JP3258720B2 - Image output equipment - Google Patents

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.

[0002]

2. Description of the Related Art In a copying machine or a printer to which an electrophotographic process is applied, an electrostatic latent image is sequentially formed on the surface of a rotating cylindrical photoreceptor or a photoreceptor formed in a belt shape by running the same. If a black or color image is formed on the formed electrostatic latent image, toner of each color is applied, developed, and transferred to a paper surface to obtain an image. Here, the photosensitive drum and the drive roller of the belt-shaped photosensitive member in the image output apparatus will be referred to as a rotating body. For this reason, if the speed of the photosensitive member fluctuates due to some influence, the output image has jitter or image unevenness. This is particularly noticeable in a digital electrophotographic technique in which writing on a photoconductor is performed by scanning a semiconductor laser. Fluctuations in the rotation speed of the photoconductor cause fluctuations in the sub-scanning direction of the writing system, resulting in a writing line. Causes a slight shift in the distance between the images, thereby causing a significant reduction in image quality.

On the other hand, in the design of a drive system of a conventional copying machine or printer, the drive target is designed to satisfy the line speed, the number of revolutions, etc. derived from the product specifications while maintaining the relationship with the allowable space. 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 have been of great interest. Therefore, when the unevenness and rotation unevenness occur in the finished product, the cause is searched for, the bearing of the drive shaft of the photoconductor is changed to a sintered product, the flywheel is connected to the drive shaft of the photoconductor,
Measures have been taken to mount a brake combining a spring and a friction member on the rotating shaft of the photoreceptor, improve gear accuracy, and use helical gears having various torsion angles.

[0004]

However, in the development of digital image output equipment, as the performance is improved, the reproducibility of one dot line by writing with a laser is strictly required, and the accuracy required for the drive system is required. Quickly became tougher. 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. This is the biggest technical challenge. The main causes of the speed fluctuation of the drive system are the speed fluctuation per one rotation of the rotating shaft of the motor, the large absolute value of one rotation component and one tooth component of the gear, and the fluctuation component and its harmonic component are driven. It was found that a 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 fluctuation component due to one tooth of the gear based on the line speed inherent 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. As 50 Hz. Also, one rotation component of the gear directly connected to the motor has 22 Hz, and 44 Hz appears as a harmonic thereof.

On the other hand, FIG. 8 shows a measurement example of a transfer function for numerically capturing the natural frequency of the drive system. In this case, the output of the impact vibration hammer and the output of the piezoelectric pickup sensor attached to one end of the photosensitive drum so as to measure the acceleration fluctuation in the rotation direction are connected to a dual-channel FFT analyzer, and the respective Fourier analyzers are used. The measurement was performed by a method for determining the ratio of spectra. From this FIG.
The peak of the natural frequency of this drive system is around 45 Hz,
It can be seen that the region where the level of the transfer function is high spreads up to around 30 to 60 Hz.

FIG. 9 shows a superposition of the fluctuation component spectrum and the transfer function. As you can see from this figure,
This drive system has a peak of a transfer function, a fluctuation component and its 2
The position of the frequency region where the second harmonic exists is overlapped. That is, it has been found that the present drive system is a system that amplifies the fluctuation component (resonates).

In fact, when the measured values of three machines having this 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 based on the premise that speed fluctuations at a source such as a motor or a gear are reduced. Focusing on the point of transfer, the transfer function,
The driving device for the rotating body is configured as follows in consideration of the concept of resonance and natural frequency and in consideration of how the transmitted fluctuation is attenuated.

First, in order to avoid resonance of the rotating body drive system, the natural frequency of the rotating body drive system and the frequency of the fluctuation component transmitted to the rotating body drive system are prevented from being coincident with each other.
Generally, 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 to avoid resonance. From the viewpoint of avoiding resonance, ω may be increased or decreased with respect to 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 is possible to realize 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 is moved to a large value and a small value by a structural change in the drive system of the data shown in FIG. The measured values of the functions are superimposed as in FIG. FIG.
Is a comparison of the peak values of the transfer functions for the above three drive systems. The structure change of FIG. 10 for reducing the rigidity of the drive system is to reduce the value of the torsional rigidity K of the drive system. The comparison of the data in FIGS. 10, 11 and 12 suggests that in order to avoid resonance, the torsional stiffness K of the drive system is reduced to move the natural frequency, and the natural frequency is lowered. In the case of a structural change in which the transfer function is moved to the side, the transfer function decreases as the natural frequency moves. This is considered to be due to the fact that the damping element becomes remarkable due to the flexible structure accompanying the structural change for moving the natural frequency, and the structure shifts to a structure in which the drive system itself absorbs the rotational fluctuation. As a result, when the natural frequency is moved to avoid resonance, a structural change to reduce the torsional rigidity K of the drive system is accompanied by a change in the magnitude of the transmission gain of the change in the rotational speed. It turns out that it is advantageous and effective in reducing the speed fluctuation.

