JP4890932B2 - Optical scanning apparatus and image forming apparatus - Google Patents

Description

The present invention is a copying machine having an optical scanning device and optical scanning device having a polygon-mirror, a printer, a facsimile, a complex machine provided with at least two functions of these relates to an image forming apparatus such as a plotter.

The polygon mirror is also called a rotary polygon mirror, and the polygon mirror and a motor for driving the polygon mirror are also called a polygon scanner.
When a polygon beam driven at a high speed by a motor is irradiated with a light beam such as a laser beam, the light beam is deflected by the reflection surface (mirror surface) of the polygon mirror and scanned on the imaging surface. An electrostatic latent image can be formed on the imaging surface by modulating the light beam with an image signal for each light scanning by each reflecting surface.
The polygon motor is not dependent on the wavelength of light and can handle light of a wide range of wavelengths, so it is widely used in laser printers, facsimiles, copiers, and the like.
With the advancement of technology, it is required to improve the efficiency of image formation and image reading. Even in equipment using a polygon motor, the reproducibility of the electrostatic latent image for the required image is improved, and at the same time, high image quality realized from high-speed scanning, Higher speed is desired.

At this time, the flatness of the mirror surface of the polygon mirror has a very high required accuracy, and in order to realize it, improvement proposals such as the cutting method and the mirror blank holding method have been made in the manufacturing method, but problems remain. Yes.
In particular, “sagging” in the mirror surface deformation is a big problem. The mirror surface deformation refers to minute unevenness when the mirror surface is mirror-finished.
As shown in FIG. 17 which is a mirror surface deformation image diagram, the mirror end surface at the beginning of cutting has a low rigidity because of the distance from the rotation axis, and a relief occurs in the mirror surface of the portion to be processed during cutting. Therefore, the cutting amount is smaller than the target cutting amount (region 1).
Compared with the end portion, the central portion has a shorter distance from the rotational axis and higher rigidity, and the occurrence of relief is light, so that the target cutting amount can be cut (region 2).
As the end portion is approached again, the rigidity decreases, and the relief of the mirror surface at the portion to be processed becomes larger as in the beginning of cutting, and becomes smaller than the target cutting amount (region 3).
Finally, the cutting bite comes off near the end, but since the part to be processed gradually decreases, the cutting stress is small and the deformation of the part to be processed becomes small. Therefore, the target cutting amount can be cut. However, since the cutting stress varies greatly, it may be cut beyond the target cutting amount (region 4).

Therefore, the mirror surface is concave from region 1 to region 3, but the end of the portion corresponding to region 4 has an extreme gradient. This portion of the region 4 is called “faced or faced part”.
In order to suppress this sagging, it is considered to control the cutting bite feed rate, rotation speed or cutting amount in the vicinity of the cutting bit missing, but it requires advanced equipment and management as a mass production process. Therefore, the production cost is not preferable.
On the other hand, in order to realize high-speed scanning in the polygon motor, there are a method of increasing the rotational speed of the polygon mirror and a method of increasing the number of reflection surfaces of the polygon mirror. However, when the number of reflecting surfaces of one polygon mirror is N, there is a relationship of θ = 720 ° / N between N and the light deflection angle θ, so the radius R of the inscribed circle of each reflecting surface is If the distance from the polygon mirror to the scanning surface is constant and the number of reflection surfaces of the polygon mirror is increased, the light deflection angle θ decreases and the length of light scanning by one reflection surface decreases.
Therefore, in order to make the optical scanning length a predetermined length, it is necessary to enlarge the entire scanning optical system or add optical components such as a mirror, which is not preferable.

