JP2001134138A - Device for driving image carrier - Google Patents

Abstract

PROBLEM TO BE SOLVED: To widen an area for attenuating a vibration by the enlargement of a substantial inertial amount without enlarging the weight and outer diameter of a fly wheel being an inertial body. SOLUTION: A second small friction roll 44 is brought into contact with a first large friction roll 42 and a rotational force is transmitted by the friction. Since the diameter of the second small friction roll 44 is smaller than that of the first large friction roll 42, the number of rotation is increased. In this case, a second large friction roll 52 with a diameter being larger than that of the roll 44 is integrally rotated. A third small friction roll 56 with a small diameter is brought into contact with the second large friction roll 52 and integrally rotated with the fly wheel 64 owing to the increase of the rotation number. Thus, an attenuating force is enlarged without increasing the weight and outer diameter of the fly wheel 64 by successively increasing the rotation number and speeding-up the rotation of the fly wheel 64.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image carrier driving device for driving an image carrier such as a photosensitive drum used in an image forming apparatus such as a laser printer and a digital copying machine.

[0002]

2. Description of the Related Art In an electrophotographic digital copying machine or printer (including a color machine), exposure on a photosensitive drum is performed by a laser beam. The diameter of this laser beam is about 50 μm in the case of 600 dpi.

[0003] Therefore, in the direction orthogonal to the sub-scanning direction, 5
An image is formed by superimposing the 0 μm lines.
If the surface speed of the photosensitive drum is constant, as shown in FIG. 7, the interval between the writing lines L by the laser beam becomes constant, and no image unevenness occurs.

[0004] However, if the surface of the photosensitive drum vibrates, as shown in FIG. 8, the interval between the write lines L by the laser beam becomes uneven. If the rotational vibration at this time has periodicity, the image becomes uneven and the image quality deteriorates. Further, in the case of a color image forming apparatus, the color tone is changed as a result of uneven density of each color.

In order to prevent such an image defect, FIG.
As a technique for stabilizing the rotational vibration of the photosensitive drum 12, as shown in FIG. 1, a flywheel 94 (Flywheel) is generally fixed to a driven shaft 92 of the photosensitive drum 12 to increase the amount of inertia. Are known.

However, since the photosensitive drum 12 is rotating at a relatively low speed, a large flywheel 94 is required. This is because the amount of inertia is only proportional to the axial length of the flywheel 94, but is proportional to the radius of rotation by the square.

In addition to the technique of mounting a flywheel on a driven shaft, as a method of increasing the amount of inertia of a rotating body, as described in JP-A-1-93888, the weight of a part of a member constituting an image carrier is reduced. Some things will be bigger.

However, it is difficult to increase the weight of the inertial body beyond the outer diameter of the photosensitive drum. Therefore, the only way to secure the amount of inertia is to respond to the length in the axial direction. It is not a cost-effective method. Therefore, there is a great restriction in terms of machine size, weight, and cost, and it is difficult to replace a consumable photosensitive drum.

In order to solve these problems, FIG.
Japanese Patent Application Laid-Open No. Hei 9-171327, a large-diameter pulley 72 fixed to a rotating shaft 70 of the photosensitive drum 12,
By winding a flat belt 78 around a small-diameter pulley 76 fixed to a speed-increasing shaft 74 arranged in parallel with the rotation shaft 70 and attaching a small flywheel 80 to the speed-increasing shaft 74, the small flywheel 80 is substantially The present applicant has devised a technique for increasing the amount of inertia.

This utilizes the characteristic that when the rotational speed of the flywheel 80 is increased, the amount of inertia increases as the square of the rotational speed of the flywheel 80.

However, the transfer characteristic of this technique is a vibration system having two degrees of freedom and generating two resonance points. The resonance point on the low frequency side is determined by a substantial amount of inertia and a spring constant of a drive system or the like. On the other hand, it has been confirmed that the resonance point on the high frequency side increases or decreases due to the rigidity between the two pulleys 72 and 76.

The portion between the two resonance points is a region where the vibration can be attenuated. The wider the region, the better. Therefore, it is desirable to increase the rigidity between the two pulleys 72 and 76 as much as possible. However, there is a practical limit in an elastic body such as the flat belt 78.

To solve this problem, Japanese Patent Application Laid-Open No. Hei 10-288915 discloses a large-diameter pulley 84 fixed to a rotating shaft 82 of a photosensitive drum 12, as shown in FIG. By directly contacting a small-diameter pulley 88 fixed to the shaft 86, the rotation speed of the flywheel 90 is increased, and a region in which vibration can be attenuated by increasing the rigidity between the pulleys 84, 88 is provided.
The high frequency side has been expanded.

