scanning cross-sectional views of an optical scanning device according to a ninth embodiment, and a diagram showing the angle dependency of the beam width of a light beam. [Figure 13] 10A and 10B are main-scanning cross-sectional views of an optical scanning device according to a tenth embodiment, and a diagram showing the angle dependency of the beam width of a light beam. [Figure 14] FIG. 2 is a sub-scanning cross-sectional view of a main part of the image forming apparatus according to the 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 both the rotation axis of the polygon mirror 5 and the optical axis of the imaging optical system 85 (the direction in which the polygon mirror 5 scans the scanned surface 7), and the sub-scanning direction is the direction parallel to the rotation axis of the polygon mirror 5.

[0010] The main scanning section is a section that includes the optical axis of the imaging optical system 85 and is perpendicular to the sub-scanning direction, and the sub-scanning section is a section that includes the optical axis of the imaging optical system 85 and is 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 parallel to the optical axis of the imaging optical system 85 as the X direction.

[0011] [First embodiment] 2. Description of the Related Art Conventionally, optical scanning devices have been used as exposure devices mounted in image forming apparatuses such as laser beam printers that use an electrophotographic process. In an optical scanning device, a light beam emitted from a light source is modulated according to an image signal from, for example, a personal computer, and is guided by an incident optical system to a deflector such as a polygon mirror (rotating polygonal mirror), and then deflected by the deflection surface of the deflector.

[0012] The deflected light beam is then focused into a spot on the photosensitive surface of a photosensitive drum, which serves as the surface to be scanned, by an imaging optical system, and the focused light beam scans the surface to be scanned, thereby exposing and recording image information. Also, various color image forming apparatuses have been proposed that form color images by scanning the photosensitive surfaces of a plurality of photosensitive drums using a plurality of optical scanning devices.

[0013] Optical scanning devices can be classified into under-filled scanning (UFS) and over-filled scanning (OFS) types depending on the relationship between the size of the incident light beam incident on the deflector and the size of the deflection surface. Specifically, in the UFS method, the width of the incident light beam incident on the deflector in the main scanning cross section is smaller than the width of the deflection surface of the deflector, whereas in the OFS method, the width of the incident light beam incident on the deflector in the main scanning cross section is larger than the width of the deflection surface of the deflector.

[0014] In the UFS system, all of the incident light beams that are incident on the deflecting surface of the deflector are deflected by the deflecting surface, and then guided to the imaging optical system (Fθ lens). On the other hand, in the OFS system, a specific deflecting surface of a polygon mirror (rotating polygonal mirror) that forms the deflector deflects the incident light beam by moving while functioning as a diaphragm in the main scanning direction, thereby cutting out the incident light beam.The deflected light beam is then guided to the imaging optical system (Fθ lens). Therefore, in the OFS system, it is easier to reduce the size of the polygon mirror that forms the deflector compared to the UFS system, and therefore it is possible to achieve faster and more precise printing in the optical scanning device.

[0015] In both the OFS and UFS systems, the light beam guided to the surface to be scanned by the imaging optical system is condensed as a beam spot in the printing area on the surface to be scanned due to the imaging performance of the imaging optical system. In this case, the UFS method can obtain a uniform spot diameter and a uniform light quantity distribution over the entire printing area on the surface to be scanned.

[0016] On the other hand, in the UFS method, if the number of deflection surfaces of the deflector is increased to achieve higher speeds, the deflector will become larger, which will result in a larger optical scanning device.In addition, the driving force of the motor that drives the deflector will increase, which will result in increased driving power, driving noise, and vibration. Furthermore, with the OFS method, even if the number of deflection surfaces is increased, the deflector can be kept from becoming larger compared to the UFS method, but it becomes difficult to achieve uniform printing because the spot diameter and light intensity vary depending on the image height on the scanned surface.

[0017] Therefore, conventionally, optical scanning devices have been proposed that include a deflector that deflects all of the incident light beam near the on-axis image height on the scanned surface as in the UFS method, while deflecting a portion of the incident light beam near the most off-axis image height on the scanned surface as in the OFS method. However, it is difficult to reduce the size and cost of such an optical scanning device. Specifically, in order to reduce the size of an optical scanning device, it is effective to perform wide-angle scanning, in which the maximum scanning angle is set large so as to reduce the distance between the deflector and the scanned surface.

[0018] However, in the above-mentioned optical scanning device, the maximum scanning angle is small, ranging from 22° to 45°, and wide-angle scanning cannot be performed, making it difficult to reduce the size. On the other hand, if the maximum scanning angle of view is increased in order to reduce the size of the optical scanning device, the following problems will arise: the spot size on the surface to be scanned will become larger, and the fluctuation in the amount of light will become more pronounced.

[0019] In the above optical scanning device, the ratio of the width of the light beam scanning the on-axial image height to the width of the light beam scanning the most off-axial image height on the scanned surface in the main scanning cross section is set to 1.2 or less. In other words, the maximum scanning angle of view is set so that the incident light beam is blocked by 20% when deflected by the deflecting surface toward the most off-axial image height. However, in the above-mentioned optical scanning device, when the incident light beam is deflected by 20% by the deflecting surface toward the most off-axis image height, the spot diameter at the most off-axis image height increases by 20% and the amount of light decreases by 20%.

[0020] In a conventional electrophotographic process, if the spot diameter in the print scanning area increases by 20% and the light amount decreases by 20%, it becomes difficult to produce uniform print. In this case, by providing an electrical correction circuit to adjust the light emission time and light intensity of the light source, it is possible to suppress spot enlargement and fluctuations in light intensity in the print scanning area, but providing such an electrical correction circuit results in an increase in the size and cost of the optical scanning device.

[0021] Furthermore, the polygon mirror used as a deflector in the optical scanning device is large, and as the size of the polygon mirror increases, the cost of materials, the labor required to process the reflective surface of the polygon mirror, and the cost of forming a film on the reflective surface increase. Furthermore, if the polygon mirror is large, the optical scanning device becomes larger and the driving force of the motor that drives the polygon mirror increases, which causes problems such as increased driving power, driving noise, and vibration.

[0022] Additionally, in the above-mentioned optical scanning device, synchronous detection for determining the timing for starting scanning on the surface to be scanned has not been fully considered. In the optical scanning device, synchronous detection is performed by scanning a synchronous detection light receiving element at the timing of scanning the outside of the print area of ​​the scanned surface.

[0023] Therefore, in the above-mentioned optical scanning device, synchronous detection is performed by deflecting a portion of the incident light beam by the deflecting surface so that the synchronous detection light receiving element is scanned, and therefore if the arrangement of the synchronous detection optical system is not given sufficient consideration, the optical scanning device will become large. Therefore, an object of this embodiment is to provide an optical scanning device that is miniaturized while maintaining high speed and high quality image recording by appropriately arranging the deflectors and optical elements.

[0024] FIG. 1 is a schematic main-scan cross-sectional view of an optical scanning device 100 according to the first embodiment. The optical scanning device 100 according to this embodiment includes a light source 1, a sub-scanning diaphragm 2, an anamorphic collimator lens 3, a main-scanning diaphragm 4, and a polygon mirror 5 (deflector). The optical scanning device 100 according to this embodiment also includes a scanning imaging lens 6 (imaging optical element), a synchronous detection light receiving element 80 (light receiving element), and a synchronous detection imaging element 81 (optical element).

[0025] The light source 1 is formed by, for example, a semiconductor laser, and has at least one light emitting point. The sub-scanning diaphragm 2 restricts the width of the light beam emitted from the light source 1 in the sub-scanning direction.

[0026] The anamorphic collimator lens 3 is a coupling optical element that has different powers in the main scanning cross section and the sub-scanning cross section, and that functions to couple the light beams that have passed through the sub-scanning stop 2 . Specifically, the anamorphic collimator lens 3 converts the light beam that has passed through the sub-scanning aperture 2 into a parallel light beam or a weakly convergent light beam in the main scanning cross section, and also converges the light beam so that it is focused near the deflection surface 51 of the polygon mirror 5 in the sub-scanning cross section.

[0027] The main scanning diaphragm 4 restricts the width of the light beam that has passed through the anamorphic collimator lens 3 in the main scanning direction. The optical scanning device 100 according to this embodiment employs a divided aperture system in which the sub-scanning aperture 2 and the main scanning aperture 4 are provided.

[0028] In other words, in the optical scanning device 100 of this embodiment, which employs a divided aperture system, the main scanning aperture 4 is positioned close to the polygon mirror 5, so that when the light source 1 has multiple light emitting points, multiple light beams can be brought close to each other on the deflection surface 51 of the polygon mirror 5. As will be described later, in the optical scanning device 100 according to this embodiment, the light beam is split on the deflecting surface 51 of the polygon mirror 5 in accordance with the scanning angle of view. Therefore, by placing the plurality of light beams close to each other on the deflecting surface 51 of the polygon mirror 5, the difference between the division ratios of the plurality of light beams can be reduced.

[0029] In addition, in the optical scanning device 100 of this embodiment, by arranging the sub-scanning aperture 2 on the light source 1 side of the anamorphic collimator lens 3, it is possible to form a conjugate image of the sub-scanning aperture 2 by the anamorphic collimator lens 3 near the scanning imaging lens 6. As a result, multiple light beams emitted from a light source 1 having multiple light-emitting points pass through positions close to each other in the scanning imaging lens 6, thereby reducing the differences between the optical characteristics of each of the multiple light beams.

[0030] The difference in the optical characteristics of each of the multiple light beams mentioned here includes, for example, a difference in spot shape caused by coma aberration due to the curvature of the scanning and imaging lens 6 in the sub-scanning cross section, and a shift in printing position caused by the refractive index distribution inside the scanning and imaging lens 6. The difference in optical characteristics between the multiple light beams mentioned here includes differences in polarization state caused by the birefringence distribution of the scanning imaging lens 6, differences in light quantity distribution caused by differences in polarization dependency of the reflectance and transmittance of optical elements provided on the optical path, etc.

[0031] For the above reasons, it is preferable that the optical scanning device 100 according to this embodiment employs a divided aperture system. In the optical scanning device 100 according to this embodiment, the sub-scanning diaphragm 2, the anamorphic collimator lens 3, and the main-scanning diaphragm 4 form an incident optical system 75 (second optical system).

[0032] The polygon mirror 5 is a rotating polygonal mirror that rotates at a uniform speed around the rotation axis of a polygon motor (not shown) and functions as a deflector that deflects the light beam emitted from the light source 1 and guided to the deflection surface 51 by the incident optical system 75 toward the scanned surface 7 (see Figure 2). The polygon mirror 5 has a regular pentagonal shape in the main scanning cross section so as to have five deflection surfaces 51, each of which is an optically reflective surface having a flat shape.

[0033] In addition, the position of the rotation axis of the polygon motor that drives the polygon mirror 5 coincides with the center 50 of the inscribed circle inscribed in each deflection surface 51 of the polygon mirror 5 in the main scanning cross section, or the center of the circumscribed circle passing through each corner of the deflection surface 51. The polygon mirror 5 can be formed by cutting out a metal block, or by forming a base material by resin molding using a mold and then providing a vapor-deposited film on the deflecting surface 51. In the optical scanning device 100 according to this embodiment, the width of the light beam immediately before it is incident on the deflecting surface 51 of the polygon mirror 5 by the incident optical system 75 is smaller than the width of the deflecting surface 51 in the main scanning cross section.

[0034] The scanning and imaging lens 6 (scanning and imaging element) focuses (guides) the light beam deflected by the polygon mirror 5 onto the surface to be scanned 7 so that a beam spot is formed on the surface to be scanned 7. Specifically, the scanning and imaging lens 6 includes an entrance surface and an exit surface each having a free-form surface shape expressed by an aspherical polynomial.

[0035] The scanning and imaging lens 6 may have a constant velocity characteristic of Y=Fθ, which scans the surface to be scanned 7 at a constant velocity, or may have a non-uniform velocity characteristic such as Y=tanθ. The scanning and imaging lens 6 can be formed by molding optical plastic using a mold. As the polygon mirror 5 rotates, the printing range from the most positive off-axis image height 71 on the side of the light source 1 (positive side in the Y direction) on the scanned surface 7 to the most negative off-axis image height 72 on the opposite side of the light source 1 (negative side in the Y direction) is scanned.

[0036] In the optical scanning device 100 according to this embodiment, the scanning and imaging lens 6 forms an imaging optical system 85 (first optical system). In the optical scanning device 100 according to this embodiment, the imaging optical system 85 is formed by a single scanning imaging lens 6 in order to reduce costs, but this is not limited to this, and the imaging optical system 85 may be formed by multiple scanning imaging lenses.

[0037] In the optical scanning device 100 according to this embodiment, the optical axis of the incident optical system 75 and the optical axis of the imaging optical system 85 are both within the main scanning cross section. Therefore, the principal ray of the light beam emitted from the light emitting point of the light source 1 arranged in the main scanning cross section is deflected by the polygon mirror 5 towards the scanned surface 7 in the main scanning cross section.

[0038] That is, the optical scanning device 100 according to this embodiment employs the above-described in-plane deflection scanning method. However, the optical scanning device 100 according to this embodiment is not limited to this, and the incident optical system 75 may be formed as an oblique incidence optical system that causes a light beam to be obliquely incident on the deflection surface 51 of the polygon mirror 5 within the sub-scan cross section, and the deflection in-plane scanning method may not be adopted.

[0039] In the optical scanning device 100 according to this embodiment, the optical axis of the incident optical system 75 is arranged to be parallel to the main scanning direction. That is, the angle between the optical axis of the incident optical system 75 and the optical axis of the imaging optical system 85, in other words, the incident light beam L immediately before it is incident on the polygon mirror 5 in the main scanning section. i The angle θ that the direction of the chief ray makes with the X axis i is set to 90 degrees.

[0040] In addition, in the optical scanning device 100 of this embodiment, a light beam (hereinafter referred to as a synchronous detection light beam) deflected by the polygon mirror 5 at a scanning angle outside the printing range on the scanned surface 7 is guided onto the synchronous detection light receiving element 80 by the synchronous detection imaging element 81. This makes it possible to determine the timing for starting printing on the scanned surface 7 in synchronization with the rotation of the polygon mirror 5.

[0041] Specifically, the synchronous detection imaging element 81 has the power to collect the synchronous detection light beam deflected by the polygon mirror 5 at least within the main scanning cross section. In addition, in the optical scanning device 100 according to this embodiment, a synchronous detection slit (not shown) extending in the sub-scanning direction and a synchronous detection edge portion (not shown) extending in the sub-scanning direction of the synchronous detection light receiving element 80 are arranged on the focal point of the synchronous detection light beam formed by the synchronous detection imaging element 81.

[0042] In the optical scanning device 100 according to this embodiment, the synchronous detection imaging element 81 forms a synchronous detection optical system. Specifically, as shown in FIG. 1, the synchronous detection optical system is arranged so that the optical axis is positioned between the traveling direction of the incident light beam on the deflecting surface 51 of the polygon mirror 5 and the traveling direction of the light beam that, when deflected by the deflecting surface 51, heads toward the most off-axis image height 71 on the plus side.

[0043] Moreover, it is desirable that the synchronous detection light beam deflected by the polygon mirror 5 is condensed by the synchronous detection imaging element 81 in the vicinity of the synchronous detection light receiving element 80 in the sub-scanning cross section. However, if the synchronous detection light beam is excessively focused in the sub-scan section by the synchronous detection imaging element 81, the detection timing by the synchronous detection light receiving element 80 may vary depending on the linearity of the synchronous detection edge portion (not shown) and the tolerance of the installation angle.

[0044] Therefore, the power of the synchronous detection imaging element 81 in the sub-scanning section is generally set so that the synchronous detection light beam is not excessively focused by the synchronous detection imaging element 81 in the sub-scanning section. On the other hand, consider a case where the synchronous detection light beam is weakly focused by the synchronous detection imaging element 81 so that the width of the synchronous detection light beam on the light receiving surface of the synchronous detection light receiving element 80 in the sub-scanning cross section is approximately the same as the width of the light receiving surface.

[0045] In this case, when the synchronous detection light beam is shifted in the sub-scanning direction due to tolerances or the like, the amount of light received by the synchronous detection light receiving element 80 of the synchronous detection light beam fluctuates, resulting in a decrease in detection accuracy. The power of the synchronous detection imaging element 81 in the sub-scan section may be determined taking the above into consideration.

[0046] The power of the synchronous detection imaging element 81 in the main scanning cross section and the power in the sub-scanning cross section may be different from each other, and the synchronous detection imaging element 81 may have rotationally symmetric power. Furthermore, the optical scanning device 100 according to this embodiment is provided with a synchronous detection optical system formed by a synchronous detection imaging element 81, but this is not limited to this, and if variations in the synchronous detection timing are acceptable, it is not necessary to provide a synchronous detection optical system.

[0047] In the optical scanning device 100 according to this embodiment, the light source 1 and the synchronous detection light receiving element 80 are mounted on a single electrical mounting board 83 (board), as shown in FIG. In other words, in the optical scanning device 100 according to this embodiment, the synchronization detection light receiving element 80 is disposed on the side where the light source 1 is disposed with respect to the optical axis of the imaging optical system 85 in the main scanning cross section. Furthermore, on the electrical mounting board 83, a light emission control unit (light amount adjustment unit) (not shown) for controlling the light emission state of the light source 1 based on the output of the synchronous detection light receiving element 80 is provided.

[0048] The light emission control unit determines the timing of the start of printing synchronized with the output timing of the synchronous detection light receiving element 80, thereby driving the light source 1 to emit light. The light emission control unit also drives the light source 1 to emit light at a predetermined light intensity or at a light intensity set during assembly adjustment.

[0049] The light emission control unit also sets the amount of emitted light according to the number of deflecting surfaces 51 of the polygon mirror 5 during assembly adjustment. The light emission control section also has a function of adjusting the amount of light emitted from the light source 1 in accordance with the sensitivity of the synchronous detection light receiving element 80 when performing synchronous detection.

[0050] As will be described later, in the optical scanning device 100 according to this embodiment, the width of the synchronous detection light beam is smaller than the width of the light beam that scans the surface to be scanned 7, and therefore the amount of energy of the synchronous detection light beam is reduced. Therefore, if the energy amount of the synchronous detection light beam is significantly reduced and it is difficult for the synchronous detection light receiving element 80 to detect the synchronous detection light beam, the amount of light emitted by the light source 1 may be increased at the time when synchronous detection is performed by the synchronous detection light receiving element 80. Alternatively, a light-receiving sensitivity adjustment section for adjusting the light-receiving sensitivity of the synchronous detection light-receiving element 80 may be provided on the electrical mounting board 83 . The light-receiving sensitivity adjusting section may adjust the light-receiving sensitivity of the synchronous detection light-receiving element 80 in accordance with the number of deflecting surfaces 51 of the polygon mirror 5.

[0051] 2(a), (b), (c), and (d) are partially enlarged schematic main-scan cross-sectional views of the vicinity of the polygon mirror 5 of the optical scanning device 100 according to this embodiment. Specifically, FIGS. 2(a) and 2(b) respectively show a diagram when scanning an axial image height 70 on the surface to be scanned 7 and a diagram when scanning a synchronous detection light receiving element 80. Specifically, Figures 2(c) and (d) respectively show a diagram of scanning the most positive off-axis image height 71 on the scanned surface 7, and a diagram of scanning the most negative off-axis image height 72 on the scanned surface 7.

