Rotatable polygon mirror, optical deflecting device, scanning optical device, and image forming apparatus

A rotatable polygon mirror including a plurality of reflecting surfaces includes first and second surfaces connecting to the reflecting surfaces provided on opposite ends, first and second protrusion portions with an annular shape, provided on the first and second surfaces and protruding inversely to each other in the rotational axis direction, about a rotational axis of the rotatable polygon mirror. A height of a top surface portion of the first protrusion portion from the first surface is higher than that of a top surface portion of the second protrusion portion from the second surface with respect to the rotational axis direction. In a case that the rotatable polygon mirrors are stacked in the rotational axis direction, a wall of an inner peripheral side of the first protrusion portion and a wall of an outer peripheral side of the second protrusion portion are engaged with each other.

FIELD OF THE INVENTION AND RELATED ART

The present invention relates to a rotatable polygon mirror, an optical deflecting device which is provided with the rotatable polygon mirror, a scanning optical device which is provided with the optical deflecting device, and an image forming apparatus which is provided with the scanning optical device.

An optical deflecting device which deflects laser light emitted from a light source according to an image signal is mounted on an image forming apparatus of an electrophotographic method such as a laser printer. A rotatable polygon mirror which reflects the laser light is mounted on the optical deflecting device.

For example, in Japanese Laid-Open Patent Application (JP-A) 2010-191470, a film forming process of a rotatable polygon mirror is proposed. As material for the rotatable polygon mirror, for example, aluminum, glass, etc. are used. Then, during the film forming process of the rotatable polygon mirror, a reflectivity is increased, an angle dependence is eliminated, and an oxidation is prevented by applying an evaporated film or an anodic oxide film to a reflecting surface of the rotatable polygon mirror.FIG.8is a view illustrating a process of applying coating liquid to the reflecting surface of the rotatable polygon mirror which is described in JP-A 2010-191470.FIG.8will be described clockwise from an upper left one. First, in order to form a reflecting film on the rotatable polygon mirror, the rotatable polygon mirror is set above the coating liquid so that it does not come into contact with the coating liquid. At this time, as shown inFIG.8, the rotatable polygon mirror is set so that a distance between a rotational axis of the rotatable polygon mirror and a surface of the coating liquid is greater than a minimum distance between the rotational axis of the rotatable polygon mirror and the reflecting surface of the rotatable polygon mirror. Then, next, the rotatable polygon mirror is rotated and the coating liquid is applied to corner portions of the rotatable polygon mirror (an area which is indicated as10inFIG.8). By rotating the rotatable polygon mirror, the coating liquid is wetted and spread over the reflecting surface, and eventually the coating liquid is applied to an entire reflecting surface4a. In this way, the coating liquid is possible to be completely applied and spread over the reflecting surface, without completely immersing the reflecting surface of the rotatable polygon mirror in the coating liquid.

Further, for example, in JP-A 2017-126008, a rotatable polygon mirror which is formed from resin is proposed.FIG.9is a view illustrating a constitution of the rotatable polygon mirror which is proposed in JP-A 2017-126008. InFIG.9, the rotatable polygon mirror45A is a rotatable polygon mirror which includes four mirror surfaces from M1through M4which are arranged around a predetermined rotational axis SL. A base material100is formed from, for example, resin, and includes four side surfaces110which correspond to the mirror surfaces from M1through M4. In the rotatable polygon mirror45A, a reflecting film is formed on each side surface110, so the surface of the reflecting film constitutes the mirror surfaces from M1through M4. In this way, it is contrived that the rotatable polygon mirror is formed from resin material instead of metal.

In order to suppress dependence of a reflectivity on an incidence angle of light entering the reflecting surface, for example, a monolayer film of a material with a desired refractive index is formed on the reflecting surface of the rotatable polygon mirror. The monolayer film is formed by a vacuum film forming method such as vapor deposition and sputtering, or by a wet film forming method using liquid solution. The patent document described above discloses a method of forming a monolayer film while a plurality of the rotatable polygon mirrors, which are objects of film forming, are stacked and multiple mounted through an axis.

