Polygon mirror, optical scanner, and image forming apparatus

Abstract

To provide a polygon mirror that can reduce mold release resistance, while preventing a variation in the width of a reflection surface according to its height.SOLUTION: A polygon mirror according to the present invention is a polygon mirror comprising a plurality of deflection surfaces, and first and second connection surfaces. The plurality of deflection surfaces include first and second deflection surfaces which are closest to each other, of the plurality of deflection surfaces. The first and second deflection surfaces each have a linear shape on a first cross section perpendicular to a rotation axis of the polygon mirror. The first connection surface is a part of a rotation surface that has a first axis closest to the first deflection surface of the plurality of deflection surfaces as a rotation axis. The second connection surface is a part of a rotation surface that has a second axis closest to the second deflection surface of the plurality of deflection surfaces as a rotation axis. A first ridge line formed by an end of the first deflection surface on a side of the second deflection surface and the first connection surface, and a second ridge line formed by an end of the second deflection surface on a side of the first deflection surface and the second connection surface, are parallel to the rotation axis of the polygon mirror.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a polygon mirror, an optical scanning device including a deflector using the polygon mirror, and an image forming apparatus including the optical scanning device. [Background technology]

[0002] Conventionally, when a polygon mirror is used in a deflector provided in an optical scanning device, it is necessary to improve the surface precision of the reflective surface serving as the deflecting surface of the polygon mirror in order to improve the optical performance of the optical scanning device. Patent document 1 discloses a polygonal mirror in which connecting surfaces are provided between adjacent reflecting surfaces that are inclined with respect to each of the adjacent reflecting surfaces, thereby reducing the demolding resistance during mold molding, thereby improving the surface precision of the reflecting surfaces. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2015-152652 A Summary of the Invention [Problem to be solved by the invention]

[0004] On the other hand, an over-filled scan (OFS) type optical scanning device is known, which scans a surface to be scanned by deflecting a light beam having a width larger than the width of the deflection surface of a deflector in the main scanning cross section using the deflection surface. In such an OFS type optical scanning device, the deflection surface of the deflector plays the role of a stop in the main scanning direction and rotates within the light beam to deflect the light beam so as to cut it out. Therefore, the width of the light beam in the main scanning direction is determined by the width of the deflecting surface in the main scanning cross section.

[0005] In the polygon mirror disclosed in Patent Document 1, connecting surfaces are provided so that the width of each reflecting surface varies depending on the height. Therefore, if the polygonal mirror disclosed in Patent Document 1 is used in a deflector provided in an OFS type optical scanning device, when the incident position of the light beam on the deflection surface shifts in the sub-scanning direction, the light beam width in the main scanning direction of the light beam changes, causing a degradation in the optical performance of the optical scanning device.

[0006] SUMMARY OF THE PRESENTLY PREFERRED EMBODIMENTS An object of the present invention is to provide a polygonal mirror capable of reducing the release resistance while suppressing the variation in the width of the reflecting surface according to the height. [Means for solving the problem]

[0007] The polygon mirror of the present invention is a polygon mirror having a plurality of deflection surfaces and first and second connecting surfaces, the plurality of deflection surfaces including first and second deflection surfaces that are closest to each other among the plurality of deflection surfaces, each of the first and second deflection surfaces having a linear shape in a first cross section perpendicular to the rotation axis of the polygon mirror, the first connecting surface being a part of a rotation surface having a first axis that is closest to the first deflection surface among the plurality of deflection surfaces as its rotation axis, and the second connecting surface being a part of a rotation surface having a second axis that is closest to the second deflection surface among the plurality of deflection surfaces as its rotation axis, and a first ridge line formed by the end of the first deflection surface on the second deflection surface side and the first connecting surface, and a second ridge line formed by the end of the second deflection surface on the first deflection surface side and the second connecting surface are parallel to the rotation axis of the polygon mirror. Effect of the Invention

[0008] According to the present invention, it is possible to provide a polygonal mirror capable of reducing the release resistance while suppressing the variation in the width of the reflecting surface according to the height. [Brief description of the drawings]

[0009] [Figure 1] 1A and 1B are main-scanning sectional view and sub-scanning sectional view of an optical scanning device including a polygon mirror according to a first embodiment. [Diagram 2]1A to 1C are a top view, a partially enlarged top view, a partially enlarged perspective view, and a partially enlarged cross-sectional view of a polygon mirror according to a first embodiment. [Diagram 3] FIG. 11 is a top view of a polygon mirror according to a modified example of the first embodiment. [Figure 4] FIG. 11 is a partially enlarged perspective view of a polygonal mirror according to a second embodiment. [Diagram 5] 13A and 13B are a top view and a partially enlarged perspective view of a polygonal mirror according to a third embodiment. [Figure 6] 13A and 13B are a top view and a partially enlarged perspective view of a polygon mirror according to a fourth embodiment. [Figure 7] FIG. 13 is a partially enlarged perspective view of a polygon mirror according to a fifth embodiment. [Figure 8] FIG. 13 is a partially enlarged perspective view of a polygon mirror according to a sixth embodiment. [Figure 9] 13A and 13B are a top view and a partially enlarged perspective view of a polygon mirror according to a seventh embodiment. [Figure 10] 2 is a sub-scanning sectional view of a main part of the image forming apparatus according to the embodiment. FIG. [Figure 11] FIG. 1 is a partially enlarged perspective view of a polygonal mirror disclosed in Patent Document 1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, the polygonal mirror according to the present embodiment will be described in detail with reference to the accompanying drawings. Note that the drawings shown below may be drawn at a scale different from the actual scale in order to facilitate understanding of the present embodiment. In the following description, the main scanning direction is the direction perpendicular to the rotation axis of the deflector and the optical axis of the optical system (the direction in which the light beam is deflected and scanned by the deflector). The sub-scanning direction is the direction parallel to the rotation axis of the deflector (polygon mirror rotation axis). The main scanning cross section is a cross section perpendicular to the sub-scanning direction. The sub-scanning cross section is a cross section perpendicular to the main scanning direction. In the following description, the optical axis direction is defined as the X direction, the main scanning direction as the Y direction, and the sub-scanning direction as the Z direction.

[0011] [First embodiment] 2. Description of the Related Art Conventionally, optical scanning devices have been used as exposure devices in image forming apparatuses such as laser beam printers that use an electrophotographic process.

[0012] Specifically, in an optical scanning device, a light beam emitted from a light source is modulated according to an image signal from an external device such as a personal computer, and is guided by an incident optical system to a deflector such as a polygon mirror (rotating polygonal mirror), and is deflected by the deflection surface of the deflector. The deflected light beam is then focused by an imaging optical system into a spot on a photosensitive drum surface that is positioned at the position of the surface to be scanned, and the spot scans the photosensitive drum surface to expose and record image information.

[0013] Also, various color image forming apparatuses have been proposed that form color images by directing light beams onto a plurality of photosensitive drums using a plurality of optical scanning devices. In recent years, in order to achieve higher speed and finer printing by optical scanning devices, an over-filled scan (OFS) method has been proposed, which involves increasing the number of faces of a polygon mirror used in a deflector.

[0014] Specifically, in an OFS optical scanning device, a light beam from a light source is converted by an incident optical system into an incident light beam having a wide light beam width in the main scanning direction, and the incident light beam is guided to a deflector. More specifically, in an OFS optical scanning device, the incident light beam has a width in the main scanning cross section that is greater than the width of the deflecting surface of the deflector.

[0015] The deflection surface of the deflector acts as an aperture in the main scanning direction while rotating within the incident light beam, thereby reflectively deflecting the incident light beam so as to cut it out, and the cut-out light beam enters the imaging optical system. The light beam incident on the imaging optical system is guided to a printing area on a photosensitive drum, which is the surface to be scanned, while forming a beam spot due to the imaging performance of the imaging optical system, and printing is performed by scanning the printing area with the light beam.

[0016] In contrast to the OFS method, a method in which an incident light beam having a width smaller than the width of the deflection surface of the deflector in the main scanning cross section is used to scan the surface to be scanned is called under-field scanning (hereinafter referred to as UFS) method. Furthermore, in the OFS system, it is easier to make the polygon mirror smaller than in the UFS system, so it is possible to achieve faster and more precise printing without increasing the size of the optical scanning device.