Therefore, in the present invention, based on such a concept, the rotating body and the drive shaft are connected on the far side to the drive transmission system of the rotating body, and an inertial load is mounted inside the rotating body, and the rotating body driving system has In addition to reducing the frequency, a dynamic damper in which an outer cylinder having an inertial load and an inner cylinder are connected by an elastic member is mounted on the drive shaft.

[0014]

Since the drive shaft and the rotating body are connected on the side far from the drive transmission system, the effective length of the drive shaft is increased, whereby 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 driving system is increased, and the natural frequency can be reduced. As a result, the natural frequency of the rotating body driving system expressed by the equation (1) is reduced. The number and the frequency of the fluctuation component can be separated, and the resonance of the rotating body drive system can be prevented to reduce the fluctuation of the rotation speed. Further, since the rigidity K of the rotating body drive system is substantially reduced, 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 eliminated and the speed fluctuation of the rotating body is eliminated,
The quality of the output image can be greatly improved.
Further, the size of the apparatus can be reduced, 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 apparatus 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 unit 3,
A drive mechanism for driving the photosensitive drum 2 and the like are attached. FIG. 2 shows the photosensitive drum 2 and the driving mechanism 4. The drive mechanism 4 includes a drive motor 5 and a gear group 6 connected thereto, 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 coated with an organic photosensitive material on its side, and has flanges 12a and 12b attached to both ends as shown in FIG. A drive shaft 13 passes through the center of the flange 12a and the like, and the flange 12b farther from the drive gear 11 and the drive shaft 13 are fixed by pins 15, and 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 above-described drive gear 11 is attached to the shaft end.
This drive gear 11 meshes with the final gear 10. Inside the photosensitive drum 2, inertia members 8 are attached to both flanges 12a and 12b on both sides, and a dynamic damper 1 is provided between the photosensitive drum 2 and the driving gear 11.
8 is attached. In addition, the dynamic damper 18
As shown in FIG. 4, it is provided inside the photosensitive drum 2.

The inertia member 8 is a ring-shaped weight made of steel, SUS, brass, or the like. The ratio of the inertia moment to the inertia moment I2 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. Elastic rubber 21 is filled between the inner cylinder 19 and the outer cylinder 20. Reference numeral 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 and weight of the outer cylinder 20, the elasticity of rubber, and the like, and can efficiently absorb and remove the vibration remaining on the photosensitive drum 2. .

As described above, the flange 12b on the side remote from the drive gear 11 and the drive shaft 13 are connected, and the photosensitive drum 2
Is provided with an inertia member 8 and a dynamic damper 18 is attached to a drive shaft 13 connected to the photosensitive drum 2, so that an inertia of a drive system including the photosensitive drum 2, the drive shaft 13 and the drive gear 11 is provided. The moment I increases,
In addition, since the distance between the drive gear 11 and the inertia member 8 is increased, the rigidity K of the drive system is substantially reduced, thereby lowering the natural frequency of the drive system. Therefore, by setting the natural frequency to an appropriate value, the natural frequency and the fluctuation component can be separated from each other in relation to the frequency of the fluctuation component generated by the drive mechanism 4, and the resonance of the photosensitive drum 2 can be reduced. Thus, the quality of the output image can be remarkably improved by rotating the photosensitive drum 2 smoothly without causing speed fluctuation.

Further, the transmission gain of the photosensitive drum 2 can be reduced because the rigidity K is substantially reduced, so that the speed fluctuation input from the final gear 10 is easily attenuated,
Since the fluctuation of the rotation speed of the photosensitive drum 2 can be suppressed and the dynamic damper 18 is attached to the drive shaft 13 connected to the photosensitive drum 2, vibrations remaining on the photosensitive drum 2 can be efficiently removed, and the rotation speed can be reduced. Fluctuations can be kept to a minimum. Therefore, the photosensitive drum 2 can be smoothly rotated at a constant speed, and the quality of an 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. In order to increase the moment of inertia I of the drive system, the inertial load of the flange itself may be increased, and the dynamic damper 18 may not necessarily be provided outside the photosensitive drum 2. In this way, as described above, the speed fluctuation can be reduced to improve the image quality, the outer shape can be reduced, the assembling process can be simplified, and the number of parts can be reduced to reduce the cost.