In such a manufacturing process, when stacking a plurality of the rotatable polygon mirror mirrors, in a case that a clearance, a rotational phase etc. between the reflecting surfaces of two adjacent rotatable polygon mirrors in a direction of the axis, are not regulated, uneven film thickness may partially occur on an inner diameter of a rotational shaft of the rotatable polygon mirror or a pedestal portion of the rotatable polygon mirror which is mounted on a rotor portion of a motor. For example, in a case that uneven film thickness occurs partially in the pedestal portion of the rotatable polygon mirror, an assembly accuracy may be damaged when the rotatable polygon mirror is mounted on the optical deflecting device and an irregular pitch of a scanning line may occur due to a plane tilt of the reflecting surface. Further, in a case that uneven film thickness is partially occurred in the inner diameter of the rotational shaft of the rotatable polygon mirror, an image quality may be damaged, since an optical performance is deteriorated due to surface deformation of the reflecting surface by an error in engagement between the rotational shaft of the rotatable polygon mirror and a rotational shaft of the optical deflecting device, etc. Therefore, it is necessary to prevent from forming film on various surfaces of the rotatable polygon mirror, which affects the assembly accuracy of the rotatable polygon mirror.

In response to the above issue, an object of the present invention is to provide a rotatable polygon mirror which prevents from forming film on surfaces that affect assembly accuracy of the rotatable polygon mirror during a film forming process of the rotatable polygon mirror.

SUMMARY OF THE INVENTION

In order to solve the problem described above, the present invention is provided with a following constitution.

According to an aspect of the present invention, there is provided a rotatable polygon mirror including a plurality of reflecting surfaces comprising, a first surface connecting to the plurality of reflecting surfaces, a second surface connecting to the plurality of reflecting surfaces and provided on a side opposite to the first surface with respect to a rotational axis direction, a first protrusion portion with an annular shape, provided on the first surface and protruding in the rotational axis direction, about a rotational axis of the rotatable polygon mirror and a second protrusion portion with an annular shape, provided on the second surface and protruding in an opposite direction to a protrusion direction of the first protrusion portion, about the rotational axis of the rotatable polygon mirror, wherein the second protrusion portion is a part to be set on a rotor of a motor, wherein a height of a top surface portion of the first protrusion portion from the first surface is higher than a height of a top surface portion of the second protrusion portion from the second surface with respect to the rotational axis direction, and wherein, in a case that a plurality of the rotatable polygon mirrors are stacked in the rotational axis direction, a wall of an inner peripheral side of the first protrusion portion and a wall of an outer peripheral side of the second protrusion portion are engaged with each other.

DESCRIPTION OF THE EMBODIMENTS

In the following, the embodiments of the present invention will be specifically described with reference to the figures.

First Embodiment

[Constitution of the Image Forming Apparatus]

FIG.1is a schematic sectional view showing a constitution of an image forming apparatus110according to the first embodiment. InFIG.1, a process cartridge102which is an image forming portion includes a photosensitive drum103on which an electrostatic latent image is formed, and a charging roller111which charges the photosensitive drum103to a predetermined electrical potential. Furthermore, the process cartridge102includes a developing roller112which adheres toner to the electrostatic latent image which is formed on the photosensitive drum103and forms a toner image. At a position opposing the photosensitive drum103which is an image bearing member, a transfer roller107, which transfers a toner image formed on the photosensitive drum103to a recording material P which is a recording medium which is fed, is arranged. Further, the scanning optical device101emits laser light L onto the photosensitive drum103according to an image data and forms an electrostatic latent image.

When the image forming apparatus110starts an image forming operation, in the process cartridge102, the photosensitive drum103is rotationally driven, and the charging roller111charges a surface of the photosensitive drum103to a uniform electrical potential. The scanning optical device101emits laser light L to the surface of the photosensitive drum103which is charged to a uniform electrical potential according to image data and form an electrostatic latent image. And toner is adhered to the electrostatic latent image which is formed on the photosensitive drum103(on the image bearing member) by the developing roller112and a toner image is formed. On the other hand, from a sheet feeding portion104on which the recording material P is stacked, the feeding roller105feeds the recording material P one by one into a feeding passage. The recording material P which is fed to the feeding passage is further fed to the transfer roller107by a feeding roller106. The toner image which is formed on the photosensitive drum103is transferred by the transfer roller107to the recording material P which is fed to the transfer roller107.

