JP3397572B2 - 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 apparatus used in an image forming apparatus such as a laser beam printer or a laser facsimile generally has a light source unit S ₀ having a semiconductor laser and a collimator lens as a unit, as shown in FIG. a rotary polygonal mirror R ₀ for deflecting and scanning the laser beam L ₀ of the generated parallel beam, has a lens F ₀ such that images on the photoreceptor surface of the rotary drum (not shown) deflection scanned laser beam, rotating The polygon mirror R ₀ and the lens F ₀ are housed in the optical box 110, and the light source unit S ₀ is the side wall 1 of the optical box 110.
10a etc. are 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 R ₀ toward an external rotary drum.

The laser light L ₀ generated from the semiconductor laser of the light source unit S ₀ is collimated by the collimator lens inside the light source unit S ₀ and is linearly focused on the reflecting surface of the rotary polygon mirror R ₀ by the cylindrical lens E ₀ . It is taken out from the window 111 of the optical box 110 toward the rotary drum through the lens F ₀ and the mirror M ₀ . In this way, the laser light imaged on the photosensitive member on the rotating drum forms an electrostatic latent image with the main scanning by the rotating polygon mirror R ₀ and the sub-scanning by the rotation of the rotating drum.

[0005] Motor H ₀ for rotating the rotary polygon mirror R ₀
Is composed of a rotor integrated with the rotary polygon mirror R ₀ and a stator mounted on the motor board G ₀ , and the stator is excited by a drive current supplied from a drive circuit on the motor board G ₀ to drive the rotor. Rotate.

The motor substrate G ₀ is fixed to a bearing portion of the motor H ₀ , and the bearing portion has a lens F ₀ and a folding mirror M.
It is fixed to the bottom wall of the optical box 110 together with ₀ . Optical box 1
The bottom wall of 10 is fastened to the main body frame 120 of the scanning optical device through a support member 112 provided at four corners 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 conventional technique, when the scanning optical device is sped up, the fundamental frequency of the motor rises and becomes equal to or exceeds the resonance frequency of the optical box. Resonance occurs during start-up, stop, or operation.

In recent years, the design value of the rotational speed of the rotary polygon mirror often reaches 20,000 rpm, and the basic frequency of the motor at this time is 350 Hz or higher. On the other hand, the resonance frequency of the optical box is generally 350 Hz or less,
In many cases, the fundamental frequency of the motor coincides with or exceeds the resonance frequency of the optical box. When the fundamental frequency of the motor matches the resonance frequency of the optical box, the resonance occurs during operation, the optical box vibrates greatly, noise is generated, and uneven pitches occur in the image. In addition, if the fundamental frequency of the motor exceeds the resonance frequency of the optical box, it is inevitable that the optical box resonates and generates a large amount of noise when the motor starts and stops.

In addition, as described above, if the material of the optical box is a resin material, its rigidity is insufficient, and vibrations due to the rotation of the motor are transmitted to the optical box, causing a problem such as deterioration of image quality.

The present invention has been made in view of the above-mentioned unsolved problems of the prior art, and generates a large amount of noise or deteriorates the image quality due to the vibration of the optical box that houses the rotary polygon mirror and the lens. An object of the present invention is to provide a scanning optical device capable of effectively avoiding troubles such as occurrences of the above.

[0011]

In order to achieve the above object, a scanning optical device of the present invention comprises a rotary polygonal mirror, a drive unit for rotating the rotary polygonal mirror, and a scanning beam of the rotary polygonal mirror formed on a photoconductor. And an optical box for accommodating the rotary polygonal mirror and the image forming optical system, and a supporting means for supporting the same. The connecting portion of the optical box to the supporting means is the optical box of the optical box. It is arranged at or above the central portion in the height direction, and is configured so that the following relationship is established between the height A of the entire optical box and the height B of the coupling portion. .

(1/3) A ≦ B ≦ A It is preferable that a reinforcing protrusion is formed on the side wall of the optical box.

[0013] It is preferable that the reinforcing projections are continuously arranged on the entire outer peripheral edge of the optical box.

[0014]

The connecting portion of the optical box to the supporting means such as the main body frame of the image forming apparatus such as a laser facsimile is arranged at the central portion in the height direction of the optical box or above it. Since the resonance frequency of the optical box is significantly increased as compared with the case where the bottom of the optical box is coupled to the supporting means, the rotating polygon mirror is
Even when the motor is rotated at a rotation speed of 000 rpm or more, there is no possibility that the fundamental frequency of the motor of the drive unit will coincide with or exceed the resonance frequency of the optical box.

