JP2000298243A - Scanning optical device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce noise, etc., due to excitation sound of a DC motor which drives and rotates a rotating polygon mirror. SOLUTION: The DC motor which drives the rotating polygon mirror 1 is composed of a rotor magnet 5 united with the rotating polygon mirror 1 and a stator coil 7 facing it. To reduce the noise which propagates from a noise source Q at the outer peripheral part of the stator coil 7 to a lid member 60, a propagation path (2L+L1) of a reflected propagated sound which is reflected by a bottom surface 50a of an optical box 50 and reaches the lid member 60 is set 1/2λlonger than the propagation path L1 of a direct propagated sound, and thus the two sounds are muted by mutual interference.

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, an LED printer, and a laser facsimile for forming an image on a transfer sheet by an electrophotographic method.

[0002]

2. Description of the Related Art A scanning optical apparatus used in an electrophotographic image forming apparatus such as a laser beam printer or a laser facsimile machine deflects and scans a light beam such as a laser beam with a rotating polygon mirror rotating at a high speed. The scanning light is imaged on a photoreceptor on a rotating drum to form an electrostatic latent image.
Next, the electrostatic latent image on the photoreceptor is visualized into a toner image by a developing device, transferred to a recording medium such as recording paper, sent to a fixing device, and printed by heating and fixing the toner on the recording medium ( Print) is performed.

In recent years, the speed of the scanning optical device has been increased, and a rotating polygon mirror having a rotating speed exceeding 30,000 rpm has been developed.

FIG. 6 shows a main part of a scanning optical device according to a conventional example, which comprises a rotating shaft 103 supported on an optical box 100 via a bearing 102 such as a ball bearing.
And a yoke 105a and a rotor magnet 10 integrally connected to a washer 104 integrated with the rotating shaft 103.
5 and a stator coil 107 fixed to a motor substrate 106 integral with the bearing housing 102a. The rotating polygon mirror 101 includes a holding spring 108a and a spring holding 10
8b, elastic pressing mechanism 108 including G ring 108c, etc.
Is pressed by the washer 104, and is integrated with the rotating shaft 103 and the rotor magnet 105 via the washer 104.

When the stator coil 107 is excited by a drive current supplied from a drive circuit on the motor board 106, the rotor magnet 105 rotates at a high speed together with the rotary polygon mirror 101, and as described above, the rotary polygon mirror 101
Is deflected and scanned by the light beam applied to the.

When the rotary polygon mirror 101 is rotated at a high speed, a dynamic imbalance occurs due to an imbalance in the mass of the entire rotating body including the rotary polygon mirror 101, the rotor magnet 105, the yoke 105a, the washer 104, the elastic pressing mechanism 108, and the like. Is generated, and due to whirling vibration caused by this,
The image quality of the image forming apparatus may be degraded. Therefore,
Balance grooves 109a and 109b are formed on the upper surface of the rotating polygon mirror 101 and the upper surface of the yoke 105a of the rotor magnet 105.
And a weight 110 or the like is adhered thereto to reduce the imbalance of the mass of the rotating body.

[0007]

However, according to the above-mentioned prior art, vibration is generated by switching the excitation of the stator coil from the motor section for rotating the rotary polygon mirror. This vibration is transmitted from the stator coil to the motor substrate and causes it to resonate, resulting in high-frequency noise called excitation noise (switching noise). Also, it acts as a vibration source for vibrating the lid member and the optical box, and causes uneven pitch of scanning lines. And the like, deteriorating the image performance.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned unsolved problems of the prior art, and reduces vibration and noise generated from a motor section of a rotary polygon mirror, thereby achieving high-quality, low-noise scanning optics. It is intended to provide a device.

[0009]

In order to achieve the above object, a scanning optical apparatus according to the present invention comprises: a rotating polygon mirror for deflecting and scanning a light beam; and a deflection scanning means comprising a DC motor for rotating and driving the rotating polygon mirror. And a housing having the deflection scanning means built therein, wherein the housing has an opposing wall disposed at a distance (L) from the noise source of the DC motor that satisfies the following relationship. And L ≒ 15c / (NPW) where c: sound speed N: steady-state rotation speed (rpm) of DC motor P: number of magnetized poles of DC motor W: number of phases of drive current of DC motor

[0010] The distance (L) between the opposed wall surfaces may be configured to satisfy the following relationship. 15c / (NPW) <L <30c / (NPW)

[0011] The opposed wall surface is preferably a bottom surface of the housing.