The recording material P to which the toner image is transferred is fed to a fixing device108, and the toner image on the recording material P is heated and pressurized by the fixing device108and is fixed on the recording material P. The recording material P on which the toner image is fixed is then discharged outside the image forming apparatus110by the discharging roller109. Incidentally, in the embodiment, the charging roller111and the developing roller112are constituted to be integrated with the photosensitive drum103in the process cartridge102, however, the charging roller111and the developing roller112may be constituted separately from the photosensitive drum103.

[Constitution of the Scanning Optical Device]

The scanning optical device101will be described by usingFIG.2.FIG.2is the perspective view illustrating the constitution of the scanning optical device101and showing a state that a cover (not shown) which closes an inside of a casing203is removed.

The laser light L which is emitted from a light source unit201is converged in a subscanning direction by a cylindrical lens202, and is limited to a predetermined beam diameter by an optical diaphragm204which is formed in a part of the casing203. The laser light L which passes through the diaphragm204is deflected by a rotatable polygon mirror3which is mounted on a motor board4of an optical deflecting device1(seeFIG.3). After that, the laser light L passes through an fθ lens205and scans over the photosensitive drum103(not shown inFIG.2) which is a scanned surface. The cylindrical lens202, the optical deflecting device1, and the fθ lens205are accommodated inside the casing203, and the light source unit201is attached to a side wall of the casing203from an outside of the casing203. Incidentally, a rotor7and a rotational shaft8will be described below.

[Constitution of the Optical Deflecting Device]

Next, the optical deflecting device1will be described by usingFIG.3. The optical deflecting device1includes the rotatable polygon mirror with the plurality of reflecting surfaces which reflect laser light, and a motor which rotates the rotatable polygon mirror, and the rotatable polygon mirror, which is rotatably driven by the motor, deflects the laser light L which is emitted from the light source unit201.

FIG.3is a sectional view of the optical deflecting device1. The optical deflecting device1includes a rotatable polygon mirror3which is formed from resin, and the rotatable polygon mirror3includes a reflecting surface33which reflects the laser light L. In addition to the rotatable polygon mirror3, the optical deflecting device1includes the motor board4which is constituted of metal plate, a bearing sleeve5which is supported by the motor board4, a stator core9awhich is fixed to the motor board4, and a stator coil9bwhich is fixed to the stator core9a. Furthermore, the optical deflecting device1includes a rotor7which is provided with a rotor magnet6, the rotational shaft8which is integrated with the rotor7, and a supporting portion2which supports the rotatable polygon mirror3.

In the optical deflecting device1, when the stator core9ais excited by a driving current which is supplied from a driving circuit which is provided with the motor board4, the rotor7which mounts the rotatable polygon mirror3rotates at high speed. And the laser light L which is emitted from the light source unit201is deflected by the reflecting surface33of the rotatable polygon mirror3which rotates at high speed.

[Constitution of the Rotatable Polygon Mirror]

Next, the rotatable polygon mirror3will be specifically described by usingFIG.4. Part (a) ofFIG.4is a perspective view of the rotatable polygon mirror3which is described inFIG.3when it is viewed from diagonally above, and part (b) ofFIG.4is a perspective view of the rotatable polygon mirror3when it is viewed from diagonally below. Further, part (c) ofFIG.4is a sectional view of the rotatable polygon mirrors3when they are cut along line A-A in a state that two of the rotatable polygon mirrors are stacked as shown in part (a) ofFIG.4.

The rotatable polygon mirror3is formed from a resin material such as cyclo-olefin resin, polycarbonate resin, or acrylic resin. The rotatable polygon mirror3is in a form of a prism shape with a square bottom. The rotatable polygon mirror3includes the reflecting surface33which forms four side surfaces of the square, a first surface31which is a top surface which is perpendicular to the four reflecting surfaces33, and a second surface32which is perpendicular to the four reflecting surface33, is provided in an opposite side of the first surface31with respect to a direction of the rotational axis and is substantially parallel to the first surface31. Furthermore, the rotatable polygon mirror3includes a center hole34which engages with the rotational shaft8of the rotor7shown inFIG.3and is a rotational center.

