JPH0252309A - Rotary polygon mirror for exposing device - Google Patents

Abstract

PURPOSE:To prevent the trouble of optical deflecting operation by providing a main body part with moment of inertia which is nearly uniform about an axis of rotation so that deformation caused by rotation becomes uniform. CONSTITUTION:The prismatic main body part 10a of the rotary polygon mirror 10 is so formed that the axially orthogonal planes, i.e. both bottom surface parts are cut in a recess and projection shape as compared with a general rotary polygon mirror. Then the main body part 10a of the rotary polygon mirror 10 is formed having nearly uniform moment of inertia about the axis of rotation. Therefore, the deformation of the main body part 10a accompanying the rotation is caused nearly uniformly about the axis of rotation and strain is generated so that the flatness of reflecting mirrors provided to the outer peripheral part of the main body part 10a is maintained. Consequently, the excellent optical deflecting operation can be maintained.

Description

Detailed Description of the Invention [Industrial Field of Application] The present invention relates to an exposure apparatus comprising a plurality of continuous flat reflecting mirrors on the outer peripheral side surface of a prismatic main body having a rotation axis at the center. Regarding rotating polygon mirrors.

[Prior Art] In an exposure writing device used in various digital image forming devices such as a digital copying machine, facsimile machine, or laser printer, an information signal corresponding to an image to be recorded is converted into optical information, and the resulting modulated Generally, information is written by scanning the surface of the photoreceptor while deflecting the light with an optical polarizer of an exposure device.

A rotating polygon mirror is an example of a polarizer in such an exposure writing device. A rotating polygon mirror is composed of a prismatic main body having a rotation axis in the center and a plurality of planar reflecting mirrors connected to each other on the outer circumferential side surface of the prismatic main body. By rotating the reflecting mirror, the reflecting mirror is rotated, and the modulated light is deflected by the rotating movement of the reflecting mirror to perform scanning.

[Problems to be Solved by the Invention] However, in recent years, image forming apparatuses have tended to have higher densities and higher speeds, and with this, the rotating polygon mirrors used as the optical polarizers have become larger and rotated at higher speeds. be. Figure 8 shows the number of printouts (horizontal axis) and the corresponding number of rotations of the rotating polygon mirror (vertical axis) when using a rotating polygon mirror with an inscribed circle of 22 mm and six surfaces. . As rotating polygon mirrors become larger and rotate at higher speeds, non-uniform deformation due to rotation becomes significant, making it impossible to maintain the flatness of the reflecting mirror, resulting in problems with the light deflection effect and the optimum beam diameter and beam intensity distribution. There is a problem that it becomes impossible to obtain. In other words, the main body of the rotating polygon mirror is formed into a prismatic shape, and the moment of inertia around the rotation axis is non-uniform.As a result, deformation due to rotation occurs in a non-uniform state around the rotation axis. . In particular, as shown by the broken line in FIG. 9, the curved portion of the rotating polygon mirror is deformed so as to protrude outward.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a rotating polygon mirror for an exposure apparatus in which deformation due to rotation is uniformly performed to maintain the flatness of the reflecting mirror and to maintain a good light deflection effect. "Target."

[Means to Solve the Problem] To achieve the above object, the invention described in claim 1 includes a plurality of continuous planar reflecting mirrors on the outer peripheral side surface of a prismatic main body having a rotation axis in the center. In the rotating polygon mirror of an exposure apparatus, the main body has a substantially uniform moment of inertia about the rotation axis, and the rotating polygon mirror of the exposure apparatus is configured to deflect modulated light and perform scanning by rotational movement of the reflecting mirror. It consists of a structure formed as follows.

The invention described in claim 2 comprises a plurality of planar reflecting mirrors successively provided on the outer circumferential side surface of a prismatic main body having a rotation axis in the center, and the rotational movement of the one reflecting mirror causes In a rotating polygon mirror for an exposure apparatus which performs scanning by deflecting modulated light, the main body is partially cut out so as to have a substantially uniform moment of inertia 1- around the rotation axis. Along with being there,
The cut-out portion of the main body is filled with a member having a lower density than the member constituting the main body.