[0052] As shown in FIG. 2(a), when scanning an axial image height 70 on the surface to be scanned 7, the incident light beam L incident on the deflecting surface 51 of the polygon mirror 5 is i is deflected by the deflecting surface 51 so as to travel along the X-axis as the scanning light beam L0. In this case, the angle (scanning angle of view) that the traveling direction of the scanning light beam L0 makes with the X axis is 0 degrees.

[0053] Also, the incident light beam L immediately before it is incident on the deflection surface 51 of the polygon mirror 5 i The width in the main scanning section is W i The width of the scanning light beam L0 in the main scanning cross section immediately after being deflected by the deflecting surface 51 is represented as W0. Furthermore, the normal 510 of the deflection surface 51 passes through the center of rotation 50 of the polygon mirror 5, and the adjacent deflection surface 52 on the downstream side of the deflection surface 51 in the rotation direction has a normal 520, while the adjacent deflection surface 53 on the upstream side of the deflection surface 51 in the rotation direction has a normal 530. The incident luminous flux L i is the chief ray L iP and marginal ray L iU and L iL The scanning light beam L0 has a principal ray L 0P and marginal ray L 0U and L 0L It has the following features.

[0054] As shown in FIG. 2(a), the width of the deflecting surface 51 of the polygon mirror 5 in the main scanning section is i Width W i It's getting bigger. The scanning light beam L0 that scans the axial image height 70 is deflected near the center of the deflecting surface 51 of the polygon mirror 5, so that W0=W i The incident light beam L is i Width W i is maintained.

[0055] Next, as shown in FIG. 2(b), when scanning the synchronous detection light receiving element 80, the incident light beam L is incident on the deflection surface 51 (first deflection surface) of the polygon mirror 5, which is at a predetermined angle (first angle) in the main scanning cross section. i is incident. The predetermined angle here is the angle that normal 510 of deflection surface 51 makes with respect to the X axis. Then, the incident light beam L incident on the deflection surface 51 of the polygon mirror 5 at the predetermined angle i is the scanning light beam L BD The light is deflected by the deflecting surface 51 so as to travel in a direction forming a predetermined angle with respect to the X axis.

[0056] At this time, the scanning light beam L immediately after being deflected by the polygon mirror 5 BD The angle that the direction of the chief ray makes with the X axis is θ BD and the scanning light beam L immediately after being deflected by the deflecting surface 51 is expressed as follows: BD The width in the main scanning section is W BD It is expressed as: The scanning light beam L BD is the chief ray L BDP and marginal ray L BDU and L BDL It has the following features.

[0057] As shown in FIG. 2(b), when the synchronous detection light receiving element 80 is scanned, the incident light beam L i A part of the light (another part) is incident on the adjacent deflecting surface 52 (second deflecting surface) on the downstream side of the deflecting surface 51 of the polygon mirror 5 in the rotation direction. The incident light beam L incident on the deflection surface 52 i A part of the scanning light beam L BD2 is deflected as

[0058] That is, in the optical scanning device 100 according to this embodiment, when scanning the synchronous detection light receiving element 80, two scanning light beams L BD and L BD2 The incident light beam L is separated (divided) by the polygon mirror 5. i is deflected. In other words, in the optical scanning device 100 according to this embodiment, the incident light beam L incident on the polygon mirror 5 whose deflection surface 51 is at the predetermined angle in the main scanning cross section. i Only a portion of the light is deflected by the deflection surface 51 .

[0059] and the scanning light beam L BDscans the center of the light receiving surface of the synchronous detection light receiving element 80 via the synchronous detection image forming element 81. On the other hand, the scanning light beam L BD2 is the scanning light beam L with respect to the X axis. BD Angle θ BD It moves in a direction that forms a different angle from the direction of the arrow.

[0060] Specifically, the scanning light beam L BD2 is the angle (θ BD The beam travels in a direction that forms an angle of −360 / N×2 degrees, where N is the number of deflecting surfaces 51 of the polygon mirror 5. In this case, if the scanning and imaging lens 6 is disposed at a sufficient distance from the polygon mirror 5, the scanning light beam L BD2 does not enter the scanning and imaging lens 6 and is not guided to the surface to be scanned 7, that is, it travels toward outside the effective area of ​​the surface to be scanned 7.

[0061] and the scanning light beam L BD2 is shielded from light by the wall surfaces, ribs, etc. of the housing (not shown) of the optical scanning device 100. In addition, the scanning light beam L BD2 is incident on the scanning and imaging lens 6, the angle θ is set so that it does not reach the scanning area (printing area) on the surface to be scanned 7. BD The number N of deflecting surfaces 51 of the polygon mirror 5 may be set.

[0062] In the optical scanning device 100 according to this embodiment, when scanning the synchronous detection light receiving element 80, the incident light beam L i are two scanning beams L BD and L BD2 It is separated (divided) into Therefore, the scanning light beam L that scans the synchronous detection light receiving element 80 BD Width W in the main scanning section BD is the incident luminous flux L i Width W in the main scanning section i It becomes smaller.

[0063] And W BD <W i When / 2 is satisfied, the scanning light beam L BD2The width in the main scanning direction of the scanning light beam L BD Width W in the main scanning direction BD By increasing the scanning light flux L BD2 The amount of light is the scanning light beam L BD The amount of light will be greater than that of the In this case, the scanning light beam L BD2 Synchronous detection may be performed by providing a synchronous detection light receiving element 80 and a synchronous detection image forming element 81 on the optical path. In addition, the scanning light beam L BD2 The light may be reflected by a synchronous detection reflecting element and guided to a synchronous detection light receiving element 80 provided on an electrical mounting board 83 .

[0064] Next, as shown in FIG. 2(c), when scanning the most off-axis image height 71 on the positive side on the surface to be scanned 7, the incident light beam L incident on the deflecting surface 51 of the polygon mirror 5 is i is the scanning light beam L max+ The light is deflected by the deflecting surface 51 so as to travel in a direction forming a predetermined angle with respect to the X axis. At this time, the scanning light beam L immediately after being deflected by the polygon mirror 5 max+ The angle that the direction of the chief ray makes with the X axis is θ max+ and the scanning light beam L immediately after being deflected by the deflecting surface 51 is expressed as follows: max+ The width in the main scanning section is W max+ It is expressed as: The scanning light beam L max+ is the chief ray L max+P and marginal ray L max+U and L max+L It has the following features.

[0065] When scanning the most off-axis image height 71 on the positive side on the surface to be scanned 7, the incident light beam L i is deflected near one end of the deflecting surface 51 in the main scanning direction, but as will be described later, the incident light beam L i All of these are deflected by the deflection surface 51. Therefore, W max+ =W i The scanning light beam L is max+ At the incident luminous flux L i Width Wi is maintained.

[0066] Next, as shown in FIG. 2(d), when scanning the minus-side most off-axis image height 72 on the scanned surface 7, the incident light beam L is incident on the deflection surface 51 (first deflection surface) of the polygon mirror 5, which is at a predetermined angle (second angle) in the main scanning cross section. i is incident. Then, the incident light beam L incident on the deflection surface 51 of the polygon mirror 5 at the predetermined angle i is the scanning light beam L max- The light is deflected by the deflecting surface 51 so as to travel in a direction forming a predetermined angle with respect to the X axis.

[0067] At this time, the scanning light beam L immediately after being deflected by the polygon mirror 5 max- The angle that the direction of the chief ray makes with the X axis is θ max- and the scanning light beam L immediately after being deflected by the deflecting surface 51 is expressed as follows: max- The width in the main scanning section is W max- It is expressed as: The scanning light beam L max- is the chief ray L max-P and marginal ray L max-U and L max-L It has the following features.

[0068] As shown in FIG. 2(d), when scanning the minus-side most off-axis image height 72 on the scanned surface 7, the incident light beam L i A part of the light is incident on the adjacent deflecting surface 53 downstream of the deflecting surface 51 of the polygon mirror 5 in the rotation direction. The incident light beam L incident on the deflection surface 53 i A part of the scanning light beam L max-2 is deflected as

[0069] That is, in the optical scanning device 100 according to this embodiment, when scanning the minus-side most off-axis image height 72 on the scanned surface 7, two scanning light beams L max- and L max-2 The incident light beam L is separated (divided) by the polygon mirror 5. i is deflected. In other words, in the optical scanning device 100 according to this embodiment, the incident light beam L incident on the polygon mirror 5 whose deflection surface 51 is at the predetermined angle in the main scanning cross section. i Only a portion of the light is deflected by the deflection surface 51 .

[0070] and the scanning light beam L max- scans the minus-side most off-axis image height 72 on the surface to be scanned 7. On the other hand, the scanning light beam L max-2 is the scanning light beam L with respect to the X axis. max- Angle θ max- It moves in a direction that forms a different angle from the direction of the arrow.

[0071] Specifically, the scanning light beam L max-2 is the angle (θ max- +360 / N×2) degrees. In this case, if the scanning and imaging lens 6 is disposed at a sufficient distance from the polygon mirror 5, the scanning light beam L max-2 Since the light does not enter the scanning and imaging lens 6, it is not guided to the surface to be scanned 7, and is blocked by the wall surfaces, ribs, etc. of the housing (not shown) of the optical scanning device 100. In addition, the scanning light beam L max-2 is incident on the scanning and imaging lens 6, the angle θ is set so that it does not reach the scanning area (printing area) on the surface to be scanned 7. max- The number N of deflecting surfaces 51 of the polygon mirror 5 may be set.

[0072] In the optical scanning device 100 according to this embodiment, when scanning the minus-side most off-axis image height 72 on the surface to be scanned 7, the incident light beam L i are two scanning beams L max- and L max-2 are separated into Therefore, the scanning light beam L that scans the minus-side most off-axis image height 72 on the scanned surface 7 max- Width W in the main scanning direction max- is the incident luminous flux L i Width W in the main scanning direction i It becomes smaller.

[0073] In the optical scanning device 100 according to this embodiment, it is preferable that the following conditional expression (1) be satisfied. W BD <W max- <W max+ ···(1)

[0074] Satisfying the conditional expression (1) means that the scanning light beam L max- and L max+ Width W max- and W max+ are the scanning light beams L BD , i.e., the width W of the synchronous detection beam BD It means to be bigger. In order to obtain a uniform printed image, it is preferable that there is little variation in the width of the scanning light beam that scans each image height in the scanning area on the surface to be scanned 7 . This is because the uniformity (tolerance) of printing is determined according to the requirements and specifications of the photosensitive drum and electrophotographic process provided in the image forming apparatus in which the optical scanning device 100 according to this embodiment is installed.

[0075] On the other hand, the synchronous detection light beam received by the synchronous detection light receiving element 80 only needs to have a necessary amount of light according to the light receiving sensitivity of the synchronous detection light receiving element 80 . The synchronous detection light receiving element 80 can be selected in consideration of the level of light receiving sensitivity according to the light energy of the synchronous detection light beam to be received.

[0076] Furthermore, by adjusting the light receiving sensitivity of the synchronous detection light receiving element 80 or the amount of light emitted by the light source 1 on the electrical mounting board 83, the amount of light of the synchronous detection light beam received by the synchronous detection light receiving element 80 can also be adjusted. However, using an electrical mounting board 83 capable of performing such adjustments increases costs, so it is not desirable to reduce the light energy of the synchronous detection light beam too much by significantly reducing the beam width of the synchronous detection light beam. Generally, costs can be reduced by setting the beam width of the synchronous detection beam to be 1 / 2 to 1 / 3 or more of the beam width of the scanning beam that scans the surface to be scanned 7.

[0077] Furthermore, in the optical scanning device 100 according to this embodiment, it is more preferable that the following conditional expression (1') be satisfied. W max+ =W i (1')

[0078] In the optical scanning device 100 according to this embodiment, the scanning light beam L max- Width W max- and the scanning light beam L max+ Width W max+ It is preferable that the difference between In the conventional UFS system, when the deflecting surface of the deflector deflects all of the incident light beams to scan the surface to be scanned, the difference can be made zero.

[0079] However, in such a UFS system, in order to deflect all light beams by the same deflection surface, it is necessary to increase the width of the deflection surface in the main scanning cross section. Therefore, increasing the number of deflecting surfaces of a deflector results in an increase in the size of the deflector.

[0080] On the other hand, in the optical scanning device 100 according to this embodiment, the beam width of each scanning beam is set so as to satisfy conditional expression (1). This makes it possible to prevent the polygon mirror 5, the optical scanning device 100 according to this embodiment, and ultimately the image forming apparatus in which the optical scanning device 100 according to this embodiment is mounted from increasing in size.

[0081] In the optical scanning device 100 according to this embodiment, the conditional expression (1) is satisfied, so that the scanning light beam L BD Width W BD is the incident luminous flux L i Width W i It becomes smaller. This allows the width of the optical surface of the synchronous detection imaging element 81, particularly the width of the entrance surface in the main scanning cross section, to be smaller than the width of the optical surface closest to the polygon mirror 5 on the optical path of the entrance optical system 75, i.e., the width of the exit surface of the anamorphic collimator lens 3 in the main scanning cross section. That is, in the optical scanning device 100 according to this embodiment, the synchronous detection image-forming element 81 can be made smaller by satisfying the conditional expression (1).

[0082] As shown in FIG. 1, in the optical scanning device 100 according to this embodiment, the synchronous detection imaging element 81 is provided between the anamorphic collimator lens 3 and the scanning imaging lens 6 in the main scanning cross section. Therefore, if the synchronous detection imaging element 81 becomes larger, it becomes necessary to increase the distance between the anamorphic collimator lens 3 and the scanning imaging lens 6 . Therefore, in the optical scanning device 100 of this embodiment, the optical surface of the synchronous detection imaging element 81 is made smaller than the optical surface of the anamorphic collimator lens 3, thereby achieving miniaturization, and ultimately miniaturization of the image forming device in which it is installed.

[0083] In the optical scanning device 100 according to this embodiment, it is preferable that the following conditional expression (2) be satisfied. 5.50≦φ-K×N×(N-1)≦13.00 (2)

[0084] In conditional expression (2), φ is the diameter [mm] of the circumscribing circle of polygon mirror 5 in the main scanning cross section, N is the number of deflecting surfaces 51 of polygon mirror 5, and K is a predetermined value between 0.52 and 0.56. In the optical scanning device 100 according to this embodiment, it is more preferable that conditional expression (2) be satisfied when K is a predetermined value equal to or greater than 0.53 and equal to or less than 0.55.

[0085] Conditional formula (2) defines an appropriate relationship between the number N of deflecting surfaces 51 of polygon mirror 5 and the diameter φ of the circumscribing circle of polygon mirror 5 in optical scanning device 100 according to this embodiment. If the lower limit of conditional expression (2) is not reached, the number N of deflecting surfaces 51 increases relative to the size of the polygon mirror 5, and the size of each of the N deflecting surfaces 51 becomes small. If the size of the deflection surface 51 becomes too small, the scanning light beam L BD , L max- and L max+ Each width W BD , W max- and W max+ is the incident luminous flux L i Width W i If it gets too small, it becomes difficult to achieve uniform printing.

[0086] On the other hand, if the upper limit of conditional expression (2) is exceeded, the number N of deflecting surfaces 51 relative to the size of the polygon mirror 5 decreases, or the size of the polygon mirror 5 relative to the number N of deflecting surfaces 51 increases. If the size of the polygon mirror 5 increases, the optical scanning device 100 according to this embodiment, and in turn the image forming apparatus in which the optical scanning device 100 according to this embodiment is mounted, will also increase in size.

[0087] That is, in the optical scanning device 100 according to this embodiment, miniaturization can be achieved by satisfying conditional expression (2). In conditional expression (2), the optimum specifications for the polygon mirror 5 can be found by setting the constant K to approximately 0.54.

[0088] In the optical scanning device 100 according to this embodiment, it is preferable that the following conditional expression (3) be satisfied.

number

[0089] Conditional expression (3) defines another appropriate relationship between the number N of deflecting surfaces 51 of polygon mirror 5 and the diameter φ of the circumscribing circle of polygon mirror 5 in optical scanning device 100 according to this embodiment. If the value is equal to or less than the lower limit of conditional expression (3), the number N of deflecting surfaces 51 increases relative to the size of the polygon mirror 5, and the size of each of the N deflecting surfaces 51 becomes small. If the size of the deflection surface 51 becomes too small, the scanning light beam L BD , L max- and L max+ Each width W BD , W max- and W max+ is the incident luminous flux L i Width W i If it gets too small, it becomes difficult to achieve uniform printing.

[0090] On the other hand, if the upper limit of conditional expression (3) is exceeded, the number N of deflecting surfaces 51 relative to the size of polygon mirror 5 decreases, or the size of polygon mirror 5 relative to the number N of deflecting surfaces 51 increases. If the size of the polygon mirror 5 increases, the optical scanning device 100 according to this embodiment, and in turn the image forming apparatus in which the optical scanning device 100 according to this embodiment is mounted, will also increase in size.

[0091] In the optical scanning device 100 according to this embodiment, by satisfying conditional expression (3), a more preferable relationship can be obtained between the number N of deflecting surfaces 51 of the polygon mirror 5 and the diameter φ of the circumscribing circle of the polygon mirror 5. In the optical scanning device 100 according to this embodiment, it is more preferable that the following conditional expression (3a) be satisfied instead of the conditional expression (3).

number

[0092] In the optical scanning device 100 according to this embodiment, it is preferable that the following conditional expression (4) be satisfied.

number

[0093] Conditional formula (4) specifies the appropriate relationship between the number N of deflection surfaces 51 of the polygon mirror 5, the diameter φ of the circumscribing circle of the polygon mirror 5, and the position of the most off-axis image height 71 on the positive side in the optical scanning device 100 of this embodiment. If the value is equal to or less than the lower limit of the conditional expression (4), the scanning angle of view when the scanning area on the surface to be scanned 7 is scanned by the deflecting surface 51 of the polygon mirror 5 becomes small. Furthermore, when the scanning angle of view becomes smaller, it is necessary to increase the distance between the polygon mirror 5 and the scanned surface 7, which results in an increase in the size of the optical scanning device 100 of this embodiment, and ultimately the image forming device in which the optical scanning device 100 of this embodiment is installed.

[0094] On the other hand, if the upper limit of conditional expression (4) is exceeded, the number N of deflecting surfaces 51 increases relative to the size of the polygon mirror 5, and the size of each of the N deflecting surfaces 51 becomes small. If the size of the deflection surface 51 becomes too small, the scanning light beam L BD , L max- and L max+ Each width W BD , W max- and W max+ is the incident luminous flux L i Width W i If it gets too small, it becomes difficult to achieve uniform printing.

[0095] In the optical scanning device 100 according to this embodiment, it is more preferable that the following conditional expression (4a) be fulfilled instead of the conditional expression (4).

number

[0096] As shown in FIG. 1, in the optical scanning device 100 according to this embodiment, the scanning light beam L guided to the synchronous detection light receiving element 80 by the polygon mirror 5 is BD travels on the light source 1 side with respect to the optical axis of the imaging optical system 85. In the optical scanning device 100 according to this embodiment, a synchronous detection imaging element 81 is disposed between the incident optical system 75 and the scanning imaging lens 6 in the main scanning cross section.