As described above, since there is a limit to increasing the number N of reflection surfaces as means for realizing high efficiency of the optical scanning apparatus, in recent years, as means for meeting the demand for downsizing and high speed of the optical scanning apparatus. There is a tendency to increase the rotational speed of the polygon mirror.
However, with the increase in the speed of the polygon mirror, the polygon mirror is a polyhedron, so noise and windage increase. In addition, workability itself is difficult with respect to flatness.
Patent Document 1 discloses a configuration that reduces windage loss during high-speed rotation by rounding the corner formed by the reflecting surface.
Patent Document 2 discloses a configuration in which a curved surface or a chamfered surface is formed at a boundary portion of a reflecting surface to reduce wind noise and reduce noise.
Patent Document 3 discloses a manufacturing method for forming a chamfered portion at the boundary portion of such a reflective surface.

JP-A-62-250409 Japanese Patent Laid-Open No. 02-149815 JP 2001-337289 A

However, the chamfering of the boundary portion of the reflection surface is a flat C-chamfer or an arc larger than the polygon mirror inscribed circle and smaller than the polygon mirror circumscribed circle as described in Patent Document 3.
Many of these chamfered polygon mirrors have multiple reflective surfaces, and in addition to this, there is a chamfered surface formed at the boundary between each reflective surface. Will be newly performed, and the processing becomes complicated.
In addition, burrs are likely to occur during processing, which makes it difficult to process. In addition, in the case of an arc larger than the polygon mirror inscribed circle and smaller than the polygon mirror circumscribed circle, the outer periphery must be processed before or after processing to form the reflecting surface of the polygon mirror, so the processing is complicated. become. In addition, as described above, burrs are easily generated during processing, and there is a difficulty that processing is troublesome.

  In addition, light is also reflected by the chamfered surface formed at the boundary, and this reflected light is applied to the optical scanning region, forming an electrostatic latent image on the imaging surface, which is originally formed. Since the quality of an image to be deteriorated may be deteriorated, depending on the optical scanning device, a device for removing light reflected by the chamfered surface (chamfered portion) or a process for making the chamfered surface non-reflective surface is applied. Measures such as are necessary.

The present invention has been made to solve the above-described problems of the prior art, and can be easily manufactured and reduced in production cost by not using a complicated manufacturing method for the polygon mirror used in the optical scanning device. The main object of the present invention is to provide an optical scanning device having a polygon mirror capable of preventing deterioration of image quality while suppressing it, and an image forming apparatus including the optical scanning device.
Another object of the present invention is to provide an image forming apparatus that hardly appears in a formed image even when light reflected by a chamfered surface formed for noise countermeasures is applied to an optical scanning region.

In order to achieve the above object, according to the first aspect of the present invention, a light source for emitting a light beam, a polygon mirror having a plurality of mirror surfaces for deflecting and scanning the light beam from the light source, and a light beam subjected to a deflection scan The polygon mirror includes the plurality of mirror surfaces and the plurality of mirrors. The optical scanning device includes an image forming unit that forms an image on a surface to be scanned and a synchronization detection unit that detects a light beam position in the main scanning direction. The chamfered shape formed at the boundary corner of the surface is formed by cutting each of the plurality of mirror surfaces with a continuous locus in the order of the rotation direction of the mirror, which is the longitudinal direction of the mirror surface. A concave surface near the end of cutting of the concave surface formed by the mirror processing of the mirror surface in the mirror blank, and formed by the cutting processing of the mirror surface Gradient, cutting start concave surface with a greater anyone section than the gradient has each of the plurality of mirror surfaces, of the said face anyone portion formed near the end of the cutting at the boundary corner of said plurality of mirror surfaces The mirror effective range, which is a range where the formation position is aligned with one of the one end in the direction along the rotation direction of the mirror surface and the same as the plurality of mirror surfaces, and can be favorably scanned on the mirror surface, The mirror effective range is set except for a beveled portion, and the effective range of the mirror is set at the same position in the mirror surface for the plurality of mirror surfaces .

In the invention described in claim 2, in the optical scanning apparatus according to claim 1, with respect to the center line in the direction along the rotation direction of the mirror surface, along the rotation direction of the mirror effective range of the mirror surface The center line of the direction is shifted to the side opposite to the direction in which the position of the surface fringe is formed.

