JP2000088060A - Vibration control device for rotor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a vibration control device for rotor, which will not generate a drive loss in the constant speed rotating condition and can certainly suppress eventual variation in the rotating speed. SOLUTION: A flange 9 of a photo-sensitive drum 8 and an inertial member 2 rotatable coaxially with the drum 8 are coupled together by a permanent magnet 3 with a strength to such a degree as allowing slip generation between the two members. Only when a variation is generated in the rotating speed of the drum 8, a friction is produced between the drum 8 and the inertial member 2 willing to maintain the speed unchangedly, and an action is applied in the direction of eliminating the difference in the speed between them 8 and 2, and the variation in the drum speed is suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vibration damping device for a rotating body used as, for example, a photosensitive member of an image forming apparatus. More specifically, the present invention relates to a vibration isolator for a rotating body that generates a load in a direction to cancel the speed variation only when the rotating speed varies in the rotating body.

[0002]

2. Description of the Related Art Heretofore, a rotating body has been used as a driving roller for a photosensitive drum or a conveyor belt of an image forming apparatus. When the rotation speed of these rotating members fluctuates, line noise called so-called pitch unevenness occurs with respect to an electrostatic latent image or a visible image formed on a photosensitive drum and an image on a recording paper carried on a conveyance belt. May cause. Therefore, in these rotating bodies, it is necessary to keep the rotating speed as constant as possible. Therefore, as a technology of a vibration isolator for preventing the rotation fluctuation of these rotating bodies,
JP-A-8-21796 and JP-A-8-11500
Is described in Japanese Patent Application Publication No.

[0003] The technology disclosed in Japanese Patent Application Laid-Open No.
A braking device composed of a sliding member and an elastic member is pressed against the photosensitive drum, and a damping action is generated by a frictional force between the sliding member and the photosensitive drum to suppress fluctuations in the rotation speed of the photosensitive drum. In Japanese Patent Application Laid-Open No. 8-11500, an oil damper is used as a braking device to act on a photosensitive drum.

[0004]

However, in each of the above two prior arts, a load is constantly applied to the photosensitive drum which is a rotating body. In such an anti-vibration device, a large torque is always required for driving the rotating body irrespective of whether or not the rotation speed of the rotating body fluctuates. That is, when the rotating body maintains a constant rotation speed, a drive loss occurs. Particularly, in an image forming apparatus of a type that forms a full-color image by superimposing images of four colors, since there are four photosensitive drums, the driving loss, that is, the power consumption loss is also quadrupled.

The present invention has been made to solve the problems of the above-described conventional vibration isolator for a rotating body. That is, the object is to eliminate a drive loss in a constant-speed rotation state in which the rotation speed of the rotating body does not fluctuate, and to effectively suppress the fluctuation when the rotation fluctuates. To provide an anti-vibration device.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a vibration isolator for a rotating body according to the present invention, comprising: an inertia member rotatable coaxially with the rotating body; And magnetic coupling means for coupling the magnetic force with the magnetic force.

In this vibration isolator for a rotating body, since the inertia member and the rotating body are magnetically coupled by the magnetic force coupling means, when the rotating body is rotating, the inertia member also rotates coaxially with the rotating body. . The inertia member in this state has an angular momentum obtained as a product of the moment of inertia and the angular velocity of rotation. For this reason, if the rotation speed of the rotating body changes, a difference in the rotation speed occurs between the rotating body and the inertial member, and the friction between the rotating body and the inertial member that attempts to maintain the same rotation speed is generated. Occurs. This friction acts in a direction in which the difference in rotation speed between the rotating body and the inertial member is to be eliminated. Therefore, fluctuations in the rotation speed of the rotating body are suppressed. However, when the rotating body maintains a constant rotating speed, there is no difference in the rotating speed between the rotating body and the inertial member, so that no friction occurs between the rotating body and the inertial member. Accordingly, in the constant-speed rotation state, the vibration isolator of the rotating body does not cause a drive loss. As described above, according to the vibration isolator of the rotating body of the present invention, it is possible to suppress the fluctuation of the rotation speed without driving loss in the constant speed rotation state.

Accordingly, in this vibration isolator for the rotating body, the strength of the coupling between the inertial member and the rotating body by the magnetic force coupling means is such that when the rotation speed of the rotating body changes, the sliding force between the two members is reduced. Is good enough to be able to occur. If the coupling by magnetic force is too strong, no slippage can occur between the two, and they will rotate as a unitary one. In this,
This is because the inertia member is merely a flywheel.