[0097] As a result, the scanning light beam L BD The optical scanning device 100 according to this embodiment can be made smaller than when synchronous detection is performed by causing the light source 1 to travel on the opposite side of the optical axis of the imaging optical system 85 to the light source 1. Furthermore, in the optical scanning device 100 according to this embodiment, the synchronous detection light receiving element 80 and the light source 1 are mounted on the same electrical mounting board 83, thereby making it possible to achieve miniaturization and cost reduction.

[0098] As described above, in the optical scanning device 100 according to this embodiment, the scanning light beam L that scans the synchronous detection light receiving element 80 BD Width W BD is the incident luminous flux L i Width W i Although it is smaller than the width W BD is preferably as large as possible. This is the scanning light beam L BD When the scanning light beam L travels toward the light source 1 with respect to the optical axis of the imaging optical system 85, BD The angle θ that the direction of travel makes with respect to the X axis BD If is not set properly, the width W BD becomes too small, the scanning light beam L BD This is because the amount of light decreases. The scanning light beam L included in the range of the light receiving sensitivity of the synchronous detection light receiving element 80 BD However, if the amount of light is reduced by the scanning light beam L, which exceeds the range of the light receiving sensitivity of the synchronous detection light receiving element 80, BD If the amount of light decreases, the accuracy of synchronization detection decreases.

[0099] In the optical scanning device 100 according to this embodiment, it is preferable that the following conditional expression (5) be satisfied.

number

[0100] In condition (5), θ i (°) is the angle formed between the optical axis of the imaging optical system 85 and the optical axis of the incident optical system 75 in the main scanning section. In addition, in condition (5), θ max+ (°) is the scanning light beam L heading toward the most off-axis image height 71 on the plus side immediately after being deflected by the polygon mirror 5 in the main scanning section. max+ is the angle that the traveling direction of the chief ray makes with respect to the optical axis of the imaging optical system 85. In addition, in condition (5), θ BD (°) is the scanning light beam L directed toward the center of the light receiving surface of the synchronous detection light receiving element 80 immediately after being deflected by the polygon mirror 5 in the main scanning cross section. BD is the angle that the traveling direction of the chief ray makes with respect to the optical axis of the imaging optical system 85.

[0101] In particular, when a synchronous detection imaging element 81 is provided to improve the synchronous detection accuracy, the synchronous detection imaging element 81 is provided between the anamorphic collimator lens 3 and the scanning imaging lens 6, and therefore interference between them must be taken into consideration. If the condition (5) is less than the lower limit, the angle θ i and angle θ BD As the difference between these becomes smaller, interference between the optical path in the incident optical system 75 and the optical path in the synchronous detection optical system becomes more likely to occur. In addition, the scanning light beam L BD Width W BD is the incident luminous flux L i Width W i If it becomes too small, it becomes difficult to maintain the accuracy of the synchronization detection.

[0102] On the other hand, if the upper limit of conditional expression (5) is exceeded, the angle θ BD becomes smaller. In this case, the scanning light beam L BD Width W BD Although the accuracy of synchronous detection can be improved by increasing , interference between the optical path in the synchronous detection optical system and the optical path in the imaging optical system 85 becomes more likely to occur. In addition, the increase in the distance between the synchronous detection light receiving element 80 and the light source 1 results in an increase in the size of the optical scanning device 100 according to this embodiment.

[0103] As described above, in the optical scanning device 100 according to this embodiment, interference between the optical path of the synchronization detection optical system and the optical path of the incident optical system 75 or the optical path of the imaging optical system 85, and the scanning light beam L BD Width W BD Considering both the decrease in BD It is important to set the This makes it possible to achieve a reduction in size of the optical scanning device 100 according to this embodiment in which the polygon mirror 5 and the synchronous detection optical system are appropriately arranged.

[0104] The scanning light beam L BD Angle θ BD The appropriate setting method for varies depending on the configuration of the imaging optical system 85 and the synchronous detection optical system. First, synchronous detection optical systems generally fall into one of the following two types.

[0105] One type is called a separate optical path type in which the synchronous detection light beam reaches the synchronous detection light receiving element without passing through each scanning and imaging lens provided in the imaging optical system. The other type is called a shared optical path type in which the synchronous detection light beam passes through at least one scanning and imaging lens provided in the imaging optical system and reaches the synchronous detection light receiving element.

[0106] In the shared optical path type, the number of optical elements can be reduced, but it is necessary to bend the optical path of the synchronous detection light beam by a folding mirror so that it heads toward the synchronous detection light receiving element. When the scanning and imaging lens is a glass lens, a shared optical path type can be adopted to reduce costs.

[0107] In addition, in the shared optical path type, it is necessary to increase the size of the scanning imaging lens in the main scanning direction so that the synchronous detection light beam, which travels at an angle relative to the optical axis of the imaging optical system that is larger than the angle of the scanning light beam that scans the surface to be scanned, can pass through. In this case, if the scanning and imaging lens is a resin lens, it is necessary to provide a certain thickness near the edge to take into account residual stress in the resin, so an increase in the size of the scanning and imaging lens in the main scanning direction results in an increase in the thickness of the center.

[0108] If the thickness of the central portion of the scanning and imaging lens increases, the time required for the molding tact time when forming the scanning and imaging lens increases, resulting in higher costs. Therefore, when the scanning and imaging lens is a resin lens, adopting a shared optical path type does not necessarily lead to cost reduction.

[0109] On the other hand, the separate optical path type has the advantage that it can suppress a decrease in accuracy of synchronization detection when the temperature of the optical scanning device rises. When the temperature of the optical scanning device rises, the wavelength of the laser that forms the light source fluctuates significantly, and if the scanning and imaging lens is a resin lens, the refractive index fluctuates significantly.

[0110] In the shared optical path type, the synchronous detection light beam passes through a portion other than the optical axis of at least one scanning and imaging lens provided in the imaging optical system, and therefore chromatic aberration of magnification occurs. That is, the apparent off-axis image height in the synchronous detection light-receiving element fluctuates, resulting in a decrease in the accuracy of synchronous detection.

[0111] The above-mentioned variations are a serious problem since they appear as misregistration in a color image forming apparatus in which images of multiple colors are superimposed on one another. Therefore, in recent years, while separate optical path types are adopted for optical scanning devices used in color image forming apparatuses, there are an increasing number of cases where shared optical path types are adopted for optical scanning devices used in monochrome image forming apparatuses.

[0112] Next, the number of scanning and imaging lenses that form the imaging optical system provided in the optical scanning device will be considered. The imaging optical system provided in the optical scanning device may be formed by a single scanning and imaging lens to reduce costs, or may be formed by multiple scanning and imaging lenses to improve optical performance.

[0113] However, while it is generally possible to reduce costs by forming the imaging optical system using a single scanning imaging lens, it may not be possible to reduce costs when the optical path is shortened to achieve compactness and the angle is widened. As described above, when the scanning and imaging lens is a resin lens, it is necessary to provide a certain thickness near the edge portion in consideration of the residual stress of the resin.

[0114] Therefore, as the angle becomes wider, the size of the scanning and imaging lens in the main scanning direction increases, which results in an increase in the thickness of the central portion. If the thickness of the central portion of the scanning and imaging lens increases, the time required for the molding tact time when forming the scanning and imaging lens increases, resulting in higher costs.

[0115] In such a case, it may be possible to reduce the total cost by forming an imaging optical system using a plurality of scanning imaging lenses with shared power. Furthermore, when the imaging optical system is formed by a single scanning imaging lens, the degree of freedom in arrangement is reduced, and the magnification tends to become high.

[0116] Therefore, when the imaging optical system is formed by a single scanning imaging lens, the separate optical path type is often adopted rather than the shared optical path type. On the other hand, when the imaging optical system is formed using multiple scanning imaging lenses, there are fewer restrictions than when it is formed using a single scanning imaging lens, so it is possible to select either the separate optical path type or the shared optical path type depending on the configuration.

[0117] In the optical scanning device 100 according to this embodiment, the synchronization detection optical system is appropriately arranged while taking the above into consideration, thereby achieving miniaturization. First, in the optical scanning device 100 according to this embodiment, when the imaging optical system is formed by a single scanning and imaging lens 6, it is preferable that the following conditional expression (6) be satisfied.

[0118]

number

[0119] If the condition (6) is less than the lower limit, the angle θ BD becomes smaller. In this case, the scanning light beam L BD Width W BD Although the accuracy of synchronous detection can be improved by increasing , interference between the optical path in the synchronous detection optical system and the optical path in the imaging optical system 85 becomes more likely to occur. In addition, the increase in the distance between the synchronous detection light receiving element 80 and the light source 1 results in an increase in the size of the optical scanning device 100 according to this embodiment.

[0120] On the other hand, if the upper limit of conditional expression (6) is exceeded, the angle θ i and angle θ BD As the difference between these becomes smaller, interference between the optical path in the incident optical system 75 and the optical path in the synchronous detection optical system becomes more likely to occur. In addition, the scanning light beam L BD Width W BD is the incident luminous flux L i Width W i If it becomes too small, it becomes difficult to maintain the accuracy of the synchronization detection.

[0121] Therefore, the interference between the optical path in the synchronous detection optical system and the optical path in the incident optical system 75 and the optical path in the imaging optical system 85, and the width W BD Considering both the decrease in the synchronous detection beam angle θ BD It is important to set the As a result, in the optical scanning device 100 according to this embodiment, the polygon mirror 5 and the synchronous detection optical system are appropriately arranged, thereby achieving miniaturization.

[0122] Next, in the optical scanning device 100 according to this embodiment, when the imaging optical system is formed by a plurality of scanning and imaging lenses 6 and a separate optical path type is adopted in which the synchronous detection light beam does not pass through any of the scanning and imaging lenses 6, it is preferable that the following conditional expression (7) be satisfied.

number

[0123] If the condition (7) is less than the lower limit, the angle θ BD becomes smaller. In this case, the scanning light beam L BD Width W BD Although the accuracy of synchronous detection can be improved by increasing , interference between the optical path in the synchronous detection optical system and the optical path in the imaging optical system 85 becomes more likely to occur. In addition, the increase in the distance between the synchronous detection light receiving element 80 and the light source 1 results in an increase in the size of the optical scanning device 100 according to this embodiment.

[0124] On the other hand, if the upper limit of conditional expression (7) is exceeded, the angle θ i and angle θ BD As the difference between these becomes smaller, interference between the optical path in the incident optical system 75 and the optical path in the synchronous detection optical system becomes more likely to occur. In addition, the scanning light beam L BD Width W BD is the incident luminous flux L i Width W i If it becomes too small, it becomes difficult to maintain the accuracy of the synchronization detection.

[0125] Therefore, the interference between the optical path in the synchronous detection optical system and the optical path in the incident optical system 75 and the optical path in the imaging optical system 85, and the width W BD Considering both the decrease in the synchronous detection beam angle θ BD It is important to set the As a result, in the optical scanning device 100 according to this embodiment, the polygon mirror 5 and the synchronous detection optical system are appropriately arranged, thereby achieving miniaturization.

[0126] Next, consider a case where the imaging optical system in the optical scanning device 100 according to this embodiment is formed by a plurality of scanning and imaging lenses 6, and a shared optical path type is adopted in which the synchronous detection light beam passes through at least one scanning and imaging lens 6. In this case, it is preferable that the following conditional expression (8) be satisfied.

[0127]

number

[0128] If the condition (8) is less than the lower limit, the angle θ BD becomes smaller. In this case, the scanning light beam L BD Width W BD Although the accuracy of synchronous detection can be improved by increasing , interference between the optical path in the synchronous detection optical system and the optical path in the imaging optical system 85 becomes more likely to occur. In addition, the increase in the distance between the synchronous detection light receiving element 80 and the light source 1 results in an increase in the size of the optical scanning device 100 according to this embodiment.

[0129] On the other hand, if the upper limit of conditional expression (8) is exceeded, the angle θ i and angle θ BDAs the difference between these becomes smaller, interference between the optical path in the incident optical system 75 and the optical path in the synchronous detection optical system becomes more likely to occur. In addition, the scanning light beam L BD Width W BD is the incident luminous flux L i Width W i If it becomes too small, it becomes difficult to maintain the accuracy of the synchronization detection.

[0130] Therefore, the interference between the optical path in the synchronous detection optical system and the optical path in the incident optical system 75 and the optical path in the imaging optical system 85, and the width W BD Considering both the decrease in the synchronous detection beam angle θ BD It is important to set the As a result, in the optical scanning device 100 according to this embodiment, the polygon mirror 5 and the synchronous detection optical system are appropriately arranged, thereby achieving miniaturization.

[0131] In the optical scanning device 100 according to this embodiment, it is more preferable that the following conditional expression (8a) be fulfilled instead of the conditional expression (8).

number

[0132] Furthermore, in the optical scanning device 100 according to this embodiment, when the imaging optical system is formed by a plurality of scanning and imaging lenses 6 and adopts a shared optical path type, it is preferable that the synchronous detection light beam passes through the scanning and imaging lens 6 that is closest to the polygon mirror 5 on the optical path among the plurality of scanning and imaging lenses 6. In the optical scanning device 100 according to this embodiment, it is preferable that the following conditional expression (9) be satisfied.

number

[0133] In condition (9), Y max- is the distance [mm] in the Y direction between the on-axis image height 70 and the minus-side most off-axis image height 72. In conditional expression (9), EA is the maximum value (larger value) [mm] of the size in the main scanning direction of the entrance surface and exit surface of the scanning and imaging lens 6 closest to the polygon mirror 5 among the multiple scanning and imaging lenses 6. In the optical scanning device 100 according to this embodiment, the conditional expression (9) is satisfied, so that the scanning and imaging lens 6 can be prevented from becoming large and a shared optical path type can be adopted.

[0134] In the optical scanning device 100 according to this embodiment, it is preferable that the following conditional expression (10) be satisfied. 4≦N≦6 (10)

[0135] Conventionally, speed has been increased by increasing the number N of deflection surfaces 51 of the polygon mirror 5, but this increase also results in an increase in size of the optical scanning device 100 of this embodiment, and ultimately of the image forming device in which the optical scanning device 100 of this embodiment is installed. Therefore, in the optical scanning device 100 according to this embodiment, it is preferable that conditional expression (10) be satisfied in consideration of the above.

[0136] In the optical scanning device 100 according to this embodiment, it is preferable that the following conditional expression (11) be satisfied. 47.0≦θ max+ ≦57.0 (11)

[0137] If the lower limit of conditional expression (11) is not reached, the imaging optical system 85 will not have a wide enough angle, making it difficult to reduce the size of the optical scanning device 100 according to this embodiment. On the other hand, if the upper limit of the conditional expression (11) is exceeded, the width in the main scanning direction of the scanning light beam that scans the surface to be scanned 7 becomes shorter than the width of the incident light beam L i Width W in the main scanning direction i If it becomes too small, the fluctuations in the light amount and spot between each image height on the surface to be scanned 7 will increase.

[0138] In the optical scanning device 100 according to this embodiment, it is preferable to arrange the light source 1 and the synchronous detection light receiving element 80 on a single electrical mounting board 83 in order to arrange the synchronous detection light receiving element 80 compactly. If an electrical mounting board different from the electrical mounting board 83 is provided to place the synchronous detection light receiving element 80, an additional holding mechanism and cable would be required for the different electrical mounting board, which would hinder miniaturization and cost reduction.

[0139] On the other hand, in the optical scanning device 100 according to this embodiment, the incident light beam L i A synchronous detection beam is generated by blocking a portion of the light. Therefore, arranging the light source 1 and the synchronous detection light receiving element 80 on a single electrical mounting board 83 reduces the angle θ BD and the incident light flux L when generating the synchronous detection light flux i This leads to an increase in the amount of kicking.

[0140] Therefore, in the optical scanning device 100 according to this embodiment, it is preferable to provide at least one reflecting element that reflects the synchronous detection light beam deflected by the polygon mirror 5 toward the synchronous detection light receiving element 80. And the angle θ BDm is the angle θ BD To be larger, i.e., θ BD <θ BDm It is preferable that the at least one reflecting element is provided so that the following condition is satisfied:

[0141] Here, the angle θ BDm (°) is the scanning light beam L that is directed toward the center of the light receiving surface of the synchronous detection light receiving element 80 immediately after being reflected by the at least one reflecting element in the main scanning cross section. BD is the angle that the traveling direction of the chief ray makes with respect to the optical axis of the imaging optical system 85. In the optical scanning device 100 according to this embodiment, it is preferable that the following conditional expression (12) be satisfied. θ BD <θ i ≦θ BDm···(12) In the optical scanning device 100 according to this embodiment, the angle θ of the synchronous detection light beam is BDm By increasing the luminous flux, it becomes easier to make the synchronous detection luminous flux travel toward the synchronous detection light receiving element 80 arranged on the electrical mounting board 83 on which the light source 1 is arranged.

[0142] Next, the main specifications of the optical scanning device 100 according to this embodiment and the arrangement of the optical elements provided in the incident optical system 75 and the imaging optical system 85 are shown in Tables 1 and 2 below, respectively. The aspherical shapes of the anamorphic collimator lens 3 and the scanning and imaging lens 6 provided in the optical scanning device 100 according to this embodiment are shown in Tables 3 and 4 below, respectively. The arrangement of the optical elements provided in the synchronous detection optical system of the optical scanning device 100 according to this embodiment is shown in Table 5 below.

[0143] [Table 1]

[0144] [Table 2]

[0145] [Table 3]

[0146] [Table 4]

[0147] [Table 5]

[0148] In Tables 3 and 4, "EX" means "×10 -X", and this also applies to the following tables. The entrance surface of the anamorphic collimator lens 3 provided in the optical scanning device 100 according to this embodiment is a rotationally symmetric aspheric surface, and has a shape expressed by the following formula (13).

number

[0149] Furthermore, the respective generatrix shapes (shapes in the main scanning cross section) of the exit surface of the anamorphic collimator lens 3 provided in the optical scanning device 100 according to this embodiment and the entrance surface and exit surface of the scanning imaging lens 6 are expressed by the following equation (14).

number

[0150] In equation (14), a local coordinate system is used in which the intersection point between the lens surface (optical surface) of each lens, which is the surface vertex of the lens surface, and the optical axis is set as the origin. Specifically, the axis in the direction of light propagation, i.e., the optical axis, is the x-axis, the axis perpendicular to the x-axis in the main scanning cross section is the y-axis, and the axis perpendicular to the x-axis and y-axis, i.e., perpendicular to the main scanning cross section, is the z-axis.

[0151] In addition, in equation (14), R is the radius of curvature (generatrix radius of curvature) in the main scanning section, and K, B2, B4, B6, B8 and B 10 is the aspherical coefficient. In addition, the aspherical coefficients K, B2, B4, B6, B8 and B 10 The respective values ​​may be different between the positive and negative sides of the Y axis.

[0152] This allows the generatrix shapes to be set asymmetrically with respect to the optical axis in the main scanning direction. Specifically, in Tables 3 and 4, the aspheric coefficient on the light source side with respect to the optical axis is Ku , B 2u , B 4u , B 6u , B 8u and B 10u , the aspheric coefficient on the side opposite the light source from the optical axis is K l , B 2l , B 4l , B 6l , B 8l and B 10l It is expressed as follows. In addition, by adding odd-order terms of Y to equation (14), the degree of freedom in design can be improved.