In the invention described in claim 3, in the optical scanning apparatus according to claim 1 or 2, wherein the chamfered shape, an arc shape along the inscribed circle of the mirror surface adjacent said by the continuous path An optical scanning device formed by a processing method for forming the mirror surface and the arc shape by cutting, and performing the mirror surface processing for finishing the mirror effective range into a mirror surface in a subsequent process.

According to a fourth aspect of the present invention, an image forming apparatus includes the optical scanning device according to any one of the first to third aspects .

According to the first or fourth aspect of the present invention, the configuration described above includes an optical scanning device having a polygon mirror that facilitates the manufacture of the polygon mirror and suppresses the production cost while preventing deterioration of the image quality. An image forming apparatus can be provided.

According to the invention described in 請 Motomeko 2, the position of the large surface sagging portion of the variation of the optical properties, Ru can be set to the mirror out of range as possible.

According to the invention described in 請 Motomeko 3, and the mirror surface, it becomes possible to simultaneously process an arc of a boundary portion of the mirror surface, shortening the processing time, the burrs by machining at the edge line portion of the mirror surface adjacent Ru can be removed.

Hereinafter, embodiments of the present invention will be described with reference to FIGS. 1 to 10.
First, an outline of the configuration of a color printer as an image forming apparatus according to the present embodiment will be described with reference to FIGS.
As shown in FIG. 1, four image forming units 3 (3Y, 3C, 3M, and 3K) and an optical scanning device that emits a light beam (optical document) are provided in a substantially central portion inside the main body case 2 of the color printer 1. 4) and an intermediate transfer belt 14 as an intermediate transfer member.
Each image forming unit 3 is a part that forms an image (toner image) of a different color. In the description of the present specification and drawings regarding these image forming unit 3 and the components of the image forming unit 3, Y, The subscripts C, M, and K indicate yellow, cyan, magenta, and black colors, respectively. The main body case 2 includes an image carrier holding member and a belt holding member, which is an iron frame made of metal, and a resin cover attached to the frame, and includes an image forming unit 3 and an optical scanning device 4. The intermediate transfer belt 14 is attached to the frame.

The four image forming units 3Y, 3C, 3M, and 3K have different colors of images formed because the colors of toners used are different, and the basic structure is the same. Each image forming unit 3 includes a photoconductor 10 (10Y, 10C, 10M, 10K) as an image carrier that is rotationally driven in the direction of an arrow, a charging unit 11, a developing unit 12, and a cleaning unit disposed around the photoconductor 10. It is comprised by the part 13 grade | etc.,.
The photoreceptor 10 is formed in a cylindrical shape and is rotationally driven by a drive source (not shown). A photosensitive layer is provided on the outer peripheral surface portion of the photoconductor 10, and the outer peripheral surface, which is the surface of the photoconductor 10, is a scanned surface.
When the light beam emitted from the optical scanning device 4 is spot-irradiated on the outer peripheral surface of the photoconductor 10, an electrostatic latent image corresponding to image information is written on the outer peripheral surface of the photoconductor 10.

The charging unit 11 uniformly charges the outer peripheral surface of the photoconductor 10, and a non-contact type is used for the photoconductor 10.
The developing unit 12 supplies toner to the photoconductor 10, and the supplied toner adheres to the electrostatic latent image written on the outer peripheral surface of the photoconductor 10, thereby forming an electrostatic latent image on the photoconductor 10. The toner image is visualized and a non-contact type is used for the photoreceptor 10.
The cleaning unit 13 cleans the residual toner adhering to the outer peripheral surface of the photoconductor 10 and employs a brush contact type in which a brush contacts the outer peripheral surface of the photoconductor 10.

  The intermediate transfer belt 14 is a loop belt formed with a resin film or rubber as a base, and a toner image formed on the photoreceptor 10 is transferred to the intermediate transfer belt 14. The intermediate transfer belt 14 is supported by a plurality of rollers 15 and is driven to rotate in the direction of the arrow. These rollers 15 are attached to the frame of the main body case 2, whereby the intermediate transfer belt 14 is attached to the frame of the main body case 2 via the rollers 15. Therefore, the roller 15 is a belt holding member that holds the intermediate transfer belt 14 together with the frame of the main body case 2.

