Rotary driving device and image forming apparatus

A rotary driving device includes a rotary shaft supported rotatably about an axis thereof on a predetermined supporting member, a rotary load body mounted on the rotary shaft to project radially outward from the rotary shaft in such a manner that the rotary load body can rotate integrally with the rotary shaft about the axis thereof, a driver for rotating the rotary shaft about the axis thereof, a disk mounted on the rotary shaft coaxially therewith for integral rotation with the rotary shaft, the disk having a mounting hole formed therein, a pendulum loosely fitted in the mounting hole, and an adjustment mechanism for adjusting a relative position relationship between a central axis position of the mounting hole and a center of gravity position of the pendulum under conditions where the disk is rotating.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a rotary driving device having a rotary load body which is driven to rotate integrally about a rotary shaft. The present invention also relates to an image forming apparatus provided with such a rotary driving device.

2. Description of the Related Art

Japanese Laid-open Patent Publication No. 2002-195348 describes an example of a conventional rotary driving device which is applied to an image forming apparatus. The rotary driving device of this Publication includes a rotary body system for rotatably supporting a rotary body, a driving system having an electric motor serving as a rotary driving source for driving the rotary body system to rotate, and a driving/transmission system interconnecting the rotary body system and the driving system.

The rotary body system includes a rotary shaft on which the rotary body is so mounted as to be able to rotate integrally with the rotary shaft and a centrifugal pendulum vibration absorber which is so mounted on the rotary shaft as to be able to rotate integrally therewith. The rotary shaft is rotatably supported by a structural part like a frame via bearings. When the electric motor is actuated, the rotary shaft, the rotary body and the centrifugal pendulum vibration absorber rotate together as a single structure.

The centrifugal pendulum vibration absorber is provided for absorbing vibration of the rotary body which rotates integrally with the rotary shaft on a common axis, and is configured to include a disk which is so mounted on the rotary shaft as to be able to rotate integrally therewith, a plurality of circular holes formed in the disk to pass therethrough at equal intervals along a circumferential direction of the disk and cylindrical pendulums loosely fitted in the individual circular holes.

When the rotary body rotates as a result of actuation of the electric motor in the centrifugal pendulum vibration absorber thus configured, the pendulums loosely fitted in the individual circular holes oscillate therein while producing pendular motion along inner surfaces of the circular holes. Vibrational energy produced by rotation of the rotary body is absorbed by the pendular motion (oscillatory motion) of the pendulums, so that the rotary body is kept from vibrating.

Provided that the aforementioned centrifugal pendulum vibration absorber is so configured that there is a difference L between the radius of each circular hole in the disk and that of each pendulum, the center of the disk is separated from the center of each circular hole by a distance R and the disk rotates at an angular velocity ω, a natural frequency ωnof vibration of each pendulum is known to be given by the following equation:
ωn=ω√{square root over (R/L)}

On the other hand, an actual frequency of vibration of the rotary body observed when the rotary body rotates at the angular velocity ω can be determined by calculation or from an experiment. Therefore, it is possible to match the natural frequency of vibration of each pendulum with the frequency of vibration of the rotary body by substituting a value of the actual frequency of vibration of the rotary body for ωnin the aforementioned equation and properly setting values of L and R so that the equation is satisfied. Under conditions where the natural frequency of vibration of each pendulum is matched to the frequency of vibration of the rotary body, vibration produced when the rotary body rotates at the angular velocity ω is effectively absorbed by the oscillatory motion of the pendulums in theory.

In the rotary driving device of Japanese Laid-open Patent Publication No. 2002-195348, however, even if the difference L between the radius of each circular hole in the disk and that of each pendulum and the distance R between the center of the disk and the center of each circular hole are determined based on the aforementioned equation so that the natural frequency ωnof vibration of each pendulum matches the frequency of vibration of the rotary body, and the circular holes are formed in the disk and the pendulums are adjusted according the setting of and L, there can be a case where a desired vibration absorbing effect can not be obtained due to errors in design or manufacture when the rotary body is actually rotated.

Also, if it is found that an appropriate vibration absorbing effect is not obtained after the circular holes are formed in the disk, it may be necessary to manufacture a new disk to achieve an intended result. Making a new disk would however results in increasing cost.

SUMMARY OF THE INVENTION

The invention is intended to provide a solution to the aforementioned problems of the prior art. Specifically, it is an object of the invention to provide a rotary driving device which can produce an improved vibration absorbing effect by properly adjusting vibration absorbing performance and contribute to a reduction in manufacturing cost by avoiding a waste of a disk once mounted on a rotary body for absorbing vibration. It is another object of the invention to provide an image forming apparatus provided with such a rotary driving device.

According to the present invention, a rotary driving device includes a rotary shaft supported rotatably about an axis thereof on a predetermined supporting member, a rotary load body mounted on the rotary shaft to project radially outward from the rotary shaft in such a manner that the rotary load body can rotate integrally with the rotary shaft about the axis thereof, a driver for rotating the rotary shaft about the axis thereof, a disk mounted on the rotary shaft coaxially therewith for integral rotation with the rotary shaft, the disk having a mounting hole formed therein, a pendulum loosely fitted in the mounting hole, and an adjustment mechanism for adjusting a relative position relationship between a central axis position of the mounting hole and a center of gravity position of the pendulum under conditions where the disk is rotating.