[0017] On the other hand, polygon mirrors used in deflectors equipped with optical scanning devices are generally manufactured by cutting aluminum blocks, but in recent years, a manufacturing technique has been proposed in which a vapor-deposited reflective surface is formed at a specified position on a base molded by resin molding. Patent Document 1 proposes a technique for improving the molding transferability when a polygon mirror used in a deflector included in an optical scanning device is molded by resin molding using a mold.

[0018] FIG. 11 shows a partially enlarged perspective view of a polygon mirror 215 disclosed in Patent Document 1. As shown in FIG. As shown in FIG. 11, the polygon mirror 215 disclosed in Patent Document 1 has a plurality of deflection surfaces, including deflection surfaces 211 and 212, each of which has a planar shape and is closest to each other. The polygon mirror also has connection surfaces 213 connected to the deflection surfaces 211 and 212, respectively. The deflection surface 211 and the connection surface 213 are connected to each other at a connection position 213a, and the deflection surface 212 and the connection surface 213 are connected to each other at a connection position 213b.

[0019] In the polygon mirror 215 disclosed in Patent Document 1, as shown in FIG. 11, the connection surface 213 is formed so as to be inclined with respect to each of the deflection surfaces 211 and 212. In the polygon mirror 215 disclosed in Patent Document 1, the connection surface 213 is inclined in this manner, which reduces the resistance (mold release resistance) when releasing the polygon mirror 215 from the mold during mold resin molding, thereby improving the molding transferability.

[0020] However, when the polygon mirror 215 disclosed in Patent Document 1 is used in a deflector of an OFS-type optical scanning device, the following problems arise. Specifically, in the polygon mirror 215 disclosed in Patent Document 1, the connecting surface 213 is inclined as described above, so that the widths of the deflection surfaces 211 and 212 in the main scanning cross section differ depending on the height in the sub-scanning direction, as shown in FIG. 11.

[0021] In other words, in the UFS method, a light beam having a light beam width smaller than the width of the deflection surface in the main scanning cross section is incident on the deflection surface, so there is almost no problem even if a polygon mirror whose deflection surface has a different width in the main scanning cross section depending on the height in the sub-scanning direction is used. On the other hand, in the OFS method, in which a light beam having a width larger than the width of the deflection surface in the main scanning cross section is incident on the deflection surface, a problem arises when a polygon mirror in which the width of the deflection surface in the main scanning cross section varies depending on the height in the sub-scanning direction is used.

[0022] That is, in the OFS method, the deflecting surface of the polygon mirror acts as an aperture in the main scanning direction while rotating within the incident light beam to cut off the incident light beam, and the cut-off light beam is deflected by the deflecting surface and guided to the imaging optical system. Furthermore, if the width in the main scanning cross section of the deflection surface, which acts as a narrowing in the main scanning direction, varies depending on the height in the sub-scanning direction, the width in the main scanning direction of the cut-off light beam will change when the height in the sub-scanning direction of the light beam incident on the deflection surface shifts due to tolerances, etc. As a result, the amount of light and the diameter of the spot on the surface to be scanned change, causing the optical performance to become unstable.

[0023] Therefore, the present embodiment aims to provide a polygonal mirror that can suppress degradation of optical performance when used in a deflector provided in an OFS-type optical scanning device while maintaining the molding transferability in mold resin molding, and an optical scanning device provided with such a polygonal mirror.

[0024] 1(a) and (b) respectively show a main-scanning sectional view and a sub-scanning sectional view of an optical scanning device 100 including a deflector 5 using a polygon mirror according to a first embodiment.

[0025] The optical scanning device 100 is suitable for use in image forming devices such as laser beam printers and multifunction printers that use an electrophotographic process. The optical scanning device 100 can also be applied to a color image forming apparatus that forms a color image by exposing a plurality of photosensitive drums. The optical scanning device 100 includes a light source 1, a diaphragm 4, a coupling lens 3, a deflector 5 (deflection device), a first imaging lens 61, and a second imaging lens 62.

[0026] The diaphragm 4 limits the width of the light beam emitted from the light source 1, and specifically, the diaphragm 4 is configured to limit the width of the light beam in the sub-scanning direction. That is, the width of the diaphragm 4 in the main scanning direction is set to be sufficiently wide so that a light beam having a width larger than the width of the deflection surface of the deflector 5 in the main scanning cross section is incident on the deflection surface.

[0027] The coupling lens 3 has anamorphic power (refractive power). The coupling lens 3 and the lower portion of the first imaging lens 61 in the sub-scanning direction convert the light beam passing through the diaphragm 4 into a parallel light beam or a weakly convergent light beam in the main scanning direction, and condense the light (convert it into a convergent light beam) so that a line image is formed on the deflection surface of the deflector 5 in the sub-scanning direction. In the optical scanning device 100, the incident optical system is constituted by the aperture 4, the coupling lens 3 and the lower part of the first imaging lens 61 in the sub-scanning direction, and the light beam emitted from the light source 1 is guided to the deflector 5 by the incident optical system and then deflected by the deflector 5.

[0028] Although the optical scanning device 100 uses the coupling lens 3 having anamorphic power as described above, the present invention is not limited to this. That is, instead of the coupling lens 3, a rotationally symmetric coupling lens and a cylindrical lens having power in the sub-scanning direction may be used. As a result, the incident light beam can be focused by a rotationally symmetric coupling lens, and then focused by a cylindrical lens having power in the sub-scanning direction so as to form a line image on the deflection surface of the deflector 5.

[0029] Next, the light beam deflected by the deflector 5 is incident on an upper portion in the sub-scanning direction of the first imaging lens 61. The light beam that has passed through the upper portion in the sub-scanning direction of the first imaging lens 61 passes through a second imaging lens 62, and is then focused (guided) onto the surface to be scanned 7, forming a beam spot on the surface to be scanned 7. As the deflector 5 rotates at a constant speed, the beam spot scans the print area on the scanned surface 7 from the most off-axis image height on the positive side to the most off-axis image height on the negative side.

[0030] In the optical scanning device 100, an imaging optical system is formed by the upper part of the first imaging lens 61 in the sub-scanning direction and the second imaging lens 62, and the light beam deflected by the deflector 5 is guided to the scanned surface 7 by the imaging optical system. The optical scanning device 100 is also provided with a synchronization detection optical system (not shown) for detecting the rotation synchronization of the deflector 5 .

[0031] In the optical scanning device 100, the width of the light beam on the deflection surface of the deflector 5 is set to be larger than the width of the deflection surface of the deflector 5 in the main scanning cross section including the optical axis of the imaging optical system. That is, the width of the light beam deflected by the deflector 5 in the main scanning direction is determined by the width of the deflecting surface of the deflector 5 in the main scanning cross section. The optical scanning device 100 employs such an OFS method.

[0032] The optical scanning device 100 uses a so-called sub-scanning oblique incidence optical system in which a light beam from the light source 1 is obliquely incident on the deflecting surface of the deflector 5 at an angle in the sub-scanning section with respect to the main-scanning section. Further, the optical scanning device 100 employs a front incidence type in which the optical axis of the incidence optical system and the optical axis of the imaging optical system coincide with each other when projected onto the main scanning cross section.

[0033] A local coordinate system is used with the intersection point with the optical axis, which is the vertex of each lens surface (optical surface), as the origin, with the direction of light travel (optical axis) defined as the X-axis, the axis perpendicular to the X-axis in the main scanning cross section as the Y-axis, and the axis perpendicular to the X-axis in the sub-scanning cross section as the Z-axis. In this case, the generatrix shapes (shapes in the main scanning cross section) of the entrance surface and exit surface of each of the coupling lens 3, the upper portion in the sub-scanning direction of the first imaging lens 61, and the second imaging lens 62 are expressed by the following formula (1).

number

[0034] In formula (1), R is the radius of curvature in the main scanning section (generatrix radius of curvature), K, B4, B6, B8, B 10 and B. 12 are the aspheric coefficients. Aspheric coefficients B4, B6, B8, B 10 and B. 12 may have different values ​​on the positive and negative sides of the Y axis. This allows the generatrix shapes to be set asymmetrically with respect to the optical axis in the main scanning direction.

[0035] Moreover, the sagittal shapes (shapes in the sub-scanning cross section) of the entrance surface and exit surface of each of the upper portion in the sub-scanning direction of the first imaging lens 61 and the second imaging lens 62 are expressed by the following formula (2).

number

[0036] The sagittal shape S shown here indicates the surface shape in a cross section perpendicular to the main-scan cross section, including a surface normal at a predetermined position on the generating line. In addition, in formula (2), M j,k is an aspheric coefficient, and the first-order (k=1) term of Z is a term that contributes to the amount of tilt in the sub-scanning cross section of the lens surface, that is, the amount of sagittal tilt.