Here, the linear expansion coefficients of these rollers 15 are the same as the linear expansion coefficients of the main body case 2. On the inner peripheral surface side (inside the loop) of the intermediate transfer belt 14, there are four pieces that press the intermediate transfer belt 14 against the photoconductor 10 in order to transfer the toner image on each photoconductor 10 onto the intermediate transfer belt 14. A transfer roller 16 is disposed.
On the outer peripheral surface side (outside the loop) of the intermediate transfer belt 14, a cleaning unit 17 that cleans residual toner, paper dust, and the like attached to the outer peripheral surface of the intermediate transfer belt 14 is disposed.
Below the four image forming units 3 and the optical scanning device 4 in the main body case 2, a paper feed cassette 5 on which the paper P (recording medium) is stacked and held is disposed.
The sheets P stacked and held in the sheet feeding cassette 5 are separated and fed in order from the highest one.

In the main body case 2, a transport path for transporting the paper P separated and fed from the paper feed cassette 5 is formed. On this conveyance path, a paper feed roller 18, a registration roller pair 60, an intermediate transfer roller 9, a fixing unit 6 having a heating roller 6a and a pressure roller 6b, a paper discharge roller pair 61, and the like are arranged.
The registration roller pair 60 is a roller that is rotationally driven intermittently at a predetermined timing. By intermittently driving the registration roller pair 60, the sheet P that has been transported to the position of the registration roller pair 60 and stopped is moved to a transfer position between the intermediate transfer belt 14 and the intermediate transfer roller 9. The toner image on the intermediate transfer belt 14 is transferred onto the paper P at this transfer position. The intermediate transfer belt 14 and the intermediate transfer roller 9 constitute a transfer portion.
The fixing unit 6 is a part that fixes the toner image transferred onto the paper P onto the paper P by applying heat and pressure. The paper P on which the toner image is fixed in the process of passing through the fixing unit 6 is discharged onto a paper discharge tray 19 formed on the upper surface of the main body case 2 by the paper discharge roller pair 61.

Next, the optical scanning device 4 will be described in detail. FIG. 2 is a horizontal sectional view showing the optical scanning device 4, and FIG. 3 is a vertical side view showing the optical scanning device 4.
As shown in FIGS. 2 and 3, the optical scanning device 4 is of a so-called counter scanning type, and includes four LD units (laser light source units) 41 (41Y, 41C, 41M) as light source units that oscillate a light beam. 41K), a polygon scanner 42 that deflects and scans the light beam from each LD unit 41 in two symmetrical directions, and forms an image of the deflected and scanned light beam in a desired size on the photosensitive member 10, for example, fθ. An image forming optical system (image forming means) 43 which is a scanning lens portion composed of a lens, a synchronization optical system (synchronization detecting means) 44 for detecting the scanning start timing of the light beam, and the light beam is folded back to the photosensitive member 10. A folding mirror 45 (45a, 45b) for guiding is provided.

The LD unit 41 is configured by a holding member 46 holding a light source 48, a collimating lens that substantially collimates the divergent light emitted from the light source 48, and a laser light emitting element driving circuit board.
The polygon scanner 42 includes a two-stage polygon mirror 49, a polygon motor 50 that rotates the polygon mirror 49, a soundproof glass 51 that covers the polygon mirror 49, and the like.
The synchronous optical system 44 includes an imaging lens 44b, an electric circuit board 44d having a photoelectric element 44c, and a holding member (not shown) that holds them.
The optical scanning device 4 converts color-separated image data input from a document reading device (scanner) or an image data output device (personal computer, word processor, facsimile receiver, etc.) (not shown) into a light source driving signal. Accordingly, the laser light emitting element 48 as a light source in each LD unit 41 is driven to emit a light beam.

