JPH0695562A - Rotor driving device - Google Patents

Abstract

PURPOSE:To enhance the quality of image by decreasing speed variation of the rotor of an electrophotographic image output apparatus. CONSTITUTION:A sensitive drum 2 is coupled with the drive shaft 13 on the farther side of a driving gear 11, and an inertial member 8 is installed inside of the drum 2, and therein is also mounted a dynamic damper 18. Thereby the inertia moment of the driving system is increased and the natural frequency is sunk to prevent resonance of the sensitive drum 2 which is a rotor, and residual vibration is absorbed, and the rotating speed is kept constant and speed variation is decreased which should lead to producing of an enhanced image 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 output device such as a digital color copying machine or a digital color printer to which an electrophotographic process is applied.

[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 photosensitive drum in the image output device and the drive roller for the belt-shaped photosensitive member will be referred to as a rotating body. Therefore, if the speed of the photosensitive member fluctuates due to some influence, jitter or image unevenness occurs 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 precision required for the drive system is improved. Became rapidly severe. 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 causes of speed fluctuations of the drive system are speed fluctuations per one rotation of the motor rotation axis, large absolute values of one rotation component and one tooth component of the gear, and those fluctuation components and their harmonic components are driven. It was found that the resonance phenomenon was caused in relation to the natural frequency of the system.

FIG. 7 shows a speed fluctuation power spectrum of a drive system of a conventional machine. According to this, the variation component due to one tooth of the gear based on the line speed peculiar to the machine 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. 8 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 vibration 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. 9 is a graph in which the fluctuation component spectrum and the transfer function are superimposed. As you can see from this figure,
This drive system has a peak of a transfer function, a fluctuation component and its 2
The positions in the frequency domain where the second harmonics exist are overlapping. 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.

FIGS. 10 and 11 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. The actual measurement values of the functions are superimposed as in FIG. In addition, FIG.
Is a comparison of 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. It can be considered by comparing the data of FIG. 10, FIG. 11 and FIG. 12 that the torsional rigidity K of the drive system is reduced to move the natural frequency in order to avoid resonance and the natural frequency is set to a lower frequency. In the case of a structural change in which the transfer function is moved to the side, the transfer function becomes smaller as the natural frequency moves. 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 rotary body and the drive shaft are connected to the drive transmission system of the rotary body on the side far from the rotary body, and an inertial load is attached to the inside of the rotary body to make the rotary body drive system unique. In addition to reducing the vibration frequency, a dynamic damper in which an outer cylinder and an inner cylinder having an inertial load are connected by an elastic member is attached to the drive shaft.

[0014]

Since the drive shaft and the rotating body are connected to each other on the side far from the drive transmission system, the effective length of the drive shaft is increased, so that the rigidity K ahead of the drive gear is substantially reduced and the inertial load is reduced. By attaching to the rotating body, the inertia moment I of the drive system becomes large, and the natural frequency can be lowered, so that the natural frequency of the rotary body drive system expressed by the equation 1 is lowered, The number and the frequency of the fluctuation component can be separated, the resonance of the rotating body drive system can be prevented, and the fluctuation of the rotation speed can be reduced. In addition, since the rigidity K of the rotating body drive system is substantially lowered, a flexible structure can be achieved, whereby the transmission gain of the rotating body drive system is reduced and the level of speed fluctuation of the rotating body can be reduced. . Furthermore, by attaching a dynamic damper to the drive shaft, the remaining specific vibration is erased and the speed fluctuation of the rotating body is eliminated,
The quality of the output image can be greatly 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 present invention will be described below with reference to the drawings.

FIG. 5 shows an 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.

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 12a and 12b attached to both ends thereof as shown in FIG. The drive shaft 13 is passed through the center of the flange 12a and the like, and the flange 12b on the side far from the drive gear 11 and the drive shaft 13 are fixed by a pin 15 to the drive gear 11
The side flange 12a and the drive shaft 13 are rotatable. The drive shaft 13 is rotatably supported by a bearing 21, and the drive gear 11 described above is attached to the shaft end,
The drive gear 11 meshes with the final gear 10. Inside the photosensitive drum 2, inertia members 8 are attached to the flanges 12a and 12b on both sides, respectively, and the dynamic damper 1 is provided between the photosensitive drum 2 and the drive gear 11.
8 is attached.

