JPH0377908A - Optical deflector - Google Patents

Abstract

PURPOSE:To suppress the degradation in the accuracy of the reflecting surfaces of a polygon mirror and to obtain high-grade output images, etc., by loading the polygon mirror by means of a washer provided on a revolving shaft, a spacer member 3 and a buffer member having rubber elasticity, etc. CONSTITUTION:The polygon mirror 1 is held by the seat 2a provided to the revolving shaft 2, the spacer member 3 and the buffer member 4, such as urethane sheet, having the rubber elasticity. Screws 5 are passed through the spacer member 3, the buffer member 4 and the polygon mirror 1 and are screwed to the female thread parts formed on the seat 2a of the revolving shaft to fix the polygon mirror 1 to revolving shaft 2. The buffer member 4 deflects and acts to internally disperse the pressure when the nonuniform pressure from the screw heads works on the same; therefore, the polygon mirror 1 is eventually pressed by the uniform pressure. The generation of strains is minimized even if the polygon mirror 1 is thermally expanded by the temp. rise. The fluctuation in the scanning position of the beam by the degradation in the accuracy of the reflecting surface of the polygon mirror 1 is suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical deflection device for scanning an irradiated object with a light beam from a light source, and particularly to an optical deflection device using a rotating polygon mirror.

[Prior Art] In recent years, laser beam printers (LBPs) that record a desired image by scanning a laser beam and flickering the laser beam to form an electrostatic latent image on a photoreceptor, and a laser beam printer (LBP) that records a desired image by scanning a laser beam and flickering the laser beam, and The following is an example of the configuration of a conventional optical deflection device, that is, a laser scanner device, which has been widely used to record an image by scanning a flickering laser beam and using silver halide photography, similar to the LBP. It is shown in Figure 6. In the figure, a laser driver 101 that receives an image signal blinks a solid-state laser element 102 at a predetermined timing, and the laser beam emitted from this solid-state laser element 102 is transmitted to a collimator lens system 103.
The light is converted into parallel light by , and is incident on the polygonal surface m 104 which rotates in the direction of arrow B. The laser beam reflected by this polygonal mirror 104 is imaged into a spot on a scanned surface (the surface of the photoreceptor drum) 106 by an f/theta lens group 105.

In such a configuration, the polygon mirror 104 is usually made of a metal whose main material is aluminum (/L), and a metal vapor film or the like is formed on the reflective surface to prevent oxidation, thereby improving strength, workability, and It satisfies various characteristics such as weight.

Furthermore, in such laser scanner devices, highly accurate balance adjustment is required for the polygon mirror and the rotation axis to prevent the reflective surface from swinging when the polygon mirror rotates, causing the beam scanning position to change for each reflective surface. It has been subjected. In addition, the polygon mirror is provided with multiple screw insertion holes (approximately 2 to 6) at equal angular intervals, and the male screws are passed through these holes and screwed into the multiple female screw holes provided on the seat of the rotating shaft. A polygon mirror is held between the screw head of the male screw and the seat so that the positional relationship between the rotating shaft and the polygon mirror does not shift due to acceleration and deceleration of rotation.

This fixing method using screws has excellent strength, and has the advantage of not causing misalignment between the rotating shaft seat and the rotating mirror even when using a large polygon mirror or rotating the polygon mirror at high speeds such as 2000 rpm. are doing.

[Problem to be solved by the invention 1 However, the pressure for fixing the polygon mirror to the seat of the rotating shaft is applied to the polygon mirror centering on the heads of the male screws that are tightened at equal angular intervals. ing. Therefore, when the polygon mirror thermally expands as the device operates and the temperature rises, the portion of the polygon mirror pressurized by the screw head and the portion of the polygon mirror of the screw advisor to which no pressure is applied to the left, The disadvantage is that the difference in the degree of expansion causes distortion, which significantly deteriorates the accuracy of the highly precisely finished reflective surface.