In this vibration isolator for a rotating body, the inertial member has a permanent magnet, and the rotating body or its flange is formed of a permanent magnet or a magnetic body to constitute the magnetic coupling means. Can be. In this case, the inertia member itself may be constituted by a permanent magnet,
A permanent magnet may be integrally attached to the inertial member. In this way, the mass of the permanent magnet can be used for the inertia moment of the inertial member, so that a stronger inertia effect can be obtained.

Alternatively, the inertia member may have a permanent magnet or a magnetic body, and the rotating body or its flange may be formed of a permanent magnet to constitute the magnetic coupling means. With this configuration, the inertia member can be made compact and can be stored inside the rotating body.

Further, in the vibration isolator for a rotating body of the present invention, a holding member for holding the inertia member in the apparatus main body is provided so that the rotating body and the inertia member can be separated. It is desirable to do. This makes it possible to provide a cartridge structure in which the rotating body can be detachably attached to the apparatus main body. Further, in the separated state, the rotating body does not include the inertia member, so that the rotating body is lightweight, and the inertia member is easily handled because it is held by the holding member.

[0012]

Embodiments of the present invention will be described below in detail with reference to the drawings. The present embodiment relates to a vibration damping device for a photosensitive drum used in an image forming apparatus such as a copy machine, a fax machine, and a printer.

As shown in the cross-sectional view of FIG. 1, the vibration isolator 1 according to the present embodiment is provided at a portion of the photosensitive drum 8 that is connected to the main body side plate 6 on the driving side surface. That is, the support shaft 7 that supports the photosensitive drum 8 is attached to the main body side plate 6 so as to be rotatable around the axis. The photosensitive drum 8 is mounted so as to be slidable in the axial direction with respect to the support shaft 7 and to rotate together with the support shaft 7. A holder 5 for holding the vibration isolator 1 is attached to a surface of the main body side plate 6 on the side of the photosensitive drum 8. The holders 5 are hook-shaped members, and are attached around three to six holders around the vibration isolator 1.

The photosensitive drum 8 has a hollow cylindrical shape. A flange 9 that is supported by a support shaft 7 and is connected to the vibration isolator 1 is attached to the end surface. The flange 9 includes a disk portion 91 having substantially the same diameter as the photosensitive drum 8, and a hub portion 92 having an inner diameter equal to or slightly larger than the support shaft 7 and fitted into the support shaft 7. As the material of the flange 9, a general steel material or ferritic stainless steel, which is a magnetic material, is used.

The vibration isolator 1 includes a ring-shaped inertia member 2,
Similarly, a ring-shaped permanent magnet 3 is integrally assembled. The inertia member 2 has a large moment of inertia in order to suppress fluctuations in the rotation of the photosensitive drum 8. The permanent magnet 3 serves to couple the inertial member 2 and the flange 9 by magnetic force, and is located on the photosensitive drum 8 side of the inertial member 2. The sliding member 4 covers the surface of the permanent magnet 3 facing the flange 9 and the inner surfaces of the permanent magnet 3 and the inertial member 2. The inner diameter of the vibration isolator 1 is the same as or slightly larger than the hub 92 of the flange 9.

In the state shown in FIG. 2 in which the photosensitive drum 8 and the flange 9 are slid with respect to the support shaft 7, the photosensitive drum 8 and the vibration isolator 1 are connected. This connection is due to the magnetic force between the flange 9 and the permanent magnet 3. However, when the rotation speed of the photosensitive drum 8 changes, the flange 9
This is a connection that is not too strong, such that slippage can occur between the sliding member 4 of the vibration isolator 1 and the sliding member 4. If the connection is too strong and no slippage can occur between the two, the rotation will be practically integral and the inertia member 2 will be no different from a normal flywheel.

[0017] Therefore, the strength of the bond between the photosensitive drum 8 and the vibration isolating apparatus 1 is provided with less than the upper limit value N _U for static friction force N _S between the flange 9 and the sliding member 4 is described below It is set to be. Incidentally, the static friction force N _S is the product M of the static friction coefficient mu _S between the magnetic force M between the flange 9 and the permanent magnet 3 in the state of FIG. 2, the flange 9 and the sliding member 4
- is a μ _S.

It is assumed that the fluctuation of the rotational speed (angular velocity) ω of the photosensitive drum 8 to be suppressed is a periodic fluctuation of a sine waveform. At this time, if the frequency of the fluctuation is represented by f and the amplitude (peak-to-peak) is represented by Δω, the angular acceleration (dω / dt) of the fluctuation is approximately given by the following equation. dω / dt = Δω · 2f (1) Here, f uses the lower limit value fmin of the allowable variation frequency of the rotational speed ω. However, since the lower limit of the spatial frequency at which the sensitivity to pitch unevenness is high is 0.5 lp / mm, fmin
The product of the system speed (the tangential speed when the photosensitive drum 8 rotates at a constant speed) and the lower limit of the spatial frequency may be used.

