JPH09269460A - Scanning optical device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the vibration of a turning mirror. SOLUTION: Since the turning mirror 5 to turn a laser beam L1 is a long bar-shaped body, it is likely to be in a resonant state by propagating the vibration caused by the rotation of a rotary polygon mirror 3. Then, a weight 10 where an attaching position is freely changeable in a length direction is added to the turning mirror 5, and the vibration propagated to the turning mirror 5 is examined by actually rotating the rotary polygon mirror 3, so that the attaching position of the weight 10 effective for preventing resonance is selected.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a scanning optical device used in an image forming apparatus such as a laser beam printer or a laser facsimile.

[0002]

2. Description of the Related Art A scanning optical apparatus used in an image forming apparatus such as a laser beam printer or a laser facsimile generally has a light source unit E having a semiconductor laser and a collimator lens as a unit as shown in FIG. It has a rotary polygon mirror R for deflecting and scanning the laser beam L ₀ of the parallel light flux thus formed, an imaging lens F for focusing the deflected and scanned laser beam on the photosensitive member on the surface of the rotary drum N shown in FIG. The rotating polygon mirror R and the imaging lens F are housed in the optical box H, and the light source unit E is mounted on the side wall of the optical box H or the like.

The upper opening of the optical box H is closed by a lid P after all the necessary parts are incorporated in the optical box H. The side wall of the optical box H is provided with a window T through which the laser beam deflected and scanned by the rotary polygon mirror R is returned to the outside of the optical box H via the _first folding mirror M ₁ . The laser light extracted to the outside of the optical box H is
It is turned back by the turning-back mirror M ₂ and reaches the rotary drum N.

The laser light L ₀ generated from the semiconductor laser of the light source unit E is collimated by the collimator lens inside the light source unit E, is linearly focused on the reflecting surface of the rotary polygon mirror R by the cylindrical lens C, and forms an image forming lens. An image is formed on the rotating drum N through the F, the first and second folding mirrors M ₁ and M ₂ . In this way, the laser light imaged on the photoconductor on the rotary drum N forms an electrostatic latent image with the main scanning by the rotary polygon mirror R and the sub-scanning by the rotation of the rotary drum N.

In recent years, miniaturization of laser beam printers, laser facsimiles, and the like has progressed, and in addition, there has been an increasing demand for wide format compatibility. For this reason, a plurality of folding mirrors are used as described above. Various measures have been taken such as changing the traveling direction of laser light and lengthening the optical path of laser light in a narrow space.

[0006]

However, according to the above-mentioned conventional technique, the folding mirror arranged in the optical path of the laser beam is a long mirror whose both ends are fixed to the optical box by leaf springs or the like. Since it is a rod-shaped body, it is in a situation where vibration is extremely likely to occur. Therefore, in order to avoid resonance caused by the rotation of the rotary polygon mirror, the number of rotations of the rotary polygon mirror, the configuration of the mounting part of the circuit board that propagates the vibration of the drive part of the rotary polygon mirror, etc. After investigating the relationship between the vibrations generated in the mirror and the mirrors in detail, the material and shape of the mirrors are designed so that the frequencies of these vibrations do not approach the natural frequency (resonance frequency) of the mirrors. And it is necessary to select the fixing method.

However, with the development of high-speed models of rotary polygon mirrors and high-quality models in which the rotational speed of rotary polygon mirrors can be switched to select a plurality of printing resolutions, vibrations that are folded back and propagated to the mirrors are extremely high. There is a tendency for complicated multi-mode vibrations, and it is extremely difficult to prevent the resonance of the mirror by folding it back and by only devising the material, shape, or fixing method of the mirror.

Further, the dynamic imbalance during rotation of the rotary polygon mirror, the processing accuracy of the optical box, the dimensional accuracy of the folding mirror, the mounting accuracy, and the like vary considerably among the scanning optical devices. Even if the above-mentioned resonance prevention measures against multi-mode vibration can be completed at the design stage, it is still impossible to avoid unexpected vibration during the operation of each scanning optical device. It is impossible to completely take anti-vibration measures for each of the folding mirrors when two folding mirrors are provided, and the vibrations of two or more folding mirrors overlap. In this case, the optical performance of the scanning optical device may be significantly deteriorated.