Thus, resonance of the optical box is prevented, and unevenness in image pitch and noise due to vibration of the optical box are avoided.

If the reinforcing protrusion is formed on the side wall of the optical box, the resonance frequency of the optical box is further increased. In addition, the rigidity of the optical box is significantly enhanced, which is effective in preventing the vibration of the motor from propagating to the optical box.

As a result, a scanning optical device having high performance and suitable for high speed can be realized.

[0018]

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 the scanning optical device according to the first embodiment with a lid member removed, which is a light source unit S _{1 in} which a semiconductor laser and a collimator lens are unitized, and the light source unit. Figure a cylindrical lens E ₁ for condensing the laser beam on the reflecting surface of the rotary polygon mirror R _1, the scanning light L ₁ is deflected scanned the scanning beam by the rotating polygonal mirror R ₁ of the parallel light beam generated from the S ₁ 2 has a lens F ₁ which is an image forming optical system for forming an image on the photosensitive member on the rotating drum D ₁ and a folding mirror M ₁ , and includes a rotating polygon mirror R ₁ , a cylindrical lens E ₁ , and a lens F _1. The folding mirror M ₁ is housed in the optical box 10. The upper opening of the optical box 10 is closed by the lid member after assembling each component in the optical box 10.

The rotating drum D ₁ is arranged outside the optical box 10, and the scanning light L ₁ is turned back and reflected by the mirror M ₁ , and is rotated from a window 11 provided on the bottom wall of the optical box 10. It is taken out toward D ₁ .

[0021] Motor H ₁ of the drive unit for rotating the rotary polygon mirror R ₁ have a rotor integral with the rotary polygon mirror R _1, the stator is integral with the motor substrate G _1, the motor substrate G
_The stator is excited by the drive current supplied from the drive circuit above ₁ to rotate the motor H ₁ .

The scanning light L ₁ for forming on a photosensitive member of the rotary drum D _1, an electrostatic latent on the photosensitive member with the sub-scanning by rotation of the main scanning and the rotary drum D ₁ by the rotation of the rotary polygon mirror R ₁ Form an image.

The side wall 10a of the optical box 10 has a supporting member 12 which is four connecting portions, and the optical box 10 has a boss portion of the main body frame 20 which is a supporting means of the scanning optical device. It is fixed to this by screwing it to 21.

It should be noted, a portion of the scanning light L ₁ of the rotating polygon mirror R ₁ are separated by detecting the mirror D ₁ as a scanning start signal is introduced into the optical fiber C _1. The semiconductor laser of the light source unit S ₁ receives the scan start signal transmitted by the optical fiber C ₁ and starts modulation for image writing.

The optical box 10 is generally made of synthetic resin,
Since the resonance frequency is 350 Hz or less, when the rotary polygon mirror R ₁ rotates at a rotation speed of 20,000 rpm or more, the optical box 10 vibrates greatly due to resonance, and significant pitch unevenness or the like occurs.

Therefore, each support member 12 is disposed near the center of the height of the side wall 10a of the optical box 10, and is screwed to the upper end of the boss portion 21 of the main body frame 20 to resonate the optical box 10. Increase the frequency.

When each support member 12 is provided near or above the center of the optical box 10 in the height direction and is fixed to the body frame 20, each support member 12 is provided at the bottom of the optical box 10.
It has been proved by experiments that the primary resonance frequency of the optical box 10 is significantly increased as compared with the case where the optical box 10 is provided and is screwed to the main body frame 20.

FIG. 3 shows the height A of the side wall 10a of the optical box 10.
3 is a graph showing the results of an experiment in which the primary resonance frequency of the optical box 10 was measured while changing the ratio k of the distance C from the support member 12 to the upper end of the side wall 10a. As you can see from this figure, k
Is 2/3 or less, that is, the mounting height B of the support member 12
However, if the height A of the optical box 10 is ⅓ or more, the primary resonance frequency of the optical box 10 is significantly increased. The reason is,
Since the vicinity of the upper end of the side wall 10a of the optical box 10 is a free end and easily vibrates as compared with the lower end constrained by the bottom wall,
From the height center of the side wall 10a to the upper side, the main body frame 20
It is presumed that the binding force of the side wall 10a is strengthened by fixing it to.

