JPH06133122A - Image forming output device - Google Patents

Abstract

PURPOSE:To improve the picture quality by decreasing speed fluctuation of a rotating body of an electronic photographic picture output device. CONSTITUTION:A flange 12 and a drive shaft 13 are devised freely turnably, a 1st connection member 18 is fitted to the drive shaft 13, a 2nd connection member 19 is fitted to a flange 12 apart from a drive gear 11 and the 1st connecting member 18 and the 2nd connecting member 19 are connected by a spring 20. Thus, the stiffness of the drive system comprising the drive shaft 13 and a photosensitive drum 2 or the like is decreased, the natural frequency of the drive system is reduced to make the natural frequency of the drive system coincident with the frequency of fluctuation of the speed delivered to the drive system. Thus, the resonance of the rotating body is prevented, the fluctuation of the speed is reduced to improve the picture quality.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming and outputting apparatus such as a digital color copying machine or a digital color printer to which an electrophotographic process is applied, and more specifically, to a photosensitive member inside the image forming and outputting apparatus. The present invention relates to a drive device for a rotating body such as a body drum.

[0002]

2. Description of the Related Art In a copying machine or a printer to which an electrophotographic process is applied, a surface of a rotating cylindrical photosensitive member or a belt-shaped photosensitive member is run to sequentially form an electrostatic latent image on the surface, If the formed electrostatic latent image is a black or color image, toners of respective colors are attached to the electrostatic latent image to develop the image, and the image is obtained by transferring it to the paper surface. (Here, the photoconductor drum in the image output device and the drive roller for the belt-shaped photoconductor will be referred to as a rotating body.) Therefore, when the speed of the photoconductor changes due to some influence such as contact with the cleaning blade. Jitter and image unevenness occur in the output image. This is particularly noticeable in the digital electrophotographic technology in which writing on the photoconductor is performed by scanning with a semiconductor laser, and the speed fluctuation of the rotation of the photoconductor becomes the speed fluctuation of the writing system in the sub-scanning direction. This causes a slight deviation in the interval between the two and causes a significant deterioration in image quality.

On the other hand, in the conventional design of a drive system such as a copying machine or a printer, the drive target should be appropriate in relation to the allowable space while satisfying the numerical values such as the line speed and the rotation speed derived from the product specifications. Emphasis was placed on exploring the placement. In other words, how to transmit the power from the power source to the drive target and what to use as a mechanical element for power transmission were of great interest. Therefore, if the unevenness or uneven rotation occurs in the finished product, search for the cause and change the bearing of the drive shaft of the photoconductor to a sintered product, or connect the flywheel to the drive shaft of the photoconductor.
Measures have been taken such as mounting a brake that combines a spring and a friction member on the rotating shaft of the photoconductor, improving gear accuracy, and using helical gears having various torsion angles.

[0004]

However, in the development of a digital image output device, as the performance is improved, the reproducibility of one dot line by writing with a laser is strictly required and the drive system is required. The accuracy also became severe rapidly. The accuracy required here is a level at which the uniformity of the writing by the laser in the sub-scanning direction is guaranteed in relation to the visual sensitivity of the visual system, and in order to achieve this, it is necessary to improve the accuracy of driving the photoconductor. This is the biggest technical issue. The main cause of speed fluctuation of the drive system is the rotating shaft 1 of the motor.
Resonance phenomenon occurs due to the speed fluctuation per rotation, the large absolute value of one rotation component and one tooth component of the gear, and the fluctuation component and its harmonic component in relation to the natural frequency of the drive system. Turned out to be that.

FIG. 8 shows a speed fluctuation power spectrum of a drive system of a conventional machine. According to this, the fluctuation component due to one gear tooth based on the machine-specific line speed has 176 Hz for the gear directly connected to the motor, 64 Hz for the second shaft, and 25 Hz for the gear directly connected to the drum. The thing of 50 Hz has appeared. Further, it has 22 Hz as one rotation component of the gear directly connected to the motor, and 44 Hz appears as its harmonic.