The inertia member 8 is a ring-shaped weight made of steel, SUS, brass or the like, and the material can be formed in a compact size as the specific gravity increases. Preferably, the inertia moment I1 of the photosensitive drum 2 and this The ratio with the inertia moment I2 of the inertia member is preferably in the range of 0.05 to 0.4.

FIG. 3 shows the dynamic damper 18. The dynamic damper 18 includes an inner cylinder 19 and an outer cylinder 20 attached to the inner cylinder 19. A rubber 21 having elasticity is filled between the inner cylinder 19 and the outer cylinder 20, and a center hole of the inner cylinder 19 is provided. 22 is integrally fixed to the drive shaft 13. The dynamic damper 18 can specify the frequency of vibration that can be absorbed by the diameter, weight, elasticity of rubber, etc. of the outer cylinder 20, and can efficiently absorb and remove the vibration that remains on the photosensitive drum 2. .

In this way, the flange 12b on the side far from the drive gear 11 and the drive shaft 13 are connected to each other, and the photosensitive drum 2
Since the inertia member 8 is provided inside and the dynamic damper 18 is attached to the drive shaft 13 connected to the photosensitive drum 2, the inertia of the drive system including the photosensitive drum 2, the drive shaft 13, and the drive gear 11 is increased. The moment I increases,
In addition, the distance from the drive gear 11 to the inertial member 8 becomes long, and the rigidity K of the drive system is substantially lowered, which reduces the natural frequency of the drive system. Therefore, this natural frequency can be set to an appropriate value, and 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, and the resonance of the photosensitive drum 2 can be prevented. This can be prevented, and the photosensitive drum 2 can be smoothly rotated without causing speed fluctuations, and the quality of the output image can be significantly improved.

Further, since the rigidity K is substantially reduced, the transmission gain of the photosensitive drum 2 can be reduced, so that the speed fluctuation input from the final gear 10 is easily attenuated,
Since the fluctuation of the rotation speed of the photoconductor drum 2 can be suppressed and the dynamic damper 18 is attached to the drive shaft 13 connected to the photoconductor drum 2, the vibration remaining on the photoconductor drum 2 can be efficiently removed and the rotation speed of the photoconductor drum 2 can be improved. Fluctuations can be kept to a minimum. Therefore, the photosensitive drum 2 can be smoothly rotated at a constant speed, and the quality of the output image can be significantly improved.

FIG. 4 shows another embodiment of the photosensitive drum 2. In this configuration, the flanges 12a and 12b are formed of a member having a large inertial load, and the dynamic damper 18 is provided inside the photoconductor 2. The flange 12a and the drive shaft 13 are rotatable. When the inertial moment I of the drive system is increased, the inertial load on the flange itself may be increased as described above, and the dynamic damper 18 does not necessarily have to be provided outside the photosensitive drum 2. By doing so, it is possible to reduce the speed fluctuation and improve the image quality, reduce the outer shape, simplify the assembly process, reduce the number of parts, and reduce the cost, as described above.

Further, the inertia member 8 may be formed by laminating thin metal plates and fixed to the flange 12. Even if the inertia member 8 is formed in this way, the photoreceptor is the same as described above. The inertial moment I of the drum 2 can be increased, and the rigidity K can be reduced to reduce the natural frequency. As a result, the natural frequency and the fluctuation component in the frequency domain can be separated, and resonance can be prevented to prevent the photosensitive member. The speed fluctuation of the drum 2 can be reduced to significantly improve the image quality, and the inertia moment I can be easily adjusted by adjusting the number of metal plates attached.

Further, the dynamic damper 18 is positioned on the opposite side of the photoconductor 2 with the drive gear 11 interposed therebetween and the drive shaft 13 is provided.
You may attach it to.

Although the flange 12a and the drive shaft 13 are slidable in the above example, a sliding bearing may be used in this portion or a ball bearing may be attached. By doing so, the dimensional accuracy of the drive shaft 13 and the flange 12 can be secured, and the drive shaft 13 and the flange 12 can be rotated more smoothly to improve the image quality.