Although it is necessary to increase the substantial amount of inertia in order to bring the low frequency side generation source into the attenuation range, the speed increase ratio must also be increased in order to prevent slippage between the pulleys 84 and 88. Due to limitations, flywheel 90
Must be increased.

However, at present, the flywheel 90 cannot be made too large for the following reasons.

That is, for example, when the outer diameter of the large-diameter pulley 84 is φ50 and the outer diameter of the small-diameter pulley 88 is φ10,
The rotation ratio can only gain 5 times. Attempting to increase the rotation ratio further increases the diameter of the large-diameter pulley, which poses a space problem.

Further, in a tandem machine, especially a small machine, the outer diameter of a pulley to be mounted on a rotating shaft is naturally limited because the distance between adjacent photosensitive drums is short, and cannot be increased. Further, if the diameter ratio of the pulleys is too large, the contact area between the pulleys becomes small, which leads to the occurrence of slip.

For these reasons, there is no other choice but to rely on the precision of the mechanical parts to put the source below 10 Hz into the attenuation range.

[0019]

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and does not increase the weight and outer diameter of the flywheel as an inertia body and increases the diameter ratio of the pulley. It is an object of the present invention to increase the substantial amount of inertia and widen a region in which vibration can be attenuated without performing the operation.

[0020]

According to the first aspect of the present invention, the driving means drives the image carrier which is scanned and exposed by the laser beam. The image carrier and the first rotating body rotate together.

The first rotating body comes into contact with the first small rotating body constituting the second rotating body, and the rotational force is transmitted by friction. Since the second small rotator has a smaller diameter than the first rotator, the rotation speed is increased. At this time, the second large rotator larger in diameter than the second small rotator also rotates integrally.

Further, the third small rotating body is in contact with the second large rotating body, and the rotational force is transmitted by friction. Since the third small rotating body has a smaller diameter than the second large rotating body, the rotation speed is increased. At this time, the third small rotating body and the inertial body rotate integrally.

As described above, by a series of operations in which the diameters of the rotating bodies on the driving side and the driven side are made different and the number of rotations is sequentially increased, for example, if the speed increasing ratio of each rotating body is M1, M2, The rotation speed of the inertial body is M1 × M2 times the rotation speed of the first rotator. In addition, the amount of inertia is (M1 × M2) ² times as compared with the case without the speed increasing mechanism.

Accordingly, it is not necessary to increase the weight and the outer diameter of the inertial body, so that the image forming apparatus can be designed to be compact. In addition, by sequentially increasing the rotation speed, compared with the case of increasing the speed by a combination of a single rotating body, without extremely increasing the diameter ratio of the rotating body in a portion transmitting each rotational force, Since the speed increase ratio can be increased in the final stage,
The rotating body can be compactly housed in the image forming apparatus, and the contact area between the rotating bodies is not reduced, so that the slip hardly occurs.

As described above, since the substantial amount of inertia can be increased, the damping force that can attenuate the generated vibration increases, and the damping region can be widened.

According to the second aspect of the present invention, the pressure applying means for adjusting the contact force between the first rotating body and the second small rotating body is provided. By adjusting the contact force, the damping force and the damping area can be tuned.

According to the third aspect of the present invention, by pressing the third small rotator against the second large rotator, the first rotator and the second rotator are pressed.
A slide means for increasing the contact force of the small rotating body is provided on the shaft portions of the second rotating body and the third small rotating body. Thereby, the degree of freedom in mounting the pressure applying means is improved.

According to the fourth aspect of the invention, the damping force and the damping area of the image carrier are adjusted by changing the material of the first rotating body and the second rotating body. That is, the damping force and the damping region can be tuned by changing the material of the first rotating body and the second rotating body and changing the rigidity.

[0029]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A driving device for an image carrier according to a first embodiment will be described below with reference to the drawings.

As shown in FIGS. 1 and 2, a cylindrical photosensitive drum 12 (image carrier) is arranged between frames 10 of an image forming apparatus arranged in parallel with each other.
It is supported by a support shaft 14 serving as a rotation center. A mechanism for forming a toner image on the surface and transferring the toner image to a sheet is provided around the photosensitive drum 12, but is omitted here.

A joint 16 is provided at one end of the support shaft 14, and the joint 16 is connected to a joint 20 fixed to a drive shaft 18. This drive shaft 18
Three points are supported by bearings 26, 28, 30 provided on the frame 10, the frame 22, and the cover 24.