Further, the first surface31of the rotatable polygon mirror3is provided with a concentric (coaxial) annular shaped protrusion portion35(first protrusion portion) which is centered on the rotational shaft8in a direction of the rotational shaft8which is engaged with the rotatable polygon mirror3. In a top surface portion of the protrusion portion35, a flat surface35S of a same height is formed. Similarly, in the second surface32of the rotatable polygon mirror3, a concentric (coaxial) annular pedestal portion36(second protrusion portion) which is protruded in an opposite direction to a protruding direction of the protrusion portion35in the direction of the rotational axis and which is centered on the rotational shaft8is provided. The pedestal portion36is an accurate surface (machined surface) which is abutted with the supporting portion2inFIG.3described above, and in the top surface portion of the pedestal portion36, a flat surface36S of a same height is formed.

As shown in part (c) ofFIG.4, in a state that two of the rotatable polygon mirrors3are stacked on top of one another, the pedestal portion36of the rotatable polygon mirror3in an upper side enters an inside of the protrusion portion35of the rotatable polygon mirror3in a lower side in a radial direction, and they have a dimensional relationship so that an outer peripheral portion of the pedestal portion36(outer peripheral side wall36outer in the radial direction) is engaged with the inner peripheral portion of the protrusion portion35(inner peripheral side wall35inner in the radial direction) over an entire peripheral direction (that is, the wall36outer and the wall35inner are in contact over the entire peripheral direction). When the protrusion portion35of the rotatable polygon mirror3is engaged with the pedestal portion36of the rotatable polygon mirror3, a gap G is formed between two of the rotatable polygon mirrors3. Further, in the rotatable polygon mirror3, a height36hof the top surface portion36S of the pedestal portion36from the second surface32is constituted to be lower than a height35h(=G) of the top surface portion35S of the protrusion portion35from the first surface31(36h<35h). Thus, as shown in part (c) ofFIG.4, in a state that two of the rotatable polygon mirrors3are stacked on top of one another, the top surface portion35S of the protrusion portion35of the rotatable polygon mirror3in the lower side is abutted with the second surface32of the rotatable polygon mirror3in the upper side. On the other hand, the top surface portion36S of the pedestal portion36of the rotatable polygon mirror3in the upper side is not abutted with the first surface31of the rotatable polygon mirror3in the lower side, and it is in a state that a gap (clearance CL) is provided.

A constitution of the film forming device for forming multilayer film of the rotatable polygon mirror3in the embodiment will be described by using part (a) and part (b) ofFIG.5. Part (a) ofFIG.5is a schematic view showing a constitution of a vacuum evaporating device as one of examples of the film forming device in the embodiment. A vacuum evaporating device500is provided with a film forming chamber501whose inside is maintained in a vacuum state and an exhaust system502which is constituted of a vacuum pump, etc. which sets the film forming chamber501to a vacuum state. In a film forming chamber501, a revolution part504which performs a revolution driving around a revolving axis503is arranged, and the revolution part504is driven by a driving mechanism505via a gear506and performs the revolution driving. A single rotating shaft part507is passed through the center holes34respectively in the plurality of rotatable polygon mirrors3which are stacked on top of one another. While the plurality of rotatable polygon mirrors3are stacked, the rotating shaft part507is mounted at an angle of Sθ to a horizontal direction of the revolution part504, and the rotating shaft part507is rotationally driven by an unshown mechanism. While the rotatable polygon mirror3is rotationally and revolvingly driven by the revolution driving of the revolution part504and the rotation driving around the rotating shaft part507, a reflecting film with desired optical characteristics is formed on the surface of the reflecting surface33.