The light beam emitted from each LD unit 41 passes through an aperture 52 for correcting tilting, a cylinder lens 53, and a folding mirror 45a (however, only for the light beams emitted from the laser light source units 41Y and 41K). 42, the beam is deflected and scanned in two symmetrical directions by a polygon mirror 49 rotated at a constant speed by a polygon motor 50.
The light beams deflected and scanned in two directions by the polygon mirror 49 of the polygon scanner 42 in two directions pass through the imaging optical system 43, are folded back by the folding mirror 45b, and are photosensitive for each color through the dustproof member 28. An electrostatic latent image is written by spot irradiation on the surface to be scanned of the body 10. At this time, the irradiation angles of the four light beams to the photosensitive member 10 are substantially the same.

On the other hand, the synchronization optical system 44 for determining the write start timing returns the light beam that has passed through the imaging optical system 43 by the synchronization detection mirror 44a and receives it, and outputs a scan start synchronization signal.
Here, since the original meaning of the synchronization detection is to take the timing of the scanning light, the synchronization optical system 44 may be installed so as to receive the light beam prior to the normal scanning. In order to detect a change in the speed (or time) of one scan, a detection means may be provided at the rear end of the scan. FIG. 2 shows a configuration in which synchronization is obtained before and after such scanning.

This embodiment will be described in detail below. First, a conventional polygon mirror will be described before describing the polygon mirror according to the present embodiment. FIG. 11 is a top view of a conventional polygon mirror, in which the boundary portion (boundary corner portion) of the reflecting surface is not chamfered. An example of the shape is a hexagon. Reference numeral 100 denotes a circumscribed circle of the hexagonal polygon mirror, 101 denotes an inscribed circle, and 102 denotes each reflecting surface.
FIG. 12 shows a polygon mirror in which a flat C-chamfer is added to the boundary portion of the reflecting surface 102. Reference numeral 103 indicates C chamfering at the boundary. FIG. 13 is an enlarged view of a portion A in FIG.
FIG. 14 shows a polygon mirror in which chamfering by an arc larger than the polygon mirror inscribed circle 101 and smaller than the polygon mirror circumscribed circle 100 is added to the boundary portion of the reflecting surface 102. Reference numeral 104 denotes a circle larger than the inscribed circle 101 and smaller than the circumscribed circle 100, and reference numeral 105 denotes a chamfer on the circle 104 at the boundary.

Next, a processing method of the mirror blank before mirror processing of these polygon mirrors will be described. FIG. 15 shows an example of a processing method of the mirror blank, and the reflective surface portions are formed in the order of 102A, 102B, 102C, 102D, 102E, and 102F in the axial direction (the direction of the arrow) by cutting.
FIG. 16 also shows another example of the processing method of the mirror blank, and the reflecting surface portions are formed in the order of 102a, 102b, 102c, 102d, 102e, and 102f in the circumferential direction (the direction of the arrow) by cutting. In the case of this cutting, the mirror blank is rotated in the rotation direction to form a reflective surface portion, or the cutting tool side is moved along the periphery of the mirror blank with a machining center or the like to form the reflective surface. Further, in this processing, burrs are generated in the ridge line portion formed by the adjacent reflecting surfaces, and therefore it is necessary to overrun the cutting tool beyond the length of the reflecting surface when finishing the reflecting surface processing. Therefore, processing time is long.
In the case of a mirror blank in which a flat C-chamfer is added to the boundary portion of the reflecting surface, the same processing as the reflecting surface processing is performed after the processing of the reflecting surface portion. Further, in the case of a mirror blank in which a chamfer by a circular arc of a circle larger than the polygon mirror inscribed circle and smaller than the polygon mirror circumscribed circle is added to the boundary portion of the reflecting surface, the machining is performed by turning or the like.