[0012] The opposed wall surface may be an inner surface of a lid member that closes an opening of the housing.

Further, it is preferable that the distance (L) between the opposed wall surfaces satisfies the following relationship. L ≒ 15c / (NPWn) where c: sound speed N: steady-state rotation speed (rpm) of DC motor P: number of magnetized poles of DC motor W: number of phases of drive current of DC motor n: natural number

It is preferable that the facing wall has a plurality of steps.

[0015]

In the DC motor that rotates the polygon mirror, the stator coil and the motor substrate that generate the excitation sound act as a noise source to vibrate the lid member and the like, causing trouble such as noise. Therefore, the sound wave of the excitation sound reflected by the opposing wall surface such as the bottom surface of the housing and reaching the lid member and the sound wave of the excitation sound directly reaching the cover member and the like from the noise source of the DC motor are reduced by about 1 /.
By shifting by two wavelengths, the excitation sound propagating to the lid member is attenuated by the interference between the so-called direct propagation sound and the reflected propagation sound.

As described above, the direct propagation sound and the reflection propagation sound are divided by 1 /.
To shift by two wavelengths, the distance (L) between the noise source and the opposing wall surface, such as the bottom surface, that faces the noise source, such as the stator coil of the DC motor, on the opposite side of the lid member, satisfies the expression (1). The configuration is as follows.

If the distance (L) satisfies the expression of claim 2, noise and vibration can be reduced in a wide speed range including when the DC motor starts up and when it rotates at a low speed. it can.

Further, if the distance (L) is configured to satisfy the expression of claim 7, a plurality of peaks of the excitation sound are attenuated, thereby effectively reducing noise and vibration. it can.

[0019]

Embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a schematic sectional view showing a main part of a scanning optical apparatus according to a first embodiment, which comprises a rotating polygon mirror 1 having a plurality of reflecting surfaces on a polygonal prism-shaped side surface, and a housing. A rotating shaft 3 rotatably supported by an optical box 50 via a bearing 2, a rotor magnet 5 integrally connected to the rotating shaft 3 via a washer 4, and a motor housing 6a. It has a stator coil 7 fixed to a motor substrate 6, and the stator coil 7 constitutes a DC motor for rotating the rotary polygon mirror 1 together with the rotor magnet 5. The rotating polygon mirror 1 has a washer 4
, And is integrated with the rotating shaft 3 through the washer 4, and constitutes a deflection scanning unit together with the DC motor.

When the stator coil 7 is excited by a drive current supplied from a drive circuit on the motor board 6, the rotor magnet 5 rotates together with the rotating shaft 3 and the rotating polygon mirror 1, and the rotating magnet 3 rotates on the reflecting surface of the rotating polygon mirror 1. The light beam such as the irradiated laser beam is deflected and scanned.

The optical box 50 incorporates an image forming lens 52 and the like together with the rotary polygon mirror 1 as described later, and an upper opening of the optical box 50 is closed by a lid member 60.

During operation of the scanning optical device, excitation noise is generated from a DC motor that rotates the rotary polygon mirror, and noise and vibration due to the excitation noise have become a problem as the speed of the device has increased. This excitation sound is transmitted to the motor board 6 via the stator core, and becomes high-frequency noise.

Here, the number of magnetized poles of the rotor magnet is P, and the number of phases of the drive current flowing through the stator coil is W,
Assuming that the steady rotational speed of the rotating polygon mirror is N (rpm), the frequency ν of the excitation sound is represented by the following equation. ν = (NPW) / 60 (1)

This excitation sound is transmitted to the motor board as described above, and a new vibration (noise) peak occurs due to the resonance of the motor board.

The peak of this vibration is generated at a frequency that is an integral multiple of the frequency ν represented by the equation (1), transmitted to the optical box fixedly holding the DC motor, and further resonated by the resonance. A second peak or the like occurs. That is, the frequency ν represented by the equation (1) is set to a first order,
Next, third, fourth, etc. noise having a plurality of peaks,
The lid member and the like are vibrated and propagate out of the scanning optical device.