In this embodiment, as described above, the resonance frequency of the optical box is increased by fixing the central portion of the side wall of the optical box or a portion located above it to the body frame.
It is intended to realize a scanning optical device in which there is no fear that the optical box resonates to cause pitch irregularity even when the rotary polygon mirror is rotated at a high speed. By using such a scanning optical device,
An image forming apparatus having good image quality and suitable for speeding up can be obtained.

FIG. 4 shows a second embodiment, which is
Similar to the first embodiment, four supporting members 32 are provided at the central portion of the side wall 30a of the optical box 30 in the height direction, and the reinforcing ribs 33, which are protrusions along the entire periphery of the optical box 30, are provided.
Is provided.

The width dimension of the reinforcing rib 33 is the same as that of each supporting member 32.
In the vicinity of, the fin 33a having a substantially triangular shape is gradually expanded to have the same width. In addition, the side wall 3 of the optical box 30
0a indicates the light source unit S _{1 as} shown in FIG.
Has a through hole 34 for penetrating the cylindrical holder S ₂ . Therefore, an annular rib 35 is provided around the through hole 34 and is integrated with the reinforcing rib 33. In this way, the entire outer peripheral edge of the optical box 30 is continuously reinforced without interruption. Incidentally, in the vicinity of the annular rib 35, a pedestal 36 having a threaded hole is provided integrally with the side wall 30a, the substrate of the light source unit S ₁ by screws to each seat 36, a light source unit S ₁ It is configured to be assembled to the optical box 30.

In the present embodiment, the rigidity of the side wall of the optical box is significantly strengthened by the reinforcing ribs, etc., whereby the resonance frequency of the optical box is further increased, and even if the rotary polygon mirror is rotated at high speed, There is no worry about the box resonating. Further, by strengthening the rigidity of the optical box, it is possible to prevent the vibration of the motor from propagating to the lens and the like through the optical box, and avoid the deterioration of the image quality due to the vibration of the lens and the like. This can greatly contribute to the improvement of image quality.

Note that, instead of the reinforcing ribs that surround the entire outer peripheral edge of the optical box, as shown in FIG. 5, only the fins 43a may be provided near the supporting member 42. It has been found that this alone has a great effect in sufficiently strengthening the rigidity of the optical box 40 and preventing resonance and the like.

The light source unit S ₁ and the rotary polygon mirror R
_The lens ₁ , the lens F ₁ , the folding mirror M _{1 and the} like are the same as those in the first embodiment, so they are designated by the same reference numerals, and the description thereof is omitted.

[0035]

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

It is possible to avoid the vibration of the optical box that houses the rotary polygon mirror and the lens, and realize a high-performance scanning optical device suitable for high speed operation.

[Brief description of drawings]

FIG. 1 is a schematic plan view showing a scanning optical device according to a first example.

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

FIG. 3 is a graph showing the results of measuring the primary resonance frequency of the optical box while changing the mounting height.

4A and 4B show a second embodiment, wherein FIG. 4A is a schematic perspective view thereof, and FIG. 4B is a perspective view showing only a portion to which a light source unit is attached in an exploded manner.

FIG. 5 is a schematic plan view showing a modification of the second embodiment.

FIG. 6 is a schematic perspective view showing a conventional example.

[Explanation of symbols]

10,30,40 Optical box 10a, 30a Side wall 11 windows 12, 32, 42 Support member 20 body frame 21,31 Boss 33 Reinforcing rib 33a, 43a fins

Claims (3)

(57) [Claims] 1. A rotary polygon mirror, a drive unit for rotating the rotary polygon mirror, an image forming optical system for forming an image of a scanning beam of the rotary polygon mirror on a photosensitive member, and the rotary polygon mirror and the image forming optical system. An optical box and a supporting means for supporting the optical box, and the connecting portion of the optical box to the supporting means is arranged in the central portion in the height direction of the optical box or above the optical box, A scanning optical device, characterized in that the following relationship is established between the height A and the height B of the connecting portion. (1/3) A ≦ B ≦ A 2. The scanning optical device according to claim 1, wherein a reinforcing protrusion is formed on a side wall of the optical box. 3. The scanning optical device according to claim 2, wherein the protrusion for reinforcement is arranged continuously over the entire outer peripheral edge of the optical box.