On the other hand, FIG. 9 shows an example of measurement of a transfer function for numerically capturing the natural frequency of the drive system. In this case, a dual-channel FFT analyzer is connected to the output of the impact excitation hammer and the output of a piezoelectric pickup sensor attached to one end of the photosensitive drum so that the acceleration fluctuation in the rotational direction can be measured. It was carried out by a method of obtaining a spectrum ratio. From this FIG.
The peak of natural frequency of this drive system is around 45Hz,
It can be seen that the region where the level of the transfer function is high spreads out in the vicinity of 30 to 60 Hz.

FIG. 10 shows the variation component spectrum and the transfer function superimposed on each other. As can be seen from FIG. 10, in the present drive system, the peak of the transfer function and the position of the frequency region where the fluctuation component and its second harmonic exist are overlapped. That is, it was found that this drive system is a system that amplifies the fluctuation component (causes resonance).

Actually, when the actually measured values of three machines having the main drive system were examined, the rotation fluctuation of the photosensitive member showed a value of 5 to 8%.

[0009]

In order to solve the above-mentioned problems, the present invention is premised on reducing the speed fluctuations at the generation source such as a motor or gear, and in addition to this, fluctuation components in the drive transmission system are also added. Focusing on the point of transfer of
In consideration of how to attenuate the transmitted fluctuation, the concept of resonance and natural frequency was taken into consideration, and the driving device for the rotating body was constructed as follows.

First, in order to avoid resonance of the rotating body drive system, it has been decided to prevent the natural frequency of the rotating body drive system from matching the frequency of the fluctuation component transmitted to the rotating body drive system.
In general, the natural frequency ω is expressed by the following equation.

[0011]

[Equation 1] In the equation, K is the torsional rigidity of the drive system, and I is the moment of inertia. The value of ω can be changed by changing the value of K or I in order to avoid resonance. From the viewpoint of avoiding resonance, ω may be set larger or smaller than the fluctuation component of the rotary drive system. A method of increasing ω can be realized by increasing K or decreasing I. Further, in order to reduce ω, it can be realized by increasing I or decreasing K.

11 and 12 show the power spectrum and the transmission of the rotational fluctuation of the drive system when the natural frequency of the drive system of the data shown in FIG. 10 is changed to a large value and a small value by the structural change. Figure 1 shows the measured values of the function.
Similar to 0, they are superposed. Further, FIG. 13 compares the peak values of the transfer function for the above three drive systems. The structural modification for lowering the rigidity of the drive system in FIG. 10 is to reduce the value of the torsional rigidity K of the drive system. Comparing the data of FIG. 11, FIG. 12, and FIG. 13, what can be considered is that in order to avoid resonance,
In the case of a structure change in which the torsional rigidity K of the drive system is reduced to move the natural frequency and the natural frequency is moved to a lower frequency side, the transfer function becomes smaller as the natural frequency moves. is there. It is considered that this is because the damping element becomes prominent due to the flexible structure due to the structural change due to the movement of the natural frequency, and the drive system itself absorbs the rotational fluctuation. As a result, when the movement of the natural frequency for avoiding the resonance is performed, the structural change to reduce the torsional rigidity K of the drive system is accompanied by the change of the transmission gain of the fluctuation of the rotation speed. It can be seen that it is advantageous and effective in reducing speed fluctuations.

Therefore, in the present invention, based on such an idea, the natural frequency of the rotating body drive system is lowered,
By interposing a low-rigidity transmission means in the rotation transmission means from the final gear to the photosensitive drum, the rigidity of the rotating body drive system is reduced.

[0014]

By reducing the rigidity K of the rotary body drive system, the natural frequency of the rotary body drive system expressed by the equation 1 is lowered, so that the natural frequency and the fluctuation component in the frequency domain can be separated and It is possible to prevent resonance of the system and reduce fluctuations in rotation speed. Furthermore, because the rigidity of the rotating body drive system has been lowered,
By achieving the flexible structure, the transmission gain of the rotating body drive system can be reduced, and the level of speed fluctuation in driving the rotating body can be reduced. As a result, the speed fluctuation of the rotating body is reduced, and the quality of the output image can be significantly improved. Further, the device can be downsized, the cost can be reduced, and the reliability of the entire system can be improved.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The rotating body of the present invention will be described below with reference to the drawings.