Part (b) ofFIG.5is a sectional view showing a close-up of the plurality of rotatable polygon mirrors3while the plurality of rotatable polygon mirrors3are stacked on the rotating shaft part507. The plurality of rotatable polygon mirrors3are stacked in an axial direction of the rotating shaft part507which is a rotational axis, so that the first surface31faces upward. At this time, as shown in part (c) ofFIG.4, the inner peripheral portion (inner peripheral wall35inner) of the protrusion portion35of the rotatable polygon mirror3is engaged with the outer peripheral portion (outer peripheral wall36outer) of the pedestal portion36. Further, an inner surface of the center hole34is to be engaged with the rotating shaft8of the rotor, so the inner surface of the center hole34should not be damaged during the film forming process. Therefore, the inner surface of the center hole34is constituted to be loosely engaged with the part507(not to come in contact with one another). Thus, while the plurality of rotatable polygon mirrors3are skewered into the part507, a length R33from a center507cof the part507to the reflecting surface33may differ for each rotatable polygon mirror. In a case that the length R33varies, a film forming state may differ among the plurality of rotatable polygon mirrors. However, as described above, the inner peripheral portion of the protrusion portion35of the rotatable polygon mirror3(inner peripheral wall35inner) is engaged with the outer peripheral portion of the pedestal portion36(outer peripheral wall36outer). As a result, the length R33is possible to be a same length among the plurality of rotatable polygon mirrors3. Incidentally, while the plurality of rotatable polygon mirrors3are skewered into the part507, both ends of the part507in the axial direction are sealed so that an evaporation material does not enter between the plurality of rotatable polygon mirrors3through the center hole34. Further, the top surface35S of the rotatable polygon mirror3in the lower side is in contact with the surface32of the rotatable polygon mirror3in the upper side. Thus, an inner diameter of the center hole34of the rotatable polygon mirror3and the pedestal portion36of the rotatable polygon mirror3become a sealed structure (enclosed state). Incidentally, while the rotatable polygon mirrors3are stacked on the rotating shaft part507, an uppermost one and a lowermost one of the rotatable polygon mirrors3in the axial direction of the rotating shaft part507are regulated in position by a regulating member (not shown).

By the constitution of the rotatable polygon mirror3described above, the center hole34of the rotatable polygon mirror3and the top surface portion36S of the pedestal portion36of the rotatable polygon mirror3, which are joint surfaces with the rotor7when assembling the optical deflecting device1, do not scrape each other during an evaporation process by the vacuum evaporating device500. As a result, it is possible to prevent a reduction in accuracy of the rotatable polygon mirror3due to scratching and scraping. Further, since the pedestal portion36is inside the protrusion portion35when the plurality of rotatable polygon mirrors3are stacked, the evaporation material is not adhered to the top surface portion36S which is a mounting surface in contact with the rotor7of the supporting portion2. Therefore, while mechanical accuracy of the top surface portion36S of the pedestal portion36is assured, it is possible to accurately assemble it to the optical deflecting device1. As a result, a reduction in optical performance due to the plane tilt (plane tilt of reflecting surface33), surface deformation (deformation of the reflecting surface33), etc. caused by the rotatable polygon mirror3is prevented, and it is possible to improve reliability of the scanning optical device101.

Further, the multilayer film, which is the reflecting surface33, is formed across each of the first surface31and the second surface32during the evaporation process by the vacuum evaporating device500. As shown in part (b) ofFIG.5, a gap G is formed so that ridge portions of the reflecting surfaces33of the rotatable polygon mirrors3adjacent to each other in a vertical direction do not come into contact with each other. As a result, the reflecting surfaces33of the rotatable polygon mirrors3adjacent to each other in the vertical direction are possible to securely ensure an appropriate clearance (gap) for stably forming film. And since an intermediary part such as a spacer in order to provide a gap between the adjacent rotatable polygon mirrors3in the vertical direction is not used, it is possible to minimize an equipment and to make a forming film method of the rotatable polygon mirrors3inexpensive and highly productive.

Furthermore, when the plurality of rotatable polygon mirrors3are stacked on the rotating shaft part507, the rotatable polygon mirror3is subjected to shear stress due to their weight and positional regulation, and, in particular, surface deformation of the rotatable polygon mirrors3is concerned. However, since a structure of the rotatable polygon mirror3is designed to hold an opposing portion of the protrusion portion35of the rotatable polygon mirror3, which is subject to shear stress, by the adjacent rotatable polygon mirror3, it is possible to suppress the surface deformation of the reflecting surface33. In this way, it is possible to assure the mechanical accuracy of the reflecting surface33during the film formation and to improve reliability.