[0037] Therefore, the aspheric coefficient M 0,1 ~M 16,1 By making the values ​​different between the positive side and the negative side of the Y axis, the sagittal tilt amounts can be set asymmetrically with respect to the optical axis in the main scanning direction. In the optical scanning device 100, M j,k The value is set to zero. However, the aspheric coefficient M j,k It is possible to improve various aberrations by intentionally setting the value of to a value other than zero.

[0038] Furthermore, r' in equation (2) is the radius of curvature (sagittal radius of curvature) in the sub-scanning cross section at a position spaced a distance Y from the optical axis in the main scanning direction, and is expressed by the following equation (3).

number

[0039] In formula (3), r is the radius of curvature of the sagittal line on the optical axis, E2, E4, E6, E8 and E 10 is the sagittal variation coefficient. In addition, the sagittal line change coefficients E2, E4, E6, E8 and E 10By making the values ​​different between the positive side and the negative side of the Y axis, the aspheric amount of the secondary line shape can be set asymmetrically with respect to the optical axis in the main scanning direction. Furthermore, in equation (3), only the even-numbered terms of Y are used, but odd-numbered terms of Y may be added.

[0040] Next, a detailed configuration of the deflector 5 using a polygon mirror according to this embodiment will be described. The deflector 5 is a six-sided polygon mirror (rotating polygon mirror) having six deflection surfaces (deflection reflection surfaces). The deflector 5 is manufactured by forming a base material by resin molding using a mold, and then providing a deposition film on the deflecting surface.

[0041] 2(a), (b), (c) and (d) respectively show a top view, a partially enlarged top view, a partially enlarged perspective view and a partially enlarged projection view of a predetermined cross section of the deflector 5.

[0042] Here, when the angle between deflection surface 531 and deflection surface 532 when projected onto the main scanning cross section is θ, the specified cross section in Figure 2(d) is a cross section that forms an angle θ / 2 with deflection surface 531 and an angle -(θ / 2) with deflection surface 532, and is parallel to rotation axis 50. That is, since the angle θ between the deflection surface 531 and the deflection surface 532 in the deflector 5 is 60°, a specific cross section in FIG. 2(d) is at 30° with respect to the deflection surface 531 in the main scanning cross section and at -30° with respect to the deflection surface 532. In other words, FIG. 2(d) shows a partially enlarged projection view of the deflector 5 as seen from the direction of the arrow 2D shown in FIG. 2(c).

[0043] The deflector 5 is configured to be rotated around a rotation shaft 50 of a polygon motor (drive unit) that fits in a shaft hole 51 . The deflector 5 has a plurality of deflection surfaces including deflection surfaces 531 and 532 (first and second deflection surfaces) arranged around the rotation axis 50.

[0044] The deflection surface is an optical surface having a planar shape parallel to the rotation axis 50, specifically a reflecting surface, in other words, the deflection surface has a linear shape in the main scanning cross section (first cross section). Further, in the deflector 5, a plurality of connecting portions, such as the connecting portion 54 connecting the deflecting surfaces 531 and 532, that connect the two closest deflecting surfaces among the plurality of deflecting surfaces are formed.

[0045] Specifically, as shown in FIGS. 2(b) and 2(c), the connecting portion 54 has connecting surfaces 541 and 542 (first and second connecting surfaces) each having a curved shape. More specifically, each of the connecting surfaces 541 and 542 has a partial cylindrical surface shape (part of the side of a cylinder, part of the cylindrical surface), and the centers of curvature of the connecting surfaces 541 and 542 at a predetermined height in the sub-scanning direction do not coincide with each other. That is, each of the coupling surfaces 541 and 542 has a shape of a surface of revolution, in other words, is a part of a surface of revolution.

[0046] The connecting surface 541 is connected to the deflecting surface 531 so as to form a boundary line 541a (first ridge line). In other words, the connecting surface 541 is connected to the deflecting surface 531 on the deflecting surface 532 side so as to form the boundary line 541a. Furthermore, the connecting surface 542 is connected to the deflecting surface 532 so as to form a boundary line 542a (second ridge line), in other words, the connecting surface 542 is connected to the deflecting surface 532 on the deflecting surface 531 side so as to form the boundary line 542a.

[0047] And the boundary lines 541 a and 542 a are parallel to the rotation axis 50 of the deflector 5 . Furthermore, the rotation axis (central axis, first rotation axis, first axis) 551 of the connecting surface 541 is closest to the deflection surface 531 connected to the connecting surface 541 among the multiple deflection surfaces. Furthermore, a rotation axis (central axis, second rotation axis, second axis) 552 of the connecting surface 542 is closest to the deflection surface 532 connected to the connecting surface 542 among the multiple deflection surfaces.

[0048] The connecting portion 54 also has an intermediate connecting surface 543 (third connecting surface) having a partial truncated cone surface shape (part of the side of a truncated cone, part of the truncated cone surface, part of the side of a truncated cone) that connects to each of the connecting surfaces 541 and 542. The connecting surface 541 and the intermediate connecting surface 543 are connected to each other so as to form a boundary line 541b (third ridge line); in other words, the intermediate connecting surface 543 is connected to the connecting surface 541 on the deflection surface 532 side so as to form the boundary line 541b. In addition, the connecting surface 542 and the intermediate connecting surface 543 are connected to each other so as to form a boundary line 542b (fourth ridge line); in other words, the intermediate connecting surface 543 is connected to the connecting surface 542 on the deflection surface 531 side so as to form the boundary line 542b.

[0049] That is, the intermediate connecting surface 543 has the shape of a surface of revolution, in other words, is a part of a surface of revolution. In the deflector 5, the rotation axes (central axes) 551, 552 and 553 of the coupling surface 541, the coupling surface 542 and the intermediate coupling surface 543, each of which has a rotation surface shape, are parallel to each other but do not coincide with each other.

[0050] As described above, the deflector 5 has a connection between the two deflection surfaces that are closest to each other. As shown in FIG. 2( c ), the boundaries of the connecting portion formed for each deflection surface, such as the boundaries 541 a and 542 a of the connecting portion 54 , are parallel to the rotation axis 50 of the deflector 5 . Therefore, the width of each deflecting surface in the main scanning cross section at each position in the sub-scanning direction is the same as each other.

[0051] As shown in FIG. 2( c ), the generatrix of the intermediate connection surface 543 having the partial truncated cone surface shape is inclined with respect to the rotation axis 50 , that is, is not parallel to the rotation axis 50 . This allows the angle of the light beam reflected by the intermediate coupling surface 543 with respect to the main scanning cross section to be different from the angle of the light beam reflected by the deflecting surfaces 531 and 532 with respect to the main scanning cross section. Therefore, it is possible to block the light beam reflected by the intermediate coupling surface 543 by a known method.

[0052] Furthermore, by inclining the intermediate coupling surface 543 with respect to the rotation axis 50, the mold release resistance during the manufacture of the deflector 5 is reduced, thereby suppressing the deterioration of the surface accuracy of the deflecting surfaces 531 and 532. Furthermore, when a reflective film is vapor-deposited onto the deflecting surface of deflector 5, the above-described configuration eliminates the need to mask connecting portion 54 to prevent flare light from being generated from connecting portion 54, thereby simplifying the manufacturing process of deflector 5.

[0053] As described above, in the deflector 5 , the connecting surface 541 is provided outside the effective area of ​​the deflecting surface 531 , and the connecting surface 542 is provided outside the effective area of ​​the deflecting surface 532 . The effective area referred to here is the effective area of ​​the scanned surface 7, i.e., the area where the light beam is incident so as to be guided to the printing area between the most off-axis image height on the positive side and the most off-axis image height on the negative side of the scanned surface 7.

[0054] That is, the connecting surfaces 541 and 542 play a role in clearly distinguishing the reflective areas and the light-shielding areas (non-reflective areas) of the deflection surfaces 531 and 532, respectively. On the other hand, the intermediate connecting surface 543 reflects the incident light beam so as to deviate it from the optical path to the scanned surface 7, and also plays a role in improving the surface accuracy of the deflection surfaces 531 and 532 by reducing the release resistance. By ensuring a sufficient area for the intermediate connection surface 543 in the deflector 5, the mold release resistance can be sufficiently reduced.