The present invention has been made in view of the above-mentioned unsolved problems of the prior art, and is based on the vibration of the folding mirror provided in the optical path of the scanning light (scanning beam) of the rotary polygon mirror. It is an object of the present invention to provide a scanning optical device capable of avoiding troubles and realizing stable optical performance even in a high-end model or the like.

[0010]

In order to achieve the above object, the scanning optical apparatus of the present invention comprises a rotary polygon mirror, a driving unit for rotating the rotary polygon mirror, and a folding mirror to scan the rotary polygon mirror. It is characterized in that it has an image forming optical system for forming an image of a beam on a photoconductor, the folding mirror is provided with a weight, and its mounting position is changeable.

The weight is preferably a member having a U-shaped cross section having an inner surface that at least partially adheres to the remaining surface of the folding mirror except the reflecting surface.

It is preferable that the folding mirror has a scale for confirming the mounting position of the weight.

The folding mirror may be provided with a guide means for guiding the weight in the lengthwise direction.

[0014]

When the rotating polygon mirror is rotated, its vibrations are reflected back through the housing such as an optical box and propagated to the mirror, and the reflected mirror is brought into a resonance state and the optical characteristics of the scanning optical device are improved. There is a risk of significant damage. Therefore, a weight is added to the folding mirror to adjust the mass distribution and the like of the folding mirror so that the frequency of the vibration and the resonance frequency (natural frequency) of the folding mirror are significantly different from each other.

However, the vibration propagating to the folding mirror becomes a complex multimode vibration due to the shape of the optical box or the dynamic unbalance of the rotary polygon mirror and its driving unit, and the design of the scanning optical device. It is difficult to grasp the resonance frequency of the mirror by turning it back in stages.

In addition, since the shape error and the assembly error of the optical box, the rotary polygonal mirror and the driving portion thereof are different for each scanning optical device, the mirror can be folded back at the design stage to accurately obtain the resonance frequency of the mirror. Even if it can cope with this, an unexpected resonance state may occur during the operation of each scanning optical device.

Therefore, the mounting position of the weight to be attached to the folding mirror is configured to be changeable, and the resonance state of the folding mirror appearing during the operation of each scanning optical device is examined to examine the weight of the weight. Select the mounting position. In this way, vibration of the folding mirror can be easily and reliably prevented.

Particularly, in the case of rotating the rotary polygon mirror at a high speed, or in a high-grade scanning optical device capable of operating by changing the rotation speed of the rotary polygon mirror, a plurality of resonance frequencies of the folding mirror appear, and a narrow frequency range appears. Concentrate on. Therefore, it is extremely difficult to take anti-vibration measures at the design stage.
The situation when the scanning optical device is actually operated often deviates from the designed value. Therefore, the weight mounting position of the folding mirror is configured to be freely changeable, and the scanning optical device is actually operated to examine the resonance state of the folding mirror and select the mounting position of the weight. Is extremely effective as a reliable and inexpensive anti-vibration measure.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described with reference to the drawings.

FIG. 1 shows a scanning optical device according to an embodiment. As shown in FIG. 1A, a laser light L ₁ generated from a light source 1 is collected by a cylindrical lens 2 into a linear light beam. The light is emitted, deflected and scanned in a predetermined scanning direction by the rotary polygon mirror 3, and returned to the image forming lens 4 which is an image forming optical system, and returned through a mirror 5 to form an image on a photoreceptor on a rotating drum (not shown). The scanning light imaged on the photoconductor forms an electrostatic latent image along with the main scanning by the rotation of the rotary polygon mirror 3 and the sub-scanning by the rotation of the rotating drum.

The scanning light, which is the scanning beam of the rotary polygon mirror 3, reaches the one end of the scanning surface, is reflected by the BD mirror 6 and is introduced into the BD sensor 7, is converted into a scanning start signal, and is converted into the light source 1. Sent. The light source 1 starts the write modulation after receiving the scanning start signal.