[0153] Furthermore, the sagittal shapes (shapes in the sub-scanning cross section) of the exit surface of the anamorphic collimator lens 3 and the entrance and exit surfaces of the scanning imaging lens 6 provided in the optical scanning device 100 according to this embodiment are expressed by the following equation (15).

number

[0154] In equation (15), r' represents the radius of curvature (sagittal radius of curvature) in the sub-scanning cross section at a position Y away from the optical axis in the main scanning direction, and is expressed by the following equation (16).

number

[0155] In equation (16), r is the radius of curvature in the sub-scan section on the optical axis, and E1, E2, E3, . . . , E 10 is the sagittal variation coefficient. In addition, the sagittal line change coefficients E2, E4, E6, E8 and E 10 The respective values ​​may be different between the positive and negative sides of the Y axis.

[0156] This allows the sagittal shapes to be set asymmetrically with respect to the optical axis in the main scanning direction. Specifically, in Tables 3 and 4, the sagittal line change coefficient on the light source side with respect to the optical axis is E 2u , E4u , E 6u , E 8u and E 10u , the sagittal change coefficient on the opposite side of the light source to the optical axis is E 2l , E 4l , E 6l , E 8l and E 10l It is expressed as follows.

[0157] FIG. 3 shows the angle dependency of the beam width in the main scanning cross section of the beam deflected by the polygon mirror 5 in the optical scanning device 100 according to this embodiment. Specifically, the angle on the horizontal axis in FIG. 3 is the rotation angle (θ max- / 2~θ max+ / 2).

[0158] That is, with regard to the angle on the horizontal axis of FIG. 3, 0°, positive angles, and negative angles correspond to an axial light beam that travels to an axial image height 70, an off-axial light beam that travels to an off-axial image height on the light source 1 side, and an off-axial light beam that travels to an off-axial image height on the opposite side from the light source 1, respectively. The luminous flux width on the vertical axis of Fig. 3 is the incident luminous flux L i Width W i It is shown as a ratio to 3, black circles indicate light beams that scan each image height on the surface to be scanned 7, while white circles indicate synchronous detection light beams that reach the center of the light-receiving surface of the synchronous detection light-receiving element 80.

[0159] As shown in FIG. 3, the optical scanning device 100 according to this embodiment satisfies the conditional expressions (1) and (1'). As shown in FIG. 3, in the optical scanning device 100 according to this embodiment, each light beam scanning each image height on the surface to be scanned 7 is an incident light beam L i Width W i It has a luminous flux width of more than 90% of that of the conventional laser. As shown in Table 1, the angles of the light beams scanning the plus-side most off-axis image height 71 and the minus-side most off-axis image height 72 are +55.7° and −55.7°, respectively.

[0160] When the beam width of the light beam incident on the surface to be scanned 7 is reduced by 10%, the spot diameter increases by 10%. In this way, when the beam width is reduced, the spot diameter increases. On the other hand, in conventional optical scanning devices, the depth of field is set to allow an increase of about 15% with respect to the spot diameter when the spot is in focus.

[0161] Therefore, even if the spot diameter fluctuates as described above in the optical scanning device 100 according to this embodiment, the printing performance is sufficient when used in an image forming apparatus. In addition, in the optical scanning device 100 according to this embodiment, the light beam width of the synchronous detection light beam is reduced as shown in FIG. 3, resulting in a decrease in the amount of light, but this is also fully tolerable as described above.

[0162] Next, the optical scanning device 100 according to this embodiment and an optical scanning device according to a comparative example will be compared with each other. The main specifications of the optical scanning device according to the comparative example are shown in Table 6 below.

[0163] [Table 6]

[0164] The optical scanning device according to the comparative example has the same configuration as the optical scanning device 100 according to the present embodiment, except that it uses a four-sided polygon mirror 5 that has one fewer deflection surface 51 than the optical scanning device 100 according to the present embodiment. Therefore, the same components are given the same reference numerals and their descriptions will be omitted. That is, in the optical scanning device of the comparative example, the distance between the center of rotation 50 of the rotation axis of the polygon mirror 5 and the deflection surface 51 in the main scanning cross section, in other words, the radius of the inscribed circle of the polygon mirror 5, is the same size as that of the optical scanning device 100 of this embodiment.

[0165] As a result, the coordinates of the deflection point on the deflection surface 51 at each rotation angle of the polygon mirror 5 in the optical scanning device according to the comparative example can be set to be the same as those in the optical scanning device 100 according to this embodiment. Therefore, since fluctuations in the focus position due to rotation of the polygon mirror 5 are suppressed in the optical scanning device of the comparative example, it is possible to use the same imaging optical system 85, incident optical system 75, and synchronous detection optical system as the optical scanning device 100 of this embodiment.

[0166] In other words, in the optical scanning device 100 of this embodiment, sufficient optical performance can be obtained when using the same imaging optical system 85, incident optical system 75, and synchronous detection optical system, whether the five-sided polygon mirror 5 or the four-sided polygon mirror 5 is used. In other words, in the optical scanning device 100 according to this embodiment, the polygon mirror 5 with five faces or the polygon mirror 5 with four faces can be selectively mounted.

[0167] On the other hand, the optical scanning device 100 of this embodiment has a larger number of deflection surfaces 51 than the optical scanning device of the comparative example, so the number of scans on the scanned surface 7 during one rotation of the polygon mirror 5 can be increased. In other words, by increasing the number of scans on the scanned surface 7 when the polygon mirror 5 makes one rotation, the printing speed of an image forming device equipped with the optical scanning device 100 of this embodiment can be improved.

[0168] Alternatively, by increasing the number of scans on the scanned surface 7 during one rotation of the polygon mirror 5, the number of rotations per unit time of the polygon mirror 5 can be reduced while maintaining the printing speed of the image forming device in which the optical scanning device 100 of this embodiment is installed. This allows the polygon motor that rotates the polygon mirror 5 to be simplified and consumes less power.

[0169] Furthermore, in the optical scanning device 100 according to this embodiment, the number of scans on the scanned surface 7 when the polygon mirror 5 makes one rotation increases, so that the number of light emitting points in the light source 1 can be reduced. For example, in the optical scanning device according to the comparative example, when the light source 1 has five light-emitting points, and in the optical scanning device 100 according to this embodiment, when the light source 1 has four light-emitting points, the printing speed of the image forming device installed therein will be the same.

[0170] Further, for example, consider a case where the light source 1 has two light emitting points in the optical scanning device according to the comparative example. In the optical scanning device 100 according to this embodiment, when the light source 1 has a single light emitting point and the rotation speed of the polygon mirror 5 is 1.6 times faster, the printing speeds of the image forming devices mounted thereon are the same.

[0171] However, in either case, it is necessary to adjust the amount of light emitted from each light-emitting point of the light source 1. In this way, by reducing the number of light emitting points of the light source 1 in the optical scanning device 100 according to this embodiment, the costs of the light source 1, the control unit that drives the light source 1, and the like can be reduced.

[0172] Next, the values ​​of the respective conditional expressions for the optical scanning device 100 according to this embodiment and the optical scanning device according to the comparative example are shown in Table 7 below.

[0173] [Table 7]

[0174] As shown in Tables 1 and 6, the width of the deflecting surface 51 of the polygon mirror 5 in the main scanning cross section is significantly larger in the optical scanning device according to the comparative example than in the optical scanning device 100 according to this embodiment. Therefore, as shown in Table 7, in the optical scanning device according to the comparative example, the width W BD and the scanning light beam L that travels to the most off-axis image height 72 on the minus side max- Width W max- is the incident luminous flux L i Width W i is the same as, i.e., not reduced.

[0175] On the other hand, the diameter of the circumscribing circle of the polygon mirror 5 as its outer shape is smaller in the optical scanning device 100 according to this embodiment than in the optical scanning device according to the comparative example. That is, in the optical scanning device 100 according to this embodiment, the polygon mirror 5 has been made smaller, which makes it possible to reduce the size of the optical scanning device 100 according to this embodiment, and in turn the size of the image forming device in which it is installed.

[0176] Furthermore, by achieving a reduction in the size of the polygon mirror 5, it is possible to reduce the size of the polygon motor that rotates the polygon mirror 5. This is because the rotation moment of the polygon mirror 5 increases as the size of the polygon mirror 5 in the main scanning cross section increases.

[0177] Furthermore, as the polygon motor becomes smaller due to the miniaturization of the polygon mirror 5, it becomes possible to reduce the power consumption of the polygon motor. Furthermore, when the diameter of the circumscribing circle of the polygon mirror 5 is reduced, the wind noise generated by the polygon mirror 5 is reduced, and the structure for blocking the wind noise can be simplified and made smaller. As described above, the optical scanning device 100 according to this embodiment can be made smaller.

[0178] Furthermore, as shown in Table 7, the optical scanning device 100 of this embodiment satisfies both conditional expression (2) when K is a constant greater than or equal to 0.52 and less than or equal to 0.56, and conditional expression (2) when K is a constant greater than or equal to 0.53 and less than or equal to 0.55. On the other hand, the optical scanning device according to the comparative example does not satisfy either conditional expression (2) when K is a constant between 0.52 and 0.56, or conditional expression (2) when K is a constant between 0.53 and 0.55.

[0179] Furthermore, while the optical scanning device 100 according to this embodiment satisfies the conditions (3), (3a), (4), (4a), and (6), the optical scanning device according to the comparative example does not satisfy them. Moreover, conditional expression (5) is satisfied in the optical scanning device 100 according to this embodiment.

[0180] Moreover, conditional expression (1) is satisfied in the optical scanning device 100 according to this embodiment, but is not satisfied in the optical scanning device according to the comparative example. Moreover, the conditional expression (1') is satisfied in the optical scanning device 100 according to this embodiment. As described above, the optical scanning device 100 according to this embodiment can be made smaller by satisfying each of the conditional expressions.

[0181] As shown in Table 7, in the optical scanning device 100 according to this embodiment, the scanning light beam L BD2 angle (θ BD -360 / N×2) and scanning light beam L max-2 angle (θ max- +360 / N×2) are both angle θ max+ and angle θ max- It is not within the range between Therefore, in the optical scanning device 100 according to this embodiment, the scanning light beam L BD2 and scanning light beam L max-2 Both of these can be shielded by a member such as a housing or a rib or the like other than the optical surface of the scanning and imaging lens 6. Furthermore, if the scanning light beam L BD2 and scanning light beam L max-2 Even if it is incident on the scanning and imaging lens 6, it does not reach the printing area of ​​the scanned surface 7, and therefore does not cause any problems in printing.

[0182] As described above, in the optical scanning device 100 of this embodiment, compared to the optical scanning devices of the comparative examples and conventional optical scanning devices, it is possible to reduce the size of the polygon mirror 5, reduce the weight of the polygon mirror 5, thereby reducing the size of the polygon motor and simplifying the soundproofing materials. This makes it possible to achieve miniaturization of the optical scanning device 100 according to this embodiment, thereby providing an optical scanning device that is small and suitable for high-quality image recording, and an image forming device equipped with this optical scanning device. In other words, by appropriately arranging the deflector and each optical element as an optical scanning device to be installed in an image forming device such as a printer, it is possible to obtain an optical scanning device that is compact while maintaining high-speed, high-quality image recording.

[0183] Although the optical scanning device 100 according to this embodiment has a configuration for scanning a single surface 7 to be scanned, the present invention is not limited to this. That is, the above configuration can also be applied to a double-sided scanning system in which a plurality of imaging optical systems are provided on both sides of the polygon mirror 5 to scan a plurality of surfaces to be scanned.

[0184] The above configuration can also be applied to an optical scanning device that employs an oblique incidence optical system that causes a light beam to be obliquely incident on the polygon mirror 5 within the sub-scanning cross section. The above configuration can also be applied to a one-sided scanning system in which multiple light beams are obliquely incident on a predetermined deflection surface of the polygon mirror 5, and the multiple light beams deflected by the predetermined deflection surface are guided by multiple imaging optical systems provided on one side of the polygon mirror 5, thereby scanning multiple surfaces to be scanned.

[0185] The above configuration can also be applied to a double-sided scanning system in which multiple light beams are obliquely incident on the two deflection surfaces of the polygon mirror 5, and the multiple light beams deflected by the two deflection surfaces are guided by multiple imaging optical systems provided on both sides of the polygon mirror 5, thereby scanning multiple surfaces to be scanned. That is, the above configuration can also be applied to a color image forming apparatus that can form a color image by scanning a plurality of surfaces to be scanned.

[0186] Furthermore, although the optical scanning device 100 according to this embodiment uses the anamorphic collimator lens 3, it is also possible to use a rotationally symmetric coupling lens and a cylindrical lens having power only in the sub-scanning direction instead.

[0187] [Second embodiment] Fig. 4(a) is a schematic main-scan cross-sectional view of an optical scanning device 200 according to the second embodiment. Note that the electrical mounting board 83 is not shown in Fig. 4(a). FIG. 4(b) shows the angle dependency of the beam width in the main scanning cross section of the beam deflected by the polygon mirror 5 in the optical scanning device 200 according to the second embodiment (corresponding to FIG. 3).

[0188] Specifically, the angle on the horizontal axis in FIG. 4(b) is the rotation angle (θ max- / 2~θ max+ / 2). The optical scanning device 200 of this embodiment has the same configuration as the optical scanning device 100 of the first embodiment, except for the different numerical values, so the same components are given the same reference numerals and their explanations are omitted.

[0189] Moreover, the main specifications of the optical scanning device 200 according to this embodiment and the arrangement of the optical elements provided in the incident optical system 75 and the imaging optical system 85 are shown in Tables 8 and 9 below, respectively. The aspherical shapes of the anamorphic collimator lens 3 and the scanning and imaging lens 6 provided in the optical scanning device 200 according to this embodiment are shown in Tables 10 and 11 below, respectively.

[0190] The arrangement of the optical elements provided in the synchronous detection optical system of the optical scanning device 200 according to this embodiment is shown in Table 12 below. The main specifications of the optical scanning device according to the comparative example are shown in Table 13 below.

[0191] [Table 8]

[0192] [Table 9]

[0193] [Table 10]

[0194] [Table 11]

[0195] [Table 12]

[0196] [Table 13]

[0197] As shown in FIG. 4(b), the optical scanning device 200 according to this embodiment satisfies the conditional expressions (1) and (1'). As shown in FIG. 4B, in the optical scanning device 200 according to this embodiment, all of the light beams scanning each image height on the surface to be scanned 7 are incident light beams L i Width W i It has a luminous flux width of more than 90% of that of the conventional laser. As shown in Table 8, the angles of the light beams scanning the plus-side most off-axis image height 71 and the minus-side most off-axis image height 72 are +51.1° and −51.1°, respectively.

[0198] The optical scanning device according to the comparative example has the same configuration as the optical scanning device 200 according to the present embodiment, except that it uses a four-sided polygon mirror 5 that has one fewer deflection surface 51 than the optical scanning device 200 according to the present embodiment. Therefore, the same components are given the same reference numerals and their descriptions will be omitted. Next, the values ​​of the respective conditional expressions for the optical scanning device 200 according to this embodiment and the optical scanning device according to the comparative example are shown in Table 14 below.

[0199] [Table 14]

[0200] As shown in Tables 8 and 13, the width of the deflecting surface 51 of the polygon mirror 5 in the main scanning cross section is significantly larger in the optical scanning device according to the comparative example than in the optical scanning device 200 according to this embodiment. Therefore, as shown in Table 14, in the optical scanning device according to the comparative example, the width W BD and the scanning light beam L that travels to the most off-axis image height 72 on the minus side max- Width W max- is the incident luminous flux L i Width W i is the same as, i.e., not reduced.

[0201] On the other hand, the diameter of the circumscribing circle of the polygon mirror 5 as its outer shape is smaller in the optical scanning device 200 according to this embodiment than in the optical scanning device according to the comparative example. That is, in the optical scanning device 200 according to this embodiment, the polygon mirror 5 has been made smaller, which makes it possible to reduce the size of the optical scanning device 200 according to this embodiment, and in turn the size of the image forming device in which it is installed.

[0202] Furthermore, by achieving a reduction in the size of the polygon mirror 5, it is possible to reduce the size of the polygon motor that rotates the polygon mirror 5. This is because the rotation moment of the polygon mirror 5 increases as the size of the polygon mirror 5 in the main scanning cross section increases.

[0203] Furthermore, as the polygon motor becomes smaller due to the miniaturization of the polygon mirror 5, it becomes possible to reduce the power consumption of the polygon motor. Furthermore, when the diameter of the circumscribing circle of the polygon mirror 5 is reduced, the wind noise generated by the polygon mirror 5 is reduced, and the structure for blocking the wind noise can be simplified and made smaller. As described above, the optical scanning device 200 according to this embodiment can be made smaller.

[0204] Furthermore, as shown in Table 14, the optical scanning device 200 of this embodiment satisfies both conditional expression (2) when K is a constant greater than or equal to 0.52 and less than or equal to 0.56, and conditional expression (2) when K is a constant greater than or equal to 0.53 and less than or equal to 0.55. On the other hand, the optical scanning device according to the comparative example does not satisfy either conditional expression (2) when K is a constant between 0.52 and 0.56, or conditional expression (2) when K is a constant between 0.53 and 0.55.

[0205] Furthermore, while the optical scanning device 200 according to this embodiment satisfies the conditions (3), (3a), (4), (4a), and (6), the optical scanning device according to the comparative example does not satisfy them. Moreover, conditional expression (5) is satisfied in the optical scanning device 200 according to this embodiment.

[0206] Moreover, conditional expression (1) is satisfied in the optical scanning device 200 according to this embodiment, but is not satisfied in the optical scanning device according to the comparative example. Moreover, the conditional expression (1') is satisfied in the optical scanning device 200 according to this embodiment. As described above, the optical scanning device 200 according to this embodiment can be made smaller by satisfying each of the conditional expressions.

[0207] As shown in Table 14, in the optical scanning device 200 according to this embodiment, the scanning light beam L BD2 angle (θ BD -360 / N×2) and scanning light beam L max-2 angle (θ max- +360 / N×2) are both angle θ max+ and angle θ max- It is not within the range between Therefore, in the optical scanning device 200 according to this embodiment, the scanning light beam L BD2 and scanning light beam L max-2 Both of these can be shielded by a member such as a housing or a rib or the like other than the optical surface of the scanning and imaging lens 6. Furthermore, if the scanning light beam L BD2 and scanning light beam L max-2Even if it is incident on the scanning and imaging lens 6, it does not reach the printing area of ​​the scanned surface 7, and therefore does not cause any problems in printing.

[0208] As described above, in the optical scanning device 200 of this embodiment, compared to the optical scanning devices of the comparative examples and conventional optical scanning devices, it is possible to reduce the size of the polygon mirror 5, reduce the weight of the polygon mirror 5, thereby reducing the size of the polygon motor and simplifying the soundproofing materials. This makes it possible to achieve miniaturization of the optical scanning device 200 according to this embodiment, thereby providing an optical scanning device that is small and suitable for high-quality image recording, and an image forming device equipped with this optical scanning device.

[0209] [Third embodiment] Fig. 5(a) is a schematic main-scan cross-sectional view of an optical scanning device 300 according to the third embodiment. Note that the electrical mounting board 83 is not shown in Fig. 5(a). FIG. 5(b) shows the angle dependency of the beam width in the main scanning cross section of the beam deflected by the polygon mirror 5 in the optical scanning device 300 according to the third embodiment (corresponding to FIG. 3).