As .DELTA..omega., The smallest value which is the amplitude of the fluctuation of the rotational speed .omega. Of the photosensitive drum 8 and which affects the image quality is used. Set the system speed to S, photoconductor drum 8
Is the radius of R, the rotational speed ω of the photosensitive drum 8 is given by ω = S / R. If the wow and flutter of the drive system is δ, then Δω = (δ · S) / R (2).

Here, assuming that the inertia moment of the inertia member 2 and the permanent magnet 3 is I, when the rotation speed ω of (dω / dt) fluctuates on the photosensitive drum 8, the flange 9 and the sliding member 4 Is expressed as F = I · (dω / dt). Considering equations (1) and (2), F = I.delta.S.2f / R. The F is an upper limit value N _U static friction force N _S acceptable.

Therefore, it is necessary that N _S ≦ I · δ · S · 2f / R (3). So as to satisfy the equation (3), the static friction force N _S is set. That is, _{M · μ S ≦ I · Δω} · 2f (4). So as to satisfy the equation (4), the magnetic force M, and static friction coefficient mu _S is set. Thus, the strength of the connection between the photosensitive drum 8 and the vibration isolator 1 is not too strong.

On the other hand, it goes without saying that the strength of the connection between the photosensitive drum 8 and the vibration isolator 1 must not be too weak. If it is too weak, it takes a long time for the vibration isolator 1 to follow up when the photosensitive drum 8 is started from the stopped state. Specifically, the rotation of the vibration isolator 1 must be stabilized between the time when a print command is issued and the time when exposure starts. Normally, the time required for stabilizing the exposure device is longer than the time required for stabilizing the drive system of the photosensitive drum 8, so that the rotation of the vibration isolator 1 should be stabilized at least within the time that the exposure device is stabilized.

[0023] Therefore, the binding strength between the photosensitive drum 8 and the vibration isolating apparatus 1, the flange 9 and the dynamic friction force between the sliding member 4 N _D is described next lower limit N _L or more It is set as follows. Incidentally, the dynamic friction force N _D is the product M · mu _D between the dynamic friction coefficient mu _D between the magnetic force M, the flange 9 and the sliding member 4
It is.

Consider a situation in which the photosensitive drum 8 starts moving first and the rotation of the vibration isolator 1 is accelerated by sliding friction therewith. When the rotation speed (angular velocity) of the vibration isolator 1 is represented by υ, the angular acceleration of rotation of the vibration isolator 1 (dυ / dt)
It is given by _{dυ / dt = N D / I} . Required time T for the rotational speed of the vibration isolating apparatus 1 by the angular acceleration catches up with the steady rotation speed omega of the photosensitive drum _{8, T = ω / (N D} / I) = (I · ω) / N D and Become.

Assuming that the time required for stabilizing the exposure apparatus is Tw, the required time T must be less than the time Tw. Therefore, (I · ω) / N _D ≦ Tw. From this, it must be _{N D ≧ (I · ω)} / Tw. When this is expressed using the radius R of the system speed S and the photosensitive drum _{8, N D ≧ (I ·} S) / a (Tw · R) (5) . So as to satisfy the equation (5), the dynamic friction force N _D is set. That is, _{M · μ D ≧ (I ·} S) / (Tw · R) (6). So as to satisfy the equation (6), the magnetic force M and the dynamic friction coefficient mu _D is set. Thus, the strength of the connection between the photosensitive drum 8 and the vibration isolator 1 is not too weak.

Further, the vibration isolator 1 is held on the main body side, and is configured to be separable from the photosensitive drum 8. Specifically, it is held by a holder 5 attached around the support shaft 7 of the main body side plate 6. The distance between the holders 5 on the side facing the photosensitive drum 8 is smaller than the diameter of the inertia member 2 in the vibration isolator 1 and larger than the diameters of the permanent magnet 3 and the sliding member 4. For this reason, the vibration isolator 1 cannot go out of the holder 5 and can move freely only inside the holder 5.

The vibration isolator for the photosensitive drum 8 configured as described above is used in a state where the photosensitive drum 8 and the vibration isolator 1 are connected as shown in FIG. When the photosensitive drum 8 is thus mounted in the main body, the inertia member 2 and the photosensitive drum 8 are magnetically coupled by the permanent magnet 3, so that the photosensitive drum 8 is rotating. Occasionally, the inertia member 2 rotates coaxially therewith. In this state, the inertia member 2 has an angular momentum obtained as a product of the moment of inertia and the angular velocity of rotation, and tries to maintain the rotational speed as it is. When the photoconductor drum 8 maintains a constant rotation speed, there is no difference in the rotation speed between the photoconductor drum 8 and the inertia member 2. No friction occurs. Therefore, no drive loss occurs in the vibration isolator 1 for the photosensitive drum 8 in the constant-speed rotation state.