[Function] In the means having the configuration described in claim 1, since the main body is formed to have a substantially uniform moment of inertia around the rotation axis, the main body due to rotation is Deformation occurs almost uniformly around the rotation axis, and as a result, distortion occurs while maintaining the flatness of the reflecting mirror provided on the outer periphery of the main body.

Further, in the means having the configuration described in claim 2, a part of the main body is cut off so as to have a substantially uniform moment of inertia around the rotation axis, and the cut part of the main body is Since the body is filled with a low-density member, the deformation of the main body due to rotation occurs almost uniformly around the axis of rotation, as in the invention described in claim 1 above, and as a result, the deformation of the main body occurs almost uniformly around the axis of rotation. Distortion is generated by maintaining the flatness of the reflector provided on the outer periphery, and the unevenness caused by cutting the main body affects the uniformity of the moment of inertia in a member with low density. The outer shape is smoothed and the wind noise is prevented from increasing.

[Example] Hereinafter, an example of the present invention will be described in detail based on the drawings.

First, we will discuss deformation due to inertial force during rotation.

When using a rotating polygon mirror by rotating it at high speed, it is first necessary to ensure safety by paying attention to centrifugal breakage. Regarding centrifugal fracture, there are two theories: the average stress theory, which states that circumferential stress acts uniformly on the diametrical cross section of the rotating body, and fracture occurs when it becomes equal to the material's tensile strength σB; There is a maximum stress theory that states that fracture occurs when cracks occur at the point where the material is in contact.

The average stress theory is applied to ductile materials such as aluminum (AI) and I (Cu). When the rotating polygon mirror is regarded as a disk having an outer radius r2 and a hole having a radius r□ in the center, the following equation holds true when the average stress σmQan is equal to the tensile strength σB of the material.

The destructive rotational angular velocity ω (rad/5ee) can be calculated from this equation 0. Here, Ω is the density of the material (kg/c
%), g is the gravitational acceleration (an/5ec2), r and r2 are the inner and outer diameters of the disc (clll).

On the other hand, the maximum stress theory is applied to brittle materials such as glass and quartz. In this case, the maximum circumferential stress σmax is σ
When B is reached, the destructive rotational speed ω can be determined based on the following conditional expression. Here, m represents Poisson's ratio.

The fracture rotational speeds of various materials calculated using the above formulas and (■) are shown below.

However, the calculation is performed assuming r, , ==r2=3 (cm).

Next, A1 with r□=1.5 (cm) and r2=3 (cm)
The approximate deformation amount when a rotating polygon mirror made by a manufacturer is rotated at 1100 Orp is determined. However, in this case, the rotating polygon mirror is calculated as being circular rather than polygonal. When converting 11000 rp into rotational angular velocity ω, it becomes ω 1047. ” For the double equation ■, Ω = 2.69 × 1.0°3 (kg
/a(), (,1=1047(rad/5ee),g
= 980 (c+n/5ee2), r□=1.5
(an), and by substituting r2=3(CIll), we get =1.5.8(kg/a). Therefore, the amount of distortion E at this time is as follows, and the amount of deformation Δγ of the rotating polygon mirror located 3 cm from the center of rotation is: Δγ=3.12X2.1 xlO5 =6.3X10"(CIll) =0.63(μnl ) In this way, the amount of deformation is proportional to the number of rotations, and when the number of rotations is 20,000 (rpm), the amount of deformation is 1 (μm) or more.

The above calculation formula assumes that the rotating polygon mirror is circular, and even more complicated deformation occurs in an actual rotating polygon mirror. At present, there is no example of accurately measuring the behavior of a rotating polygon mirror during high-speed rotation, but an all-purpose device consisting of a laser light source 1 and a detector 2 that receives the emitted light facing each other as shown in FIG. The outline is understood. That is, the light emitted from the laser light source 1 is directed so that a part of it passes through the convex boundary between the surfaces of the rotating polygon mirror 3, and the change in the amount of light received by the detector 2 is measured. The deformation of the rotating polygon mirror 3 is grasped by this. According to such measurements, r2=3
(cm), a rotating polygon mirror with six faces is about 10,000 (
rpm), the boundary convex portion between the reflecting surfaces of the rotating polygon mirror is considered to be deformed by several μm in the centrifugal direction. Further, from the simulation results using the finite element method, it has been concluded that the rotating polygon mirror undergoes non-uniform deformation around the axis of rotation as shown in FIG. 9. The above-mentioned problems occur due to such non-uniform deformation.