Incidentally, shapes of the protrusion portion35and the pedestal portion36in the embodiment may be protrude in the direction of the rotational axis of the rotatable polygon mirror3more than the reflecting surface33, and may be a dimensional relationship in which the inner peripheral portion of the protrusion portion35is engaged with at least a part of the outer peripheral portion of the pedestal portion36. For example, in a case that there is a small gap or rattling, as long as the shapes are such that the pedestal portion36of the rotatable polygon mirror3enters inside the protrusion portion35of the rotatable polygon mirror3, the shapes of the protrusion portion35and the pedestal portion36may not be same as ones shown inFIG.4, parts (a) to (c).

As described above, according to the embodiment, it is possible to prevent the accurate surface which affects the assembly accuracy of the rotatable polygon mirror from forming film during the film forming process of the rotatable polygon mirror.

The shapes of the protrusion portion and the pedestal portion of the rotatable polygon mirror in the embodiment 1 are annular shapes which are concentric circles centered on the rotational axis of the rotatable polygon mirror. In an embodiment 2, the rotatable polygon mirror with different shapes of the protrusion portion and the pedestal portion from ones in the embodiment 1.

[Constitution of the Rotatable Polygon Mirror]

FIG.6, parts (a) to (c) is a schematic view illustrating of a shape of a rotatable polygon mirror30in the embodiment. Part (a) ofFIG.6is a perspective view of the rotatable polygon mirror30when it is viewed from diagonally above, and part (b) ofFIG.6is a perspective view of the rotatable polygon mirror30when it is viewed from diagonally below. Further, part (c) ofFIG.6is a sectional view of the rotatable polygon mirrors30when they are cut along line B-B in a state that two of the rotatable polygon mirrors30are stacked as shown in part (a) ofFIG.6.

The rotatable polygon mirror30in the embodiment is formed from a resin material, similar to the rotatable polygon mirror3in the embodiment 1. Further, the rotatable polygon mirror30is in a form of a prism shape with a square bottom, similar to the rotatable polygon mirror3in the embodiment 1. And the rotatable polygon mirror30includes the reflecting surface33which forms four side surfaces of the square, a first surface31which is a top surface which is perpendicular to the four reflecting surfaces33, and the second surface32which is a bottom surface perpendicular to the four reflecting surface33and is opposed to and substantially parallel to the first surface. Furthermore, the rotatable polygon mirror30includes the center hole34which engages with the rotational shaft8of the rotor7of the optical deflecting device1and is a rotational center.

Further, the first surface31of the rotatable polygon mirror30is provided with the concentric (coaxial) annular shaped protrusion portion35which is centered on the rotational shaft8in the direction of the rotational shaft8which is engaged with the rotatable polygon mirror30. And four recessed portions35′, which are formed by cutting the protrusion portions35, are provided at substantially equal intervals for a purpose of gate releasing when the rotatable polygon mirror30is formed, for example. Therefore, the top surface portion of the protrusion portion35is not a constant height like in the embodiment 1, but is a flat surface with steps at the recessed portions35′. Further, in the second surface32of the rotatable polygon mirror30, a concentric (coaxial) annular pedestal portion36which is centered on the rotational shaft8is provided in the opposite direction to the protruding direction of the protrusion portion35with respect to the rotational shaft8with which the rotatable polygon mirror30is engaged. And in order to assemble the rotatable polygon mirror30stably to the supporting portion2in a side of the rotor7, the accurate surfaces, which are abutted with the supporting portion2of the rotor7, are limited to only three portions of the convex portions36′ which are protruded from the top surface portion of the pedestal portion36. And when the plurality of rotatable polygon mirrors30in the embodiment are stacked around the center hole34through which the rotational axis passes, the rotatable polygon mirror30is constituted that the inner peripheral wall of the inner peripheral portion of the protrusion portion35is engaged with at least a part of the outer peripheral wall of the outer peripheral portion of the pedestal portion36.