However, a change in the rotation speed of the photosensitive drum 8 causes a difference in rotation speed between the photosensitive drum 8 and the inertial member 2, so that the rotation speed of the photosensitive drum 8 and that of the inertia member 2 are maintained. Friction occurs with the inertial member 2. This friction acts in a direction in which the difference in rotational speed between the photosensitive drum 8 and the inertial member 2 is to be eliminated. Therefore, the fluctuation of the rotation speed of the photosensitive drum 8 is suppressed. In a situation where there is a difference in rotational speed between the photosensitive drum 8 and the inertial member 2, an eddy current flows through the disk portion 91 of the flange 9 based on the magnetic field of the permanent magnet 3. The iron loss due to the eddy current also has the effect of eliminating the difference in rotation speed between the photosensitive drum 8 and the inertial member 2.

Since the vibration isolator 1 is held in the holder 5 attached to the main body side plate 6, the photosensitive drum 8 can be separated from the vibration isolator 1 by pulling the photosensitive drum 8 leftward in the drawing. Further, it is possible to adopt a cartridge structure in which the photosensitive drum 8 can be detached from the apparatus main body by pulling it further to the left from the state shown in FIG. In this case, since the photosensitive drum 8 in the separated state does not include the inertial member 2 and the permanent magnet 3, the weight is light.
Further, since the vibration isolator 1 is held by the holder 5 and does not fall off from the main body of the device, it is easy to handle.

As described above in detail, in the vibration damping device 1 for the photosensitive drum 8 according to the present embodiment, the inertial member 2 held on the side of the main body side plate 6 is moved by the magnetic force of the permanent magnet 3. The flange 9 of the drum 8 is connected. Therefore, only when the rotation speed of the photosensitive drum 8 changes, friction occurs between the photosensitive drum 8 and the inertial member 2 that is to maintain the rotation speed. It acts in a direction in which the difference in rotation speed between the inertia member 2 and the inertial member 2 is to be eliminated, and fluctuations in the rotation speed of the photosensitive drum 8 are suppressed. Here, when the photoconductor drum 8 maintains a constant rotation speed, there is no difference in the rotation speed between the photoconductor drum 8 and the inertia member 2. No friction occurs between them. Therefore, the fluctuation of the rotation speed of the photosensitive drum 8 is suppressed without causing a drive loss in the constant speed rotation state.

The present embodiment is merely an example, and does not limit the present invention. Therefore, naturally, the present invention can be variously modified and modified without departing from the gist thereof. For example, although the permanent magnet 3 is integrally attached to the inertial member 2, a heavy permanent magnet may be used, and the permanent magnet 3 itself may be used as the inertial member. Alternatively, contrary to the present embodiment, the flange of the photosensitive drum 8 may be formed of a permanent magnet, and the inertial member 2 may include a magnetic material such as a general steel material. Of course, permanent magnets can be used for both. Further, the vibration isolator 1 can be housed inside the photosensitive drum 2 as well as attached to the main body.

[0032]

As is apparent from the above description, according to the present invention, there is no drive loss in the constant speed rotation state where the rotation speed of the rotating body does not fluctuate, and only when the rotation speed fluctuates. There is provided a vibration damping device for a rotating body that can surely suppress the fluctuation.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a vibration isolator (separated state) of a rotating body according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view of a vibration isolator (in a coupled state) of a rotating body according to the embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Vibration isolator 2 Inertial member 3 Permanent magnet 4 Sliding member 5 Holder 6 Main body side plate 7 Support shaft 8 Photoconductor drum 9 Flange

Claims (5)

[Claims] 1. An inertia member rotatable coaxially with a rotating body,
A vibration isolator for a rotating body, comprising: a magnetic force coupling unit that couples the inertial member and the rotating body with a magnetic force. 2. The vibration isolator for a rotating body according to claim 1, wherein when the rotation speed of the rotating body changes.
A vibration isolator for a rotating body, wherein slippage may occur between the inertial member and the rotating body. 3. The vibration isolator for a rotating body according to claim 1, wherein the inertia member has a permanent magnet, and the rotating body or its flange is formed of a permanent magnet or a magnetic body. A vibration isolator for a rotating body. 4. The vibration isolator for a rotating body according to claim 1, wherein the inertia member has a permanent magnet or a magnetic body, and the rotating body or its flange is formed of a permanent magnet. A vibration isolator for a rotating body. 5. The method according to claim 1, wherein:
In the vibration isolator for a rotating body described in (1), the rotating body has a holding member for holding the inertia member in a device main body, and the rotating body and the inertia member can be separated from each other. Anti-vibration device.