JP3408080B2 - Scanning optical device - Google Patents

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 device used in an image forming apparatus such as a laser beam printer or a laser facsimile generally has a light source unit 101 having a semiconductor laser and a collimator lens as a unit, as shown in FIG. The rotary polygon mirror 102 has a rotary polygon mirror 102 for deflecting and scanning the parallel laser beam L ₀ of the parallel light flux, a lens 103 for focusing the deflected and scanned laser light on a photosensitive member on the surface of a rotary drum (not shown), and the like. And lens 103 is optical box 11
0, and the light source unit 101 is the optical box 11
No. 0 side wall 110a or the like is assembled.

The upper opening of the optical box 110 is the optical box 110.
After incorporating all the necessary parts inside, it is closed by a lid member (not shown). The lid member is an optical box 110.
Is a flat plate that is in contact with the upper end of the side wall 110a of the above, and is fixed to the optical box 110 by a known method such as screwing. In addition,
A window 111 is provided on the bottom wall of the optical box 110 to take out the laser beam deflected and scanned by the rotary polygon mirror 102 toward an external rotary drum.

The laser light L ₀ generated from the semiconductor laser of the light source unit 101 is collimated by the collimator lens inside the light source unit 101, linearly condensed by the cylindrical lens 101a on the reflecting surface of the rotary polygon mirror 102, and the lens 103 It is taken out from the window 111 of the optical box 110 toward the rotary drum through the folding mirror 104. In this way, the laser light imaged on the photoconductor on the rotating drum forms an electrostatic latent image with the main scanning by the rotating polygon mirror 102 and the sub-scanning by the rotation of the rotating drum.

A motor 1 for driving the rotary polygon mirror 102 to rotate.
Reference numeral 02a includes a rotor integrated with the rotary polygon mirror 102 and a stator mounted on the motor board. The stator is excited by a drive current supplied from a drive circuit on the motor board to rotate the rotor.

The bottom wall of the optical box 110 is provided with supporting members 112 provided at the four corners, and a main body frame 12 of the scanning optical device is provided.
It is fastened to 0 by a known method such as screwing. The optical box 110 is integrally formed of a generally known resin material.

[0007]

However, according to the above-mentioned prior art, during the rotation of the rotary polygonal mirror, its vibration propagates to the folding mirror through the optical box, which causes the folding mirror to vibrate and generate the laser beam. There is an unsolved problem that the image forming position fluctuates and image deterioration such as pitch unevenness occurs.

The folding mirror is a long object arranged along the side wall at one end of the optical box, and is itself in a state where it is extremely susceptible to vibration. In addition, the bottom wall of the optical box has a window for extracting the laser light at a portion located directly below the folding mirror, so that the rigidity of the optical box is lowered particularly near the folding mirror, which causes local Vibration is likely to occur.

In recent years, the rotational speed of the rotary polygon mirror has become 20,0.
A scanning optical device that reaches 00 rpm has also been developed, and in such a scanning optical device, the fundamental frequency of the motor that rotates the rotary polygon mirror is 350 Hz or higher. On the other hand, since the resonance frequency of the optical box is generally 350 Hz or less, there is a possibility that a resonance state may occur during start-up or operation of the motor.

As shown in FIG. 5, the vibration of the rotary polygon mirror motor causes a waviness in the optical axis direction (X-axis direction) on the side wall 110a of the optical box 110, and an arrow appears on the folding mirror 104 adjacent thereto. Induces rotational vibration as indicated by R.

Particularly, in an A size printer or the like, the effective length W of the folding mirror 104 is required to exceed 200 mm. Therefore, rotational vibration of the folding mirror 104 greatly increases the speed and size of the scanning optical device. It becomes an obstacle.

The present invention has been made in view of the above-mentioned unsolved problems of the prior art, and provides a scanning optical device which can greatly contribute to the improvement of image quality and the speeding up of printing by reducing the vibration of the folding mirror. It is intended to be provided.

[0013]

In order to achieve the above object, the scanning optical device of the present invention comprises a rotary polygon mirror rotated by a driving means, and a folding mirror arranged in the optical path of the scanning light. An optical box that houses the folding mirror and the rotary polygon mirror is provided, and the optical box has a side wall of a double wall structure in a portion near the folding mirror.

The cross section of the side wall of the double wall structure may be a U-shape that faces upward or downward.

The cross section of the side wall of the double wall structure may be H-shaped having a horizontal rib at the center of the height.

[0016]

The rigidity is strengthened by locally forming the double wall structure on the side wall of the optical box in the region close to the folding mirror. As a result, it is possible to prevent the side wall near the folding mirror from being largely deformed due to the vibration caused by the rotation of the rotary polygon mirror, and to avoid the rotational vibration of the folding mirror and to significantly improve the image quality. Further, by eliminating the local lack of rigidity of the optical box, the vibration resistance of the entire optical box can be enhanced, and the speedup of the scanning optical device can be greatly promoted.

[0017]

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

FIG. 1 is a plan view showing a scanning optical device according to an embodiment with a lid member removed, which is a light source unit 1 in which a semiconductor laser and a collimator lens are unitized, and the light source unit 1 A cylindrical lens 1a for condensing the generated parallel-beam laser light on the reflecting surface of the rotary polygon mirror 2 and a scanning light L ₁ deflected and scanned by the rotary polygon mirror 2 are imaged on a photoconductor on the rotary drum D. It has a lens 3 and a folding mirror 4, and the rotary polygon mirror 2, the cylindrical lens 1 a, the lens 3 and the folding mirror 4 are housed in an optical box 10. The upper opening of the optical box 10 is closed by a lid member (not shown) after assembling each component in the optical box 10.