These and other objects, features and advantages of the invention will become more apparent upon a reading of the following detailed description along with the accompanying drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1is a perspective view showing a basic structure of a rotary driving device1according to the present invention. As shown inFIG. 1, the rotary driving device1includes a rotary shaft2mounted rotatably about an axis thereof between two frames (supporting member) F, a cylindrical rotary load body3which is fitted on the rotary shaft2to protrude radially outward therefrom along the entire circumference of the rotary shaft2so that the rotary load body3can rotate integrally with the rotary shaft2about the axis thereof, a driving motor (driver)4for rotating the rotary shaft2about the axis thereof, and a centrifugal pendulum vibration absorber5fitted on the rotary shaft2so that the centrifugal pendulum vibration absorber5can rotate integrally with the rotary shaft2on the same axis therewith.

There is provided a gear mechanism4abetween the driving motor4and the rotary shaft2. A driving force of the driving motor4is transmitted to the rotary shaft2via the gear mechanism4a, causing the rotary shaft2to rotate.

The centrifugal pendulum vibration absorber5includes a disk6fitted on the rotary shaft2on the same axis therewith so that the disk6can rotate integrally with the rotary shaft2, a plurality of circular mounting holes7formed in the disk6at equal intervals along a circumferential direction of the disk6, and centrifugal pendulums (pendulums)8loosely fitted in the individual mounting holes7. While the disk6has four mounting holes7formed therein in the illustrated basic structure, the number of the mounting holes7is not limited to four but may be less than or more than four.

FIG. 2is a front view of the centrifugal pendulum vibration absorber5shown for explaining a natural frequency of vibration of each centrifugal pendulum8. The disk6rotates about the rotary shaft2andFIG. 2shows a state in which the centrifugal pendulums8are positioned radially most outward in the respective mounting holes7due to a centrifugal force produced by rotation of the disk6about the rotary shaft2.

Provided that the centrifugal pendulum vibration absorber5shown inFIG. 2is so configured that a center axis position C1of each mounting hole7is separated from a center axis position C of the disk6by a distance R, a center position O1of each centrifugal pendulum8is separated from the center axis position C1of the pertinent mounting hole7by a distance L under conditions where an outer peripheral surface of each centrifugal pendulum8is in contact with an inner peripheral surface of the pertinent mounting hole7, the disk6rotates at an angular velocity ω, and each centrifugal pendulum8has a natural frequency ωnof vibration, there is a relationship expressed by the following equation as previously mentioned:
ωn=ω√{square root over (R/L)}  (1)

When the frequency of vibration of the rotary driving device1determined by gear meshing conditions, eccentricity of the rotary load body3and cogging or the like of the driving motor4is known, the centrifugal pendulum vibration absorber5will be brought into a state in which the centrifugal pendulums8completely absorb vibration of the rotary driving device1by setting the frequency of vibration of the rotary driving device1to be equal to the natural frequency of vibration of the centrifugal pendulums8.

Therefore, the centrifugal pendulum vibration absorber5exhibits a maximum vibration absorbing effect if the aforementioned equation is satisfied, that is, by substituting the frequency of vibration of the rotary driving device1for ωnand the angular velocity of the disk6for ω in equation (1) above and setting values of R and L so that equation (1) is satisfied. Even though the values of R and L are so set, however, the value of ωnwill not become equal to the frequency of vibration of the rotary driving device1if a dimensional error occurs in any of the mounting holes7or if the frequency of vibration of the rotary driving device1can not be exactly determined. Consequently, it will become impossible for the centrifugal pendulum vibration absorber5to exhibit a sufficient vibration absorbing effect in this case.

To cope with the aforementioned problem, the rotary driving device1of this embodiment is configured such that the centrifugal pendulum vibration absorber5has an adjustment mechanism9which makes it possible to vary the distance R between the center axis position C1of each mounting hole7and the center axis position C of the disk6.

Centrifugal pendulum vibration absorbers51,52,53according to first to third embodiments of the invention having different types of adjustment mechanisms9are described hereinbelow with reference toFIGS. 3A to 8B.

First Embodiment

FIGS. 3A and 3Bare perspective views of the centrifugal pendulum vibration absorber51according to the first embodiment,FIG. 3Abeing an exploded perspective view andFIG. 3Bbeing a perspective assembly view.FIGS. 4A and 4Bare cross-sectional views taken along lines IV-IV ofFIG. 3B,FIG. 4Ashowing a state in which a stationary disk element611and a movable disk element612are most separated from each other andFIG. 4Bshowing a state in which the stationary disk element611and the movable disk element612are located closest to each other.

As shown inFIGS. 3A and 3B, the centrifugal pendulum vibration absorber51of the first embodiment includes a disk61having a dual-disk structure and a plurality of spherical bodies (pendulums)81fitted in mounting holes71formed in the disk61.

The disk61includes the stationary disk element611which is mounted on the rotary shaft2in such a manner that the stationary disk element611is kept from moving along an axial direction of the rotary shaft2and the movable disk element612which is so mounted on the rotary shaft2to be movable along the axial direction on the right side of the stationary disk element611as illustrated inFIGS. 3A and 3B. The stationary disk element611has an inner cylindrical part611aprojecting from a right surface of the stationary disk element611on a common axis therewith (as illustrated inFIGS. 3A and 3B), and the movable disk element612has an outer cylindrical part612aprojecting therefrom on a common axis therewith. The inside diameter of the inner cylindrical part611ais made slightly larger than the outside diameter of the rotary shaft2, so that the rotary shaft2is passed through the inner cylindrical part611ain sliding contact therewith.