A drive motor 32 (for example, a stepping motor) for rotating the drive shaft 18 is mounted on the frame 22. A small gear 34 is fixed to the rotation shaft of the drive motor 32, and the small gear 34 meshes with a large gear 36. The large gear 36 is supported by the frame 22 so as to rotate integrally with the small gear 38.

The small gear 38 is meshed with a large gear 40 fixed to the drive shaft 18. Thus, when the drive motor 32 is driven to rotate, the small gear 34 and the large gear 3
6, the rotation speed is reduced by the small gear 38 and the large gear 40, the support shaft 14 rotates together with the drive shaft 18, and the photosensitive drum 12 rotates at a low speed in the sub-scanning direction.

On the other hand, a disk-shaped or column-shaped first large friction roll 42 is fixed to the drive shaft 18. The first large friction roll 42 contacts a second small friction roll 44 having a diameter smaller than that of the first large friction roll 42 to transmit a rotational force by friction.

The second small friction roll 44 applies a second large friction having a diameter larger than that of the second small friction roll 44 to a second rotating shaft 50 supported by bearings 46 and 48 provided on the frame 10 and the cover 24. The double friction roller 54 is fixed integrally with the roll 52.

The second large friction roll 52 contacts a third small friction roll 56 having a smaller diameter than the second large friction roll 52 to transmit a rotational force by friction. Third small friction roll 5
6 is fixed to a third rotating shaft 62 supported by bearings 58 and 60 provided on the frame 10 and the cover 24. A flywheel 64 for stabilizing the surface speed of the photosensitive drum 12 is fixed to the third rotating shaft 62.

As described above, the diameters of the driving-side friction roller and the driven-side friction roller are made different from each other, and the friction rollers are brought into contact with each other and are rotated in conjunction with each other. Speeded up. By fixing the flywheel 64 to the third rotating shaft 62, the speed increase ratio between the first large friction roll 42 and the second small friction roll 44 and the speed increase ratio between the second small friction roll 44 and the third small friction roll 56 It is possible to obtain an inertia amount which is twice the speed-up ratio.

Here, the outer diameter of the first large friction roll 42 that rotates integrally with the photosensitive drum 12 is A mm, and the outer diameter of the second small friction roll 44 on the smaller diameter side of the double friction roll 54 is B.
mm, the outer diameter of the second large friction roll 52 on the large diameter side is Cmm,
Assuming that the outer diameter of the third small friction roll 56 coaxial with the flywheel 64 is Dm, the speed increase ratio is represented by A / B × C / D.

Further, as the inertial energy E, E =
The effect of (A / B × C / D) ² can be obtained.

Therefore, compared to the case where the flywheel 94 is directly mounted on the drive shaft 18 of the photosensitive drum 12 (see FIG. 9), the same effect can be obtained by mounting the flywheel having the inertia of 1 / E. It is possible.

For example, the outer diameter of the first large friction roll 42 of the photosensitive drum 12 is φ50, the outer diameter of the second small friction roll 44 on the small diameter side of the double friction roll 54 is φ10, and the second large friction on the large diameter side. Outer diameter of roll 52 is φ40, flywheel 6
Assuming that the outer diameter of the third small friction roll 56 coaxial with 4 is φ10, the speed increase ratio is 50/10 × 40/10 = 20.

Therefore, the rotation speed of the flywheel 64 can be made 20 times the rotation speed of the photosensitive drum 12. Further, since the effect of the square of the rotation ratio can be obtained as the amount of inertia, the effect of 400 (20 ² ) times can be obtained in this case.

This is one-fourth of the case where the flywheel is directly mounted on the drive shaft of the photosensitive drum in order to suppress the generated vibration of the drive system such as the gears and the drive motor.
This shows that a flywheel (inertia body) having an inertia amount of 00 can obtain the same effect.

For this reason, in this embodiment, the flywheel 6
Since there is no need to increase the weight and outer diameter of the image forming apparatus 4, the image forming apparatus can be designed compact. In addition, by sequentially increasing the rotation speed of the drive shaft 18, the friction roll at the portion transmitting each rotational force is compared with the conventional case where the speed is increased by the combination of a single friction roll. The speed increase ratio can be freely set without extremely increasing the diameter ratio.

If the diameter ratio of the friction rolls is about 5, the contact area between the friction rolls does not become too small, so that the slip hardly occurs.