In the present embodiment, as shown in FIGS. 4 and 5, along the inscribed circle 81 of the adjacent reflecting surface 80, the ridge line portion (boundary corner portion) of the adjacent reflecting surface (mirror surface) 80 of the polygon mirror 49. An arcuate chamfered shape (chamfered portion) 82 is formed.
Since the chamfered shape 82 is formed outside the effective range portion of the reflecting surface 80, the chamfered shape 82 has a smaller radius than the arc of the chamfer 105 shown in FIG. FIG. 5 is an enlarged view of a portion B in FIG.
FIG. 6 shows a mirror blank processing method according to the present embodiment, and 80 a 1, 80 a 2, 80 b 1, 80 b 2, 80 c 1, 80 c 2, 80 d 1, 80 d 2, 80 e 1, 80 e 2 in the circumferential direction (arrow direction) by cutting with a machining center. , 80f1 and 80f2 in order, the reflective surface 80 and the chamfered shape 82 are formed in a continuous locus.
By this processing method, the processing time can be greatly shortened without generating burrs at the reflecting surface 80, the chamfered shape 82, and the boundary portion thereof.
Then, the mirror surface processing which finishes a mirror effective range (after-mentioned) to a mirror surface is implemented.

  FIG. 7 is a three-dimensional view of the polygon mirror 49 in FIG. 6, in which the mirror blank upper surface 83 and the ridgeline portion 85 of the reflecting surface 80, the mirror blank upper surface 83 and the ridgeline portion 86 of the chamfered shape 82, which are not shown, are the same as the upper surface. Further, the chamfering of the mirror blank lower surface 84 and the ridge line portion of the reflecting surface 80, and the mirror blank lower surface 84 and the ridge line portion of the chamfered shape 82 are also carried out by the above processing method.

FIG. 8 shows an image of the mirror surface deformation amount (mirror surface deformation image) in the polygon mirror 49 and how to set the mirror effective range.
Here, the mirror effective range (mirror surface effective range) means a range in which optical scanning can be satisfactorily performed on the mirror surface 80.
The mirror effective range eliminates the beveled portion, thereby improving the flatness of the mirror effective range with high accuracy.
However, it is necessary to set the mirror effective range at the same position in the mirror surface 80 for each mirror surface 80. On the other hand, no matter what the surface is.
In other words, it is possible to improve the deflection scanning function of the polygon mirror 49 as a whole by accepting the occurrence of surface fringes that are unavoidable in terms of processing technology and aligning the positions on the mirror surfaces 80.
That is, the formation position of the beveled portion is set to each mirror surface at one end in a direction (longitudinal direction of the mirror surface) along the polygon scanner rotation direction (arrow direction: hereinafter referred to simply as “rotation direction”) of the mirror surface 80. 80 is the same.

Further, the center line n1 in the direction along the rotation direction of the mirror surface 80 does not coincide with the center line n2 in the direction along the rotation direction in the mirror effective range of the mirror surface 80.
That is, with respect to the center line n1 in the direction along the rotation direction of the mirror surface 80, the center line n2 in the direction along the rotation direction in the mirror effective range of the mirror surface 80 is the direction in which the position of the surface fringe is located. Shifted to the opposite side.
In FIG. 8, the chamfered shape by the processing method shown in FIG. 6 is omitted (the same applies to FIGS. 9 and 10). Of course, matching the formation positions of the beveled portions to the same is not limited to the polygon mirror having a chamfered shape by the processing method shown in FIG.

FIG. 9 shows a synchronization detection range and an image formation range within the mirror effective range. The range for image formation is concave, and changes when the scanning angular velocity is slow-fast-slow compared to when the mirror surface 80 is flat. If the amount of light beam is constant, the amount of light changes on the scanned surface as high-low-high. When a constant light amount is obtained on the surface to be scanned, simple light emission time control is possible.
The synchronization detecting means 44 is arranged so as to detect the light beam position of the light beam reflected at the end of the mirror effective range on the opposite side of the mirror surface 80 in the direction in which the position of the surface fringe is formed.
In the present embodiment, the light beam reflected at the end of the effective range of the mirror located downstream in the rotation direction is further detected.
You may arrange | position so that the light beam reflected in the edge part of the mirror effective range located in the upstream of a rotation direction may be detected.
FIG. 10 shows an abnormal surface portion in which minute dust and dirt around the polygon mirror 49 adhere to the mirror surface 80 due to the turbulent flow at the tip of the mirror surface caused by high-speed rotation, and the mirror surface 80 is often clouded white in many cases. The abnormal surface portion and the beveled portion are arranged in the same direction as the rotation direction of the mirror surface 80.