Part (c) ofFIG.6is a sectional view of the rotatable polygon mirrors30when they are cut along line B-B in a state that two of the rotatable polygon mirrors30, which are shown in part (a) ofFIG.6, are stacked on top of each other, and is also a schematic view showing a close-up of the rotatable polygon mirrors30in a state of a section when the rotatable polygon mirrors30are stacked on the rotating shaft part507of the vacuum evaporating device500in the embodiment 1. The rotatable polygon mirrors30are stacked in an axial direction of the rotating shaft part507so that the first surface31faces upward. At this time, the gap G is formed. Incidentally, in a case that the rotatable polygon mirrors30are stacked on the rotating shaft part507, an uppermost one and a lowermost one of the rotatable polygon mirrors30in the axial direction of the rotating shaft part507are regulated in position by the regulating member (not shown).

The inner diameter of the center hole34of the rotatable polygon mirror30and the pedestal portion36of the rotatable polygon mirror30become a sealed structure (enclosed state), when the inner peripheral wall of the inner peripheral portion of the protrusion portion35of the rotatable polygon mirror30is engaged with at least a part of the outer peripheral wall of the outer peripheral portion of the pedestal portion36of the rotatable polygon mirror30. In this way, the inner diameter of the center hole34of the rotatable polygon mirror30and the convex portion36′ of the pedestal portion36of the rotatable polygon mirror30are sealed. As a result, it is possible to prevent reduction in surface accuracy of the convex portion36′ which is a mounting surface.

Further, by providing recessed portion shape or convex portion shape in the protrusion portion35and the pedestal portion36of the rotatable polygon mirror30, it is possible to expand degree of freedom for designing the protrusion portion35and the pedestal portion36. For example, the rotatable polygon mirror30may vibrate during rotation due to unbalance caused by an accuracy error of the reflecting surface33of the laser light or a fact that a rotational center is not perfectly arranged at an engaging portion between the center hole34and the rotational shaft. Therefore, for a purpose of preventing the vibration caused by the unbalance, it is possible to provide an adhesive portion, in which a light curing type adhesive, etc. is applied and adhered, with the protrusion portion35of the rotatable polygon mirror30in order to prevent the vibration by correcting a balance.

As described above, according to the embodiment, it is possible to prevent the accurate surface which affects the assembly accuracy of the rotatable polygon mirror from forming film during the film forming process of the rotatable polygon mirror.

The shapes of the protruding portion and the pedestal portion of the rotatable polygon mirrors in the embodiment 1 and the embodiment 2 are annular shapes which are concentric circles centered on the rotational axis of the rotatable polygon mirror. In an embodiment 3, the rotatable polygon mirror which includes the protrusion portion and the pedestal portion with different shapes from the embodiment 1 and the embodiment 2.

[Constitution of the Rotatable Polygon Mirror]

FIG.7is a schematic view illustrating a shape of the rotatable polygon mirror300in the embodiment. Part (a) ofFIG.7is a perspective view of the rotatable polygon mirror300when it is viewed from diagonally above, and part (b) ofFIG.7is a perspective view of the rotatable polygon mirror300when it is viewed from diagonally below. Further, part (c) ofFIG.7is a sectional view of the rotatable polygon mirrors300when they are cut along line C-C in a state that two of the rotatable polygon mirrors are stacked as shown in part (a) ofFIG.7.

The rotatable polygon mirror300in the embodiment is formed from a resin material, similar to the rotatable polygon mirror3in the embodiment 1 and the rotatable polygon mirror30in the embodiment 2. Further, the rotatable polygon mirror300is in a form of a prism shape with a square bottom, similar to the rotatable polygon mirror3in the embodiment 1 and the rotatable polygon mirror30in the embodiment 2. And the rotatable polygon mirror300includes the reflecting surface33which forms four side surfaces of the square, a first surface31which is a top surface which is perpendicular to the four reflecting surfaces33, and the second surface32which is a bottom surface perpendicular to the four reflecting surface33and is opposed to and substantially parallel to the first surface31. Furthermore, the rotatable polygon mirror300includes the center hole34which engages with the rotational shaft8of the rotor7of the optical deflecting device1and is the rotational center.