The inside diameter of the outer cylindrical part612ais made slightly larger than the outside diameter of the inner cylindrical part611a, so that the outer cylindrical part612acan be fitted on the inner cylindrical part611ain sliding contact therewith. The inner cylindrical part611aand the outer cylindrical part612aare formed to have approximately the same length. Also, as illustrated inFIGS. 3A and 3B, the amount of leftward projection of the outer cylindrical part612afrom the movable disk element612is made slightly smaller than the diameter of each spherical body81.

In the inner cylindrical part611a, there is formed a through hole611bpassing radially through the inner cylindrical part611a. Also, the rotary shaft2has a threaded hole21radially tapped therein at an appropriate position. On the other hand, in a portion of the outer cylindrical part612aprojecting rightward from the movable disk element612, there is formed a slot612bextending along an axial direction of the outer cylindrical part612aand passing therethrough.

After aligning the slot612bwith the through hole611b, the outer cylindrical part612aof the movable disk element612is fitted on the inner cylindrical part611aof the stationary disk element611. Then, after fitting the rotary shaft2into the inner cylindrical part611aso that the threaded hole21aligns with the through hole611b, a screw (locking member) B is screwed into the threaded hole21through the slot612band the through hole611b, whereby the stationary disk element611is kept from moving along the axial direction. On the other hand, the movable disk element612can be moved back and forth along the axial direction of the rotary shaft2within a particular movable range defined by the slot612b.

Therefore, the movable disk element612is fixed to the rotary shaft2when the screw B is fastened after setting a desired distance between the stationary disk element611and the movable disk element612by moving the movable disk element612back and forth along the rotary shaft2.

In the stationary disk element611and the movable disk element612, there are formed at their surface the aforementioned plurality (four in each disk element611,612in this embodiment) of mounting holes71at equal intervals along a circumferential direction so that the mounting holes71in the stationary disk element611align with those in the movable disk element612. The mounting holes71formed in the stationary disk element611are hereinafter referred to as stationary disk element side mounting holes (first mounting holes)711and the mounting holes71formed in the movable disk element612are hereinafter referred to as movable disk element side mounting holes (second mounting holes)712.

As shown inFIGS. 4A and 4B, each of the stationary disk element side mounting holes711formed in the stationary disk element611has a generally trumpet-like cross-sectional shape gradually increasing in diameter toward an opposing surface of the movable disk element612. Similarly, each of the movable disk element side mounting holes712formed in the movable disk element612has a generally trumpet-like cross-sectional shape gradually increasing in diameter toward an opposing surface of the stationary disk element611. The stationary disk element side mounting holes711and the movable disk element side mounting holes712are formed to have the same dimensions.

There is provided an adjuster613between the stationary disk element611and the movable disk element612while fitted on the inner cylindrical part611a. The adjuster613of this embodiment is made of soft synthetic resin foam. Under conditions where the outer cylindrical part612aof the movable disk element612is fitted on the inner cylindrical part611aof the stationary disk element611and set in position by tightening the screw B, the adjuster613is caused to elastically deform by compression. As a consequence, the adjuster613exerts an elastic force which serves to hold the movable disk element612in a stably mounted state.

The spherical bodies81are made to have a diameter slightly larger than a minimum inside diameter of each of the mounting holes711,712. Therefore, when fitted in the respective mounting holes711,712, the spherical bodies81are sandwiched between the stationary disk element611and the movable disk element612as shown inFIGS. 4A and 4Band, thus, the spherical bodies81will not come out of the mounting holes711,712.

In the centrifugal pendulum vibration absorber51of the first embodiment, an adjustment mechanism9afor adjusting a relative position relationship (i.e., the distance L shown inFIGS. 4A and 4B) between a center axis position C1of each mounting hole71and a center position O1(i.e., the center of gravity) of the corresponding spherical body81is configured with the movable disk element612which can be moved back and forth along the axial direction of the rotary shaft2and the screw B for keeping the movable disk element612from moving along the axial direction.

The centrifugal pendulum vibration absorber51of the first embodiment thus configured makes it possible to freely set the distance between the stationary disk element611and the movable disk element612by loosening the screw B and removing the same from the threaded hole21and through hole611bof the inner cylindrical part611aso that the stationary disk element611and the movable disk element612are in a desired state between the state shown inFIG. 4Ain which the stationary disk element611and the movable disk element612are most separated from each other and the state shown inFIG. 4Bin which the stationary disk element611and the movable disk element612are located closest to each other.

When the distance between the stationary disk element611and the movable disk element612is maximized as shown inFIG. 4A, a distance S between the center O1of each spherical body81, positioned radially outward due to a centrifugal force produced by rotary motion of the centrifugal pendulum vibration absorber51around the rotary shaft2, and a center axis C of the rotary shaft2takes a maximum value S1. On the other hand, when the distance between the stationary disk element611and the movable disk element612is minimized as shown inFIG. 4B, the distance S between the center O1(the center of gravity) of each spherical body81and the center axis C of the rotary shaft2takes a minimum value S2.