Therefore, the vibration of the lid member 60 due to the excitation sound is attenuated as follows. The distance from the center of the axial thickness of the outer peripheral portion of the stator coil 7 which is the noise generating point (noise source) Q of the DC motor to the lid member 60 is L ₁ , and the noise source Q is the opposing wall surface. Let L be the distance to the bottom surface 50a of the box 50.

The sound propagation path (2L + L ₁ ) reflected from the noise source Q on the bottom surface 50a of the optical box 50 and reaching the lid member 60
However, if the distance L is set so as to be longer by の of the wavelength λ of the propagated sound, ie, λλ, than the propagation path L ₁ of the sound directly propagating to the lid member 60, Vibration and noise can be avoided by causing two sound waves to interfere with each other.
That is, by delaying the phase of the direct propagation sound and the reflection propagation sound by 波長 wavelength, the vibration of the lid member 60 can be reduced, and troubles such as noise due to this can be avoided. The above condition is represented by the following equation. (2 × L + L ₁ ) −L ₁ = (1/2) λ (2) From equation (2), L = (1/4) λ (3) Assuming that the sound speed is c. , C = νλ, and therefore, from equations (1) and (3), L = 15c / (NPW) (4) For example, c = 340 m / s, N = 10000 rpm, P
= 6 poles and W = 3 phases, from equation (4), L = (15
× 340) / (10000 × 6 × 3) = 28.3 (m
m)

Therefore, the optical box 50 is removed from the stator coil 7.
Is set to 28.3 (mm). With such a configuration, the excitation sound of the DC motor is attenuated by interfering with the inside of the optical box 50, and noise leaking to the outside, image quality deterioration due to vibration, and the like can be avoided.

FIG. 2 shows a first modification. In this configuration, a concave portion 50b, which is an annular groove, is provided on the bottom wall of the optical box 50, and the distance from the noise source Q to the bottom surface of the concave portion 50b is L, thereby satisfying the expression (4). .

The outer diameter D ₁ and inner diameter D ₂ of the recess 50b are:
When the diameter D ₀ of the circumscribed circle of the rotary polygon mirror 1 and the outer diameter D ₃ of the stator coil 7 are set, a relationship of D ₂ <D ₃ <D ₀ <D ₁ is established.

The excitation sound propagating in the lid member 60 is attenuated by the reflected sound propagating from the bottom surface of the recess 50b. Only the thickness of a part of the optical box needs to be increased, which contributes to the miniaturization of the optical box. The advantage of being able to do so is added.

FIG. 3 shows a second modification. This is the first
In the same manner as the modified example, a curved portion 50c having a radius of curvature L that satisfies Expression (4) is provided on the bottom wall of the optical box 50. The wall surrounding the noise source Q satisfies the condition of the expression (4) in a wide range, and has the added advantage that the sound due to the reflected propagation sound can be more effectively attenuated.

FIG. 4 shows a second embodiment. In the first embodiment, the primary peak generated at the fundamental frequency of the noise is silenced. However, when resonating with the motor substrate or the optical box, the fundamental frequency is n (natural number). Double and tertiary peaks are doubled. Therefore, the following conditions are set. L = 15c / (NPWn) (5) C = 340 m / s, N = 10000 rpm, P = 6 poles,
By substituting W = 3 phases into equation (5), n = 1, 2, 3, 4
In each case, the condition for silencing the noise due to the primary peak is L = 28.3 mm The condition for silencing the noise due to the secondary peak is L / 2 = 14.15 mm The condition for silencing the noise due to the tertiary peak is L / 3 = 9.43 mm The condition for silencing the noise due to the fourth peak is L / 4 = 7.08 mm.

In general, a plurality of noises having a natural frequency which is a natural number multiple of the primary frequency are often generated at the same time. Therefore, a plurality of step-shaped portions 71 to 7 corresponding to the equation (5) are generally used.
By forming 4 on the bottom wall of the optical box 70, a plurality of noise peaks can be silenced at the same time.

Stepped portions 71 to 74 at the bottom of the optical box 70
Are arranged below the opposing portion of the rotor magnet 5 and the stator coil 7 and constitute a plurality of step-shaped grooves formed on a concentric circle centered on the rotating shaft 3. That is, in the direction of rotation of the DC motor, the depth of the groove is L / 4, adjacent thereto is L / 3, L / 2, L, and L / 2, L / 3, L /
4 and the step-shaped portions 71 to 74 are periodically repeated. Since the rotary polygon mirror 1, the rotor magnet 5, the stator coil 7, and the like are the same as those in the first embodiment, they are denoted by the same reference numerals, and description thereof will be omitted.