[0055] In the deflector 5, the coupling surface 541 and the intermediate coupling surface 543 are discontinuously connected to each other at a boundary line 541b, and the coupling surface 542 and the intermediate coupling surface 543 are discontinuously connected to each other at a boundary line 542b. However, in order to reduce the demolding resistance when manufacturing the deflector 5, the connecting surface 541 and the intermediate connecting surface 543 may be connected to each other by a C-chamfer, an R-chamfer or a spline, and the connecting surface 542 and the intermediate connecting surface 543 may be connected to each other by a C-chamfer, an R-chamfer or a spline. When performing the R chamfering, it is preferable to set the R to about 0.2 mm to 1.0 mm.

[0056] Furthermore, when the angle between deflection surface 531 and deflection surface 532 when projected onto the main scanning cross section (first cross section) is θ, the area of ​​each of connecting surfaces 541 and 542 when projected onto a cross section (second cross section) that forms an angle θ / 2 with respect to deflection surface 531 and is parallel to rotation axis 50 is So. Furthermore, when the area of ​​the intermediate coupling surface 543 when projected onto the cross section is taken as Sc, in the deflector 5 according to this embodiment, it is preferable that the following conditional expression (4) be satisfied. Sc-2So≧0 (4)

[0057] The radius of curvature of each of the coupling surfaces 541 and 542 is Ro, and the radius of curvature of the intermediate coupling surface 543 is Rc. At this time, in the deflector 5, it is preferable that the value of the radius of curvature Ro of each of the coupling surfaces 541 and 542 is set small, and specifically, it is preferable that it is set to about 0.1 mm to 1.0 mm.

[0058] By thus reducing the value of the radius of curvature Ro of each of coupling surfaces 541 and 542, the direction in which the light beam is reflected by coupling surfaces 541 and 542 and the direction in which the light beam is reflected by deflection surfaces 531 and 532 can be made significantly different from each other. Since the boundary lines 541a and 542a of the deflecting surfaces 531 and 532 are clearly defined, the deflecting surfaces 531 and 532 function as apertures in the main scanning direction in the OFS method.

[0059] On the other hand, if the value of the radius of curvature Ro of each of the connecting surfaces 541 and 542 is made too small, such as less than 0.1 mm, the resin will not be sufficiently filled into the mold when the deflector 5 is resin-molded, and the resin will be likely to stick to the mold. Therefore, the mold release resistance increases, and the surface accuracy of the deflection surface decreases.

[0060] By thus reducing the value of the radius of curvature Ro of the coupling surface 541, the deflection surface 531 connected to the coupling surface 541 among the multiple deflection surfaces becomes closest to the rotation axis (center axis) 551 of the coupling surface 541. Similarly, by reducing the value of the radius of curvature Ro of the connecting surface 542, the deflection surface 532 connected to the connecting surface 542 among the multiple deflection surfaces becomes closest to the rotation axis (center axis) 552 of the connecting surface 542.

[0061] In addition, in the deflector 5, it is preferable that the value of the radius of curvature Rc of the intermediate connecting surface 543 is greater than or equal to the value of the radius of curvature Ro of each of the connecting surfaces 541 and 542, and is set as large as possible to reduce the release resistance. In the deflector 5, the intermediate coupling surface 543 may be a flat surface, that is, the value of the radius of curvature Rc of the intermediate coupling surface 543 may be infinite.

[0062] Furthermore, when the area of ​​each of the deflecting surfaces 531 and 532 is denoted by Sr, it is preferable that the deflector 5 satisfies the following conditional expression (5). 0.5(Sc+2So) <Sr<7(Sc+2So) ···(5)

[0063] In the OFS method, the deflection surface acts as an aperture in the main scanning direction, so the width of the deflection surface is uniquely determined by determining the focal length of the imaging optical system, the spot size on the scanned surface 7, and the wavelength of the light beam emitted from the light source 1. In this case, if the value of the area Sr of the deflecting surface falls below the lower limit of the conditional expression (5), the circumscribing circle of the deflector 5 becomes large, and the deflector 5 ends up becoming large in size. On the other hand, if the value of the area Sr of the deflection surface exceeds the upper limit value of conditional formula (5), the area of ​​the connecting portion 54 becomes relatively small, which increases the resistance to release from the mold when the deflector 5 is resin-molded, thereby reducing the surface accuracy of the deflection surface.

[0064] It is more preferable that the deflector 5 satisfies the following conditional formula (5a) instead of conditional formula (5). (Sc+2So) <Sr<3(Sc+2So) ···(5a)

[0065] As described above, in the deflector 5 using the polygon mirror according to this embodiment, a connection portion is formed between the two deflection surfaces that are closest to each other, and the connection portion is provided with a first connection surface that connects to one of the deflection surfaces and a second connection surface that connects to the other deflection surface. The connection portion has an intermediate connection surface that connects to the first connection surface and the second connection surface, and while the generatrix of each of the first connection surface and the second connection surface is parallel to the rotation axis 50 of the deflector 5, the generatrix of the intermediate connection surface is non-parallel to the rotation axis 50 of the deflector 5, i.e., inclined.

[0066] This reduces the mold release resistance when the deflector 5 is molded using a metal mold, thereby improving the mold transferability. Moreover, in the deflector 5, the width of each deflection surface in the main scanning cross section does not vary depending on the position in the sub-scanning direction.

[0067] Therefore, when the deflector 5 is mounted on an OFS type optical scanning device 100, even if the height in the sub-scanning direction of the light beam incident on the deflection surface shifts due to tolerances, etc., the fluctuation in the light beam width of the light beam deflected toward the scanned surface 7 can be suppressed. As a result, fluctuations in the light amount and diameter of the spot on the scanned surface 7, that is, deterioration in the optical performance of the optical scanning device 100, can be suppressed.

[0068] This embodiment can also be applied to a deflector 5a having four deflection surfaces as shown in FIG. 3(a) or a deflector 5b having eight deflection surfaces as shown in FIG. 3(b). Similarly, this embodiment may be applied to deflectors having different numbers of deflecting surfaces, such as five, seven or ten.

[0069] In addition, in the polygon mirror of this embodiment, the first connecting surface and the second connecting surface, such as connecting surface 541 and connecting surface 542, have the same partial rotation surface shape, but as long as the first connecting surface and the second connecting surface satisfy the above-mentioned configuration, they may have different partial rotation surface shapes. In addition, in the polygonal mirror of this embodiment, as long as connecting surface 541, connecting surface 542 and intermediate connecting surface 543 satisfy the above-mentioned configuration, the partial surface of revolution may have a partial elliptical cylinder shape (part of the side of an elliptical cylinder) shape or a partial parabolic cylinder shape (part of the side of a parabolic cylinder) shape.

[0070] [Second embodiment] FIG. 4 is a partially enlarged perspective view of a deflector 15 using a polygonal mirror according to the second embodiment. The deflector 15 of this embodiment has the same configuration as the deflector 5 of the first embodiment, except for the shape of the intermediate connection surface 543, and therefore the same configurations are given the same reference numbers and will not be described.

[0071] Specifically, the intermediate connecting surface 543 formed on the deflector 15 has a partial cylindrical surface (part of the side of a cylinder) shape, and the rotation axis (central axis) 553 is non-parallel to the rotation axis 50 of the deflector 15, i.e., inclined with respect to the rotation axis 50. On the other hand, the rotation axes (central axes) of the coupling surfaces 541 and 542 having the partial cylindrical surface shape are parallel to the rotation axis 50 of the deflector 15 but do not coincide with each other.

[0072] In the deflector 15 , the generatrix of the intermediate coupling surface 543 , which has a part-cylindrical surface shape, is inclined with respect to the rotation axis 50 of the deflector 15 , i.e. is non-parallel to the rotation axis 50 of the deflector 15 . This allows the angle of the light beam reflected by the intermediate coupling surface 543 with respect to the main scanning cross section to be different from the angle of the light beam reflected by the deflecting surfaces 531 and 532 with respect to the main scanning cross section. Therefore, it is possible to block the light beam reflected by the intermediate coupling surface 543 by a known method.

[0073] In addition, by inclining the generatrix of the intermediate connecting surface 543 with respect to the rotation axis 50 of the deflector 15, the resistance to demolding during manufacturing of the deflector 15 is reduced, thereby suppressing the deterioration of the surface accuracy of the deflection surfaces 531 and 532.