In this way, when distortion occurs in a polygon mirror due to thermal expansion, even if the rotation is perfectly balanced, the scanning position of the beam will shift for each facet of the polygon mirror opposite the elbow, and the quality of the image obtained will deteriorate significantly. It turns out.

In particular, in devices that require high-speed rotation, energy losses such as high-frequency iron loss and wind loss increase in the motor section that generates the rotational driving force, and the amount of heat generated in the motor section becomes extremely large. A major problem is deterioration of image quality due to distortion due to thermal expansion of the mirror.

On the other hand, in order to correct the uneven pressure caused by the screw fixation described above, a method has been considered in which a spacer is inserted between the screw head and the polygon mirror to alleviate the pressure transmitted from the screw head to the polygon mirror.
If the spacer is not as thick as the polygon mirror, it will not be possible to obtain uniform pressure, and the thickness of the spacer will increase the size of the device.
This has drawbacks such as increased power consumption and heat generation in the motor due to increased rotational moment, and the center of gravity of the rotating shaft that supports the polygon mirror becomes high, making the rotational balance unstable and hindering high-speed rotation of the polygon mirror. .

Therefore, in view of the above-mentioned problems, an object of the present invention is to provide an optical deflection device that uses screws to fix the polygon mirror on the seat of the rotating shaft, while preventing deterioration of the precision of the reflective surface of the polygon mirror due to thermal expansion. Our goal is to provide the following.

[Means for Solving the Problems] In the present invention, which achieves the above object, in an optical deflection device that uses a rotating polygon mirror to scan a light beam from a light source such as a semiconductor laser onto a cicada object, A polygon mirror is held between a seat, a spacer member, and a cushioning member such as a urethane sheet having rubber elasticity that is sandwiched between the spacer member and the polygon opening, a screw is passed through the spacer member, the buffer member, and the polygon mirror, and then the polygon mirror is rotated. The polygon mirror is fixed to the rotating shaft by screwing into a female thread formed on the seat of the shaft.

More specifically, the spacer member is a disk having an outer diameter that is approximately the same as the seat of the rotating shaft, the relaxation member is a rubber elastic sheet that also has an outer diameter that is approximately the same as the seat, or The spacer member and the buffer member may be separate members or may be integrally molded.

[Operation J] According to the present invention having the above configuration, a buffer member having rubber elasticity or the like is interposed between the spacer member that relieves the pressure from the screw head and the polygon mirror, so that the pressure from the screw head is reduced. When uneven pressure is applied, the buffer member bends and works to internally disperse the pressure, so the polygon mirror is held down with uniform pressure. Therefore, even if the polygon mirror thermally expands due to a rise in temperature, the occurrence of distortion is suppressed to a minimum, and variations in the beam scanning position due to a decrease in the precision of the reflective surface of the polygon mirror are suppressed to the utmost.

[Example] Figure 1 shows an example of the present invention. In the figure, 1 is 8.
A polygon mirror made of aluminum (Aβ) alloy having a reflective surface 1a, 2 a rotating shaft for rotating the polygon jQ1 fixed on the seat 2a, 3 rotating when the polygon at and the rotation axis 2 are fixed. It is a balance ring as a spacer member for attaching a balance weight for balancing, and has approximately the same outer diameter as the above-mentioned dust 2a, and 4 is a urethane sheet that is a buffer member with rubber elasticity, and has a rubber hardness of 75 degrees. Wall thickness 1mm
The 0-rotation shaft 2 and the balance ring 3 are made of mild steel, and the surface is chemically nickel plated.

A hole 11 for fitting the rotating shaft 2 is formed in the center of the polygonal mirror 1, and has the function of aligning the rotational center of the rotating shaft 2 and the polygonal mirror 1.

On the outside of the hole 11, four mounting holes 12 are formed at equal angular intervals on a substantially circle centered on the center of the polygon mirror 1, and these are coaxial with the hole 11 (the center axis of the hole is parallel to (that is) maintained.