The reason why the rotating polygon mirror causes non-uniform deformation as shown in FIG. 9 is that the moment of inertia at the outer periphery of the rotating polygon mirror is not made uniform around the axis of rotation. That is, the first
When the rotating polygon mirror is divided into small parts as shown in Figure 0,
The moment of inertia 1- applied to the minute volume outside the inscribed circle of the rotating polygon mirror is not uniform in the circumferential direction of the inscribed circle, and is high-speed near the convex boundary between the reflecting surfaces of the rotating polygon mirror. During rotation, a large moment of inertia is applied and a pulling force is applied to the outside. Therefore, it is considered that the rotating polygon mirror undergoes deformation as shown in FIG. 9 during high speed rotation.

The moment of inertia represents the amount of inertia against rotational motion, and is determined by the shape and mass of the rotating polygon mirror. In particular, when the density is constant, the amount determined only by the shape of the rotating object is multiplied by the total mass M of the rotating object. The moment of inertia of the convex portion located outside the inscribed circle of the rotating polygon mirror shown in FIG. 11 will be determined.

The radius of the inscribed circle of the rotating polygon mirror is r□, and the radius of the circumscribed circle is r2
and r, 1, lo, and dr are defined as shown in FIG. First, from Figure 11, r2-r:
1=r2-r・1:1° Therefore, □11+・・・・・・・・・■ z-r1. Also, since the minute area dm in the shaded area in the figure is ldr, substituting this into the above equation yields dm=1odr or 1;). Moment of inertia that you can stop even if you want to do it 1-
■I = f ” r”dm−’−−f’ r” ”
Z Knee]. -'-dr et al. g
'r r'2 r□ g, and rearranging this gives the following. On the other hand, the relationship between 1o and r2, the number of surfaces N of the rotating polygon mirror, and the radius of the inscribed circle r.
01110■ r2=r', -...■. By substituting these equations (2) and (0) into equation (2) and sorting them out, the obtained moment of inertia E is as follows.

FIG. 1 shows a rotating polygon mirror 10 in one embodiment of the present invention. The prismatic body portion 1 of this rotating polygon mirror 10
0a is formed so that the plane orthogonal to the axis, that is, both bottom surfaces of a general rotating polygon mirror shown by the broken line, are cut out in an uneven shape, and the cross section along the I-1 line and the ■-■ line 2 and 3, respectively. Cross section along I-1 line and ■
■It is connected linearly with the cross section along the line. To find the length y of the ridge line 10c of each convex portion where the planar reflective surfaces iob intersect, we need to calculate the moment of inertia in the cross section of FIG. 2, which is the plane 1-1 in FIG. It is sufficient to find y such that the moment of inertia in the cross section shown in FIG.

The moment of inertia of the cross section shown in FIG. 2 is as follows. −
In the force cylinder 3 diagram, -(1-y)2r2-X-T(a-y):rz holds, so ■:ar2+(y-a)x 0110110100. ■
Using , the moment of inertia ■ is.

■=fr+　p　arz”(y-”ゝ゛・dx ogr? ]2 Just find y.

Therefore, we obtain. Then, by substituting the formula (■) into the formula 0 and rearranging it, we get 4a 3π a 3 N3... Therefore, if the length y of the ridge line of the convex portion of the rotating polygon mirror is set to the value expressed by the above formula (0), the moment of inertia around the axis of rotation will be made uniform. For example, if the thickness a of an 8-sided rotating polygon mirror is 51, then a=5
．． If y=3.59 (mm), which is obtained by substituting N=8 into equation (2), is used, a rotating polygon mirror with a uniform moment of inertia can be obtained. Note that equation (2) is determined only by the number of surfaces and maximum thickness of the rotating polygon mirror.

In such an embodiment, since the main body of the rotating polygon mirror is formed to have a substantially uniform moment of inertia around the rotation axis, deformation of the main body due to rotation or around the rotation axis may occur. The distortion occurs almost uniformly, and as a result, the distortion occurs while maintaining the flatness of the reflecting mirror provided on the outer periphery of the main body.

In the embodiment shown in FIG. 4, the cross section along line I-1 and the cross section along line nu are connected by a quadratic curve.