[0074] As described above, in the deflector 15 using the polygon mirror according to this embodiment, a connection portion is formed between the two deflection surfaces that are closest to each other, and the connection portion is provided with a first connection surface that connects to one of the deflection surfaces and a second connection surface that connects to the other deflection surface. The connection portion has an intermediate connection surface that connects to the first connection surface and the second connection surface, and while the generatrix of each of the first connection surface and the second connection surface is parallel to the rotation axis 50 of the deflector 15, the generatrix of the intermediate connection surface is non-parallel to the rotation axis 50, i.e., inclined.

[0075] This reduces the mold release resistance when the deflector 15 is molded using a metal mold, thereby improving the mold transferability. Moreover, in the deflector 15, the width of each deflecting surface in the main scanning cross section does not vary depending on the position in the sub-scanning direction.

[0076] Therefore, when the deflector 15 is mounted on an OFS type optical scanning device 100, even if the height in the sub-scanning direction of the light beam incident on the deflection surface shifts due to tolerances, etc., the fluctuation in the light beam width of the light beam deflected toward the scanned surface 7 can be suppressed. As a result, fluctuations in the light amount and diameter of the spot on the scanned surface 7, that is, deterioration in the optical performance of the optical scanning device 100, can be suppressed.

[0077] [Third embodiment] 5(a) and (b) respectively show a top view and a partially enlarged perspective view of a deflector 25 using a polygon mirror according to the third embodiment. The deflector 25 of this embodiment has the same configuration as the deflector 5 of the first embodiment, except for the shape of the intermediate connection surface 543, and therefore the same configurations are given the same reference numbers and will not be described.

[0078] Specifically, the intermediate coupling surface 543 formed on the deflector 25 has a planar shape. The intermediate coupling surface 543 is non-parallel to the rotation axis 50 of the deflector 25 , that is, inclined with respect to the rotation axis 50 .

[0079] In other words, the intermediate connecting surface 543 can also be interpreted as having a partial cylindrical surface shape, i.e., a partial surface of revolution shape, with an infinite radius of curvature due to a rotation axis that is not parallel to the rotation axis 50, i.e., inclined with respect to the rotation axis 50. On the other hand, the rotation axes (central axes) of the coupling surfaces 541 and 542 having the partial cylindrical surface shape are parallel to the rotation axis 50 of the deflector 25 but do not coincide with each other.

[0080] In the deflector 25 , the intermediate coupling surface 543 having a planar shape is inclined with respect to the rotation axis 50 of the deflector 25 , i.e., is non-parallel to the rotation axis 50 of the deflector 25 . This allows the angle of the light beam reflected by the intermediate coupling surface 543 with respect to the main scanning cross section to be different from the angle of the light beam reflected by the deflecting surfaces 531 and 532 with respect to the main scanning cross section. Therefore, it is possible to block the light beam reflected by the intermediate coupling surface 543 by a known method.

[0081] In addition, by inclining the intermediate coupling surface 543 with respect to the rotation axis 50 of the deflector 25, the resistance to demolding during the manufacture of the deflector 25 is reduced, thereby preventing a decrease in the surface accuracy of the deflection surfaces 531 and 532.

[0082] As described above, in the deflector 25 using the polygonal mirror according to this embodiment, a connection portion is formed between the two deflection surfaces that are closest to each other, and the connection portion is provided with a first connection surface that connects to one of the deflection surfaces and a second connection surface that connects to the other deflection surface. The connection portion has an intermediate connection surface that connects to the first connection surface and the second connection surface, and while the generatrix of each of the first connection surface and the second connection surface is parallel to the rotation axis 50 of the deflector 25, the intermediate connection surface is non-parallel to the rotation axis 50 of the deflector 25, i.e., inclined.

[0083] This reduces the mold release resistance when the deflector 25 is molded using a metal mold, thereby improving the mold transferability. Moreover, in the deflector 25, the width of each deflecting surface in the main scanning cross section does not vary depending on the position in the sub-scanning direction.

[0084] Therefore, when the deflector 25 is mounted on an OFS type optical scanning device 100, even if the height in the sub-scanning direction of the light beam incident on the deflection surface shifts due to tolerances, etc., the fluctuation in the light beam width of the light beam deflected toward the scanned surface 7 can be suppressed. As a result, fluctuations in the light amount and diameter of the spot on the scanned surface 7, that is, deterioration in the optical performance of the optical scanning device 100, can be suppressed.

[0085] [Fourth embodiment] 6(a) and (b) respectively show a top view and a partially enlarged perspective view of a deflector 35 using a polygon mirror according to the fourth embodiment. The deflector 35 according to this embodiment has the same configuration as the deflector 5 according to the first embodiment, except that a first intermediate coupling surface 544 and a second intermediate coupling surface 545 are provided instead of the intermediate coupling surface 543. Therefore, the same configurations are denoted by the same reference numerals and will not be described.

[0086] Specifically, deflector 35 is provided with a first intermediate connecting surface 544 (third connecting surface) and a second intermediate connecting surface 545 (fourth connecting surface) each having a partial truncated cone surface shape (part of the side of a truncated cone, part of the side of a truncated cone) that connect connecting surfaces 541 and 542. The connecting surface 541 and the first intermediate connecting surface 544 are connected to each other so as to form a boundary line 541b (third ridge line); in other words, the first intermediate connecting surface 544 is connected to the connecting surface 541 on the deflection surface 532 side so as to form a boundary line 541b.

[0087] In addition, the connecting surface 542 and the second intermediate connecting surface 545 are connected to each other so as to form a boundary line 542b (fourth ridge line); in other words, the second intermediate connecting surface 545 is connected to the connecting surface 542 on the deflection surface 531 side so as to form the boundary line 542b. Furthermore, the first intermediate connecting surface 544 and the second intermediate connecting surface 545 are connected to each other so as to form a boundary line (fifth ridge line); in other words, the second intermediate connecting surface 545 is connected to the first intermediate connecting surface 544 on the deflection surface 532 side so as to form a boundary line.

[0088] The rotation axes (central axes) 554 and 555 of the first intermediate connection surface 544 and the second intermediate connection surface 545 are non-parallel to the rotation axis 50 of the deflector 35, that is, inclined with respect to the rotation axis 50, and do not coincide with each other. On the other hand, the rotation axes (central axes) of the coupling surfaces 541 and 542 having the partial cylindrical surface shape are parallel to the rotation axis 50 of the deflector 35 but do not coincide with each other.

[0089] In the deflector 35, the generatrices of the first intermediate connecting surface 544 and the second intermediate connecting surface 545, each of which has a partial truncated cone surface shape, are inclined with respect to the rotation axis 50 of the deflector 35, i.e., non-parallel to the rotation axis 50 of the deflector 35. This allows the angle of the light beam reflection direction by first intermediate coupling surface 544 and second intermediate coupling surface 545 to differ from the angle of the light beam reflection direction by deflection surfaces 531 and 532 to the main scanning cross section. Therefore, it is possible to block the light beam reflected by first intermediate coupling surface 544 and second intermediate coupling surface 545 using a known method.

[0090] In addition, by inclining the generatrix of each of the first intermediate connecting surface 544 and the second intermediate connecting surface 545 with respect to the rotation axis 50 of the deflector 35, the resistance to demolding when manufacturing the deflector 35 is reduced, thereby suppressing the decrease in surface accuracy of the deflection surfaces 531 and 532.

[0091] As described above, in the deflector 35 using the polygonal mirror according to this embodiment, a connection portion is formed between the two deflection surfaces that are closest to each other, and the connection portion is provided with a first connection surface that connects to one of the deflection surfaces and a second connection surface that connects to the other deflection surface. The connecting portion is provided with a first intermediate connecting surface connected to the first connecting surface, and a second intermediate connecting surface connected to the second connecting surface and the first intermediate connecting surface. While the generatrix of each of the first connecting surface and the second connecting surface is parallel to the rotation axis 50 of the deflector 35, the generatrix of each of the first intermediate connecting surface and the second intermediate connecting surface is non-parallel, i.e., inclined, to the rotation axis 50 of the deflector 35.

[0092] This reduces the mold release resistance when the deflector 35 is molded using a metal mold, thereby improving the mold transferability. Moreover, in the deflector 35, the width of each deflection surface in the main scanning cross section does not vary depending on the position in the sub-scanning direction.

[0093] Therefore, when the deflector 35 is mounted on an OFS type optical scanning device 100, even if the height in the sub-scanning direction of the light beam incident on the deflection surface shifts due to tolerances, etc., the fluctuation in the light beam width of the light beam deflected toward the scanned surface 7 can be suppressed. As a result, fluctuations in the light amount and diameter of the spot on the scanned surface 7, that is, deterioration in the optical performance of the optical scanning device 100, can be suppressed.