The seat 2a of the rotating shaft 2 for receiving the multi-face [1] has a highly accurate flat surface, and female threads 13 are cut in four places at equal angular intervals at positions with the same diameter as the small holes 12 formed on the multi-face [1]. There is.

The balance ring 3 is finished to have an outer diameter that is approximately the same as the outer diameter of the seat 2a provided on the rotating shaft 2.

Four small holes 14 are drilled at equal angular intervals at positions with the same diameter as the female thread 13 cut in the rotating shaft 2, and a hole 15 with the same diameter as the hole 1.1 of the polygon mirror L is drilled in the center. It is being Furthermore,
The urethane sheet 4, which is a buffer member, is provided with a circular groove 16 for attaching the balance weight while maintaining coaxiality with the center hole 15, and is finished to have an outer diameter that is approximately the same as the outer diameter of the seat 2a. Four small holes 17 having the same shape as the small holes 14 of the ring 3 are bored at equal angular intervals.

The above components are assembled as follows. First, the polygon mirror 1 is fitted onto the rotating shaft 2, then the urethane sheet 4 is fitted onto it, and then the balance ring 3 is fitted onto it.
Four male screws 5 from above the balance ring 3 are passed through the small hole 14, the small hole 17, and the mounting hole 12, and finally screwed into the female screw 13 provided on the rotating shaft 20 seat 2a. As a result, the polygon mirror 1 is held between the head 5a of the male screw 5 and the seat 2a of the rotating shaft 2, and is fixed to the rotating shaft 2.

In the above configuration, between the head 5a of the male screw 5 and the seat 2a of the rotary shaft 2, the polygon mirror 1 is securely mounted so that the positional relationship between the rotary shaft 2 and the polygon mirror 1 does not shift due to acceleration or deceleration of rotation. Fixed.

Next, FIGS. 2 and 3 compare the pressure distribution on the polygon mirror holding surface between the above embodiment and an example in which a buffer member such as the urethane sheet 4 is not sandwiched between the balance ring 3 and the polygon mirror 1. Shown below. In Figures 2 and 3, the tightening torque of the screw 5 is 1
2 kg-cm, and the wall thickness of balance ring 3 is 3 m.
m, and the wall thickness of the multifaceted It was set to 7 mm.

Figure 2 (a) shows the pressure distribution between the urethane sheet 4 and the polygon mirror l, Figure 2 ('b) shows the pressure distribution between the polygon mirror l and the seat 2a5, and the same applies to Figure 3. , the figure (a) shows the space between the balance ring 3 and the polygon mirror 1, and the figure (b) shows the space between the balance ring 3 and the polygon mirror 1.
The pressure distribution between and seat 2a is shown.

Furthermore, for comparison, Fig. 4 shows an example in which the polygon mirror 1 is directly held down with a torque of 12 kg-Cm using 50 screws without using the balance ring 3, and Fig. 4 (a) shows the screw head and polygon mirror. 1, the same figure (b) shows the pressure distribution between the polygon mirror 1 and the seat 2a.

This pressure distribution was measured using a pressure-sensitive film that uses microcapsules. Indicates that the physical pressure is low.

In the above embodiment shown in FIG. 2, the balance ring 3 subjected to pressure from the head of the screw 5 is distorted and unevenly transmits pressure to the urethane sheet 4; however, the pressure applied to the urethane sheet 4 is The sheet 4 is deformed to diffuse stress. Therefore, due to the deformation of the urethane sheet 4, the polygon mirror 1
As shown in FIG. 2(a), the pressure applied to the pressure has a nearly uniform distribution, and as shown in FIG. It can be seen that pressure is transmitted.

On the other hand, when the polygon mirror 1 is directly pushed by the balance ring 3 shown in Fig. 3, the aluminum balance ring 3 is slightly distorted due to the pressure of the screw head, and the pressure is dispersed to some extent inside. Most of the pressure will be applied locally to the polygon mirror 1 directly under the screw head.