With such a configuration, it is possible to obtain a rotating polygon mirror in which the uniformity of the moment of inertia around the rotation axis is further improved.

Although not shown in the drawings, it is also possible to make a hole or the like in the axial direction on a line connecting the rotation axis of the prismatic main body and the convex portion, thereby making the moment of inertia 1 more uniform.

Furthermore, in the embodiment shown in FIGS. 5 and 6, the cutout portion of the main body 20a is filled with a filling member 20b made of a resin material, a rubber material, or the like having a lower density than the aluminum member constituting the main body. It is formed to maintain the same outer diameter shape as a general rotating polygon mirror. The density of the resin member or rubber member used for the filling member 20b is 0.9 to 1.0 (g/
cn(), which is considerably smaller than the density of 2.69 (g/at!) of aluminum constituting the main body portion 20a.

In this embodiment, the density of the filling member 20b that fills the uneven portion due to the removal of the main body portion 20a can be suppressed to a low level, and the deformation caused by the rotation of the filling member 20b can be suppressed.
It will be separated from 0a. Therefore, the outer shape of the rotating polygon mirror is smoothed so as not to affect the uniformity of the moment of inertia and deformability, and as a result, an increase in wind noise due to rotation is prevented. .

[Effects of the Invention] As described above, the main body of the rotating polygon mirror in the invention described in claim 1 has a substantially uniform inertia around the rotation axis so that deformation due to rotation is uniformly performed. Since it is configured to have a moment of 1-, the flatness of the reflecting mirror provided on the side of the main body can be maintained well even during high-speed rotation, and there is no problem with the light deflection effect. This makes it possible to stably obtain the optimum beam diameter and beam intensity distribution.

In addition, in the rotating polygon mirror according to the invention set forth in claim 2, a part of the main body portion is cut off so that the rotation axis is fixed so that deformation due to rotation is uniformly performed and a smooth outer shape is maintained. Since the main body has a substantially uniform moment of inertia at the center and the cutout portion of the main body is filled with a member having a lower density than the members constituting the main body, the effect of the invention described in claim 1 above is achieved. In addition, it is possible to prevent wind noise from increasing due to rotation.

[Brief explanation of the drawing]

FIG. 1 is an external perspective view of a rotating polygon mirror according to an embodiment of the present invention, FIGS. 2 and 3 are sectional views taken along lines 1-1 and nn in FIG. 1, and FIG. 4. 5 and 6 are external perspective views of a rotating polygon mirror in other embodiments of the present invention, and FIG. 7 is a configuration explanatory diagram showing a measuring device in which a laser light source and a detector 2 are arranged facing each other. Fig. 8 is a diagram showing the number of printed 1-out sheets and the corresponding rotation speed of the rotating polygon mirror when a rotating polygon mirror is used, and Fig. 9 is a diagram showing the non-uniform deformation around the rotation axis of the rotating polygon mirror. FIG. 10 is a plane explanatory diagram of the rotating polygon mirror when the rotating polygon mirror is micro-divided, and FIG. 11 is a plane diagram showing the convex portions arranged outside the inscribed circle of the rotating polygon mirror. It is an explanatory diagram. 10...Rotating polygon mirror, 10a, 20a...Prismatic main body, 10b...Plane reflecting surface, 10c...
Ridge line of each convex portion, 20b...Filling member. (1 other person) Shinkyougai 6 Figure 1. Buri〉Doaud'&General

Claims (1)

[Claims] 1. A plurality of planar reflecting mirrors are successively provided on the outer peripheral side surface of a prismatic main body having a rotation axis at the center, and the modulated light is deflected by the rotational movement of the reflecting mirrors. A rotating polygon mirror for an exposure apparatus configured to perform scanning, wherein the main body is formed to have a substantially uniform moment of inertia about a rotation axis. 2. A plurality of planar reflecting mirrors are successively provided on the outer peripheral side surface of a prismatic main body having a rotation axis at the center, and scanning is performed by deflecting modulated light by rotating the reflecting mirrors. In the rotating polygon mirror of the exposure device, the main body is partially cut out so as to have a substantially uniform moment of inertia around the rotation axis, and the cut out part of the main body has a main body. A rotating polygon mirror for an exposure apparatus, characterized in that it is filled with a member having a lower density than the members constituting the part.