The above-described arrangement of the first embodiment makes it possible to arbitrarily set the distance S between the center O1of each spherical body81and the center axis C of the rotary shaft2in the range between the maximum value S1and the minimum value S2under conditions where the centrifugal pendulum vibration absorber51rotates by moving the movable disk element612within the movable range thereof back and forth along the axial direction of the rotary shaft2. This means that vibration absorbing performance of the centrifugal pendulum vibration absorber51can be corrected, if inappropriate, by fine adjustment of the distance S between the center O1of each spherical body81and the center axis C of the rotary shaft2performed by adjusting the distance between the stationary disk element611and the movable disk element612on a trial-and-error basis.

Second Embodiment

FIGS. 5A and 5Bare perspective views of the centrifugal pendulum vibration absorber52according to the second embodiment,FIG. 5Abeing an exploded perspective view andFIG. 5Bbeing a perspective assembly view.FIGS. 6A and 6Bare cross-sectional views taken along lines VI-VI ofFIG. 5B,FIG. 6Ashowing a state in which each of truncated conical bodies82is most separated from the rotary shaft2andFIG. 6Bshowing a state in which each of the truncated conical bodies82is located closest to the rotary shaft2.FIG. 6Cis a fragmentary perspective view cut away along lines VI-VI ofFIG. 5B.

As shown inFIGS. 5A and 5B, the centrifugal pendulum vibration absorber52of the second embodiment includes a generally thick-walled partially hollowed disk62which is fixedly fitted on the rotary shaft2on a common axis therewith, the partially hollowed disk62having a plurality of cutout spaces (cavities)65formed therein as will be described later, a plurality (four in this embodiment) of mounting holes72formed in the partially hollowed disk62at equal intervals along a circumferential direction thereof, the aforementioned plurality of truncated conical bodies (pendulums)82fitted in the corresponding mounting holes72, and adjustment mechanisms9bfor adjusting a relative position relationship (i.e., the distance L) between a center axis position C1of each mounting hole72and a center axis O2(FIGS. 6Aand6B) of the corresponding truncated conical body82.

The partially hollowed disk62has a cylindrical projecting part621protruding rightward from a right surface of the partially hollowed disk62as illustrated inFIG. 5A, as if passing through the partially hollowed disk62at a center position thereof. The inside diameter of the cylindrical projecting part621is made slightly larger than the outside diameter of the rotary shaft2, so that the rotary shaft2can be passed through the cylindrical projecting part621in sliding contact therewith. In the cylindrical projecting part621, there is formed a through hole622passing radially through the cylindrical projecting part621so that a screw B can be fitted in the through hole622. When the screw B is tightly screwed into the threaded hole21in the rotary shaft2through the through hole622, the partially hollowed disk62can rotate integrally with the rotary shaft2about the axis thereof.

The partially hollowed disk62has the aforementioned plurality of cutout spaces or cavities65which are formed by cutting out portions of the partially hollowed disk62inward toward the mounting holes72from an outer peripheral surface of the partially hollowed disk62at locations corresponding to the corresponding mounting holes72. These cutout spaces65are for fitting the truncated conical bodies82which will be described later in detail. On the right surface of the partially hollowed disk62(as illustrated inFIG. 5A), there are formed a plurality of bushes651protruding rightward at locations corresponding to the respective cutout spaces65. These bushes651serve to support later-described adjusting screws92in a stable state.

As illustrated inFIG. 5A, each of the truncated conical bodies82is shaped such that a right end surface has a minimum diameter and a left end surface has a maximum diameter, so that each of the truncated conical bodies82diminishes from the left end surface to the right end surface, forming a tapered circumferential surface821. The maximum diameter of each truncated conical body82(i.e., the diameter of the left end surface of each truncated conical body82shown inFIG. 5A) is made slightly smaller than the diameter of each mounting hole72and the thickness of each truncated conical body82is made approximately equal to that of the partially hollowed disk62.

In the second embodiment, a pair of ring-like stopper plates66are screwed to the partially hollowed disk62on both sides as shown inFIG. 5Bfor closing off the individual mounting holes72to prevent the truncated conical bodies82fitted in the mounting holes72from coming off. In this configuration, each truncated conical body82fitted in the mounting hole72is allowed to freely move in a direction perpendicular to an axial direction (i.e., in a radial direction) within the mounting hole72under conditions where movement of each truncated conical body82in the axial direction within the partially hollowed disk62is restricted by the pair of ring-like stopper plates66.

Each of the adjustment mechanisms9bincludes an adjusting tab91fitted in the pertinent cutout space65such that the adjusting tab91can move back and forth along a thickness direction of the partially hollowed disk62, the aforementioned adjusting screw92serving as a moving member for moving the adjusting tab91back and forth in the cutout space65along the thickness direction of the partially hollowed disk62, the adjusting screw92being fitted in the pertinent cutout space65passing through the bush651and the adjusting tab91, and an E-ring93fitted on a left end of the adjusting screw92(as illustrated inFIGS. 6A and 6B) so that the adjusting screw92will not come off under conditions where the adjusting screw92is passed through the partially hollowed disk62.

Each of the adjusting tabs91has a generally rectangular shape in front view as shown inFIG. 5A. Each adjusting tab91has a thickness approximately one-quarter of the thickness (left-to-right dimension as illustrated inFIGS. 6A and 6B) of each cutout space65and a width (i.e., a circumferential dimension measured when each adjusting tab91is fitted in the pertinent cutout space65) slightly smaller than the circumferential dimension of the cutout space65. An end surface of each adjusting tab91facing the center of the partially hollowed disk62is shaped to form a tapered peripheral surface911which remains in contact with the tapered circumferential surface821of the pertinent truncated conical body82. Also, each adjusting tab91has a threaded hole912formed therein into which the adjusting screw92is screwed.