FIG. 6 shows the entire electrophotographic image output device using the rotating body of the present invention. This electrophotographic image output device 3
1 is a photosensitive drum 2 as a rotating body, a developing section 3,
A drive mechanism for driving the photosensitive drum 2 and the like are attached. FIG. 2 shows the photosensitive drum 2 and the drive mechanism 4. The drive mechanism 4 includes a drive motor 5 and a gear group 6 connected to the drive motor 5, and a drive gear 11 of the photosensitive drum 2 is connected to a final gear 10 of the gear group 6.

FIG. 1 shows the photosensitive drum 2. The photosensitive drum 2 is made of a cylindrical aluminum base material whose side surface is coated with an organic photosensitive material, and has flanges 12 attached to both ends thereof. The left and right flanges 12 and the drive shaft 13 are not fixed, but are rotatably fitted to the drive shaft 13. The drive shaft 13 is rotatably supported by a bearing 21, and the drive gear 11 described above is attached to the shaft end.

A first connecting member 18 is integrally fixed to the drive shaft 13 with a pin 35, and a spring 20 is attached between the first connecting member 18 and the second connecting member 19. The second connecting member 19 is rotatable with respect to the drive shaft 13 and is fixed to the flange 12 with a screw 36. The spring 20 transmits the force of the first connecting member 18 and the second connecting member 19 in the rotational direction to substantially connect the two, and has a spring property in the rotational direction to allow some bending. .

Thus, the photosensitive drum 2 and the drive shaft 13 are
Since and are connected via the spring 20, the rigidity of the photosensitive drum 2 viewed from the final gear 10 in the rotational direction, that is, the torsional rigidity is decreased, and the natural frequency is decreased. Therefore, the natural frequency and the fluctuation component can be separated in relation to the frequency of the fluctuation component generated in the drive mechanism 4, resonance of the photoconductor drum 2 can be prevented, and the speed fluctuation of the photoconductor drum 2 is caused. It is possible to remarkably improve the quality of an image that is smoothly rotated and output.

Further, as a result of the structural change to reduce the rigidity of the photoconductor drum 2, the transmission gain of the photoconductor drum 2 can be reduced, so that the speed fluctuation from the final gear 10 can be easily attenuated, and the photoconductor drum 2 can be further reduced. The fluctuation of the rotation speed can be suppressed.

FIG. 3 shows another embodiment. This uses a coupling 22, and the coupling 22 connects the flange 12 and the drive shaft 13. The coupling 22 includes a first fixing member 23, a second fixing member 24, and a rubber 27 provided between the first fixing member 23 and the second fixing member 24. First fixing member 23
And the rubber 27, and the second fixing member 24 and the rubber 27 are adhered to each other with an adhesive or the like.
Is fixed to the drive shaft 13 by a pin 35, and the second fixing member 24 is fixed to the flange 12 with a screw 36.

Therefore, the final gear 1 as in the above embodiment.
0 and the photosensitive drum 2 are a low-rigidity member, that is, a rubber 27.
This is the same as the connection with the above, and resonance can be prevented, and the image quality output by rotating the photosensitive drum 2 smoothly without causing speed fluctuations can be significantly improved. In addition, as a result of the structural change to reduce the rigidity of the photoconductor drum 2, the transfer gain of the photoconductor drum 2 can be reduced, so that the speed fluctuation from the final gear 10 is easily attenuated, and the rotation speed of the photoconductor drum 2 is reduced. Fluctuations can be suppressed.

FIG. 4 shows another embodiment. This is one in which the flange 12b on the side far from the drive gear 11 is formed with a thin rib 14 as shown in FIG. 5 to reduce the rigidity in the rotational direction, and the flange 12a on the drive gear 11 side rotates on the drive shaft 13. The rib 12b is connected to the drive shaft 13 with a pin 35. Even in this case, the rigidity of the photosensitive drum 2 can be reduced, the natural frequency can be reduced, resonance with the fluctuation component from the drive mechanism 4 can be prevented, the rotation speed can be made constant, and the transmission gain can be reduced. It is possible to remarkably improve the quality of the image output by smoothly rotating the image.