1 is a schematic configuration diagram of an image forming apparatus according to an embodiment of the present invention. 1 is a schematic horizontal sectional view of an optical scanning device. It is a vertical side view of an optical scanning device. It is a top view of a polygon mirror. It is an enlarged view of the B section of FIG. It is a top view which shows the cutting process order of a polygon mirror. It is a perspective view of a polygon mirror. It is a figure which shows the mirror surface deformation | transformation image in a polygon mirror, and a mirror surface effective range. It is a figure which shows the relationship between the range for image formation in the mirror surface effective range, and the range for synchronous detection. It is a figure which shows the positional relationship of the abnormal surface part with respect to the rotation direction of a polygon mirror. It is a top view of the conventional polygon mirror without chamfering. It is a top view of the polygon mirror which has the conventional C chamfering. It is an enlarged view of the A section of FIG. It is a top view of the polygon mirror which has the chamfer of the conventional circular arc shape. It is a perspective view which shows the cutting method of the conventional polygon mirror. It is a top view which shows the other cutting method of the conventional polygon mirror. It is a top view which shows the mirror surface deformation | transformation image which has a face part produced by the cutting process in the conventional polygon mirror.

Explanation of symbols

4 optical scanning device 43 imaging means 44 synchronization detecting means 48 light source 49 polygon mirror 80 mirror surface 82 chamfered shape n1, n2 center line

Claims (4)

A light source that emits a light beam, a polygon mirror having a plurality of mirror surfaces that deflect and scan the light beam from the light source, an imaging unit that forms an image on the surface to be scanned, and a main scanning direction In the optical scanning device having the synchronous detection means for detecting the light beam position of
The polygon mirror has a rotation direction of the mirror in which each of the plurality of mirror surfaces and a chamfered shape formed at a boundary corner of the plurality of mirror surfaces is a longitudinal direction of the mirror surface with respect to each of the plurality of mirror surfaces. With a mirror blank formed by cutting along a continuous trajectory in the direction of direction,
The mirror blank is formed by mirror processing of the mirror surface, and the concave surface formed near the end of cutting of the concave surface formed by the cutting processing of the mirror surface is a surface bevel portion that is larger than the gradient of the concave surface at the beginning of cutting. Each having a plurality of mirror surfaces;
The position of the beveled portion formed near the end of cutting at the boundary corners of the plurality of mirror surfaces is the same as that of the plurality of mirror surfaces at one end in the direction along the rotation direction of the mirror surfaces. aligned to,
The mirror effective range, which is a range where the optical scanning can be satisfactorily performed on the mirror surface, is set except for the drooping portion, and the mirror effective range is set at the same position in the mirror surface for the plurality of mirror surfaces. An optical scanning device characterized by that . The optical scanning device according to claim 1,
To center line of the direction along the rotation direction of the mirror surface, the center line of the direction along the rotation direction of the mirror effective range of the mirror surface, opposite to the direction in which the forming position of the surface sag portion An optical scanning device characterized by being shifted to The optical scanning device according to claim 1 or 2 ,
The chamfered shape is an arc shape along an inscribed circle of the adjacent mirror surfaces;
The mirror surface and the arc shape are formed by the cutting by the continuous trajectory, and the mirror surface processing is performed in a subsequent process to finish the mirror effective range to a mirror surface. Optical scanning device . An image forming apparatus comprising the optical scanning device according to claim 1 .

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