Under conditions where each adjusting tab91fitted within the pertinent cutout space65with the tapered peripheral surface911facing the center of the partially hollowed disk62, the adjusting screw92is inserted into the cutout space65through the bush651and tightened into the threaded hole912in the adjusting tab91. The adjusting screw92passes to the outside of the partially hollowed disk62through a hole formed in a wall surface of the partially hollowed disk62located on an opposite side of the bush651of each cutout space65. The E-ring93is fitted on that part of the adjusting screw92which protrudes to the outside of the partially hollowed disk62. Consequently, the adjusting screws92are screwed into the respective adjusting tabs91to support the adjusting tabs91and thus fitted in the partially hollowed disk62in such a manner that the adjusting screws92will not come off.

When the partially hollowed disk62rotates on the rotary shaft2, a centrifugal force produced by the rotary motion of the partially hollowed disk62causes the truncated conical bodies82to move radially outward within the respective mounting holes72so that the tapered circumferential surfaces821of the truncated conical bodies82go into contact with the tapered peripheral surfaces911of the respective adjusting tabs91.

The centrifugal pendulum vibration absorber52of the second embodiment thus configured makes it possible to move each adjusting tab91, into which the adjusting screw92is screwed, back and forth within the cutout space65along the thickness direction of the partially hollowed disk62by turning the pertinent adjusting screw92clockwise and counterclockwise about an axis thereof. The above-described arrangement of the second embodiment makes it possible to set the adjusting tabs91at a desired position between the state shown inFIG. 6Ain which each adjusting tab91is located most rightward and the state shown inFIG. 6Bin which each adjusting tab91is located most leftward.

When each adjusting tab91is located most rightward, the tapered peripheral surface911of each adjusting tab91is in contact with a right part of the tapered circumferential surface821of the pertinent truncated conical body82so that the truncated conical body82is set at a position most separated from the rotary shaft2.

On the other hand, when each adjusting tab91is located most leftward, the tapered peripheral surface911of each adjusting tab91is in contact with a left part of the tapered circumferential surface821of the pertinent truncated conical body82so that the truncated conical body82is set at a position closest to the rotary shaft2.

Since the centrifugal pendulum vibration absorber52of the second embodiment makes it possible to easily vary the distance between the truncated conical bodies82and the rotary shaft2by moving the adjusting tabs91back and forth, it is possible to find a position of each truncated conical body82best suited for obtaining desired vibration absorbing performance on a trial-and-error basis.

Also, since the positions of the truncated conical bodies82can be adjusted individually, it is possible to perform a fine adjustment for obtaining the desired vibration absorbing performance compared to a case where all of the centrifugal pendulums8are adjusted likewise as a whole.

Third Embodiment

FIGS. 7A and 7Bare perspective views of the centrifugal pendulum vibration absorber53according to the third embodiment,FIG. 7Abeing an exploded perspective view andFIG. 7Bbeing a perspective assembly view.FIGS. 8A and 8Bare cross-sectional views taken along lines VIII-VIII ofFIG. 7B,FIG. 8Ashowing a state in which each of spherical bodies81is set at a position most separated from the rotary shaft2andFIG. 8Bshowing a state in which the spherical bodies81are located closest to the rotary shaft2.

As shown inFIG. 7A, the centrifugal pendulum vibration absorber53of the third embodiment includes a single thick-walled disk63which is fixedly mounted on the rotary shaft2on a common axis therewith, a plurality (four in this embodiment) of conical holes (mounting holes)73formed in the thick-walled disk63at equal intervals along a circumferential direction thereof, the aforementioned plurality of spherical bodies (pendulums)81fitted in the respective conical holes73, and an adjustment mechanism9cfor adjusting a relative position relationship between a center axis position C1of each conical hole73and a center position O1(i.e., the center of gravity) of the corresponding spherical body81.

The thick-walled disk63has a cylindrical projecting part631protruding rightward from a right surface of the thick-walled disk63as illustrated inFIG. 7A, as if passing through the thick-walled disk63at a center position thereof. The inside diameter of the cylindrical projecting part631is made slightly larger than the outside diameter of the rotary shaft2, so that the rotary shaft2can be inserted through the cylindrical projecting part631in sliding contact therewith. In the cylindrical projecting part631, there is formed a through hole632passing radially through the cylindrical projecting part631so that a screw (locking member) B can be fitted in the through hole632. When the screw B is tightly screwed into a threaded hole21in the rotary shaft2through a slot942formed in a later-described outer cylindrical part (projecting part)941and the through hole632, the thick-walled disk63can rotate integrally with the rotary shaft2about the axis thereof.

Each of the conical holes73has a generally trumpet-like cross-sectional shape gradually increasing in diameter from a left side of the thick-walled disk63to a right side thereof as illustrated inFIG. 7A. An inner peripheral surface of each conical hole73is shaped to form a tapered circumferential surface731.

The diameter of each spherical body81is made slightly larger than a minimum diameter of each conical hole73on a left side thereof as illustrated inFIGS. 8A and 8B. Therefore, the spherical bodies81will not come off leftward from the conical holes73.

The adjustment mechanism9cincludes a positioning disk94for positioning the spherical bodies81under conditions where the spherical bodies81fitted in the respective conical holes73are kept from coming off leftward as illustrated inFIG. 7A, and the aforementioned screw B for fixing the positioning disk94to the rotary shaft2through the through hole632in the cylindrical projecting part631.