The light source 1, the rotary polygon mirror 3, the imaging lens 4 and the like are attached to the side wall and the bottom wall of an optical box 8 which is integrated with the main body frame of the scanning optical device. The rotary drum is arranged outside the optical box 8, and a window 9 for taking out scanning light from the optical box 8 toward the rotary drum is provided on the bottom wall of the optical box 8. Further, the upper opening of the optical box 8 is closed by a lid member (not shown), and the lid member is screwed to the optical box 8 at its peripheral edge.

As shown in FIG. 1B, the folding mirror 5 has a rod-shaped main body 5a elongated in the main scanning direction, and both ends thereof are integrated with the optical box 8 by leaf springs (not shown). It is pressed by a mirror support. In this way, the optical box 8
The folding mirror 5 fixed to has a weight 10,
This is added to the remaining part of the folding mirror 5 except the reflecting surface 5b.

The weight 10 is turned back so that the resonance frequency of the turning mirror 5 is largely deviated from the frequency of vibration caused by the rotation of the drive motor, which is the driving portion of the rotary polygonal mirror 3, and the mass distribution of the turning mirror 5 and the like. It is provided to adjust the. The main body of the weight 10 is a member having a U-shaped cross section, which surrounds the remaining surface of the folding mirror 5 except for the reflecting surface 5b, and has an inner surface at least a portion of which is folded back and closely adheres to the mirror 5. The weight 10 is slidable in the length direction of the weight 10 by a human force or a tool, and the weight 10
It is configured such that it can be fixed to the mirror 5 by folding only at an arbitrary position in the length direction thereof by the frictional force with the mirror 5 or the elastic force of the weight 10 itself.

The vibrations that are reflected from the drive motor or the like and are propagated to the mirror 5 during rotation of the rotary polygon mirror 3 are the number of faces (number of mirror surfaces) of the rotary polygon mirror 3 and the number of poles of the magnet of the drive motor. Has a fundamental frequency according to the above, and has a plurality of vibration modes depending on the shape of the optical box 8 and the dynamic unbalance of the entire rotating body including the rotary polygon mirror 3 and the drive motor. Therefore, it is difficult to accurately select the mounting position of the weight 10 corresponding thereto at the design stage, and even if the mounting position of the weight 10 is assembled according to the design value, the shape error of the optical box 8 and the rotary polygon mirror 3 Due to the assembling error and the like, the frequency of the vibration propagating to the folding mirror 5 often deviates from what was predicted at the design stage, and it is difficult to prevent the folding mirror 5 from resonating. Further, in the case of a high-end model in which the rotational speed of the rotary polygon mirror 3 is changed in several stages, it becomes even more difficult to avoid the resonance of the folding mirror 5.

Therefore, for each scanning optical device, first, the weight 10 is folded back and attached at an appropriate position on the mirror 5 to rotate the rotary polygon mirror 3, and a large vibration is generated during its rising and during operation. When doing so, the frequency characteristic of the vibration propagating to the reflecting surface 5b of the folding mirror 5 is examined and the mounting position of the weight 10 is changed.

For example, the material of the folding mirror 5 has a density of 2450 kg / m ³ , Young's modulus of 8 × 10 ¹⁰ pa, the folding mirror 5 has a thickness of 5 mm, a width of 10 mm, and a length of 263 m.
m, and weighs 5g at its center, the width S ₁ 7 mm, height S
_When a weight 10 of ₂ 14 mm and a thickness S _{3 of} 9 mm is attached, when the frequency characteristic of vibration measured on the reflection surface 5b of the folding mirror 5 is represented by the graph (a) shown by the solid line in FIG. When the weight 10 is folded back and moved by 10 mm in the length direction of the mirror 5, the vibration of the reflection surface 5b of the folded mirror 5 changes to the graph (b) shown by the broken line in the figure. That is, when the weight 10 is located at the center of the folding mirror 5, the primary peak of vibration is 188 Hz,
The secondary peak is 310Hz and the tertiary peak is 380H
It can be seen that the z- and fourth-order peaks at 550 Hz are shifted to 205 Hz, 340 Hz, 380 Hz, and 580 Hz, respectively.

As described above, by adjusting the mounting position of the weight of the folding mirror for each scanning optical device and changing the resonance frequency of the folding mirror, the vibration is effectively avoided, The optical performance of the image forming apparatus can be greatly improved.