[0210] Specifically, the angle on the horizontal axis in FIG. 5(b) is the rotation angle (θ max- / 2~θ max+ / 2). The optical scanning device 300 of this embodiment has the same configuration as the optical scanning device 100 of the first embodiment, except for the different numerical values, so the same components are given the same reference numerals and their explanations are omitted.

[0211] Furthermore, the main specifications of the optical scanning device 300 according to this embodiment and the arrangement of the optical elements provided in the incident optical system 75 and the imaging optical system 85 are shown in Tables 15 and 16 below, respectively. The aspherical shapes of the anamorphic collimator lens 3 and the scanning and imaging lens 6 provided in the optical scanning device 300 according to this embodiment are shown in Tables 17 and 18 below, respectively.

[0212] The arrangement of the optical elements provided in the synchronous detection optical system of the optical scanning device 300 according to this embodiment is shown in Table 19 below. The main specifications of the optical scanning device according to the comparative example are shown in Table 20 below.

[0213] [Table 15]

[0214] [Table 16]

[0215] [Table 17]

[0216] [Table 18]

[0217] [Table 19]

[0218] [Table 20]

[0219] As shown in FIG. 5(b), the optical scanning device 300 according to this embodiment satisfies the conditional expressions (1) and (1'). As shown in FIG. 5B, in the optical scanning device 300 according to this embodiment, all of the light beams scanning each image height on the surface to be scanned 7 are incident light beams L i Width W i It has a luminous flux width of more than 90% of that of the conventional laser. As shown in Table 15, the angles of the light beams scanning the plus-side most off-axis image height 71 and the minus-side most off-axis image height 72 are +47.2° and −47.2°, respectively.

[0220] The optical scanning device according to the comparative example has the same configuration as the optical scanning device 300 according to the present embodiment, except that it uses a four-sided polygon mirror 5 that has one fewer deflection surface 51 than the optical scanning device 300 according to the present embodiment. Therefore, the same components are given the same reference numerals and their explanations will be omitted. Next, the values ​​of the respective conditional expressions for the optical scanning device 300 according to this embodiment and the optical scanning device according to the comparative example are shown in Table 21 below.

[0221] [Table 21]

[0222] As shown in Tables 15 and 20, the width of the deflecting surface 51 of the polygon mirror 5 in the main scanning cross section is significantly larger in the optical scanning device according to the comparative example than in the optical scanning device 300 according to this embodiment. Therefore, as shown in Table 21, in the optical scanning device according to the comparative example, the width W BD and the scanning light beam L that travels to the most off-axis image height 72 on the minus side max- Width W max- is the incident luminous flux L i Width W i is the same as, i.e., not reduced.

[0223] On the other hand, the diameter of the circumscribing circle of the polygon mirror 5 as its outer shape is smaller in the optical scanning device 300 according to this embodiment than in the optical scanning device according to the comparative example. That is, in the optical scanning device 300 according to this embodiment, the polygon mirror 5 has been made smaller, which makes it possible to reduce the size of the optical scanning device 300 according to this embodiment, and in turn the size of the image forming device in which it is installed.

[0224] Furthermore, by achieving a reduction in the size of the polygon mirror 5, it is possible to reduce the size of the polygon motor that rotates the polygon mirror 5. This is because the rotation moment of the polygon mirror 5 increases as the size of the polygon mirror 5 in the main scanning cross section increases.

[0225] Furthermore, as the polygon motor becomes smaller due to the miniaturization of the polygon mirror 5, it becomes possible to reduce the power consumption of the polygon motor. Furthermore, when the diameter of the circumscribing circle of the polygon mirror 5 is reduced, the wind noise generated by the polygon mirror 5 is reduced, and the structure for blocking the wind noise can be simplified and made smaller. As described above, the optical scanning device 300 according to this embodiment can be made smaller.

[0226] Furthermore, as shown in Table 21, the optical scanning device 300 of this embodiment satisfies both conditional expression (2) when K is a constant greater than or equal to 0.52 and less than or equal to 0.56, and conditional expression (2) when K is a constant greater than or equal to 0.53 and less than or equal to 0.55. On the other hand, the optical scanning device according to the comparative example does not satisfy either conditional expression (2) when K is a constant between 0.52 and 0.56, or conditional expression (2) when K is a constant between 0.53 and 0.55.

[0227] Furthermore, the optical scanning device 300 according to the present embodiment satisfies the conditional expressions (3), (3a), (4), and (4a), but the optical scanning device according to the comparative example does not satisfy them. Moreover, the conditions (5) and (6) are satisfied in the optical scanning device 300 according to this embodiment.

[0228] Moreover, conditional expression (1) is satisfied in the optical scanning device 300 according to this embodiment, but is not satisfied in the optical scanning device according to the comparative example. Moreover, the conditional expression (1') is satisfied in the optical scanning device 300 according to this embodiment. As described above, the optical scanning device 300 according to this embodiment can be made smaller by satisfying each of the conditional expressions.

[0229] As shown in Table 21, in the optical scanning device 300 according to this embodiment, the scanning light beam L BD2 angle (θBD -360 / N×2) and scanning light beam L max-2 angle (θ max- +360 / N×2) are both angle θ max+ and angle θ max- It is not within the range between Therefore, in the optical scanning device 300 according to this embodiment, the scanning light beam L BD2 and scanning light beam L max-2 Both of these can be shielded by a member such as a housing or a rib or the like other than the optical surface of the scanning and imaging lens 6. Furthermore, if the scanning light beam L BD2 and scanning light beam L max-2 Even if it is incident on the scanning and imaging lens 6, it does not reach the printing area of ​​the scanned surface 7, and therefore does not cause any problems in printing.

[0230] As described above, in the optical scanning device 300 according to this embodiment, compared to the optical scanning devices according to the comparative examples and conventional optical scanning devices, it is possible to reduce the size of the polygon mirror 5, reduce the weight of the polygon mirror 5, thereby reducing the size of the polygon motor, and simplify the soundproofing materials. This makes it possible to achieve miniaturization of the optical scanning device 300 according to this embodiment, thereby providing an optical scanning device that is small and suitable for high-quality image recording, and an image forming device equipped with this optical scanning device.

[0231] [Fourth embodiment] Fig. 6(a) is a schematic main-scan cross-sectional view of an optical scanning device 400 according to the fourth embodiment. Note that an electrical mounting board 83 is not shown in Fig. 6(a). FIG. 6(b) shows the angle dependency of the beam width in the main scanning cross section of the beam deflected by the polygon mirror 5 in the optical scanning device 400 according to the fourth embodiment (corresponding to FIG. 3).

[0232] Specifically, the angle on the horizontal axis in FIG. 6(b) is the rotation angle (θ max- / 2~θ max+ / 2). The optical scanning device 400 of this embodiment has the same configuration as the optical scanning device 100 of the first embodiment, except for the different numerical values, so the same components are given the same reference numerals and their explanations are omitted.

[0233] Furthermore, the main specifications of the optical scanning device 400 according to this embodiment and the arrangement of the optical elements provided in the incident optical system 75 and the imaging optical system 85 are shown in Tables 22 and 23 below, respectively. The aspherical shapes of the anamorphic collimator lens 3 and the scanning and imaging lens 6 provided in the optical scanning device 400 according to this embodiment are shown in Tables 24 and 25 below, respectively.

[0234] The arrangement of the optical elements provided in the synchronous detection optical system of the optical scanning device 400 according to this embodiment is shown in Table 26 below. The main specifications of the optical scanning device according to the comparative example are shown in Table 27 below.

[0235] [Table 22]

[0236] [Table 23]

[0237] [Table 24]

[0238] [Table 25]

[0239] [Table 26]

[0240] [Table 27]

[0241] As shown in FIG. 6(b), the optical scanning device 400 according to this embodiment satisfies conditional expression (1). As shown in FIG. 6B, in the optical scanning device 400 according to this embodiment, all of the light beams scanning each image height on the surface to be scanned 7 are incident light beams L i Width W i It has a luminous flux width of more than 90% of that of the conventional laser. As shown in Table 22, the angles of the light beams scanning the plus-side most off-axis image height 71 and the minus-side most off-axis image height 72 are +49.0° and −49.0°, respectively.

[0242] The optical scanning device according to the comparative example has the same configuration as the optical scanning device 400 according to the present embodiment, except that it uses a five-faceted polygon mirror 5 that has one fewer deflection surface 51 than the optical scanning device 400 according to the present embodiment. Therefore, the same components are given the same reference numerals and their descriptions will be omitted. Next, the values ​​of the respective conditional expressions for the optical scanning device 400 according to this embodiment and the optical scanning device according to the comparative example are shown in Table 28 below.

[0243] [Table 28]

[0244] As shown in Tables 22 and 27, the width of the deflecting surface 51 of the polygon mirror 5 in the main scanning cross section is significantly larger in the optical scanning device according to the comparative example than in the optical scanning device 400 according to this embodiment. Therefore, as shown in Table 28, in the optical scanning device according to the comparative example, the width W BD is the incident luminous flux L i Width W i is the same as, i.e., not reduced. As shown in Table 28, the scanning light beam L that travels to the most off-axis image height 71 on the positive side in the optical scanning device according to the comparative example is max+ Width W max+and the scanning light beam L proceeding to the minus side most off-axis image height 72 max- Width W max- Also, the incident luminous flux L i Width W i is the same as

[0245] On the other hand, the diameter of the circumscribing circle of the polygon mirror 5 as its outer shape is smaller in the optical scanning device 400 according to this embodiment than in the optical scanning device according to the comparative example. That is, in the optical scanning device 400 according to this embodiment, the polygon mirror 5 has been made smaller, which makes it possible to reduce the size of the optical scanning device 400 according to this embodiment, and in turn the size of the image forming device in which it is installed.

[0246] Furthermore, by achieving a reduction in the size of the polygon mirror 5, it is possible to reduce the size of the polygon motor that rotates the polygon mirror 5. This is because the rotation moment of the polygon mirror 5 increases as the size of the polygon mirror 5 in the main scanning cross section increases.

[0247] Furthermore, as the polygon motor becomes smaller due to the miniaturization of the polygon mirror 5, it becomes possible to reduce the power consumption of the polygon motor. Furthermore, when the diameter of the circumscribing circle of the polygon mirror 5 is reduced, the wind noise generated by the polygon mirror 5 is reduced, and the structure for blocking the wind noise can be simplified and made smaller. As described above, the optical scanning device 400 according to this embodiment can be made smaller.

[0248] Furthermore, as shown in Table 28, the optical scanning device 400 of this embodiment satisfies both conditional expression (2) when K is a constant greater than or equal to 0.52 and less than or equal to 0.56, and conditional expression (2) when K is a constant greater than or equal to 0.53 and less than or equal to 0.55. On the other hand, the optical scanning device according to the comparative example does not satisfy either conditional expression (2) when K is a constant between 0.52 and 0.56, or conditional expression (2) when K is a constant between 0.53 and 0.55.

[0249] Furthermore, while the optical scanning device 400 according to this embodiment satisfies the conditions (3), (3a), (4), (4a), and (6), the optical scanning device according to the comparative example does not satisfy them. Moreover, conditional expression (5) is satisfied in the optical scanning device 400 according to this embodiment.

[0250] Moreover, conditional expression (1) is satisfied in the optical scanning device 400 according to this embodiment, but is not satisfied in the optical scanning device according to the comparative example. As described above, the optical scanning device 400 according to this embodiment can be made smaller by satisfying each of the conditional expressions.

[0251] As shown in Table 28, in the optical scanning device 400 according to this embodiment, the scanning light beam L BD2 angle (θ BD -360 / N×2) and scanning light beam L max-2 angle (θ max- +360 / N×2) are both angle θ max+ and angle θ max- It is not within the range between As shown in Table 28, in the optical scanning device 400 according to this embodiment, the scanning light beam L max+2 angle (θ max+ -360 / N×2) also has an angle θ max+ and angle θ max- It is not within the range between

[0252] Here, the scanning light beam L max+2 The incident light beam L when scanning the most off-axis image height 71 on the positive side on the scanned surface 7 i A part of the scanned light beam L max+ The deflection surface adjacent to a given deflection surface deflects the incident light beam L i is the light beam generated by deflecting the remainder of the beam. Therefore, in the optical scanning device 400 according to this embodiment, the scanning light beam L BD2 , L max+2 and L max-2Any of these can be shielded from light by a member such as a housing or a rib or the like other than the optical surface of the scanning and imaging lens 6. Furthermore, if the scanning light beam L BD2 , L max+2 and L max-2 Even if it is incident on the scanning and imaging lens 6, it does not reach the printing area of ​​the scanned surface 7, and therefore does not cause any problems in printing.

[0253] As described above, in the optical scanning device 400 according to this embodiment, compared to the optical scanning devices according to the comparative examples and conventional optical scanning devices, it is possible to reduce the size of the polygon mirror 5, reduce the weight of the polygon mirror 5, thereby reducing the size of the polygon motor, and simplify the soundproofing materials. This makes it possible to achieve miniaturization of the optical scanning device 400 according to this embodiment, thereby providing an optical scanning device that is small and suitable for high-quality image recording, and an image forming device equipped with this optical scanning device.

[0254] [Fifth embodiment] Fig. 7(a) is a schematic main-scan cross-sectional view of an optical scanning device 500 according to the fifth embodiment. Note that the electrical mounting board 83 is not shown in Fig. 7(a). FIG. 7(b) shows the angle dependency of the beam width in the main scanning cross section of the beam deflected by the polygon mirror 5 in the optical scanning device 500 according to the fifth embodiment (corresponding to FIG. 3).

[0255] Specifically, the angle on the horizontal axis in FIG. 7B is the rotation angle (θ max- / 2~θ max+ / 2). The optical scanning device 500 of this embodiment has the same configuration as the optical scanning device 100 of the first embodiment, except for the different numerical values, so the same components are given the same reference numerals and their explanations are omitted.

[0256] Furthermore, the main specifications of the optical scanning device 500 according to this embodiment and the arrangement of the optical elements provided in the incident optical system 75 and the imaging optical system 85 are shown in Tables 29 and 30 below, respectively. The aspherical shapes of the anamorphic collimator lens 3 and the scanning and imaging lens 6 provided in the optical scanning device 500 according to this embodiment are shown in Tables 31 and 32 below, respectively.

[0257] The arrangement of the optical elements provided in the synchronous detection optical system of the optical scanning device 500 according to this embodiment is shown in Table 33 below. The main specifications of the optical scanning device according to the comparative example are shown in Table 34 below.

[0258] [Table 29]

[0259] [Table 30]

[0260] [Table 31]

[0261] [Table 32]

[0262] [Table 33]

[0263] [Table 34]

[0264] As shown in Table 29, the angles of the light beams scanning the plus-side most off-axis image height 71 and the minus-side most off-axis image height 72 are +51.1° and −51.1°, respectively.

[0265] The optical scanning device according to the comparative example has the same configuration as the optical scanning device 500 according to the present embodiment, except that it uses a three-faceted polygon mirror 5 that has one fewer deflection surface 51 than the optical scanning device 500 according to the present embodiment. Therefore, the same components are given the same reference numerals and their descriptions will be omitted. Next, the values ​​of the respective conditional expressions for the optical scanning device 500 according to this embodiment and the optical scanning device according to the comparative example are shown in Table 35 below.

[0266] [Table 35]

[0267] As shown in Tables 29 and 34, the width of the deflecting surface 51 of the polygon mirror 5 in the main scanning cross section is significantly larger in the optical scanning device according to the comparative example than in the optical scanning device 500 according to this embodiment. Therefore, as shown in Table 35, in the optical scanning device according to the comparative example, the width W of the synchronous detection light beam BD is the incident luminous flux L i Width W i is the same as, i.e., not reduced.

[0268] On the other hand, the diameter of the circumscribing circle of the polygon mirror 5 as its outer shape is smaller in the optical scanning device 500 according to this embodiment than in the optical scanning device according to the comparative example. That is, in the optical scanning device 500 according to this embodiment, the polygon mirror 5 has been made smaller, which makes it possible to reduce the size of the optical scanning device 500 according to this embodiment, and in turn the size of the image forming device in which it is installed.

[0269] Furthermore, by achieving a reduction in the size of the polygon mirror 5, it is possible to reduce the size of the polygon motor that rotates the polygon mirror 5. This is because the rotation moment of the polygon mirror 5 increases as the size of the polygon mirror 5 in the main scanning cross section increases.

[0270] Furthermore, as the polygon motor becomes smaller due to the miniaturization of the polygon mirror 5, it becomes possible to reduce the power consumption of the polygon motor. Furthermore, when the diameter of the circumscribing circle of the polygon mirror 5 is reduced, the wind noise generated by the polygon mirror 5 is reduced, and the structure for blocking the wind noise can be simplified and made smaller. As described above, the optical scanning device 500 according to this embodiment can be made smaller.

[0271] Furthermore, as shown in Table 35, the optical scanning device 500 of this embodiment satisfies both conditional expression (2) when K is a constant greater than or equal to 0.52 and less than or equal to 0.56, and conditional expression (2) when K is a constant greater than or equal to 0.53 and less than or equal to 0.55. On the other hand, the optical scanning device according to the comparative example does not satisfy either conditional expression (2) when K is a constant between 0.52 and 0.56, or conditional expression (2) when K is a constant between 0.53 and 0.55.

[0272] Furthermore, while the optical scanning device 500 according to this embodiment satisfies the conditions (3), (3a), (4), (4a), and (6), the optical scanning device according to the comparative example does not satisfy them. Moreover, conditional expression (5) is satisfied in the optical scanning device 500 according to this embodiment.

[0273] Moreover, conditional expression (1) is satisfied in the optical scanning device 500 according to this embodiment, but is not satisfied in the optical scanning device according to the comparative example. Moreover, the conditional expression (1') is satisfied in the optical scanning device 500 according to this embodiment. As described above, the optical scanning device 500 according to this embodiment can be made smaller by satisfying each of the conditional expressions.

[0274] FIG. 8 is a partially enlarged schematic main scanning cross-sectional view of the vicinity of the polygon mirror 5 of the optical scanning device 500 according to this embodiment. As shown in Table 29, the polygon mirror 5 provided in the optical scanning device 500 according to this embodiment has four deflection surfaces 51, and the angle θ that the optical axis of the incident optical system 75 makes with the optical axis of the imaging optical system 85 is i is 90 degrees.

[0275] 8, when the synchronous detection light receiving element 80 is scanned, the incident light beam L incident on the deflecting surface 51 of the polygon mirror 5 is i A part of the scanning light beam L BD The light is deflected by the deflecting surface 51 so as to travel in a direction forming a predetermined angle with respect to the X axis. On the other hand, the incident light beam L that was not deflected by the deflecting surface 51 when scanning the synchronous detection light receiving element 80 i The remaining part (another part) of the scanning light beam L BD2 As a result, the light proceeds without being deflected by any of the deflecting surfaces of the polygon mirror 5. That is, the scanning light beam L BD2 The angle that the traveling direction of the light beam makes with the optical axis of the imaging optical system 85 is −90°.