[0094] In the polygon mirror according to this embodiment, the first intermediate coupling surface and the second intermediate coupling surface, such as the first intermediate coupling surface 544 and the second intermediate coupling surface 545, have the same partial surface of revolution shape. However, as long as the first intermediate connecting surface and the second intermediate connecting surface satisfy the above-mentioned configuration, they may have different partial revolution surface shapes.

[0095] [Fifth embodiment] FIG. 7 shows a partially enlarged perspective view of a deflector 45 using a polygonal mirror according to the fifth embodiment. The deflector 45 of this embodiment has the same configuration as the deflector 35 of the fourth embodiment, except for the different shapes of the first intermediate connecting surface 544 and the second intermediate connecting surface 545. Therefore, the same reference numbers are used for the same configurations and their descriptions are omitted.

[0096] Specifically, deflector 45 is provided with first intermediate coupling surface 544 and second intermediate coupling surface 545, which connect coupling surfaces 541 and 542 in coupling portion 54 and each have a partial cylindrical surface (a part of the side surface of a cylinder) shape. The coupling surface 541 and the first intermediate coupling surface 544 are connected to each other so as to form a boundary line 541b, and the coupling surface 542 and the second intermediate coupling surface 545 are connected to each other so as to form a boundary line 542b. Additionally, the first intermediate connecting surface 544 and the second intermediate connecting surface 545 are connected to each other so as to form a boundary line.

[0097] The rotation axes (central axes) 554 and 555 of the first intermediate coupling surface 544 and the second intermediate coupling surface 545 formed on the deflector 45 are parallel to the rotation axis 50 of the deflector 45 but do not coincide with each other. Further, the rotation axes (central axes) of the coupling surfaces 541 and 542 each having a partial cylindrical surface shape are parallel to the rotation axis 50 of the deflector 45 but do not coincide with each other.

[0098] In the deflector 45 , the generatrices of the first intermediate coupling surface 544 and the second intermediate coupling surface 545 each having a partial cylindrical surface shape are parallel to the rotation axis 50 of the deflector 45 . On the other hand, the radius of curvature of each of the first intermediate connecting surface 544 and the second intermediate connecting surface 545 is set to be sufficiently larger than the radius of curvature of each of the connecting surfaces 541 and 542 . Therefore, by reducing the mold release resistance when manufacturing the deflector 45, it is possible to suppress a decrease in the surface accuracy of the deflecting surfaces 531 and 532.

[0099] As described above, in the deflector 45 using the polygonal mirror according to this embodiment, a connection portion is formed between the two deflection surfaces that are closest to each other, and the connection portion is provided with a first connection surface that connects to one of the deflection surfaces and a second connection surface that connects to the other deflection surface. The connecting portion is provided with a first intermediate connecting surface connected to the first connecting surface, and a second intermediate connecting surface connected to the second connecting surface and the first intermediate connecting surface. The generatrices of the first intermediate connecting surface and the second intermediate connecting surface are parallel to the rotation axis 50 of the deflector 45, while the radii of curvature of the first intermediate connecting surface and the second intermediate connecting surface are set to be sufficiently larger than the radii of curvature of the first connecting surface and the second connecting surface.

[0100] This reduces the mold release resistance when the deflector 45 is molded using a metal mold, thereby improving the mold transferability. Moreover, in the deflector 45, the width of each deflecting surface in the main scanning cross section does not vary depending on the position in the sub-scanning direction.

[0101] Therefore, when the deflector 45 is mounted on an OFS type optical scanning device 100, even if the height in the sub-scanning direction of the light beam incident on the deflection surface shifts due to tolerances, etc., the fluctuation in the light beam width of the light beam deflected toward the scanned surface 7 can be suppressed. As a result, fluctuations in the light amount and diameter of the spot on the scanned surface 7, that is, deterioration in the optical performance of the optical scanning device 100, can be suppressed.

[0102] [Sixth embodiment] FIG. 8 is a partially enlarged perspective view of a deflector 55 using a polygon mirror according to the sixth embodiment. The deflector 55 of this embodiment has the same configuration as the deflector 35 of the fourth embodiment, except for the different shapes of the first intermediate connecting surface 544 and the second intermediate connecting surface 545. Therefore, the same reference numbers are used for the same configurations and their descriptions are omitted.

[0103] Specifically, deflector 55 is provided with a first intermediate connecting surface 544 and a second intermediate connecting surface 545, each of which has a partial truncated cone surface shape (part of the side of a truncated cone, part of the side of a truncated cone) that connect connecting surfaces 541 and 542 at connecting portion 54. The coupling surface 541 and the first intermediate coupling surface 544 are connected to each other so as to form a boundary line 541b, and the coupling surface 542 and the second intermediate coupling surface 545 are connected to each other so as to form a boundary line 542b. Additionally, the first intermediate connecting surface 544 and the second intermediate connecting surface 545 are connected to each other so as to form a boundary line.

[0104] The rotation axes (central axes) of the first intermediate coupling surface 544 and the second intermediate coupling surface 545 are parallel to the rotation axis 50 of the deflector 55 but do not coincide with each other. Further, the rotation axes (central axes) of the coupling surfaces 541 and 542 each having a partial cylindrical surface shape are parallel to the rotation axis 50 of the deflector 55 but do not coincide with each other.

[0105] In the deflector 55 , the generatrices of the first intermediate connecting surface 544 and the second intermediate connecting surface 545 having a partial truncated cone surface shape are inclined with respect to the rotation axis 50 of the deflector 55 , i.e., non-parallel to the rotation axis 50 of the deflector 55 . This allows the angle of the light beam reflection direction by first intermediate coupling surface 544 and second intermediate coupling surface 545 to differ from the angle of the light beam reflection direction by deflection surfaces 531 and 532 to the main scanning cross section. Therefore, it is possible to block the light beam reflected by first intermediate coupling surface 544 and second intermediate coupling surface 545 using a known method.

[0106] In addition, by inclining the generatrix of each of the first intermediate connecting surface 544 and the second intermediate connecting surface 545 with respect to the rotation axis 50 of the deflector 55, the resistance to demolding when manufacturing the deflector 55 is reduced, thereby suppressing the decrease in surface accuracy of the deflection surfaces 531 and 532.

[0107] As described above, in the deflector 55 using the polygonal mirror of this embodiment, a connection portion is formed between the two deflection surfaces that are closest to each other, and the connection portion is provided with a first connection surface that connects to one of the deflection surfaces and a second connection surface that connects to the other deflection surface. The connecting portion is provided with a first intermediate connecting surface connected to the first connecting surface, and a second intermediate connecting surface connected to the second connecting surface and the first intermediate connecting surface. While the generatrix of each of the first connecting surface and the second connecting surface is parallel to the rotation axis 50 of the deflector 55, the generatrix of each of the first intermediate connecting surface and the second intermediate connecting surface is non-parallel to the rotation axis 50 of the deflector 55, i.e., inclined.

[0108] This reduces the mold release resistance when the deflector 55 is molded using a metal mold, thereby improving the mold transferability. Moreover, in the deflector 55, the width of each deflecting surface in the main scanning cross section does not vary depending on the position in the sub-scanning direction.

[0109] Therefore, when the deflector 55 is mounted on an OFS type optical scanning device 100, even if the height in the sub-scanning direction of the light beam incident on the deflection surface shifts due to tolerances, etc., the fluctuation in the light beam width of the light beam deflected toward the scanned surface 7 can be suppressed. As a result, fluctuations in the light amount and diameter of the spot on the scanned surface 7, that is, deterioration in the optical performance of the optical scanning device 100, can be suppressed.

[0110] [Seventh embodiment] 9(a) and (b) respectively show a top view and a partially enlarged perspective view of a deflector 65 using a polygon mirror according to the seventh embodiment. The deflector 65 of this embodiment does not have an intermediate connecting surface 543, and has the same configuration as the deflector 5 of the first embodiment, except that the shapes of the connecting surfaces 541 and 542 are different. Therefore, the same reference numbers are used for the same configuration and descriptions thereof are omitted.

[0111] Specifically, in deflector 65, connecting surfaces 541 and 542 each have a partial truncated cone surface shape (part of the side of a truncated cone, part of the side of a truncated cone) and are connected to each other to form a boundary line (sixth ridge line). The rotation axes (central axes) of the connecting surfaces 541 and 542 are non-parallel to the rotation axis 50 of the deflector 65, that is, inclined with respect to the rotation axis 50, and do not coincide with each other.