Since a plurality of noise peaks having the outer periphery of the stator coil as the noise source Q can be silenced simultaneously,
Vibration propagating to the lid member can be extremely effectively attenuated.
The other points are the same as in the first embodiment.

In the first and second embodiments, the direct propagation sound propagating directly from the noise source to the lid member and the reflected propagation sound propagating at the bottom of the optical box and propagating to the lid member interfere with each other. , Is a configuration to muffle the noise in the lid member,
The reverse is also acceptable. That is, the direct propagation sound propagating directly from the noise source to the bottom of the optical box and the reflected propagation sound propagating from the noise source to the optical box and reflected by the inner surface of the lid member, which is the opposite wall, interfere with each other, and It is also possible to adopt a configuration for silencing noise.

In the above embodiment, the noise is reduced by using the outer peripheral portion of the stator coil as a noise source.
Distance L from the motor board to the opposing wall such as the bottom of the optical box
Is set so as to satisfy Expression (4) and Expression (5).

The conditions of the equations (4) and (5) need not be strict equations, but may be approximate values in consideration of design restrictions and the like. Also, as described above, the inner rotor type DC
The motor is not limited to the motor, and may be an outer rotor type motor.

Further, the DC motor for rotating the rotary polygon mirror tends to have a noticeable start-up sound particularly from a stationary state to a steady state. Therefore, it is particularly desirable to reduce this type of noise. Therefore, for example, assuming that the steady rotational speed of the DC motor is N, the rotational speed region for damping is:
The range is from the half value of the steady speed to the steady speed.

That is, instead of the equation (4), the following equation is established: 15c / (NPW) <L <30c / (NPW) (6) Noise in a rather wide frequency band including noise at the time can be reduced.

FIG. 5 shows the entire scanning optical device, which includes a light source 51 for generating a light beam such as a laser beam and a cylindrical beam for condensing the laser beam linearly on the reflection surface of the rotary polygon mirror 1. A lens 51a for deflecting and scanning the light beam by the rotation of the rotary polygon mirror 1;
2 and the photoreceptor 5 on the rotating drum via the mirror 53
4 is imaged. The imaging lens 52 is a spherical lens unit 52
a, a toric lens unit 52b, etc., and a so-called fθ function for correcting the scanning speed and the like of a point image formed on the photoconductor 54.

When the rotary polygon mirror 1 is rotated by the DC motor, its reflecting surface rotates at a constant speed around the axis of the rotary polygon mirror 1 as shown by an arrow A. As described above, the angle between the optical path of the light beam generated from the light source 51 and collected by the cylindrical lens 51a and the normal to the reflection surface of the rotary polygon mirror 1, that is, the angle of incidence of the light beam on the reflection surface is Since the reflection angle changes with the rotation of the rotary polygon mirror 1 over time and the reflection angle also changes, the point image formed by condensing the light beam on the photoconductor 54 moves in the direction indicated by the arrow Y (main scanning direction). I do.

The imaging lens 52 condenses the light beam (scanning light) reflected by the rotary polygon mirror 1 on the photosensitive member 54 into a point image having a predetermined spot shape, and also moves the point image in the main scanning direction. Is a complex lens designed to keep the scanning speed of the lens at a constant speed.

The point image formed on the photoreceptor 54 is electrostatically generated by the main scanning by the rotation of the rotary polygon mirror 1 and the sub-scanning by the rotation of the rotating drum having the photoreceptor 54 about its axis. Form a latent image.

Around the photosensitive member 54, a charging device for uniformly charging the surface of the photosensitive member 54, and a charging device for visualizing an electrostatic latent image formed on the surface of the photosensitive member 54 into a toner image. A developing device, a transfer device for transferring the toner image to recording paper or the like (both not shown), and the like are arranged, and recording information by a light beam generated from the light source 51 is printed on recording paper or the like.

The detection mirror 55 reflects the light beam on the upstream side in the main scanning direction with respect to the optical path of the light beam incident on the recording element writing start position Y ₁ on the photosensitive member 54.
The light is introduced to the light receiving surface of a light receiving element 56b having a photodiode or the like via a condenser lens 56a. Light receiving element 56b
Outputs a scan start signal for detecting a scan start position (write start position) when the light receiving surface is irradiated with the light beam.