[0276] As shown in Table 35, in the optical scanning device 500 according to this embodiment, the scanning light beam L BD2 The angle of -90° and the scanning beam L max-2 angle (θ max- +360 / N×2) are both angle θ max+ and angle θ max- It is not within the range between Therefore, in the optical scanning device 500 according to this embodiment, the scanning light beam L BD2 and scanning light beam L max-2 Both of these can be shielded by a member such as a housing or a rib or the like other than the optical surface of the scanning and imaging lens 6. Furthermore, if the scanning light beam L BD2 and scanning light beam L max-2 Even if it is incident on the scanning and imaging lens 6, it does not reach the printing area of ​​the scanned surface 7, and therefore does not cause any problems in printing.

[0277] As described above, in the optical scanning device 500 according to this embodiment, compared to the optical scanning devices according to the comparative examples and conventional optical scanning devices, it is possible to reduce the size of the polygon mirror 5, reduce the weight of the polygon mirror 5, thereby reducing the size of the polygon motor, and simplify the soundproofing materials. This makes it possible to achieve miniaturization of the optical scanning device 500 according to this embodiment, thereby providing an optical scanning device that is small and suitable for high-quality image recording, and an image forming device equipped with this optical scanning device.

[0278] [Sixth embodiment] Fig. 9(a) is a schematic main-scan cross-sectional view of an optical scanning device 600 according to the sixth embodiment. Note that an electrical mounting board 83 is not shown in Fig. 9(a). FIG. 9(b) shows the angle dependency of the beam width in the main scanning cross section of the beam deflected by the polygon mirror 5 in the optical scanning device 600 according to the sixth embodiment (corresponding to FIG. 3).

[0279] Specifically, the angle on the horizontal axis in FIG. 9(b) is the rotation angle (θ max- / 2~θ max+ / 2). The optical scanning device 600 according to this embodiment has the same configuration as the optical scanning device 100 according to the first embodiment, except that the numerical values ​​are different and the imaging optical system 85 is formed by two scanning imaging lenses 61 and 62. Therefore, the same components are denoted by the same reference numerals and their explanations are omitted.

[0280] Furthermore, the main specifications of the optical scanning device 600 according to this embodiment and the arrangement of the optical elements provided in the incident optical system 75 and the imaging optical system 85 are shown in Tables 36 and 37 below, respectively. The aspherical shapes of the anamorphic collimator lens 3 and the two scanning and imaging lenses 61 and 62 provided in the optical scanning device 600 according to this embodiment are shown in Tables 38 and 39 below, respectively.

[0281] The arrangement of the optical elements provided in the synchronous detection optical system of the optical scanning device 600 according to this embodiment is shown in Table 40 below. The main specifications of the optical scanning device according to the comparative example are shown in Table 41 below.

[0282] [Table 36]

[0283] [Table 37]

[0284] [Table 38]

[0285] [Table 39]

[0286] [Table 40]

[0287] [Table 41]

[0288] As shown in FIG. 9(b), the optical scanning device 600 according to this embodiment satisfies the conditional expressions (1) and (1'). As shown in FIG. 9B, in the optical scanning device 600 according to this embodiment, all of the light beams scanning each image height on the surface to be scanned 7 are incident light beams L i Width W i It has a luminous flux width of more than 90% of that of the conventional laser. As shown in Table 36, the angles of the light beams scanning the plus-side most off-axis image height 71 and the minus-side most off-axis image height 72 are +49.0° and −49.0°, respectively.

[0289] The optical scanning device according to the comparative example has the same configuration as the optical scanning device 600 according to the present embodiment, except that it uses a five-faceted polygon mirror 5 that has one fewer deflection surface 51 than the optical scanning device 600 according to the present embodiment. Therefore, the same components are given the same reference numerals and their descriptions will be omitted. Next, the values ​​of the respective conditional expressions for the optical scanning device 600 according to this embodiment and the optical scanning device according to the comparative example are shown in Table 42 below.

[0290] [Table 42]

[0291] As shown in Tables 36 and 41, the width of the deflecting surface 51 of the polygon mirror 5 in the main scanning cross section is significantly larger in the optical scanning device according to the comparative example than in the optical scanning device 600 according to this embodiment. Therefore, as shown in Table 42, in the optical scanning device according to the comparative example, the width W BD and the scanning light beam L that travels to the most off-axis image height 72 on the minus side max- Width W max- is the incident luminous flux L i Width W i is the same as, i.e., not reduced.

[0292] On the other hand, the diameter of the circumscribing circle of the polygon mirror 5 as its outer shape is smaller in the optical scanning device 600 according to this embodiment than in the optical scanning device according to the comparative example. That is, in the optical scanning device 600 according to this embodiment, the polygon mirror 5 has been made smaller, which makes it possible to reduce the size of the optical scanning device 600 according to this embodiment, and in turn the size of the image forming device in which it is installed.

[0293] Furthermore, by achieving a reduction in the size of the polygon mirror 5, it is possible to reduce the size of the polygon motor that rotates the polygon mirror 5. This is because the rotation moment of the polygon mirror 5 increases as the size of the polygon mirror 5 in the main scanning cross section increases.

[0294] Furthermore, as the polygon motor becomes smaller due to the miniaturization of the polygon mirror 5, it becomes possible to reduce the power consumption of the polygon motor. Furthermore, when the diameter of the circumscribing circle of the polygon mirror 5 is reduced, the wind noise generated by the polygon mirror 5 is reduced, and the structure for blocking the wind noise can be simplified and made smaller. As described above, the optical scanning device 600 according to this embodiment can be made smaller.

[0295] Furthermore, as shown in Table 42, the optical scanning device 600 of this embodiment satisfies both conditional expression (2) when K is a constant greater than or equal to 0.52 and less than or equal to 0.56, and conditional expression (2) when K is a constant greater than or equal to 0.53 and less than or equal to 0.55. On the other hand, the optical scanning device according to the comparative example does not satisfy either conditional expression (2) when K is a constant between 0.52 and 0.56, or conditional expression (2) when K is a constant between 0.53 and 0.55.

[0296] Furthermore, while the optical scanning device 600 according to this embodiment satisfies the conditions (3), (3a), (4), (4a), and (7), the optical scanning device according to the comparative example does not satisfy them. Moreover, conditional expression (5) is satisfied in the optical scanning device 600 according to this embodiment.

[0297] Moreover, conditional expression (1) is satisfied in the optical scanning device 600 according to this embodiment, but is not satisfied in the optical scanning device according to the comparative example. Moreover, the conditional expression (1') is satisfied in the optical scanning device 600 according to this embodiment. As described above, the optical scanning device 600 according to this embodiment can be made smaller by satisfying each of the conditional expressions.

[0298] As shown in Table 42, in the optical scanning device 600 according to this embodiment, the scanning light beam L BD2 angle (θBD -360 / N×2) and scanning light beam L max-2 angle (θ max- +360 / N×2) are both angle θ max+ and angle θ max- It is not within the range between Therefore, in the optical scanning device 600 according to this embodiment, the scanning light beam L BD2 and scanning light beam L max-2 Both of these can be shielded by a member such as a housing or a rib or the like other than the optical surface of the scanning and imaging lens 6. Furthermore, if the scanning light beam L BD2 and scanning light beam L max-2 Even if it is incident on the scanning and imaging lens 6, it does not reach the printing area of ​​the scanned surface 7, and therefore does not cause any problems in printing.

[0299] As described above, in the optical scanning device 600 according to this embodiment, compared to the optical scanning devices according to the comparative examples and conventional optical scanning devices, it is possible to reduce the size of the polygon mirror 5, reduce the weight of the polygon mirror 5, thereby reducing the size of the polygon motor, and simplify the soundproofing materials. This makes it possible to achieve miniaturization of the optical scanning device 600 according to this embodiment, thereby providing an optical scanning device that is small and suitable for high-quality image recording, and an image forming device equipped with this optical scanning device.

[0300] [Seventh embodiment] Fig. 10(a) is a schematic main-scan cross-sectional view of an optical scanning device 700 according to the seventh embodiment. Note that the electrical mounting board 83 is not shown in Fig. 10(a). FIG. 10(b) shows the angle dependency of the beam width in the main scanning cross section of the beam deflected by the polygon mirror 5 in the optical scanning device 700 according to the seventh embodiment (corresponding to FIG. 3).

[0301] Specifically, the angle on the horizontal axis in FIG. 10(b) is the rotation angle (θ max- / 2~θ max+ / 2). The optical scanning device 700 according to this embodiment has the same configuration as the optical scanning device 600 according to the sixth embodiment, except for the different numerical values. Therefore, the same components are denoted by the same reference numerals, and the description thereof will be omitted.

[0302] Furthermore, the main specifications of the optical scanning device 700 according to this embodiment and the arrangement of the optical elements provided in the incident optical system 75 and the imaging optical system 85 are shown in Tables 43 and 44 below, respectively. The aspherical shapes of the anamorphic collimator lens 3 and the two scanning and imaging lenses 61 and 62 provided in the optical scanning device 700 according to this embodiment are shown in Tables 45 and 46 below, respectively.

[0303] The arrangement of the optical elements provided in the synchronous detection optical system of the optical scanning device 700 according to this embodiment is shown in Table 47 below. The main specifications of the optical scanning device according to the comparative example are shown in Table 48 below.

[0304] [Table 43]

[0305] [Table 44]

[0306] [Table 45]

[0307] [Table 46]

[0308] [Table 47]

[0309] [Table 48]

[0310] As shown in FIG. 10(b), the optical scanning device 700 according to this embodiment satisfies the conditional expressions (1) and (1'). As shown in FIG. 10B, in the optical scanning device 700 according to this embodiment, all of the light beams scanning each image height on the surface to be scanned 7 are incident light beams L i Width W i It has a luminous flux width of more than 90% of that of the conventional laser.

[0311] The optical scanning device according to the comparative example has the same configuration as the optical scanning device 700 according to the present embodiment, except that it uses a five-faceted polygon mirror 5 that has one fewer deflection surface 51 than the optical scanning device 700 according to the present embodiment. Therefore, the same components are given the same reference numerals and their descriptions will be omitted. Next, the values ​​of the respective conditional expressions for the optical scanning device 700 according to this embodiment and the optical scanning device according to the comparative example are shown in Table 49 below.

[0312] [Table 49]

[0313] As shown in Tables 43 and 48, the width of the deflecting surface 51 of the polygon mirror 5 in the main scanning cross section is much larger in the optical scanning device according to the comparative example than in the optical scanning device 700 according to this embodiment. Therefore, as shown in Table 49, in the optical scanning device according to the comparative example, the width W of the synchronous detection light beam BD and the scanning light beam L that travels to the most off-axis image height 72 on the minus side max- Width W max- is the incident luminous flux L i Width W i is the same as, i.e., not reduced.

[0314] On the other hand, the diameter of the circumscribing circle of the polygon mirror 5 as its outer shape is smaller in the optical scanning device 700 according to this embodiment than in the optical scanning device according to the comparative example. That is, in the optical scanning device 700 according to this embodiment, the polygon mirror 5 has been made smaller, which makes it possible to reduce the size of the optical scanning device 700 according to this embodiment, and in turn the size of the image forming device in which it is installed.

[0315] Furthermore, by achieving a reduction in the size of the polygon mirror 5, it is possible to reduce the size of the polygon motor that rotates the polygon mirror 5. This is because the rotation moment of the polygon mirror 5 increases as the size of the polygon mirror 5 in the main scanning cross section increases.

[0316] Furthermore, as the polygon motor becomes smaller due to the miniaturization of the polygon mirror 5, it becomes possible to reduce the power consumption of the polygon motor. Furthermore, when the diameter of the circumscribing circle of the polygon mirror 5 is reduced, the wind noise generated by the polygon mirror 5 is reduced, and the structure for blocking the wind noise can be simplified and made smaller. As described above, the optical scanning device 700 according to this embodiment can be made smaller.

[0317] Furthermore, as shown in Table 49, the optical scanning device 700 of this embodiment satisfies both conditional expression (2) when K is a constant greater than or equal to 0.52 and less than or equal to 0.56, and conditional expression (2) when K is a constant greater than or equal to 0.53 and less than or equal to 0.55. On the other hand, the optical scanning device according to the comparative example does not satisfy either conditional expression (2) when K is a constant between 0.52 and 0.56, or conditional expression (2) when K is a constant between 0.53 and 0.55.

[0318] Furthermore, while the optical scanning device 700 according to this embodiment satisfies the conditions (3), (3a), (4), (4a), and (7), the optical scanning device according to the comparative example does not satisfy them. Moreover, conditional expression (5) is satisfied in the optical scanning device 700 according to this embodiment.

[0319] Moreover, conditional expression (1) is satisfied in the optical scanning device 700 according to this embodiment, but is not satisfied in the optical scanning device according to the comparative example. Moreover, the conditional expression (1') is satisfied in the optical scanning device 700 according to this embodiment. As described above, the optical scanning device 700 according to this embodiment can be made smaller by satisfying each of the conditional expressions.

[0320] As shown in Table 49, in the optical scanning device 700 according to this embodiment, the scanning light beam L BD2 angle (θ BD -360 / N×2) and scanning light beam L max-2 angle (θ max- +360 / N×2) are both angle θ max+ and angle θ max- It is not within the range between Therefore, in the optical scanning device 700 according to this embodiment, the scanning light beam L BD2 and scanning light beam L max-2 Both of these can be shielded by a member such as a housing or a rib or the like other than the optical surface of the scanning and imaging lens 6. Furthermore, if the scanning light beam L BD2 and scanning light beam L max-2 Even if it is incident on the scanning and imaging lens 6, it does not reach the printing area of ​​the scanned surface 7, and therefore does not cause any problems in printing.

[0321] As described above, in the optical scanning device 700 according to this embodiment, compared to the optical scanning devices according to the comparative examples and conventional optical scanning devices, it is possible to reduce the size of the polygon mirror 5, reduce the weight of the polygon mirror 5, thereby reducing the size of the polygon motor, and simplify the soundproofing materials. This makes it possible to achieve miniaturization of the optical scanning device 700 according to this embodiment, thereby providing an optical scanning device that is small and suitable for high-quality image recording, and an image forming device equipped with this optical scanning device.

[0322] [Eighth embodiment] Fig. 11(a) is a schematic main-scanning cross-sectional view of an optical scanning device 800 according to the eighth embodiment. Note that an electrical mounting board 83 is not shown in Fig. 11(a). FIG. 11(b) shows the angle dependency of the beam width in the main scanning cross section of the beam deflected by the polygon mirror 5 in the optical scanning device 800 according to the eighth embodiment (corresponding to FIG. 3).

[0323] Specifically, the angle on the horizontal axis in FIG. 11(b) is the rotation angle (θ max- / 2~θ max+ / 2). The optical scanning device 800 according to this embodiment has the same configuration as the optical scanning device 600 according to the sixth embodiment, except for the different numerical values. Therefore, the same components are denoted by the same reference numerals, and the description thereof will be omitted.

[0324] Furthermore, the main specifications of the optical scanning device 800 according to this embodiment and the arrangement of the optical elements provided in the incident optical system 75 and the imaging optical system 85 are shown in Tables 50 and 51 below, respectively. The aspherical shapes of the anamorphic collimator lens 3 and the two scanning and imaging lenses 61 and 62 provided in the optical scanning device 800 according to this embodiment are shown in Tables 52 and 53 below, respectively.

[0325] The arrangement of the optical elements provided in the synchronous detection optical system of the optical scanning device 800 according to this embodiment is shown in Table 54 below. The main specifications of the optical scanning device according to the comparative example are shown in Table 55 below.

[0326] [Table 50]

[0327] [Table 51]

[0328] [Table 52]

[0329] [Table 53]

[0330] [Table 54]

[0331] [Table 55]

[0332] As shown in FIG. 11(b), the optical scanning device 800 according to this embodiment satisfies the conditional expressions (1) and (1'). As shown in FIG. 11B, in the optical scanning device 800 according to this embodiment, all of the light beams scanning each image height on the surface to be scanned 7 are incident light beams L i Width W i It has a luminous flux width of more than 90% of that of the conventional laser.

[0333] The optical scanning device according to the comparative example has the same configuration as the optical scanning device 800 according to the present embodiment, except that it uses a four-sided polygon mirror 5 that has one fewer deflection surface 51 than the optical scanning device 800 according to the present embodiment. Therefore, the same components are given the same reference numerals and their descriptions will be omitted. Next, the values ​​of the respective conditional expressions for the optical scanning device 800 according to this embodiment and the optical scanning device according to the comparative example are shown in Table 56 below.

[0334] [Table 56]

[0335] As shown in Tables 50 and 55, the width of the deflecting surface 51 of the polygon mirror 5 in the main scanning cross section is much larger in the optical scanning device according to the comparative example than in the optical scanning device 800 according to this embodiment. Therefore, as shown in Table 56, in the optical scanning device according to the comparative example, the width W of the synchronous detection light beam BD and the scanning light beam L that travels to the most off-axis image height 72 on the minus side max- Width W max- is the incident luminous flux L i Width W i is the same as, i.e., not reduced.

[0336] On the other hand, the diameter of the circumscribing circle of the polygon mirror 5 as its outer shape is smaller in the optical scanning device 800 according to this embodiment than in the optical scanning device according to the comparative example. That is, in the optical scanning device 800 according to this embodiment, the polygon mirror 5 has been made smaller, which makes it possible to reduce the size of the optical scanning device 800 according to this embodiment, and in turn the size of the image forming device in which it is installed.

[0337] Furthermore, by achieving a reduction in the size of the polygon mirror 5, it is possible to reduce the size of the polygon motor that rotates the polygon mirror 5. This is because the rotation moment of the polygon mirror 5 increases as the size of the polygon mirror 5 in the main scanning cross section increases.

[0338] Furthermore, as the polygon motor becomes smaller due to the miniaturization of the polygon mirror 5, it becomes possible to reduce the power consumption of the polygon motor. Furthermore, when the diameter of the circumscribing circle of the polygon mirror 5 is reduced, the wind noise generated by the polygon mirror 5 is reduced, and the structure for blocking the wind noise can be simplified and made smaller. As described above, the optical scanning device 800 according to this embodiment can be made smaller.

[0339] Furthermore, as shown in Table 56, the optical scanning device 800 of this embodiment satisfies both conditional expression (2) when K is a constant greater than or equal to 0.52 and less than or equal to 0.56, and conditional expression (2) when K is a constant greater than or equal to 0.53 and less than or equal to 0.55. On the other hand, the optical scanning device according to the comparative example does not satisfy either conditional expression (2) when K is a constant between 0.52 and 0.56, or conditional expression (2) when K is a constant between 0.53 and 0.55.

[0340] Furthermore, while the optical scanning device 800 according to this embodiment satisfies the conditions (3), (3a), (4), (4a), and (7), the optical scanning device according to the comparative example does not satisfy them. Moreover, conditional expression (5) is satisfied in the optical scanning device 800 according to this embodiment.

[0341] Moreover, conditional expression (1) is satisfied in the optical scanning device 800 according to this embodiment, but is not satisfied in the optical scanning device according to the comparative example. Moreover, the conditional expression (1') is satisfied in the optical scanning device 800 according to this embodiment. As described above, the optical scanning device 800 according to this embodiment can be made smaller by satisfying each of the conditional expressions.

[0342] As shown in Table 56, in the optical scanning device 800 according to this embodiment, the scanning light beam L BD2 angle (θ BD -360 / N×2) and scanning light beam L max-2 angle (θ max- +360 / N×2) are both angle θ max+ and angle θ max- It is not within the range between Therefore, in the optical scanning device 800 according to this embodiment, the scanning light beam L BD2 and scanning light beam L max-2 Both of these can be shielded by a member such as a housing or a rib or the like other than the optical surface of the scanning and imaging lens 6. Furthermore, if the scanning light beam L BD2 and scanning light beam L max-2Even if it is incident on the scanning and imaging lens 6, it does not reach the printing area of ​​the scanned surface 7, and therefore does not cause any problems in printing.