Further, the inertia member 8 may be formed by laminating a thin metal plate and fixing it to the flange 12. Even when the inertia member 8 is formed in this manner, the photosensitive member is formed in the same manner as described above. The natural frequency can be reduced by increasing the moment of inertia I of the drum 2 and decreasing the rigidity K. As a result, the natural frequency can be separated from the fluctuation component in the frequency domain, and resonance can be prevented to prevent the photosensitive member. The image quality can be remarkably improved by reducing the speed fluctuation of the drum 2, and the moment of inertia I can be easily adjusted by adjusting the number of metal plates attached.

Further, the dynamic damper 18 is located on the opposite side of the photosensitive member 2 with the drive gear
It may be attached to.

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

In the above description, the rotating body itself is the photosensitive drum 2, but the photosensitive drum 2 does not have to be a rotating body. As shown in FIG. An image output device may be used in which the driving roller 26 that drives the drive 25 is a rotating body of the present invention. Also in this case, by using each of the above-described embodiments for the drive roller 26, the drive roller 26 can be rotated without speed fluctuation, and therefore, the photosensitive member 25 can be transferred at a constant speed. Can be improved.

As described above, the flange 12b remote 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 a rotating body such as the photosensitive drum 2. Moment of inertia I of mounted rotating body drive system
, The natural frequency is lowered so that the frequency does not match the frequency of the speed fluctuation transmitted to the rotating body drive system.
6 can be prevented, and the photosensitive drum 2 or the photosensitive member 25 can be rotated or transported at a constant speed without causing speed fluctuation, thereby significantly improving image quality.
Further, since the rigidity K is substantially reduced, the transmission gain of the photosensitive drum 2 or the drive roller 26 is reduced, and the speed fluctuation is hardly transmitted, so that the speed fluctuation of the photosensitive drum 2 or the photoconductor 25 can be reduced. In addition, by attaching the dynamic damper 18 to the drive shaft 13 of the photosensitive drum 2, the remaining vibration can be absorbed, and the image quality can be significantly improved. Furthermore, it can be realized by a compact mechanism, the size of the device can be reduced, the cost can be reduced, and the reliability of the whole system can be significantly improved.

[0028]

[0029]

According to the image output apparatus of the present invention, the driving system is constituted by a driving unit connected to a driving motor and driven, and a rotating unit driving system which is connected to the driving shaft and rotates at a constant speed. By fixing the drive shaft and the flange far from the drive gear mounted on the shaft, mounting an inertial load inside the rotating body, and further installing a dynamic damper on the drive shaft inside the rotating body, these drive systems 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 of the drive motor, and the resonance of the rotating body can be prevented. Can be rotated. In addition, since the rigidity is substantially reduced, the transmission gain of the rotating body drive system can be reduced, the transmission of the fluctuation can be suppressed, the speed fluctuation of the rotating body can be reduced, 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, image quality, particularly image unevenness such as step unevenness and pitch unevenness occurring in the sub-scanning direction of the writing system is reduced, and a remarkable improvement in image quality is obtained. In addition, a device having a complicated and large-sized mechanism in the prior art can be realized by a simple and compact mechanism, and thereby the cost can be reduced. Further, the simplification of the mechanism can significantly improve the reliability of the entire system.

[Brief description of the 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 the entire rotating body drive system.

FIG. 3 is a 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 a speed variation of a conventional photosensitive drum.

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

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

FIG. 10 is a graph showing the transfer function of the photoconductor driving 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 together 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

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI H04N 1/31 F16F 15/30 Z (56) References JP-A-3-288183 (JP, A) JP, U) JP-A 2-104373 (JP, U) JP-A 4-105236 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) G03G 15/00 550 G03G 21 / 00 350-352 G03G 21/16-21/18 F16F 15/00-15/36 H04N 1/04 H04N 1/31

Claims (1)

(57) [Claims] 1. An image output apparatus comprising: a driving system including a rotating body and a driving shaft for rotating the rotating body; and a motor and a driving transmission system for rotating the driving system. Drive shaft close to the drive transmission system
Image while the rotatable have side integrally fixed to the far side to the drive transmission system, is attached an inertial load on the rotary body, characterized in that fitted with dynamic damper to the drive shaft of the rotary body Output machine
Bowl .