The condenser lens 56a and the light receiving element 56b are disposed between the imaging lens 52 and the rotary polygon mirror 1, and the detection mirror 55 reflects the light beam below the scanning surface of the scanning light.

The light source 51 generates a light beam corresponding to a signal given from a processing circuit 57 for processing information from a host computer. The signal given to the light source 51 is
The processing circuit 57 corresponds to information to be written to the photoconductor 54, and the processing circuit 57 uses the signal representing the information corresponding to one scanning line, which is a locus formed by a point image formed on the surface of the photoconductor 54, as one unit, Give to. This information signal is transmitted in synchronization with a scanning start signal given from the light receiving element 56b through the line 56c.

The rotary polygon mirror 1, the imaging lens 52 and the like are housed in an optical box 50, and the light source 51 and the like are mounted on the side wall of the optical box 50. After assembling the rotary polygon mirror 1, the imaging lens 52, and the like to the optical box 50, the lid member 60 is attached to an opening above the optical box 50.

[0052]

Since the present invention is configured as described above, the following effects can be obtained.

The excitation sound of the DC motor that rotationally drives the rotating polygonal mirror leaks out of the optical box and generates loud noise, or the image forming lens or the like is vibrated through a lid member or the like to cause the image forming apparatus to vibrate. A scanning optical device with low noise and high image quality can be realized by avoiding troubles such as deterioration of image performance.

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

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing a main part of a scanning optical device according to a first embodiment.

FIG. 2 is a schematic sectional view showing a first modification.

FIG. 3 is a schematic sectional view showing a second modification.

FIG. 4 is a schematic cross-sectional view showing a second embodiment.

FIG. 5 is a diagram illustrating the entire scanning optical device.

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

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Rotating polygon mirror 3 Rotating axis 5 Rotor magnet 6 Motor board 7 Stator coil 50, 70 Optical box 50a Bottom surface 50b Recess 50c Curved part 60 Lid member 71-74 Step-shaped part

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Susumu Ikuma 3-30-2 Shimomaruko, Ota-ku, Tokyo F-term in Canon Inc. (reference) 2H045 AA14 AA15 AA33 DA41 5H605 AA05 BB05 BB14 BB19 CC01 CC02 DD21 DD23 EA15 EA18 GG21

Claims (10)

[Claims] 1. A rotary polygon mirror for deflecting and scanning a light beam, a deflection scanning means comprising a DC motor for rotating and driving the rotary polygon mirror, and a housing incorporating the deflection scanning means, wherein the housing is A scanning optical device comprising: a facing wall disposed at a distance (L) satisfying the following relationship from a noise source of the DC motor. L ≒ 15c / (NPW) where c: sound speed N: steady-state rotation speed (rpm) of DC motor P: number of magnetized poles of DC motor W: number of phases of drive current of DC motor 2. The apparatus according to claim 1, wherein the distance (L) between the opposed wall surfaces satisfies the following relationship.
The scanning optical device according to claim 1. 15c / (NPW) <L <30c / (NPW) 3. The scanning optical device according to claim 1, wherein the opposed wall surface is a bottom surface of the housing. 4. The scanning optical device according to claim 1, wherein the opposing wall surface is a bottom surface of a recess provided in a bottom wall of the housing. 5. The scanning optical device according to claim 1, wherein the opposing wall surface is provided on a curved portion of a bottom wall of the housing. 6. The scanning optical device according to claim 1, wherein the opposed wall surface is an inner surface of a lid member that closes an opening of the housing. 7. The scanning optical apparatus according to claim 1, wherein the distance (L) between the opposed wall surfaces satisfies the following relationship. L ≒ 15c / (NPWn) where c: sound speed N: steady-state rotation speed (rpm) of DC motor P: number of magnetized poles of DC motor W: number of phases of drive current of DC motor n: natural number 8. The scanning optical device according to claim 7, wherein the opposed wall has a plurality of step-shaped portions. 9. The scanning optical device according to claim 1, wherein the noise source is an outer peripheral portion of a stator coil of the DC motor. 10. The scanning optical device according to claim 1, wherein the noise source is a motor substrate of a DC motor.