Further, the first surface31of the rotatable polygon mirror300is provided with an annular shaped protrusion portion350which is constituted that a D-cut portion351, a D-cut portion352, a D-cut portion353, and a D-cut portion354, which are arranged corresponding to each reflecting surface33, are connected. Similarly, the second surface32of the rotatable polygon mirror300is provided with an annular shaped pedestal portion360which is constituted that a D-cut portion361, a D-cut portion362, a D-cut portion363, and a D-cut portion364, which are arranged corresponding to each reflecting surface33, are connected. When the protrusion portion350and the pedestal portion360are divided by a line connecting a center of the central hole34which is the rotational axis of the rotatable polygon mirror300, and vertices of both end portions of each reflecting surface33, shapes of each area of the protrusion portion350and the pedestal portion360, which are divided, are identical shapes and rotationally symmetrical shapes around the rotational axis.

The D-cut portion351, the D-cut portion352, the D-cut portion353, and the D-cut portion354of the protrusion portion350which are formed on the first surface31, and the D-cut portion361, the D-cut portion362, the D-cut portion363, and the D-cut portion364of the pedestal portion360which are formed on the second surface32, correspond to each reflecting surface33. And, as shown in part (c) ofFIG.7, for each 90 degree phase of the reflecting surface33, the D-cut portion of the protrusion portion350and the D-cut portion of the pedestal portion360, which are corresponded, are determined, and the rotatable polygon mirror300is constituted that the inner wall of the D-cut portion of the protrusion portion350and the outer wall of the pedestal portion360, which are corresponded, are engaged. Further, as shown in part (c) ofFIG.7, the rotatable polygon mirror300is constituted that a height of the pedestal portion360from the second surface32is lower than a height of the protrusion portion350from the first surface31. Thus, as shown in part (c) ofFIG.7, when the rotatable polygon mirrors300are stacked, a top surface portion of the protrusion portion350of the rotatable polygon mirror300in a lower side is abutted with the second surface32of the rotatable polygon mirror300in an upper side. On the other hand, a top surface portion of the pedestal portion360of the rotatable polygon mirror300in the upper side is not abutted with the first surface31of the rotatable polygon mirror3in the lower side, and a gap (clearance) is provided. Further, the gap G is formed depending on a height in which the protrusion portion350of the rotatable polygon mirror300and the pedestal portion360of the rotatable polygon mirror300are engaged.

Part (c) ofFIG.7is a sectional view of the rotatable polygon mirrors300when they are cut along line C-C in a state that two of the rotatable polygon mirrors300, which are shown in part (a) ofFIG.7, are stacked on top of each other, and is also a schematic view showing a close-up of the rotatable polygon mirrors300in a state of a section when the rotatable polygon mirrors300are stacked on the rotating shaft part507of the vacuum evaporating device500in the embodiment 1. The rotatable polygon mirrors300are stacked in the axial direction of the rotating shaft part507so that the first surface31faces upward. Incidentally, in a case that the rotatable polygon mirrors300are stacked on the rotating shaft part507, an uppermost one and a lowermost one of the rotatable polygon mirrors300in the axial direction of the rotating shaft part507are regulated in position by the regulating member (not shown).

Due to the D-cut shapes of the protrusion portion350of the rotatable polygon mirror300and the pedestal portion360of the rotatable polygon mirror300described above, it is possible to securely align rotational phases of the reflecting surfaces33of each rotatable polygon mirror300in which film is formed during an evaporation by using the vacuum evaporating device500. As a result, it is possible to ensure high quality and stable mass production of the rotatable polygon mirrors300, since it is prevented that the reflecting surfaces33, which are overlapping each other, are hidden and variations are occurred in states of film formations on each of the reflecting surfaces33which are adjacent to each other in a vertical direction by shifting of the rotational phases of the plurality of rotatable polygon mirrors300.

As described above, the rotatable polygon mirror300in the embodiment is possible to achieve the same effects as in the embodiments described above, and in addition, it is possible to prevent the variations in the states of film formations of the reflecting surfaces33since it is possible to securely align the rotational phases of the reflecting surfaces33.

As described above, according to the embodiment, it is possible to prevent the accurate surface which affects the assembly accuracy of the rotatable polygon mirror from forming film during the film forming process of the rotatable polygon mirror.

This application claims the benefit of Japanese Patent Application No. 2021-087164 filed on May 24, 2021, which is hereby incorporated by reference herein in its entirety.