The first large friction roll 42, the double friction roll 54, and the third small friction roll 56 are formed of metal, resin, or the like, and the outer peripheral surface is roughened to increase the friction coefficient. . Further, a material having a high coefficient of friction may be formed in a thin layer on the outer peripheral surface. Materials that increase the coefficient of friction include elastomers such as urethane elastomers and silicone rubbers, and those that form a layer on the outer peripheral surface include inorganic fine particles of ceramic or diamond.

The first large friction roll 42, the double friction roll 54, and the third small friction roll 56 are
It is configured so that dust does not enter from outside and slip does not occur.

Next, a description will be given of an advantageous reason why the configuration in which the speed of the flywheel as the inertial body is increased by the friction roll as in the present embodiment.

The vibration transmission characteristic of this embodiment can be considered as a vibration system having two degrees of freedom. Factors that can be controlled in the two-degree-of-freedom vibration system include the rigidity K1 from the drive motor 32 to the photosensitive drum 12, the amount of inertia J1 of the photosensitive drum 12 having no degree of freedom depending on image forming conditions, and the like, the photosensitive drum. 1
2 and the rigidity K2 up to the flywheel 64 for attenuating the vibration, and the inertia amount J2 of the flywheel 64.

From these factors and the natural frequency,
It is necessary to adjust the frequency response characteristics so that the vibration generation frequency falls within the attenuation region of the drive transmission characteristics.

In order to set the resonance frequency on the low side low, the amount of inertia J of the flywheel for attenuating vibration is set.
However, the rotation of the photosensitive drum 12 is transmitted to the flywheel 64 at an increased speed, so that the amount of inertia is increased without changing the mass.

Here, the angular momentum of the drive shaft 18 when the speed is not increased is represented by A = (1) where α is the angular speed of the drive shaft 18.
/ ²⁾ · J · ω 2 become. On the other hand, if the rotational speed ratio of the flywheel 64 for attenuating the vibration with the photosensitive drum 12 is increased as R1 / R2, the angular momentum becomes A = (1 /
2) · J2 · ((R1 / R2) · ω) ² , and the angular momentum can be increased by the square of the ratio of the outer diameter.

In order to set the resonance frequency on the high side high, it is necessary to increase the rotational rigidity of the photosensitive drum 12 and the flywheel 64 for attenuating the vibration so as to generate a rotational speed difference. There is. To do this,
The rigidity is set high by selecting the thickness of the rotating shaft, the rigidity of the frame supporting the rotating shaft, the material and thickness of the roll that gives the speed difference, and the like.

As a result, as shown in FIG. 3, the two resonance frequencies can be set apart from each other, and by setting the vibration occurring at the frequency between the two resonance frequencies, the stable vibration can be attenuated.

The method of transmitting the rotational force by contacting the friction roll does not become a new vibration source unlike the method of transmitting the rotational force by a gear.

Next, among the parameters constituting the two-degree-of-freedom vibration system, which parameters contribute to the natural frequency fn1, the maximum minus gain G, and the natural frequency fn2 shown in FIG. Will be described.

The amount of inertia including the speed increase ratio greatly contributes to the parameter for determining the resonance frequency of fn1. Therefore, fn1 can determine the optimum frequency by tuning the outer diameter of each friction roll and the flywheel.

The larger the maximum minus gain G is, the larger the damping energy that can attenuate the generated vibration is. Also, the fn2 can be shifted to the high frequency side, so that the damping region can be widened.

Here, as a parameter contributing to the maximum minus gain G, it was found that the rigidity between the first large friction roll 42 and the double friction roll 54 coaxial with the photosensitive drum was large.

More specifically, the holding force between the photosensitive drum 12 and the first large friction roll 42 with respect to the drive shaft 18, the material (rigidity) of the first large friction roll 42, the material (rigidity) of the double friction roll 54, and the The contact force between the one large friction roll 42 and the double friction roll 54 is a parameter.

The graph of FIG. 3 shows the case where the rigidity between the first large friction roll 42 and the double friction roll 54 is high, and the fourth graph shows the case of the first large friction roll 42 and the double friction roll 54. It shows the case where the rigidity between them is low,
The comparison shows how the maximum minus gain G and fn2 change. Thus, an optimal transfer function can be configured by tuning the parameters.

In the second embodiment, one of the parameters, the first large friction roll 42 and the double friction roll 54
An example in which the contact force with the contact is adjusted is shown.

The basic structure of the second embodiment is the same as that of the first embodiment. However, as shown in FIG. 5, the bearing 46 supporting the second rotating shaft 50 is slidable with respect to the frame 10 by the bracket 96. The difference is that the bearing 48 is held slidably toward the first large friction roll 42 with respect to the cover 24 by the bracket 96 with respect to the cover 24.