Although the rotator itself is the photoconductor drum 2 in the above, the photoconductor drum 2 need not be the rotator, and as shown in FIG. 6, it has a belt-shaped photoconductor 25. The image output device in which the drive roller 26 for driving the drive device 25 is the rotating body of the present invention may be used. Even in this case, by using each of the above-described embodiments 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 output image quality is remarkably improved. Can be improved.

As described above, the flange 12b on the side far from the drive gear 11 and the drive shaft 13 are fixed to reduce the substantial rigidity K, and the inertia member 8 is attached to the rotating body such as the photosensitive drum 2. Moment of inertia I of the rotating body drive system attached
Is increased so that the natural frequency is lowered so as not to match the frequency of the speed fluctuation transmitted to the rotating body drive system. Therefore, the photosensitive drum 2 or the driving roller 2
6 can be prevented from rotating, and the photoconductor drum 2 or the photoconductor 25 can be rotated or transported at a constant speed without causing speed fluctuations, whereby the image quality can be remarkably improved.
Further, since the rigidity K is substantially reduced, the transmission gain of the photoconductor drum 2 or the drive roller 26 is reduced, and it is difficult to transmit the speed fluctuation, and the speed fluctuation of the photoconductor drum 2 or the photoconductor 25 can be reduced. At the same time, by attaching the dynamic damper 18 to the drive shaft 13 of the photosensitive drum 2, residual vibration can be absorbed and the image quality can be significantly improved. 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.

The inertia member 8 and the dynamic damper 18 in the above-described example may be combined in any manner.

[0029]

According to the rotating body drive apparatus of the present invention, in the rotating body drive system including the drive shaft connected to the drive motor and driven, and the rotating body which is connected to the drive shaft and is rotated at a constant speed, By fixing the flange on the side far from the drive gear attached to the drive shaft and the drive shaft, attaching an inertial load inside the rotating body, and further installing a dynamic damper on the drive shaft, the natural frequency of these drive systems Lower
The frequency of the fluctuation component generated by the rotation of the drive motor and the gear connected thereto can be set so as not to match the natural frequency, resonance of the rotor can be prevented, and the rotor can be rotated without speed fluctuation. In addition, since the rigidity is substantially reduced, the transmission gain of the rotating body drive system can be reduced, the transmission of fluctuations can be suppressed and the speed fluctuations of the rotating body can be made smaller, and a dynamic damper is attached to the drive shaft. As a result, the remaining vibration can be reliably removed, and the image quality can be significantly improved. As a result, the image quality, especially the step unevenness that occurs in the sub-scanning direction of the writing system and the image unevenness called pitch unevenness are reduced,
A significant improvement in image quality is obtained. Further, in the prior art, a device having a complicated and large-sized mechanism can be realized by a simple and compact mechanism, and the cost can be reduced by this. Further, since the mechanism is simplified, the reliability of the entire system can be significantly improved.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of a photosensitive drum according to the present invention.

FIG. 2 is a perspective view showing an entire rotary body drive system.

FIG. 3 is a cross-sectional view showing a dynamic damper.

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

FIG. 5 is a sectional view showing an electrophotographic image output device according to the present invention.

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

FIG. 7 is a graph showing speed fluctuations of a conventional photosensitive drum.

FIG. 8 is a graph showing a transfer function of a conventional photoconductor drive system.

FIG. 9 is a graph showing a speed fluctuation power spectrum of a conventional photoconductor and a transfer function of a photoconductor drive system together.

FIG. 10 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. 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 reduced.

FIG. 12 is a graph showing a peak value of a transfer function of each drive system.

[Explanation of symbols]

 2 Photoconductor drum 8 Inertial member 11 Drive gear 12 Flange 13 Drive shaft 18 Dynamic damper 25 Photoconductor 26 Drive roller

Claims (1)

[Claims] 1. An image output device having a drive system including a rotating body and a drive shaft for rotating the rotating body, and a motor and a drive transmitting system for rotating the drive system. A drive device for a rotary body, characterized in that the rotary body and the drive shaft are connected to each other on a remote side, an inertial load is attached to the rotary body, and a dynamic damper is attached to the drive shaft.