[0343] As described above, in the optical scanning device 800 according to this embodiment, compared to the optical scanning devices according to the comparative examples and conventional optical scanning devices, it is possible to reduce the size of the polygon mirror 5, reduce the weight of the polygon mirror 5, thereby reducing the size of the polygon motor, and simplify the soundproofing materials. This makes it possible to achieve miniaturization of the optical scanning device 800 according to this embodiment, thereby providing an optical scanning device that is small and suitable for high-quality image recording, and an image forming device equipped with this optical scanning device.

[0344] [Ninth embodiment] Fig. 12(a) is a schematic main-scan cross-sectional view of an optical scanning device 900 according to the ninth embodiment, in which the electrical mounting board 83 is omitted. FIG. 12(b) shows the angle dependency of the beam width in the main scanning cross section of the beam deflected by the polygon mirror 5 in the optical scanning device 900 according to the ninth embodiment (corresponding to FIG. 3).

[0345] Specifically, the angle on the horizontal axis in FIG. 12(b) is the rotation angle (θ max- / 2~θ max+ / 2). The optical scanning device 900 according to this embodiment has the same configuration as the optical scanning device 600 according to the sixth embodiment, except that the numerical values ​​are different and a synchronization detection reflecting element 82 (reflecting element) is newly provided. Therefore, the same components are given the same reference numerals and their explanations are omitted.

[0346] Furthermore, the main specifications of the optical scanning device 900 according to this embodiment and the arrangement of the optical elements provided in the incident optical system 75 and the imaging optical system 85 are shown in Tables 57 and 58 below, respectively. The aspherical shapes of the anamorphic collimator lens 3 and the two scanning and imaging lenses 61 and 62 provided in the optical scanning device 900 according to this embodiment are shown in Tables 59 and 60 below, respectively.

[0347] The arrangement of the optical elements provided in the synchronous detection optical system of the optical scanning device 900 according to this embodiment is shown in Table 61 below. The main specifications of the optical scanning device according to the comparative example are shown in Table 62 below.

[0348] [Table 57]

[0349] [Table 58]

[0350] [Table 59]

[0351] [Table 60]

[0352] [Table 61]

[0353] [Table 62]

[0354] As shown in FIG. 12(b), the optical scanning device 900 according to this embodiment satisfies conditional expression (1). As shown in FIG. 12B, in the optical scanning device 900 according to this embodiment, all of the light beams scanning each image height on the surface to be scanned 7 are incident light beams L i Width W iIt has a luminous flux width of more than 90% of that of the conventional laser.

[0355] The optical scanning device according to the comparative example has the same configuration as the optical scanning device 900 according to the present embodiment, except that it uses a five-faceted polygon mirror 5 that has one fewer deflection surface 51 than the optical scanning device 900 according to the present embodiment. Therefore, the same components are given the same reference numerals and their descriptions will be omitted. Next, the values ​​of the respective conditional expressions for the optical scanning device 900 according to this embodiment and the optical scanning device according to the comparative example are shown in Table 63 below.

[0356] [Table 63]

[0357] As shown in FIG. 12A, in the optical scanning device 900 according to this embodiment, the scanning light beam L deflected by the deflecting surface 51 of the polygon mirror 5 when scanning the synchronous detection light receiving element 80 is BD After passing through the scanning imaging lens 61, the light is reflected by the synchronous detection reflecting element 82. The scanning light beam L reflected by the synchronous detection reflecting element 82 BDm The traveling direction of the light beam 81 is parallel to the Y direction, that is, forms an angle of 90° with respect to the optical axis of the imaging optical system 85. Therefore, in the optical scanning device 900 according to this embodiment, as shown in Table 63, conditional expression (12) is satisfied.

[0358] As shown in Tables 57 and 62, the width of the deflecting surface 51 of the polygon mirror 5 in the main scanning cross section is much larger in the optical scanning device according to the comparative example than in the optical scanning device 900 according to this embodiment. Therefore, as shown in Table 63, in the optical scanning device according to the comparative example, the width W BD is the incident luminous flux L i Width W i is the same as, i.e., not reduced. As shown in Table 63, the scanning light beam L that travels to the positive-side most off-axis image height 71 in the optical scanning device according to the comparative example is max+Width W max+ and the scanning light beam L proceeding to the minus side most off-axis image height 72 max- Width W max- Also, the incident luminous flux L i Width W i is the same as

[0359] On the other hand, the diameter of the circumscribing circle of the polygon mirror 5 as its outer shape is smaller in the optical scanning device 900 according to this embodiment than in the optical scanning device according to the comparative example. That is, in the optical scanning device 900 according to this embodiment, the polygon mirror 5 has been made smaller, which makes it possible to reduce the size of the optical scanning device 900 according to this embodiment, and in turn the size of the image forming device in which it is installed.

[0360] Furthermore, by achieving a reduction in the size of the polygon mirror 5, it is possible to reduce the size of the polygon motor that rotates the polygon mirror 5. This is because the rotation moment of the polygon mirror 5 increases as the size of the polygon mirror 5 in the main scanning cross section increases.

[0361] Furthermore, as the polygon motor becomes smaller due to the miniaturization of the polygon mirror 5, it becomes possible to reduce the power consumption of the polygon motor. Furthermore, when the diameter of the circumscribing circle of the polygon mirror 5 is reduced, the wind noise generated by the polygon mirror 5 is reduced, and the structure for blocking the wind noise can be simplified and made smaller. As described above, the optical scanning device 900 according to this embodiment can be made smaller.

[0362] Also, as shown in Table 63, the optical scanning device 900 of this embodiment satisfies both conditional expression (2) when K is a constant greater than or equal to 0.52 and less than or equal to 0.56, and conditional expression (2) when K is a constant greater than or equal to 0.53 and less than or equal to 0.55. On the other hand, the optical scanning device according to the comparative example does not satisfy either conditional expression (2) when K is a constant between 0.52 and 0.56, or conditional expression (2) when K is a constant between 0.53 and 0.55.

[0363] Furthermore, the conditions (3), (3a), (4), (4a), (8) and (8a) are satisfied in the optical scanning device 900 according to this embodiment, but are not satisfied in the optical scanning device according to the comparative example. Moreover, conditional expression (5) is satisfied in the optical scanning device 900 according to this embodiment.

[0364] Moreover, conditional expression (1) is satisfied in the optical scanning device 900 according to this embodiment, but is not satisfied in the optical scanning device according to the comparative example. As described above, the optical scanning device 900 according to this embodiment can be made smaller by satisfying each of the conditional expressions.

[0365] As shown in Table 63, in the optical scanning device 900 according to this embodiment, the scanning light beam L BD2 angle (θ BD -360 / N×2) and scanning light beam L max-2 angle (θ max- +360 / N×2) are both angle θ max+ and angle θ max- It is not within the range between As shown in Table 63, in the optical scanning device 900 according to this embodiment, the scanning light beam L max+2 angle (θ max+ -360 / N×2) also has an angle θ max+ and angle θ max- It is not within the range between

[0366] Therefore, in the optical scanning device 900 according to this embodiment, the scanning light beam L BD2 , L max+2 and L max-2 Any of these can be shielded from light by a member such as a housing or a rib or the like other than the optical surface of the scanning and imaging lens 6. Furthermore, if the scanning light beam L BD2 , L max+2 and L max-2 Even if it is incident on the scanning and imaging lens 6, it does not reach the printing area of ​​the scanned surface 7, and therefore does not cause any problems in printing.

[0367] As described above, in the optical scanning device 900 according to this embodiment, compared to the optical scanning devices according to the comparative examples and conventional optical scanning devices, it is possible to reduce the size of the polygon mirror 5, reduce the weight of the polygon mirror 5, thereby reducing the size of the polygon motor, and simplify the soundproofing materials. This makes it possible to achieve miniaturization of the optical scanning device 900 according to this embodiment, thereby providing an optical scanning device that is small and suitable for high-quality image recording, and an image forming device equipped with this optical scanning device.

[0368] [Tenth embodiment] Fig. 13(a) is a schematic main-scanning cross-sectional view of an optical scanning device 1000 according to a tenth embodiment. Note that the electrical mounting board 83 is not shown in Fig. 13(a). FIG. 13(b) shows the angle dependency of the beam width in the main scanning cross section of the beam deflected by the polygon mirror 5 in the optical scanning device 1000 according to the tenth embodiment (corresponding to FIG. 3).

[0369] Specifically, the angle on the horizontal axis in FIG. 13(b) is the rotation angle (θ max- / 2~θ max+ / 2). The optical scanning device 1000 according to this embodiment has the same configuration as the optical scanning device 900 according to the ninth embodiment, except for the different numerical values. Therefore, the same components are denoted by the same reference numerals, and the description thereof will be omitted.

[0370] Furthermore, the main specifications of the optical scanning device 1000 according to this embodiment and the arrangement of the optical elements provided in the incident optical system 75 and the imaging optical system 85 are shown in Tables 64 and 65 below, respectively. The aspherical shapes of the anamorphic collimator lens 3 and the two scanning and imaging lenses 61 and 62 provided in the optical scanning device 1000 according to this embodiment are shown in Tables 66 and 67 below, respectively.

[0371] The arrangement of the optical elements provided in the synchronous detection optical system of the optical scanning device 1000 according to this embodiment is shown in Table 68 below. The main specifications of the optical scanning device according to the comparative example are shown in Table 69 below.

[0372] [Table 64]

[0373] [Table 65]

[0374] [Table 66]

[0375] [Table 67]

[0376] [Table 68]

[0377] [Table 69]

[0378] As shown in FIG. 13(b), the optical scanning device 1000 according to this embodiment satisfies the conditional expressions (1) and (1'). As shown in FIG. 13(b), in the optical scanning device 1000 according to this embodiment, all of the light beams scanning each image height on the surface to be scanned 7 are incident light beams L i Width W i It has a luminous flux width of more than 90% of that of the conventional laser.

[0379] The optical scanning device according to the comparative example has the same configuration as the optical scanning device 1000 according to the present embodiment, except that it uses a five-faceted polygon mirror 5 that has one fewer deflection surface 51 than the optical scanning device 1000 according to the present embodiment. Therefore, the same components are given the same reference numerals and their descriptions are omitted. Next, the values ​​of the respective conditional expressions for the optical scanning device 1000 according to this embodiment and the optical scanning device according to the comparative example are shown in Table 70 below.

[0380] [Table 70]

[0381] As shown in FIG. 13A, in the optical scanning device 1000 according to this embodiment, the scanning light beam L deflected by the deflecting surface 51 of the polygon mirror 5 when scanning the synchronous detection light receiving element 80 is BD After passing through the scanning imaging lens 61, the light is reflected by the synchronous detection reflecting element 82. The scanning light beam L reflected by the synchronous detection reflecting element 82 BDm The traveling direction of the light beam 81 is parallel to the Y direction, that is, forms an angle of 90° with respect to the optical axis of the imaging optical system 85. Therefore, in the optical scanning device 1000 according to this embodiment, as shown in Table 70, conditional expression (12) is satisfied.

[0382] As shown in Tables 64 and 69, the width of the deflecting surface 51 of the polygon mirror 5 in the main scanning cross section is much larger in the optical scanning device according to the comparative example than in the optical scanning device 1000 according to this embodiment. Therefore, as shown in Table 70, in the optical scanning device according to the comparative example, the width W BD and the scanning light beam L that travels to the most off-axis image height 72 on the minus side max- Width W max- is the incident luminous flux L i Width W i is the same as, i.e., not reduced.

[0383] On the other hand, the diameter of the circumscribing circle of the polygon mirror 5 as its outer shape is smaller in the optical scanning device 1000 according to this embodiment than in the optical scanning device according to the comparative example. That is, in the optical scanning device 1000 according to this embodiment, the polygon mirror 5 has been made smaller, which makes it possible to reduce the size of the optical scanning device 1000 according to this embodiment, and in turn the size of the image forming device in which it is installed.

[0384] Furthermore, by achieving a reduction in the size of the polygon mirror 5, it is possible to reduce the size of the polygon motor that rotates the polygon mirror 5. This is because the rotation moment of the polygon mirror 5 increases as the size of the polygon mirror 5 in the main scanning cross section increases.

[0385] Furthermore, as the polygon motor becomes smaller due to the miniaturization of the polygon mirror 5, it becomes possible to reduce the power consumption of the polygon motor. Furthermore, when the diameter of the circumscribing circle of the polygon mirror 5 is reduced, the wind noise generated by the polygon mirror 5 is reduced, and the structure for blocking the wind noise can be simplified and made smaller. As described above, the optical scanning device 1000 according to this embodiment can be made smaller.

[0386] Furthermore, as shown in Table 70, the optical scanning device 1000 of this embodiment satisfies both conditional expression (2) when K is a constant greater than or equal to 0.52 and less than or equal to 0.56, and conditional expression (2) when K is a constant greater than or equal to 0.53 and less than or equal to 0.55. On the other hand, the optical scanning device according to the comparative example does not satisfy either conditional expression (2) when K is a constant between 0.52 and 0.56, or conditional expression (2) when K is a constant between 0.53 and 0.55.

[0387] Furthermore, while the optical scanning device 1000 according to this embodiment satisfies the conditions (3), (3a), (4), (4a), (8), and (8a), the optical scanning device according to the comparative example does not satisfy them. Moreover, conditional expression (5) is satisfied in the optical scanning device 1000 according to this embodiment.

[0388] Moreover, conditional expression (1) is satisfied in the optical scanning device 1000 according to this embodiment, but is not satisfied in the optical scanning device according to the comparative example. Moreover, the conditional expression (1') is satisfied in the optical scanning device 1000 according to this embodiment. As described above, the optical scanning device 1000 according to this embodiment can be made smaller by satisfying each of the conditional expressions.

[0389] As shown in Table 70, in the optical scanning device 1000 according to this embodiment, the scanning light beam L BD2 angle (θ BD -360 / N×2) and scanning light beam L max-2 angle (θ max- +360 / N×2) are both angle θ max+ and angle θ max- It is not within the range between Therefore, in the optical scanning device 1000 according to this embodiment, the scanning light beam L BD2 and scanning light beam L max-2 Both of these can be shielded by a member such as a housing or a rib or the like other than the optical surface of the scanning and imaging lens 6. Furthermore, if the scanning light beam L BD2 and scanning light beam L max-2 Even if it is incident on the scanning and imaging lens 6, it does not reach the printing area of ​​the scanned surface 7, and therefore does not cause any problems in printing.

[0390] As described above, in the optical scanning device 1000 of this embodiment, compared to the optical scanning devices of the comparative examples and conventional optical scanning devices, it is possible to reduce the size of the polygon mirror 5, reduce the weight of the polygon mirror 5, thereby reducing the size of the polygon motor and simplifying the soundproofing materials. This makes it possible to achieve miniaturization of the optical scanning device 1000 according to this embodiment, thereby providing an optical scanning device that is small and suitable for high-quality image recording, and an image forming device equipped with this optical scanning device.

[0391] The values ​​of the respective conditional expressions in the optical scanning devices according to the first to tenth embodiments are shown in Table 71 below.

[0392] [Table 71]

[0393] [Image forming device] FIG. 14 is a sub-scanning cross-sectional view of a main part of an image forming apparatus 104 including an optical scanning device 1100 according to any one of the first to tenth embodiments.

[0394] As shown in FIG. 14, the image forming apparatus 104 receives code data Dc output from an external device 117 such as a personal computer. The input code data Dc is then converted into image data (dot data) Di by a printer controller 111 provided inside the image forming apparatus 104.

[0395] Next, the converted image data Di is input to the optical scanning device 1100, and the optical scanning device 1100 emits a light beam 103 modulated according to the image data Di, and the photosensitive surface (scanned surface) of the photosensitive drum 101 is scanned in the main scanning direction by the light beam 103. A photosensitive drum 101, which is an electrostatic latent image carrier (photosensitive member), is rotated clockwise by a motor 115 as shown in FIG. As the photosensitive drum 101 rotates, the photosensitive surface of the photosensitive drum 101 moves in a sub-scanning direction perpendicular to the main scanning direction.

[0396] Above the photosensitive drum 101, a charging roller 102 for uniformly charging the surface of the photosensitive drum 101 is provided so as to come into contact with the surface. The surface of the photosensitive drum 101 charged by the charging roller 102 is irradiated with a light beam 103 scanned by an optical scanning device 1100 .

[0397] As described above, the light beam 103 is modulated based on the image data Di, and an electrostatic latent image is formed on the surface of the photosensitive drum 101 by irradiating the surface with the light beam 103 . The formed electrostatic latent image is developed into a toner image by a developing device 107 disposed so as to contact the photosensitive drum 101 further downstream in the rotation direction from the position on the photosensitive drum 101 where the light beam 103 is irradiated.

[0398] Next, the toner image developed by the developing device 107 is transferred onto a sheet of paper 112, which is a transfer material, by a transfer roller 108 (transfer device) disposed below the photosensitive drum 101 so as to face the photosensitive drum 101. The paper 112 is stored in a paper cassette 109 in front of the photosensitive drum 101 (on the right side in FIG. 14), but can also be fed manually. A paper feed roller 110 is disposed at the end of the paper cassette 109, and feeds paper 112 in the paper cassette 109 into the transport path.

[0399] The paper 112 onto which the unfixed toner image has been transferred in this manner is transported to the fixing device 150 disposed behind the photosensitive drum 101 (on the left side in FIG. 14). The fixing unit 150 is composed of a fixing roller 113 having a fixing heater therein and a pressure roller 114 disposed so as to be in pressure contact with the fixing roller 113 .

[0400] Then, the paper 112 conveyed from the transfer roller 108 is heated and pressed by the pressure contact portion between the fixing roller 113 and the pressure roller 114, so that the unfixed toner image on the paper 112 is fixed. Further, a paper discharge roller 116 is disposed behind the fixing unit 150 , and the paper 112 on which the toner image has been fixed is discharged to the outside of the image forming apparatus 104 .

[0401] Although not shown in FIG. 14, the printer controller 111 controls the various components in the image forming device 104, such as the motor 115, and the polygon motor in the optical scanning device 1100, in addition to the above-mentioned data conversion. Furthermore, although the image forming apparatus 104 for monochrome printing has been described above, the above configuration can also be applied to a color image forming apparatus for multiple colors. 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.