Therefore, from the balance ring 3 to the polygon mirror 1, as shown in FIG.
As shown in FIG. 3(b), pressure is applied non-uniformly, and the pressure is transmitted to the surface of the seat 2a of the rotating shaft 2 while being diffused inside the polygon mirror 1, as shown in FIG. 3(b).

Furthermore, in the example shown in Fig. 4, high pressure is generated only where the polygon mirror 1 and the screw head are in contact (Fig. 4 (a)), and the pressure distribution remains uneven even through the polygon mirror 1. It is transmitted to the surface of the seat 2a (Fig. 4(b)).

Next, the polygon mirror l fixed to the rotating shaft 2 using the polygon mirror fixing method shown in this embodiment, FIGS.
The results of measuring how the flatness of the reflecting surface 1a of the polygon mirror 1 changes by increasing the temperature using an interference fringe measurement method are as follows.

In the fixing method of FIG. 2 according to the present invention, even when the temperature was raised by 30 degrees, the flatness of the reflecting surface 1a was only about 1.2 times worse than that at room temperature, whereas in FIG. In the example shown in Fig. 4, the distortion was approximately 2.5 times, and in the example shown in Fig. 4, the distortion was approximately 3.1 times.

From these results, it can be seen that in the examples according to the present invention, it is possible to press the polygon mirror with uniform pressure, and a decrease in the precision of the reflective surface of the polygon mirror can be suppressed even when the temperature rises.

FIG. 5 shows an example in which the balance ring 23 and the buffer member 24 are not separate bodies (but are integrally molded).

As for the molding method, after cutting out the CR rubber sheet, polyurethane rubber sheet, etc. which is the buffer member 24, it is glued to the balance ring 23, or after baking the CR rubber etc. 24 on the balance ring 3, the surface is polished. There are methods to obtain flatness.

[Effect of the Invention J As explained above, according to the present invention, by sandwiching the polygon mirror between the seat provided on the rotating shaft, the spacer member, and the buffer member having rubber elasticity, the polygon mirror can be held under uniform pressure. Even if the temperature rises due to heat generated by the motor during operation, deterioration in the precision of the reflective surface of the polygon mirror is suppressed, and variations in the scanning position of the light beam are suppressed to the utmost. Therefore, it is possible to obtain high-quality output images.

[Brief explanation of drawings]

FIG. 1 is a perspective exploded view showing an embodiment according to the present invention, FIGS. 2(a) and (b) are views showing pressure distribution on the front and back surfaces of a polygon mirror of an optical deflection device according to the present invention, and FIG. 3(a) , (b) is a diagram showing the pressure distribution on the front and back surfaces of the polygon mirror in an example where no buffer member is used,
FIGS. 4(a) and 4(b) are diagrams showing the pressure distribution on the front and back surfaces of the polygon mirror in an example in which the polygon mirror is fixed to the rotating shaft using direct screws, and FIG. 5 is a diagram showing another embodiment according to the present invention. 6 are explanatory diagrams of the operation of the optical deflection device. l...Polygon mirror, 2...Rotation axis, 2a...
... Seat, 3.23 ... Balance ring, 4.24
...Buffer member. 5...screw

Claims (1)

[Scope of Claims] 1. In an optical deflection device using a rotating polygon mirror for scanning a light beam from a light source onto an irradiated object, a seat provided on a rotating shaft;
The polygon mirror is held between a spacer member and a buffer member sandwiched between the spacer member and the polygon mirror, a screw is passed through the spacer member, the buffer member, and the polygon mirror, and a screw is inserted into the female thread formed in the seat of the rotating shaft. An optical deflection device characterized in that a polygon mirror is fixed to a rotating shaft by aligning the polygon mirrors together. 2. The optical deflection device according to claim 1, wherein the spacer member is a disc having substantially the same outer diameter as the seat. 3. The optical deflection device according to claim 1, wherein the buffer member is made of a material having rubber elasticity. 4. The optical deflection device according to claim 1, wherein the buffer member and the spacer member are integrally molded.