The rotary drum D is arranged outside the optical box 10, and the scanning light L ₁ is reflected by the folding mirror 4 and goes toward the rotary drum D from a window 11 provided on the bottom wall of the optical box 10. Taken out.

A motor 2a, which is a driving means for rotating the rotary polygon mirror 2, has a rotor integral with the rotary polygon mirror 2 and a stator integral with the motor substrate, and is supplied from a drive circuit on the motor substrate. The drive current excites the stator to rotate the motor 2a.

Scanning light L focused on the photosensitive member of the rotating drum D
₁ is the main scanning by the rotation of the rotary polygon mirror 2 and the rotary drum D.
An electrostatic latent image is formed on the photoconductor in association with the sub-scanning due to the rotation of.

The side wall 10a of the optical box 10 has a plurality of supporting members 12, and the optical box 10 is fixed to each of the supporting members 12 by screwing each supporting member 12 to the main body frame 13 of the scanning optical device.

A part of the scanning light L ₁ of the rotary polygon mirror 2 is separated by the detection mirror 5 as a scanning start signal,
It is introduced into the optical fiber 6. The semiconductor laser of the light source unit 1 receives the scanning start signal transmitted by the optical fiber 6 and starts modulation for image writing.

The folding mirror 4 is a long object arranged along one side wall 10a at one end of the optical box 10, and both ends thereof are integrated with the optical box 10 as shown in FIG. 1 (b). Since it is only supported by the mirror support 14, it is in a state where it is extremely susceptible to vibration. In addition, on the bottom wall of the optical box 10, a window 11 for taking out the scanning light L ₁ is opened at a portion located directly below the folding mirror 4,
Local rigidity shortage occurs in this vicinity.

Therefore, the side wall 10a of the optical box 10 is locally provided with a double wall structure along the folding mirror 4 to enhance the rigidity of this portion. It consists of a hollow wall 20 with an upwardly facing U-shaped cross section, the bottom of which is an optical box 10.
It is one with the bottom wall. Further, the hollow portion 20a is divided into a plurality of sections by the vertical ribs 21 arranged at equal intervals in the Y-axis direction. If the side wall 10a of the optical box 10 is locally strengthened by such a double wall structure, the side wall 10a undulates near the folding mirror 4 even if the vibration of the motor 2a of the rotary polygon mirror 2 propagates. As a result, troubles such as rotational vibration of the folding mirror 4 can be avoided.

In addition, the rigidity of the optical box 10 as a whole can be improved by reinforcing the most rigid part of the optical box 10. By increasing the resonance frequency of the optical box 10 in this way, speeding up of the scanning optical device can be greatly promoted.

In place of the hollow wall 20 having a U-shaped cross section that opens upwardly at a part of the side wall 10a of the optical box 10, as shown in FIG. 2, an H-shaped cross section having a horizontal rib 30a at the center of height. Hollow wall 30 may be used, or, as shown in FIG. 3, a hollow wall 40 having an inverted U-shaped cross section that opens downward may be used.

According to the present embodiment, the rigidity required to prevent the vibration of the folding mirror and the like is secured by simply forming a part of the side wall of the optical box into a double wall structure, and the vibration of the folding mirror and the like are secured. It is possible to avoid deterioration of image quality such as pitch unevenness due to.

Further, by eliminating the local lack of rigidity of the optical box, the vibration resistance of the entire optical box can be improved and the speeding up of the scanning optical device can be greatly promoted.

[0030]

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

It is possible to prevent the folding mirror from vibrating during the rotation of the rotary polygon mirror, which can greatly contribute to the improvement of image quality and the speeding up of printing. By using such a scanning optical device,
A high-performance image forming apparatus suitable for high speed can be realized.

[Brief description of drawings]

FIG. 1 shows a scanning optical device according to an embodiment,
(A) is a perspective view showing the whole, (b) is A- of (a).
It is a fragmentary sectional view taken along the line A.

FIG. 2 is a partial cross-sectional view showing a modified example of the device of FIG.

FIG. 3 is a partial cross-sectional view showing another modified example of the apparatus of FIG.

FIG. 4 is a perspective view showing a conventional example.

FIG. 5 is a diagram illustrating rotational vibration of a folding mirror.

[Explanation of symbols]

2 rotating polygon mirror 3 lenses 4 folding mirror 10 Optical box 11 windows 12 Support member 13 body frame 20, 30, 40 hollow wall

Claims (3)

(57) [Claims] 1. A rotary polygon mirror rotated by a driving means, and a folding mirror arranged in an optical path of scanning light thereof.
A scanning optical device comprising: an optical box that houses the folding mirror and the rotary polygonal mirror, and the optical box has a side wall of a double wall structure in a portion near the folding mirror. 2. The scanning optical device according to claim 1, wherein the side wall of the double wall structure has a U-shaped cross section that faces upward or downward. 3. The scanning optical device according to claim 1, wherein the cross section of the side wall of the double wall structure is H-shaped having a horizontal rib at the center of height.