In particular, in the case of using a plurality of folding mirrors or in a scanning optical device in which a rotary polygon mirror is rotated at high speed, troubles caused by the vibrations of the folding mirrors may cause a significant deterioration in image quality. Therefore, as described above, it is extremely important to take detailed anti-vibration measures for each scanning optical device.

As shown in FIG. 3, if the scale 5d is provided on the upper end surface 5c of the folding mirror 5 with oily ink or the like so that the mounting position of the weight 10 can be confirmed, It is very convenient when adjusting the mounting position of the weight 10, and the efficiency of the assembly work can be greatly improved.

Further, instead of the weight 10 having a U-shaped cross section which surrounds the surface of the folding mirror 5, as shown in FIG.
A long groove 15c, which is a guide means, is formed on each of the upper end surface 15a and the lower end surface 15b of the folding mirror 15, and the weight 20
The locking member 20a provided in the above may be slidably engaged with each long groove 15c. In this case, there is an added advantage that the width of the reflecting surface of the folding mirror 15 can be expanded to the entire height of the folding mirror 15.

Further, as shown in FIG. 5, a flat weight 30 is integrally connected with a spring 31 which is an elastic member, and is folded back by the spring 31 to elastically clamp the mirror 5. May be.

Alternatively, as shown in FIG. 6, a convex portion 40a, which is an engaging portion, is provided on the inner surface of the weight 40 having a U-shaped cross section, and these are folded back to form a deformed portion on each end surface of the mirror 55. The weight 40 may be fixed by engaging with the recess 55a.

[0034]

Since the present invention is configured as described above, it has the following effects.

The trouble due to the vibration of the folding mirror provided in the optical path of the scanning light (scanning beam) of the rotary polygonal mirror is avoided, and the stable optical performance is achieved even in a high-grade model or a high-speed scanning optical device. Can be realized.

By mounting such a scanning optical device, it is possible to greatly contribute to the high performance of the image forming apparatus.

[Brief description of drawings]

FIG. 1 shows a scanning optical device according to one embodiment,
(A) is a schematic perspective view showing the whole, (b) is a perspective view showing only the folding mirror, and (c) is a sectional view of (b).

FIG. 2 is a graph showing a frequency characteristic of vibration generated in a folding mirror.

FIG. 3 is a perspective view showing a folding mirror according to a first modification.

4A and 4B show a folding mirror according to a second modification, wherein FIG. 4A is a perspective view thereof, and FIG. 4B is a sectional view thereof.

5A and 5B show a folding mirror according to a third modification, wherein FIG. 5A is a perspective view thereof, and FIG. 5B is a sectional view showing only a weight.

6A and 6B show a folding mirror according to a fourth modification, wherein FIG. 6A is a perspective view thereof, and FIG. 6B is a sectional view thereof.

FIG. 7 is a schematic perspective view showing a scanning optical device according to a conventional example.

8 is a cross-sectional view showing the scanning optical device of FIG.

[Explanation of reference numerals] 1 light source 3 rotating polygon mirror 4 imaging lens 5, 15, 55 folding mirror 8 optical box 9 window 10, 20, 30, 40 weight

Claims (7)

[Claims] 1. A rotary polygonal mirror, a drive unit for rotating the rotary polygonal mirror, and an image forming optical system for forming an image of a scanning beam of the rotary polygonal mirror on a photoconductor through a folding mirror. A scanning optical device, wherein the mirror is provided with a weight, and the mounting position of the mirror is freely changeable. 2. The mounting position of the weight is changeable in the length direction of the folding mirror.
A scanning optical device as described. 3. The member according to claim 1, wherein the weight is a member having a U-shaped cross section, the member having an inner surface that at least partially adheres to the remaining surface of the folding mirror except the reflecting surface. Scanning optics. 4. The scanning optical device according to claim 1, wherein the folding mirror includes a scale for confirming a mounting position of the weight. 5. The scanning optical device according to claim 1, wherein the folding mirror includes guide means for guiding the weight in the lengthwise direction. 6. The scanning optical device according to claim 1, wherein the weight has an elastic member that elastically clamps the folding mirror. 7. The scanning optical device according to claim 1, wherein the weight has an engaging portion that is engageable with each of the plurality of deformed portions provided on the folding mirror.