The positioning disk94has the aforementioned outer cylindrical part941projecting rightward therefrom on a common axis with the positioning disk94as illustrated inFIGS. 7A and 7B. The inside diameter of the outer cylindrical part941is made slightly larger than the outside diameter of the cylindrical projecting part631. Therefore, when the outer cylindrical part941is fitted over the cylindrical projecting part631, the positioning disk94can be moved back and forth along a direction in which the cylindrical projecting part631extends.

The aforementioned slot942is formed in the outer cylindrical part941of the positioning disk94to extend in an axial direction thereof at a location corresponding to the through hole632in the cylindrical projecting part631. With the outer cylindrical part941of the positioning disk94fitted on the cylindrical projecting part631of the thick-walled disk63, the rotary shaft2is inserted into the cylindrical projecting part631. Then, with the slot942in the outer cylindrical part941, the through hole632in the cylindrical projecting part631and the threaded hole21in the rotary shaft2aligned with one another, the screw B is passed through the slot942and the through hole632and screwed into the threaded hole21. As a consequence, the centrifugal pendulum vibration absorber53of the third embodiment is assembled as illustrated inFIG. 7B.

In the third embodiment, an adjuster613like that of the first embodiment is placed between the thick-walled disk63and the positioning disk94. This arrangement serves to mount the positioning disk94in position to the thick-walled disk63in a stable state.

In the centrifugal pendulum vibration absorber53of the third embodiment thus configured, the positioning disk94can be moved back and forth along the axial direction of the rotary shaft2within a particular movable range defined by the slot942in the outer cylindrical part941upon loosening the screw B. When the centrifugal pendulum vibration absorber53rotates about the rotary shaft2integrally therewith under conditions where the positioning disk94is located most rightward as illustrated inFIG. 8A, the spherical bodies81fitted in the respective conical holes73move along the tapered circumferential surfaces731thereof and are positioned most outward in radial directions due to a centrifugal force produced by the rotary motion of the centrifugal pendulum vibration absorber53. In this condition, the difference L between the center axis position C1of each conical hole73and the center position O1(i.e., the center of gravity) of the corresponding spherical body81takes a maximum value.

On the other hand, when the centrifugal pendulum vibration absorber53rotates about the rotary shaft2integrally therewith under conditions where the positioning disk94is located most leftward as illustrated inFIG. 8B, the individual spherical bodies81are forced leftward by the positioning disk94and thus positioned most inward along the radial directions in the respective conical holes73. In this condition, the difference L between the center axis position C1of each conical hole73and the center position O1(i.e., the center of gravity) of the corresponding spherical body81takes a minimum value (“0” in the illustrated example ofFIG. 8B).

The above-described arrangement of the third embodiment makes it possible to freely set each spherical body81at a desired position between the position most separated from the rotary shaft2as shown inFIG. 8Aand the position closest to the rotary shaft2as shown inFIG. 8Bby moving the positioning disk94back and forth along the axial direction of the rotary shaft2. If the screw B is tightened under conditions where each spherical body81has been set in the desired position in the aforementioned fashion, the positioning disk94properly positioned relative to the thick-walled disk63is held stably mounted thereto.

As thus far described in detail, the rotary driving device1according to the foregoing embodiments includes the rotary shaft2mounted rotatably about the axis thereof between the predetermined frames F, the rotary load body3which is fitted on the rotary shaft2to project radially outward therefrom so that the rotary load body3can rotate integrally with the rotary shaft2about the axis thereof, the driving motor4for rotating the rotary shaft2about the axis thereof, and the centrifugal pendulum vibration absorber5fitted on the rotary shaft2so that the centrifugal pendulum vibration absorber5can rotate integrally with the rotary shaft2on the same axis therewith as shown inFIGS. 1 and 2.

The centrifugal pendulum vibration absorber5includes the disk6in which the mounting holes7are formed to pass therethrough at equal intervals along the circumferential direction of a single circle (having one fixed radius), and the adjustment mechanism9for adjusting the relative position relationship between the center axis position of each mounting hole7and the center position (center of gravity) of the corresponding centrifugal pendulum8.

In the rotary driving device1thus configured, it is possible to absorb vibration of the rotary driving device1produced when the driving motor4is actuated to rotate the rotary shaft2about the axis thereof by oscillatory motion of the centrifugal pendulums8fitted in the respective mounting holes7.

There can however be a case where an intended level of vibration absorbing effect is not obtained. In such a case, the relative position relationship between the center axis position of each mounting hole7and the center position (center of gravity) of the corresponding centrifugal pendulum8is to be finely adjusted so that the distance L between the center position O1of each centrifugal pendulum8whose outer peripheral surface is in contact with the inner peripheral surface of the pertinent mounting hole7and the center axis position C1of the pertinent mounting hole7would be varied. The distance L can be varied in this manner without varying the distance R between the center axis position C1of each mounting hole7and the center axis position C of the disk6as mentioned in the aforementioned equation (1) or without varying the size of each centrifugal pendulum8(that is, by replacing the disk6or the centrifugal pendulums8). This approach makes it possible to match the value of the natural frequency ωnof vibration of the centrifugal pendulums8with the frequency of vibration of the rotary driving device1on a trial-and-error basis. Consequently, it is possible to provide an improved vibration absorbing effect with respect to the vibration of the rotary driving device1by producing proper oscillatory motion of the centrifugal pendulums8.