Further, in the above, the rotating body itself is the photosensitive drum 2
However, the photosensitive drum 2 need not be a rotating body,
As shown in FIG. 7, the image output device may have a belt-shaped photoconductor 25 and the driving roller 26 for driving the photoconductor 25 may be the rotating body of the present invention. Even in this case, by using the above-described embodiment as the drive roller 26, the drive roller 26 can be rotated without speed fluctuation, and therefore the photoconductor 25 can be transported at a constant speed, so that the image quality to be output is significantly improved. Can be made.

As described above, the natural frequency can be lowered by reducing the rigidity of the rotating body drive system,
Since the frequency of the speed fluctuation transmitted to the drive system is not matched, the photosensitive drum 2 or the drive roller 2
6 can be prevented from resonating and the rigidity is reduced, so that the transmission gain of the photosensitive drum 2 or the driving roller 26 is reduced, and it becomes difficult for the speed fluctuation to be transmitted. It can be rotated or transported at a constant speed without causing fluctuations, which can significantly improve the image quality. Further, it can be realized with a compact mechanism, the apparatus can be downsized, the cost can be reduced, and the reliability of the entire system can be significantly improved.

[0026]

According to the rotating body drive apparatus of the present invention, the rigidity of the rotating body drive system including the rotating body and the drive shaft for driving the rotating body is reduced to reduce the natural frequencies of these components, thereby reducing the drive motor. Further, since the frequency is set so as not to match the frequency of the fluctuation component generated by the rotation of the gear connected thereto, resonance of the rotating body can be prevented and the rotating body can be rotated without speed fluctuation. Further, the transmission gain of the drive system can be reduced, the transmission of fluctuations can be suppressed, and the speed fluctuations of the rotating body can be further reduced. As a result, image quality, in particular, image unevenness called step unevenness and pitch unevenness that occur in the sub-scanning direction of the writing system is reduced, and the image quality is remarkably improved. In addition, a device that has a complicated and large size in the conventional technology can be realized by a simple and compact mechanism.
Moreover, the cost can be reduced by this. Furthermore, the simplification of the mechanism has significantly improved the reliability of the entire system.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an example of a photosensitive drum.

FIG. 2 is a perspective view showing a rotary body drive system according to the present invention.

FIG. 3 is a cross-sectional view showing another embodiment of the photosensitive drum.

FIG. 4 is a sectional view showing another embodiment of the photosensitive drum.

FIG. 5 is a front view showing a flange.

FIG. 6 is a sectional view showing an electrophotographic image output device according to the present invention.

FIG. 7 is a sectional view showing an electrophotographic image output device according to the present invention.

FIG. 8 is a graph showing a power spectrum of speed fluctuation of a conventional photoconductor.

FIG. 9 is a graph showing a transfer function of a conventional photoconductor drive system.

FIG. 10 is a graph showing a speed fluctuation power spectrum of a conventional photoconductor and a transfer function of a photoconductor drive system together.

FIG. 11 is a graph showing the transfer function of the photoconductor drive system and the speed fluctuation power spectrum of the photoconductor when the natural frequency is increased.

FIG. 12 is a graph showing the transfer function of the photoconductor drive system and the speed fluctuation power spectrum of the photoconductor when the natural frequency is reduced.

FIG. 13 is a graph showing a peak value of a transfer function of each drive system.

[Explanation of symbols]

 2 photoconductor drum 11 drive gear 12 flange 13 drive shaft 25 photoconductor 26 drive roller

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location H04N 1/31 9186-5C

Claims (2)

[Claims] 1. An image forming output device having a drive system including a rotary body and a drive shaft for rotating the rotary body, and a motor and a drive transmission system for rotating the drive system. In order to avoid resonance, (However, ω is the natural frequency of the drive system, K is the torsional rigidity of the drive system, and I is the moment of inertia of the drive system.) An image forming and outputting apparatus characterized by having a drive system having a reduced height. 2. The image forming output device according to claim 1, wherein the drive shaft and the rotating body are connected by an elastic member including an elastic or viscoelastic element.