[0112] In the deflector 65 , the generatrix of each of the coupling surfaces 541 and 542 having a partial truncated cone surface shape is inclined with respect to the rotation axis 50 of the deflector 65 , that is, is non-parallel to the rotation axis 50 of the deflector 65 . This allows the angles of the light beam reflected by the connecting surfaces 541 and 542 with respect to the main scanning cross section to be different from the angles of the light beam reflected by the deflecting surfaces 531 and 532 with respect to the main scanning cross section. Therefore, it is possible to block the light beams reflected by each of the connecting surfaces 541 and 542 by a known method.

[0113] The boundaries 541a and 542a coincide with the predetermined generatrices of the coupling surfaces 541 and 542, respectively. Furthermore, a boundary line 541 a formed between the connecting surface 541 and the deflecting surface 531 , and a boundary line 542 a formed between the connecting surface 542 and the deflecting surface 532 are parallel to the rotation axis 50 of the deflector 65 .

[0114] On the other hand, the generatrix of the coupling surfaces 541 and 542 other than the boundary line 541 a and the boundary line 542 a is inclined with respect to the rotation axis 50 of the deflector 65 . This reduces the mold release resistance when manufacturing the deflector 65, thereby suppressing the deterioration of the surface accuracy of the deflecting surfaces 531 and 532.

[0115] As described above, in the deflector 65 using the polygonal mirror of this embodiment, a connection portion is formed between the two deflection surfaces that are closest to each other, and the connection portion is provided with a first connection surface that connects to one of the deflection surfaces, and a second connection surface that connects to the other deflection surface and the first connection surface. Furthermore, the generatrix of the first connecting surface other than the boundary line formed with the one deflection surface, and the generatrix of the second connecting surface other than the boundary line formed with the other deflection surface are non-parallel, i.e., inclined, to the rotation axis 50 of the deflector 65.

[0116] This reduces the mold release resistance when molding the deflector 65 with a metal mold, thereby improving the molding transferability. Moreover, in the deflector 65, the width of each deflecting surface in the main scanning cross section does not vary depending on the position in the sub-scanning direction.

[0117] Therefore, when the deflector 65 is mounted on an OFS type optical scanning device 100, even if the height in the sub-scanning direction of the light beam incident on the deflection surface shifts due to tolerances, etc., the fluctuation in the light beam width of the light beam deflected toward the scanned surface 7 can be suppressed. As a result, fluctuations in the light amount and diameter of the spot on the scanned surface 7, that is, deterioration in the optical performance of the optical scanning device 100, can be suppressed.

[0118] Although the preferred embodiments have been described above, the present invention is not limited to these embodiments, and various modifications and variations are possible within the scope of the present invention.

[0119] [Image forming device] FIG. 10 shows a sub-scanning sectional view of a main part of an image forming apparatus 104 provided with an optical scanning device 100 including a deflector using a polygon mirror according to any one of the first to seventh embodiments.

[0120] The image forming apparatus 104 is, for example, an electrophotographic printer, and receives code data Dc output from an external device 117 such as a personal computer. The input code data Dc is then converted by the printer controller 111 in the image forming apparatus 104 into image data (dot data) Di.

[0121] Next, the converted image data Di is input to the optical scanning device 100, and the optical scanning device 100 emits a light beam (light flux) 103 modulated in accordance with the input image data Di. Then, the photosensitive surface of the photosensitive drum 101 is scanned in the main scanning direction by the emitted light beam 103.

[0122] A photosensitive drum 101 serving as an electrostatic latent image carrier (photosensitive member) is rotated by a motor 115 . As the photosensitive surface of the photosensitive drum 101 rotates, it moves in a sub-scanning direction perpendicular to the main scanning direction relative to the light beam 103 .

[0123] A charging roller 102 for uniformly charging the surface of the photosensitive drum 101 is provided above the photosensitive drum 101 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 the optical scanning device 100 .

[0124] 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 thus formed electrostatic latent image is developed into a toner image by a developing unit 107 disposed so as to come into contact with the photosensitive drum 101 further downstream in the cross section of the rotation of the photosensitive drum 101 than the irradiation position of the light beam 103 .

[0125] Next, the toner image developed by the developing unit 107 is transferred onto a sheet of paper 112 serving as a transfer material by a transfer roller (transfer unit) 108 disposed below the photosensitive drum 101 so as to face the photosensitive drum 101 . Paper 112 is stored in a paper cassette 109 in front of the photosensitive drum 101 (on the right side in FIG. 10), but it can also be fed manually.

[0126] 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. Then, the paper 112 onto which the unfixed toner image has been transferred as described above is further transported to a fixing device behind the photosensitive drum 101 (on the left side in FIG. 10).

[0127] The fixing unit is composed of a fixing roller 113 having an internal fixing heater (not shown), and a pressure roller 114 arranged so as to be in pressure contact with the fixing roller 113 . Then, the paper 112 conveyed from the transfer roller 108 is heated while being pressed at 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, and the paper 112 on which the toner has been fixed is discharged to the outside of the image forming apparatus 104 .

[0128] Although not shown in FIG. 10, the printer controller 111 not only converts the data described above, but also controls each component within the image forming device 104, including the motor 115, and the polygon motor within the optical scanning device 100. Furthermore, although the image forming device 104 is a type of image forming device that prints in monotone, the optical scanning device 100 equipped with a deflector using a polygonal mirror according to this embodiment can also be used as a color image forming device that scans and draws on multiple photosensitive drums with multiple light beams.

[0129] The disclosure of this embodiment includes the following configuration. (Configuration 1) A polygon mirror having a plurality of deflection surfaces and first and second connecting surfaces, the plurality of deflection surfaces including first and second deflection surfaces that are closest to each other among the plurality of deflection surfaces, each of the first and second deflection surfaces having a linear shape in a first cross section perpendicular to the rotation axis of the polygon mirror, the first connecting surface being a part of a rotation surface having a first axis that is closest to the first deflection surface among the plurality of deflection surfaces as its rotation axis, and the second connecting surface being a part of a rotation surface having a second axis that is closest to the second deflection surface among the plurality of deflection surfaces as its rotation axis, and a first ridge line formed by the end of the first deflection surface on the second deflection surface side and the first connecting surface, and a second ridge line formed by the end of the second deflection surface on the first deflection surface side and the second connecting surface are parallel to the rotation axis of the polygon mirror. (Configuration 2) A polygonal mirror according to configuration 1, characterized in that the first and second connecting surfaces are part of a cylindrical surface or part of a frustum of a cone. (Configuration 3) A polygonal mirror according to configuration 1 or 2, characterized in that it is provided with a third connecting surface which is part of the rotation surface, and a third ridge is formed by the end of the first connecting surface on the side of the second deflection surface and the third connecting surface. (Configuration 4) A polygonal mirror according to configuration 3, characterized in that a fourth ridgeline is formed by the end of the third connecting surface on the side of the second deflection surface and the end of the second connecting surface on the side of the first deflection surface. (Configuration 5) A polygonal mirror according to configuration 3 or 4, characterized in that the third connecting surface is part of a cylindrical surface, part of a truncated cone surface or part of a plane, and the rotation axis of the third connecting surface is non-parallel to the rotation axis of the polygonal mirror. (Configuration 6) A polygon mirror described in any one of configurations 3 to 5, characterized in that the condition Sc-2So≧0 is satisfied, where θ is the angle between the first and second deflection surfaces when projected onto a first cross section, So is the area of ​​the first and second connecting surfaces when projected onto a second cross section that forms an angle θ / 2 with respect to the first deflection surface and is parallel to the rotation axis of the polygon mirror, and Sc is the area of ​​the third connecting surface when projected onto the second cross section. (Configuration 7) The polygon mirror according to any one of configurations 3 to 6, wherein the value of the radius of curvature of the third connecting surface is equal to or greater than the values ​​of the radius of curvature of the first and second connecting surfaces. (Configuration 8) When projected onto the first cross-section, the angle between the first and second deflection surfaces is θ. When projected onto a second cross-section that forms an angle of θ / 2 with the first deflection surface and is parallel to the rotation axis of the polyhedron mirror, the area of the first and second connection surfaces is So. When projected onto the second cross-section, the area of the third connection surface is Sc. When the areas of the first and second deflection surfaces are Sr, the polyhedron mirror according to any one of Configurations 3 to 7, characterized in that it satisfies the condition 0.5(Sc + 2So) < Sr < 7(Sc + 2So). (Configuration 9) The polyhedron mirror according to Configuration 3, comprising a fourth connection surface that is part of the rotation surface, wherein a fourth ridge line is formed by the end of the second connection surface on the side of the first deflection surface and the fourth connection surface, and a fifth ridge line is formed by the end of the third connection surface on the side of the second deflection surface and the end of the fourth connection surface on the side of the first deflection surface. (Configuration 10) The polyhedron mirror according to Configuration 9, wherein the third and fourth connection surfaces are part of a cylindrical surface or part of a conical frustum surface. (Configuration 11) The polyhedron mirror according to Configuration 9 or 10, wherein at least one of the rotation axes of the third and fourth connection surfaces is non-parallel to the rotation axis of the polyhedron mirror. (Configuration 12) The polyhedron mirror according to Configuration 1 or 2, wherein a sixth ridge line is formed by the end of the first connection surface on the side of the second deflection surface and the end of the second connection surface on the side of the first deflection surface. (Configuration 13) The polyhedron mirror according to any one of Configurations 1 to 12, wherein the first and second ridge lines coincide with a predetermined generatrix of the first and second connection surfaces. (Configuration 14) A deflection device comprising the polyhedron mirror according to any one of Configurations 1 to 13 and a drive unit for rotating the polyhedron mirror around the rotation axis of the polyhedron mirror. (Configuration 15) An optical scanning device comprising the deflection device according to Configuration 14 for deflecting a light beam from a light source to scan a surface to be scanned in a main scanning direction, and an imaging optical system for condensing the light beam deflected by the deflection device onto the surface to be scanned. (Configuration 16) The optical scanning device according to Configuration 15, wherein in a main scanning cross-section including the optical axis of the imaging optical system, the width of the light beam at the deflection surface of the deflection device is larger than the width of the deflection surface. (Structure 17) An optical scanning device according to structure 15 or 16, comprising an incident optical system which focuses a light beam from a light source in a sub-scanning cross section and guides the light to a deflection device, wherein the optical axes of the incident optical system and the imaging optical system are parallel to each other when projected onto the main-scanning cross section. (Configuration 18) In the optical scanning device according to configuration 17, the incident optical system causes a light beam to be obliquely incident on the deflection device in the sub-scanning cross section. (Configuration 19) An image forming apparatus comprising: an optical scanning device according to any one of configurations 15 to 18; a developing unit which develops an electrostatic latent image formed on a surface to be scanned by the optical scanning device into a toner image; a transfer unit which transfers the developed toner image to a transfer material; and a fixing unit which fixes the transferred toner image to the transfer material. (Configuration 20) An image forming apparatus comprising: an optical scanning device according to any one of configurations 15 to 18; and a printer controller that converts a signal output from an external device into image data and inputs the image data to the optical scanning device. [Explanation of symbols]