Even after the disk6on which the mounting holes7are formed with the centrifugal pendulums8loosely fitted in the mounting holes7is once mounted on the rotary shaft2, it is possible to effectively suppress the vibration of the rotary driving device1by means of the adjustment mechanism9on a trial-and-error basis as described above if a desired vibration absorbing effect is not obtained. Therefore, unlike the case of a conventional arrangement, it is not necessary to replace the disk6or the centrifugal pendulums8with new ones when the desired vibration absorbing effect is not obtained. This makes it possible to prevent a cost increase and an intricate task needed for replacing relevant components.

The adjustment mechanism9aof the first embodiment shown inFIGS. 3A,3B,4A and4B includes the movable disk element612slidably mounted on the rotary shaft2wherein the stationary disk element611has the stationary disk element side mounting holes711formed therein, each of the stationary disk element side mounting holes711constituting one part of the mounting hole71, and the movable disk element612has the movable disk element side mounting holes712formed therein, each of the movable disk element side mounting holes712constituting another part of the mounting hole71.

In the first embodiment, the centrifugal pendulums8of the present invention are configured with the spherical bodies81having a diameter larger than that of the mounting holes71. The spherical bodies81are sandwiched between the stationary disk element611and the movable disk element612with each of the spherical bodies81loosely fitted in each pair of facing mounting holes711,712. The adjustment mechanism9aalso includes the locking member (screw B) for keeping the movable disk element612from moving.

In the aforementioned structure, the movable disk element612is moved back and forth along the rotary shaft2to vary the distance between the stationary disk element611and the movable disk element612and, then, the movable disk element612is fixed by securing the locking member in position. As the movable disk element612is fixed in this fashion, it is possible to vary the distance between the center axis of the rotary shaft2and the center of gravity position of each spherical body81when a centrifugal force produced by rotation of the rotary shaft2about the center axis thereof is exerted on the spherical bodies81. It is possible to improve the vibration absorbing effect by finely adjusting the aforementioned distance.

The movable disk element612has the outer cylindrical part612aprojecting in the axial direction of the rotary shaft2from a surface of the movable disk element612opposite to a surface thereof facing the stationary disk element611. The outer cylindrical part612ahas the slot612bformed therein, the slot612bextending along the axial direction of the rotary shaft2, and the rotary shaft2has the threaded hole21tapped into an outer peripheral surface of the rotary shaft2at a location corresponding to the slot612b. In this structure, the screw B screwed into the threaded hole21through the slot612bis used as the aforementioned locking member.

Therefore, the movable disk element612can be moved back and forth along the rotary shaft2upon loosening the screw B screwed into the threaded hole21through the slot612b. Then, the movable disk element612is set at a fixed position on the rotary shaft2if the screw B is tightened after adjusting the distance between the stationary disk element611and the movable disk element612.

As the screw B is used as the locking member as discussed above, the locking member can be made in a simple structure and the distance between the stationary disk element611and the movable disk element612can be properly maintained in a reliable fashion.

The second embodiment shown inFIGS. 5A,5B,6A and6C employs the truncated conical bodies82as the centrifugal pendulums8of the present invention, each of the truncated conical bodies82fitted in one of the mounting holes72gradually decreasing in diameter from one side of the partially hollowed disk62toward the other side thereof. Each of the adjustment mechanisms9bincludes the adjusting tab91fitted in one of the cutout spaces65formed in the partially hollowed disk62to connect to one of the mounting holes72, part of the adjusting tab91being in contact with the tapered circumferential surface821of the pertinent truncated conical body82, as well as the moving member (adjusting screw92) for moving the adjusting tab91back and forth in the pertinent cutout space65along the thickness direction of the partially hollowed disk62.

In the aforementioned structure, a contact point of each adjusting tab91on the tapered circumferential surface821of the pertinent truncated conical body82varies if each adjusting tab91is moved back and forth along the axial direction of the rotary shaft2(that is, along the thickness direction of the partially hollowed disk62) by manipulating the moving member. Thus, the center of gravity position of each truncated conical body82shifts in a radial direction of the partially hollowed disk62and, as a result, the distance between the center of gravity position of each truncated conical body82and the center axis of the rotary shaft2varies. This makes it possible to finely adjust the vibration absorbing effect.

In this structure, each of the adjusting screws92passed from one side of the partially hollowed disk62to the opposite side thereof and screwed into the adjusting tab91therethrough in the pertinent cutout space65is used as the moving member for moving the adjusting tab91. It is possible to move each adjusting tab91back and forth along the thickness direction of the partially hollowed disk62by turning the pertinent adjusting screw92clockwise and counterclockwise about the axis thereof.

As each of the adjusting screws92is used as the moving member as discussed above, the moving member can be made in a simple structure.

The third embodiment shown inFIGS. 7A,7B,8A and8B employs the conical holes73as the mounting holes7formed in the thick-walled disk63to pass therethrough, each of the conical holes73gradually decreasing in diameter from one side of the thick-walled disk63toward the other side thereof. Also, this embodiment employs the spherical bodies81as the centrifugal pendulums8, the diameter of each spherical body81is made larger than the minimum diameter of each conical hole73and the thickness of the thick-walled disk63.