The bracket 96 is pressed against the first large friction roll 42 by a compression spring 98 that receives a reaction force from the receiving plate 100, and the bracket 96 is in contact with the second small friction roll 44 of the double friction roll 54 and the first large friction roll 44. The contact force with the roll 42 is increased to increase the rigidity. The third small friction roll 56 coaxial with the flywheel 64 and the second large friction roll 52 of the double friction roll 54 need only have a contact force that does not cause slip.

Note that, instead of the compression spring 98, the bracket 96 is attached to the first large friction roll 42 by a tension spring.
The contact force between the second small friction roll 44 and the first large friction roll 42 may be increased by pulling to the side.

Further, as a modification, as shown in FIG. 6, the bearings 58 and 60 supporting the third rotating shaft 62 are attached to the frame 10 and the cover 24 by the bracket 102.
The third small friction roller 56 is pressed against the second large friction roller 52 by a compression spring 98 so as to be slidable toward the second large friction roller 52, and the first large friction roller 44 is pressed against the second small friction roller 44 of the double friction roller 54. A force that presses 42 may be generated.

In the present embodiment, an example has been described in which the rotation of the photosensitive drum is stabilized. However, for example, the rotation of a roll for running the photosensitive belt can be stabilized.

[0068]

According to the present invention, since the weight and the outer diameter of the inertial body are not increased, and the substantial inertia amount is increased without increasing the diameter ratio of the rotating body, The region where vibration can be attenuated can be widened.

[Brief description of the drawings]

FIG. 1 is a side sectional view of a driving device of an image carrier according to a first embodiment.

FIG. 2 is a front view showing a friction roll of the driving device of the image carrier according to the first embodiment.

FIG. 3 is a graph showing a frequency response of a mechanism for transmitting a rotational force to a flywheel by a friction roll.

FIG. 4 is a graph showing a frequency response of a mechanism for transmitting a rotational force to a flywheel by a friction roll.

FIG. 5 is a side sectional view of a driving device of an image carrier according to a second embodiment.

FIG. 6 is a side sectional view of a driving device of an image carrier according to a modification. It is a side sectional view.

FIG. 7 is a conceptual diagram showing a writing interval by a laser beam.

FIG. 8 is a conceptual diagram showing a writing interval by a laser beam.

FIG. 9 is a perspective view of a driving device in which a flywheel is attached to a driving shaft of a photosensitive drum.

FIG. 10 is a side sectional view showing a mechanism for transmitting a rotational force to a flywheel by a belt.

FIG. 11 is a side sectional view showing a mechanism for transmitting rotational force to a flywheel with a single friction roll.

DESCRIPTION OF SYMBOLS 12 Photoconductor drum (image carrier) 18 Drive shaft 42 First large friction roll (first rotating body) 44 Second small friction roll (second small rotating body) 52 Second large friction roll (No. Two large rotating bodies) 54 Double friction roll (second rotating body) 56 Third small friction roll (third small rotating body) 64 Flywheel (inertia body) 98 Compression spring (pressure applying means) 100 Bracket (slide means) 102 Bracket (Slide means)

Claims (4)

[Claims] 1. A driving unit for driving an image carrier that is scanned and exposed by a laser beam, a first rotator that rotates together with the image carrier, and has a smaller diameter than the first rotator and contacts the first rotator. And a second rotating body that is provided with a second small rotating body that transmits torque by friction and a second large rotating body that rotates integrally with the second small rotating body and has a larger diameter than the second small rotating body. A third rotating body having a diameter smaller than that of the second large rotating body, the rotating body being integrated with the third small rotating body, having a third rotating body having a smaller diameter than the second large rotating body, the rotating body being in contact with the second large rotating body and being transmitted with friction by friction; A driving device for an image carrier, characterized in that: 2. The driving device for an image carrier according to claim 1, further comprising a pressure applying unit for adjusting a contact force between the first rotator and the second small rotator. 3. A sliding means for increasing a contact force between the first rotating body and the second small rotating body by pressing the third small rotating body against the second large rotating body, and 3. The driving device for an image carrier according to claim 2, wherein the driving device is provided on a shaft portion of the three small rotating bodies. 4. The image forming apparatus according to claim 1, wherein the damping force and the damping area of the image carrier are adjusted by changing the material of the first rotating body and the second rotating body. A driving device for an image carrier according to any one of the above.