[0402] The disclosure of this embodiment includes the following configuration. (Configuration 1) An optical scanning device comprising: a deflector that deflects a light beam from a light source to scan a surface to be scanned in a main scanning direction; and a first optical system that guides the light beam deflected by the deflector to the surface to be scanned; wherein, in the main scanning cross section, the width of the light beam immediately before it is incident on a first deflection surface of the deflector is smaller than the width of the first deflection surface; and when the first deflection surface is at a first angle in the main scanning cross section, only a portion of the light beam incident on the deflector is deflected by the first deflection surface and reaches the surface to be scanned. (Configuration 2) The optical scanning device according to configuration 1, further comprising a light receiving element that receives a part of the light beam deflected by the first deflecting surface at the first angle. (Configuration 3) The optical scanning device according to configuration 2, wherein the light receiving element is disposed on the same side as the light source with respect to the optical axis of the first optical system in the main scanning cross section. (Configuration 4) An optical scanning device according to configuration 2 or 3, comprising a second optical system that causes a light beam from a light source to be incident on a deflector, and an optical element that guides a portion of the light beam deflected by a first deflection surface at a first angle to a light receiving element, wherein in the main scanning cross section, the width of the incident surface of the optical element is smaller than the width of the optical surface closest to the deflector on the optical path of the second optical system. (Configuration 5) The optical scanning device according to any one of configurations 2 to 4, further comprising a reflecting element that reflects a part of the light beam deflected by the first deflecting surface at the first angle. (Configuration 6) In the main scanning section, the angle that the traveling direction of the principal ray of the light beam immediately before it is incident on the reflecting element makes with the optical axis of the first optical system is defined as θ BD θ is the angle that the traveling direction of the chief ray of the light beam immediately after being reflected by the reflecting element makes with the optical axis of the first optical system. BDm When this is done, θ BD <θ BDm 6. The optical scanning device according to configuration 5, wherein the following conditions are satisfied: (Configuration 7) In the main scanning section, the angle formed by the traveling direction of the principal ray of the light beam immediately before it is incident on the deflector with respect to the optical axis of the first optical system is defined as θ. i When this is done, θ BD <θ i ≦θ BDm 7. The optical scanning device according to configuration 6, wherein the following conditions are satisfied: (Configuration 8) The optical scanning device according to any one of configurations 2 to 7, further comprising a light source and a substrate on which the light source and the light receiving element are disposed. (Configuration 9) The optical scanning device according to any one of configurations 2 to 8, further comprising a light-receiving sensitivity adjusting section that adjusts the light-receiving sensitivity of the light-receiving element in accordance with the number of deflection surfaces of the deflector. (Configuration 10) An optical scanning device described in any one of configurations 1 to 9, characterized in that when the first deflection surface is at a first angle, another portion of the light beam incident on the deflector that is not deflected by the first deflection surface is deflected by a second deflection surface adjacent to the first deflection surface. (Configuration 11) An optical scanning device described in any one of configurations 1 to 10, characterized in that when the first deflection surface is at a first angle, another portion of the light beam incident on the deflector that is not deflected by the first deflection surface proceeds outside the effective area of ​​the scanned surface. (Configuration 12) An optical scanning device described in any one of configurations 1 to 11, characterized in that, in the main scanning cross section, when the first deflection surface is at a second angle, only a portion of the light beam incident on the deflector is deflected by the first deflection surface. (Configuration 13) The optical scanning device according to configuration 12, wherein a portion of the light beam deflected by the first deflecting surface at the second angle proceeds to an effective area of ​​the surface to be scanned. (Configuration 14) An optical scanning device according to Configuration 13, characterized in that a portion of the light beam deflected by the first deflection surface at the second angle proceeds to the most off-axis image height on the side of the scanned surface opposite to the side on which the light source is located. (Configuration 15) An optical scanning device described in any one of configurations 1 to 14, characterized in that the condition 5.50≦φ-K×N×(N-1)≦13.00 is satisfied, where φ [mm] is the diameter of the circumscribed circle in the main scanning cross section of the deflector, N is the number of deflection surfaces of the deflector, and K is a predetermined value between 0.52 and 0.56. (Configuration 16) An optical scanning device described in any one of configurations 1 to 15, characterized in that in the main scanning cross section, the width of a portion of the light beam deflected by the first deflection surface at a first angle is smaller than the width of the light beam immediately before it is incident on the first deflection surface. (Configuration 17) An optical scanning device described in any one of configurations 1 to 16, characterized in that when the diameter of the circumscribed circle in the main scanning section of the deflector is φ [mm] and the number of deflection surfaces of the deflector is N, the condition 6.00<(φ+15) / N<7.40 is satisfied. (Configuration 18) The diameter of the circumscribing circle in the main scanning section of the deflector is φ, the number of deflecting surfaces of the deflector is N, and the distance between the on-axis image height on the scanned surface in the main scanning direction and the most off-axis image height on the side where the light source is located is Y. max+ When this is done, the result is 22.60 <Y max+ 18. The optical scanning device according to any one of configurations 1 to 17, wherein the condition: / (φ / N)<37.00 is satisfied. (Configuration 19) In the main scanning section, the angle that the traveling direction of the principal ray of the light beam immediately before it enters the deflector makes with the optical axis of the first optical system is defined as θ i θ is the angle formed by the traveling direction of the chief ray of the light beam directed toward the most off-axis image height on the side where the light source is located immediately after being deflected by the deflector, with the optical axis of the first optical system. max+ θ is the angle formed by the direction of travel of the principal ray of the light beam directed toward the center of the light receiving surface of the light receiving element immediately after being deflected by the deflector with respect to the optical axis of the first optical system. BD When 1.78<(θ i +θ max+ ) / θ BD 19. The optical scanning device according to any one of configurations 1 to 18, wherein the condition <2.33 is satisfied. (Configuration 20) The first optical system is formed by a single optical element, and in the main scanning section, the angle formed by the traveling direction of the chief ray of the light beam directed toward the most off-axis image height on the side where the light source is located immediately after being deflected by the deflector with respect to the optical axis of the first optical system is θ. max+ [°], and the angle that the direction of travel of the chief ray of the light beam directed toward the center of the light receiving surface of the light receiving element immediately after being deflected by the deflector makes with the optical axis of the first optical system is θ. BD [°], when the number of deflection surfaces of the deflector is N, 0.23<(θ BD -θ max+ 20. The optical scanning device according to any one of configurations 1 to 19, wherein the optical scanning device satisfies the condition: ) / (360 / N)<0.35. (Configuration 21) The first optical system is formed by a plurality of optical elements, and a part of the light beam deflected by the first deflecting surface at the first angle is received by the light receiving element without passing through the first optical system, and the angle that the traveling direction of the chief ray of the light beam directed toward the most off-axis image height on the side where the light source is located immediately after being deflected by the deflector in the main scanning cross section makes with the optical axis of the first optical system is defined as θ. max+ [°], and the angle that the direction of travel of the chief ray of the light beam directed toward the center of the light receiving surface of the light receiving element immediately after being deflected by the deflector makes with the optical axis of the first optical system is θ. BD [°], where N is the number of deflection surfaces of the deflector, 360 / N-45<θ BD -θ max+ 20. The optical scanning device according to any one of configurations 1 to 19, wherein the condition <360 / N / 2 is satisfied. (Configuration 22) The first optical system is formed by a plurality of optical elements, and a part of the light beam deflected by the first deflecting surface at the first angle passes through at least one optical element included in the first optical system and is then received by a light receiving element, and the angle that the direction of travel of the chief ray of the light beam directed toward the most off-axis image height on the side where the light source is located immediately after being deflected by the deflector in the main scanning cross section forms with the optical axis of the first optical system is defined as θ. max+ [°], and the angle that the direction of travel of the chief ray of the light beam directed toward the center of the light receiving surface of the light receiving element immediately after being deflected by the deflector makes with the optical axis of the first optical system is θ. BD [°], where N is the number of deflection surfaces of the deflector, 0.145<(θBD -θ max+ 20. The optical scanning device according to any one of configurations 1 to 19, wherein the optical scanning device satisfies the condition: ) / (360 / N)<0.182. (Configuration 23) An optical scanning device according to Configuration 22, characterized in that a portion of the light beam deflected by the first deflection surface at the first angle passes through the optical element among the plurality of optical elements that is closest to the deflector on the optical path. (Configuration 24) In the main scanning section, the width of the light beam deflected by the first deflecting surface and directed toward the center of the light receiving surface of the light receiving element is defined as W BD The width of the light beam deflected by the first deflecting surface and directed toward the most off-axis image height on the side where the light source is located is W max+ The width of the light beam deflected by the first deflecting surface and directed toward the most off-axis image height on the opposite side to the side where the light source is located is W max- When W BD <W max- <W max+ 24. The optical scanning device according to any one of configurations 1 to 23, wherein the following conditions are satisfied: (Configuration 25) The width of the light beam incident on the deflector in the main scanning section is W i When W max+ =W i 25. The optical scanning device according to claim 24, wherein the following conditions are satisfied: (Configuration 26) An optical scanning device according to any one of configurations 1 to 25, characterized in that, when the number of deflecting surfaces of the deflector is N, the condition 4≦N≦6 is satisfied. (Configuration 27) In the main scanning section, the angle formed by the traveling direction of the chief ray of the light beam directed toward the most off-axis image height on the side where the light source is located immediately after being deflected by the deflector with respect to the optical axis of the first optical system is θ max+ [°], 47.0≦θ max+ 27. The optical scanning device according to any one of configurations 1 to 26, wherein the condition of ≦57.0 is satisfied. (Configuration 28) An optical scanning device described in any one of configurations 1 to 27, characterized in that it comprises a light source and a light intensity adjustment unit that adjusts the light intensity of the light beam emitted from the light source depending on the number of deflection surfaces of the deflector. (Configuration 29) The optical scanning device according to any one of configurations 1 to 28, wherein the deflector is a polygonal mirror that rotates around a rotation axis. (Configuration 30) An image forming apparatus comprising an optical scanning device according to any one of configurations 1 to 29, a developing unit that develops an electrostatic latent image formed on a surface to be scanned 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 31) An image forming apparatus comprising an optical scanning device according to any one of configurations 1 to 29, and a printer controller that converts a signal output from an external device into image data and inputs it to the optical scanning device. [Explanation of symbols]

[0403] 1 light source 5 Polygon mirror (deflector) 7 Scanned surface 51 Deflection surface (first deflection surface) 85 Imaging optical system (first optical system) 100 Optical scanning device

Claims

1. a deflector that deflects a light beam from a light source to scan the surface to be scanned in a main scanning direction; a first optical system that guides the light beam deflected by the deflector to the surface to be scanned, In the main scanning cross section, the width of the light beam immediately before it is incident on a first deflecting surface of the deflector is smaller than the width of the first deflecting surface; an optical scanning device characterized in that, in a main scanning cross section, when the first deflecting surface is at a first angle, only a portion of the light beam incident on the deflector is deflected by the first deflecting surface and reaches the scanned surface.

2. 2. The optical scanning device according to claim 1, further comprising a light receiving element that receives the part of the light beam deflected by the first deflecting surface at the first angle.

3. 3. The optical scanning device according to claim 2, wherein the light receiving element is disposed on the same side as the light source with respect to the optical axis of the first optical system in the main scanning cross section.

4. a second optical system that causes the light beam from the light source to be incident on the deflector; an optical element that guides the portion of the light beam deflected by the first deflection surface at the first angle to the light receiving element, 3. The optical scanning device according to claim 2, wherein, in the main scanning cross section, the width of the incident surface of said optical element is smaller than the width of the optical surface closest to said deflector on the optical path of said second optical system.

5. 3. The optical scanning device according to claim 2, further comprising a reflecting element that reflects the part of the light beam deflected by the first deflecting surface at the first angle.

6. In the main scanning cross section, the angle that the traveling direction of the chief ray of the light beam immediately before it is incident on the reflecting element makes with the optical axis of the first optical system is defined as θ. ＢＤ θ is the angle that the traveling direction of the chief ray of the light beam immediately after being reflected by the reflecting element makes with the optical axis of the first optical system. ＢＤｍ When i ＢＤ <θ ＢＤｍ 6. The optical scanning device according to claim 5, wherein the following conditions are satisfied:

7. The angle formed by the traveling direction of the principal ray of the light beam immediately before it is incident on the deflector in the main scanning section with respect to the optical axis of the first optical system is defined as θ. ｉ When i ＢＤ <θ ｉ ≦θ ＢＤｍ 7. The optical scanning device according to claim 6, wherein the following conditions are satisfied:

8. the light source; The optical scanning device according to claim 2 , further comprising a substrate on which the light source and the light receiving element are disposed.

9. 3. The optical scanning device according to claim 2, further comprising a light-receiving sensitivity adjusting unit that adjusts the light-receiving sensitivity of the light-receiving element in accordance with the number of deflection surfaces of the deflector.

10. 2. The optical scanning device according to claim 1, wherein when the first deflection surface is at the first angle, another portion of the light beam incident on the deflector that is not deflected by the first deflection surface is deflected by a second deflection surface adjacent to the first deflection surface.

11. 2. The optical scanning device according to claim 1, wherein when the first deflection surface is at the first angle, another portion of the light beam incident on the deflector that is not deflected by the first deflection surface travels outside the effective area of ​​the scanned surface.

12. 2. The optical scanning device according to claim 1, wherein, in the main scanning cross section, when the first deflecting surface is at a second angle, only a portion of the light beam incident on the deflector is deflected by the first deflecting surface.

13. 13. The optical scanning device according to claim 12, wherein the part of the light beam deflected by the first deflecting surface at the second angle advances to an effective area of ​​the surface to be scanned.

14. 14. The optical scanning device according to claim 13, wherein the portion of the light beam deflected by the first deflection surface at the second angle travels to an off-axis image height on the opposite side of the scanned surface from the side on which the light source is located.

15. When the diameter of the circumscribing circle in the main scanning cross section of the deflector is φ [mm], the number of deflecting surfaces of the deflector is N, and K is a predetermined value between 0.52 and 0.56, 5.50≦φ-K×N×(N-1)≦13.00 2. The optical scanning device according to claim 1, wherein the following conditions are satisfied:

16. 2. The optical scanning device according to claim 1, wherein, in a main scanning cross section, a width of the portion of the light beam deflected by the first deflection surface at the first angle is smaller than a width of the light beam immediately before it is incident on the first deflection surface.

17. When the diameter of the circumscribing circle in the main scanning cross section of the deflector is φ [mm] and the number of deflecting surfaces of the deflector is N, 6.00<(φ+15) / N<7.40 2. The optical scanning device according to claim 1, wherein the following conditions are satisfied:

18. The diameter of the circumscribing circle in the main scanning cross section of the deflector is φ, the number of deflecting surfaces of the deflector is N, and the distance between the on-axis image height on the scanned surface in the main scanning direction and the most off-axis image height on the side where the light source is disposed is Y. ｍａｘ＋ When 22.600Y ｍａｘ＋ / (φ / N) <37.00 2. The optical scanning device according to claim 1, wherein the following conditions are satisfied:

19. In the main scanning cross section, the angle that the traveling direction of the chief ray of the light beam immediately before it is incident on the deflector makes with respect to the optical axis of the first optical system is defined as θ. ｉ θ is the angle formed by the traveling direction of the chief ray of the light beam directed toward the most off-axis image height on the side where the light source is disposed, immediately after being deflected by the deflector, with respect to the optical axis of the first optical system. ｍａｘ＋ θ is the angle formed by the traveling direction of the chief ray of the light beam directed toward the center of the light receiving surface of the light receiving element immediately after being deflected by the deflector with respect to the optical axis of the first optical system. ＢＤ When 1.78<(θ) ｉ +θ ｍａｘ＋ ) / θ ＢＤ <2.33 2. The optical scanning device according to claim 1, wherein the following conditions are satisfied:

20. the first optical system is formed by a single optical element, In the main scanning cross section, the angle formed by the traveling direction of the chief ray of the light beam directed toward the most off-axis image height on the side where the light source is disposed immediately after being deflected by the deflector with respect to the optical axis of the first optical system is θ. ｍａｘ＋ [°], and the angle formed by the traveling direction of the chief ray of the light beam directed toward the center of the light receiving surface of the light receiving element immediately after being deflected by the deflector with respect to the optical axis of the first optical system is θ. ＢＤ [°], where N is the number of deflection surfaces of the deflector, 0.23<(θ) ＢＤ -θ ｍａｘ＋ ) / (3V0)<035 2. The optical scanning device according to claim 1, wherein the following conditions are satisfied:

21. the first optical system is formed by a plurality of optical elements, the portion of the light beam deflected by the first deflection surface at the first angle is received by a light receiving element without passing through the first optical system; In the main scanning cross section, the angle formed by the traveling direction of the chief ray of the light beam directed toward the most off-axis image height on the side where the light source is disposed immediately after being deflected by the deflector with respect to the optical axis of the first optical system is θ. ｍａｘ＋ [°], and the angle formed by the traveling direction of the chief ray of the light beam directed toward the center of the light receiving surface of the light receiving element immediately after being deflected by the deflector with respect to the optical axis of the first optical system is θ. ＢＤ [°], where N is the number of deflection surfaces of the deflector, 360 / N-45<θ ＢＤ -θ ｍａｘ＋ <360 / N / 2 2. The optical scanning device according to claim 1, wherein the following conditions are satisfied:

22. the first optical system is formed by a plurality of optical elements, the portion of the light beam deflected by the first deflection surface at the first angle is received by a light receiving element after passing through at least one of the optical elements included in the first optical system, In the main scanning cross section, the angle formed by the traveling direction of the chief ray of the light beam directed toward the most off-axis image height on the side where the light source is disposed immediately after being deflected by the deflector with respect to the optical axis of the first optical system is θ. ｍａｘ＋ [°], and the angle formed by the traveling direction of the chief ray of the light beam directed toward the center of the light receiving surface of the light receiving element immediately after being deflected by the deflector with respect to the optical axis of the first optical system is θ. ＢＤ [°], where N is the number of deflection surfaces of the deflector, 0.145<(θ) ＢＤ -θ ｍａｘ＋ ) / (3V0)<0182 2. The optical scanning device according to claim 1, wherein the following conditions are satisfied:

23. 23. The optical scanning device according to claim 22, wherein the portion of the light beam deflected by the first deflection surface at the first angle passes through the optical element among the plurality of optical elements that is closest to the deflector on the optical path.

24. In the main scanning cross section, the width of the light beam deflected by the first deflecting surface and directed toward the center of the light receiving surface of the light receiving element is defined as W ＢＤ , the width of the light beam deflected by the first deflecting surface and directed toward the most off-axis image height on the side where the light source is disposed is W ｍａｘ＋ The width of the light beam deflected by the first deflecting surface and directed toward the most off-axis image height on the opposite side to the side where the light source is disposed is W ｍａｘ－ When W ＢＤ <W ｍａｘ－ <W ｍａｘ＋ 2. The optical scanning device according to claim 1, wherein the following conditions are satisfied:

25. The width of the light beam incident on the deflector in the main scanning section is W ｉ When W ｍａｘ＋ =W ｉ 25. The optical scanning device according to claim 24, wherein the following condition is satisfied:

26. When the number of deflection surfaces of the deflector is N, 4≦N≦6 2. The optical scanning device according to claim 1, wherein the following conditions are satisfied:

27. In the main scanning cross section, the angle formed by the traveling direction of the chief ray of the light beam directed toward the most off-axis image height on the side where the light source is disposed immediately after being deflected by the deflector with respect to the optical axis of the first optical system is θ. ｍａｘ＋ When [゜] is used, 47.0≦θ ｍａｘ＋ ≦57.0 2. The optical scanning device according to claim 1, wherein the following conditions are satisfied:

28. the light source; 2. The optical scanning device according to claim 1, further comprising a light amount adjusting unit that adjusts the amount of light of the light beam emitted from the light source in accordance with the number of deflecting surfaces of the deflector.

29. 2. The optical scanning device according to claim 1, wherein the deflector is a polygonal mirror that rotates around a rotation axis.

30. 30. 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 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.

31. 30. 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.

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