[0130] 5 Deflector (polygon mirror) 50 Rotational Axis 531 Deflection surface (first deflection surface) 532 Deflection surface (second deflection surface) 541 Connection surface (first connection surface) 541a Boundary line (first ridge) 542 Connection surface (second connection surface) 542a Boundary line (second ridge) 551 Rotation axis (first axis) 552 Rotation axis (second axis)

Claims

1. A polygonal mirror including a plurality of deflection surfaces and first and second coupling surfaces, the plurality of deflection surfaces include first and second deflection surfaces that are closest to each other among the plurality of deflection surfaces, each of the first and second deflection surfaces has a linear shape in a first cross section perpendicular to a rotation axis of the polygon mirror; the first coupling surface is a part of a surface of rotation having a first axis as a rotation axis, the first axis being the closest to the first deflection surface among the plurality of deflection surfaces; the second coupling surface is a part of a surface of rotation having a second axis, which is the closest to the second deflection surface among the plurality of deflection surfaces, as a rotation axis; A polygon mirror characterized in that a first ridge line formed by the end of the first deflection surface on the side of the second deflection surface and the first connecting surface, and a second ridge line formed by the end of the second deflection surface on the side of the first deflection surface and the second connecting surface are parallel to a rotation axis of the polygon mirror.

2. 2. The polygon mirror according to claim 1, wherein the first and second connecting surfaces are parts of a cylindrical surface or a frustum of a cone.

3. a third coupling surface that is a portion of the surface of revolution; 2. The polygon mirror according to claim 1, wherein a third ridgeline is formed by an end of said first connecting surface on the side of said second deflection surface and said third connecting surface.

4. 4. The polygon mirror according to claim 3, wherein a fourth ridgeline is formed by an end of the third connecting surface on the side of the second deflection surface and an end of the second connecting surface on the side of the first deflection surface.

5. The third connecting surface is a part of a cylindrical surface, a part of a truncated cone surface, or a part of a plane, 4. The polygon mirror according to claim 3, wherein the axis of rotation of the third coupling surface is non-parallel to the axis of rotation of the polygon mirror.

6. When an angle between the first and second deflection surfaces when projected onto the first cross section is θ, an area of ​​the first and second connection surfaces when projected onto a second cross section that forms an angle θ / 2 with respect to the first deflection surface and is parallel to the rotation axis of the polygon mirror is So, and an area of ​​the third connection surface when projected onto the second cross section is Sc, Sc-2So≧0 4. The polygon mirror according to claim 3, wherein the following condition is satisfied:

7. 4. The polygon mirror according to claim 3, wherein the value of the radius of curvature of the third connecting surface is equal to or greater than the values ​​of the radius of curvature of the first and second connecting surfaces.

8. When an angle between the first and second deflection surfaces when projected onto the first cross section is θ, an area of ​​the first and second connection surfaces when projected onto a second cross section that forms an angle θ / 2 with respect to the first deflection surface and is parallel to the rotation axis of the polygon mirror is So, an area of ​​the third connection surface when projected onto the second cross section is Sc, and an area of ​​the first and second deflection surfaces is Sr, 0.5(Sc+2So)<Sr<7(Sc+2So) 4. The polygon mirror according to claim 3, wherein the following condition is satisfied:

9. a fourth coupling surface that is a portion of the surface of revolution; a fourth ridgeline is formed by an end of the second connecting surface on the side of the first deflection surface and the fourth connecting surface, 4. The polygon mirror according to claim 3, wherein a fifth ridgeline is formed by an end of the third connecting surface on the side of the second deflection surface and an end of the fourth connecting surface on the side of the first deflection surface.

10. 10. The polygon mirror according to claim 9, wherein the third and fourth connecting surfaces are parts of a cylindrical surface or a truncated cone surface.

11. 10. The polygon mirror according to claim 9, wherein the rotation axis of at least one of the third and fourth coupling surfaces is non-parallel to the rotation axis of the polygon mirror.

12. 2. The polygon mirror according to claim 1, wherein a sixth ridgeline is formed by an end of the first connecting surface on the side of the second deflection surface and an end of the second connecting surface on the side of the first deflection surface.

13. 2. The polygon mirror according to claim 1, wherein the first and second ridgelines coincide with predetermined generatrices of the first and second connecting surfaces.

14. A polygonal mirror according to any one of claims 1 to 13; and a drive unit for rotating the polygon mirror about an axis of rotation of the polygon mirror.

15. a deflection device according to claim 14, which deflects a light beam from a light source to scan a surface to be scanned in a main scanning direction; an imaging optical system that focuses the light beam deflected by the deflection device on the surface to be scanned.

16. 16. The optical scanning device according to claim 15, wherein in a main scanning cross section including an optical axis of the imaging optical system, a width of the light beam on the deflecting surface of the deflecting device is larger than a width of the deflecting surface.

17. an incidence optical system that condenses the light beam from the light source in a sub-scanning cross section and guides the light beam to the deflection device; 16. The optical scanning device according to claim 15, wherein the optical axes of the incident optical system and the imaging optical system are parallel to each other when projected onto a main scanning cross section.

18. 18. The optical scanning device according to claim 17, wherein the incident optical system makes the light beam obliquely incident on the deflection device in a sub-scanning cross section.

19. 16. An image forming apparatus comprising: an optical scanning device according to claim 15; a developing unit which develops an electrostatic latent image formed on the scanned surface by the optical scanning device into a toner image; a transfer unit which transfers the developed toner image onto a transfer material; and a fixing unit which fixes the transferred toner image onto the transfer material.

20. 16. An image forming apparatus comprising: the optical scanning device according to claim 15; and a printer controller for converting a signal output from an external device into image data and inputting the image data to the optical scanning device.

Images