The adjustment mechanism9cincludes the positioning disk94which is located face to face with the thick-walled disk63on one side thereof and mounted on the rotary shaft2movably along the axial direction thereof on the common axis with the rotary shaft2, as well as the locking member (screw B) for keeping the positioning disk94from moving.

The adjustment mechanism9cthus configured keeps the spherical bodies81from coming off the conical holes73with the aid of the positioning disk94mounted face to face with the thick-walled disk63on one side thereof where each conical hole73has the maximum diameter. In this configuration, part of each spherical body81protrudes from the pertinent conical hole73toward the positioning disk94.

The amount of projection of the spherical bodies81from the thick-walled disk63can be varied by moving the positioning disk94back and forth along the axial direction of the rotary shaft2. When the thick-walled disk63is caused to rotate about the rotary shaft2integrally therewith, the distance between the center axis of the rotary shaft2and the center of gravity position of each spherical body81varies according to the amount of projection of the spherical bodies81. This makes it possible to finely adjust the vibration absorbing effect.

The positioning disk94has the outer cylindrical part (projecting part)941projecting along the axial direction of the rotary shaft2from a surface of the positioning disk94opposite to a surface thereof facing the thick-walled disk63. The outer cylindrical part941has the slot942formed therein, the slot942extending along the axial direction of the rotary shaft2. It is possible to securely fix the positioning disk94to the rotary shaft2and thus position the spherical bodies81in the respective conical holes73by tightening the screw B.

As the screw B which is passed through the slot942and screwed into the threaded hole21is used as the locking member, the locking member can be made in a simple structure.

An image forming apparatus10of the invention employing one of the centrifugal pendulum vibration absorbers51,52,53of the foregoing first to third embodiments is now described with reference toFIGS. 9 and 10.FIG. 9is a perspective view showing the external appearance of the image forming apparatus10of the fourth embodiment, andFIG. 10is a frontal cross-sectional view showing the internal construction of the image forming apparatus10. As depicted inFIGS. 9 and 10, the symbols −X/+X denotes a left-right direction and the symbols −Y/+Y denotes a front-rear direction. In particular, −X represents a leftward direction, +X represents a rightward direction, −Y represents a frontward direction and +Y represents a rearward direction.

The image forming apparatus10is a so-called internal exit tray type copying machine having a main apparatus body11. Referring toFIGS. 9 and 10, the main apparatus body11includes an image forming section12, a fixing section13, a sheet storage section14, a sheet discharge section15, an image reading section16and an operating section17. The sheet discharge section15is formed by creating a recessed portion in part of the main apparatus body11beneath the image reading section16. The image forming apparatus10is referred to as the internal exit tray type for this reason.

The main apparatus body11has a lower body portion111having a generally parallelepipedic shape, a generally flat-shaped upper body portion112located above the lower body portion111face to face therewith, and an interconnecting portion113located between the upper body portion112and the lower body portion111. The interconnecting portion113is a structural portion erected upright from a left part of the lower body portion111for joining the lower body portion111and the upper body portion112to each other, forming the sheet discharge section15therebetween. The upper body portion112is supported at a left part thereof on an upper end part of the interconnecting portion113.

The image forming section12, the fixing section13and the sheet storage section14are provided inside the lower body portion111, while the image reading section16is mounted in the upper body portion112. In this embodiment, the operating section17is mounted to the upper body portion112in such a manner that the operating section17juts out frontward from a front end part of the upper body portion112as shown inFIG. 9.

The sheet storage section14includes a pair of upper and lower paper cassettes141which can be removed from and inserted into the main apparatus body11. Each of these paper cassettes141holds a stack P1of printing sheets (image carrying media) P. When executing an image forming task (print job), the image forming apparatus10pulls out the printing sheets P one after another and feeds each printing sheet P into the image forming section12to carry out the image forming task.

The sheet discharge section15located between the lower body portion111and the upper body portion112has an internal discharge tray151formed on a top surface of the lower body portion111. Each printing sheet P carrying a toner image transferred thereto is output from the image forming section12and normally delivered onto internal discharge tray151from a lower part of the interconnecting portion113.

The image reading section16includes contact glass161fitted in an upper opening of the upper body portion112for placing a document to be scanned, a document pressing cover162which can be swung up and down for holding the document placed on the contact glass161, and a scanner mechanism163for scanning an image of the document placed on the contact glass161. Analog information concerning the document image read by the scanner mechanism163is converted into a digital signal which is output to a later-described exposure unit123for execution of the image forming task.

The operating section17is for entering information concerning an image forming task to be executed. The operating section17includes a power switch170, numeric keys171and various other keys used for entering the number of prints to be produced on the printing sheets (printing media) P, for instance, a liquid crystal display (LCD) panel172used for entering information by touch-screen operation and displaying comments, as well as a start key173used for initiating the image forming task. When the start key173is pressed, the image forming apparatus10begins to scan the document image and carries out a sequence of successive steps for performing the image forming task until a specified number of sheets P carrying toner images are output.

Provided on a right side of the lower body portion111immediately above the paper storage section14is a manual feed tray18which is mounted swingably on a pivot shaft181at a lower end so that the manual feed tray18can be flipped up and down between a closed position at which the manual feed tray18closes off a manual feed slot and an open position at which the manual feed tray18projects in the rightward direction.

As illustrated inFIG. 10, there are provided a sheet convey unit184and an interconnect unit185between the manual feed tray18and a later-described vertical paper convey path101. The printing sheet P manually fed from the manual feed tray18is led into the vertical paper convey path101through the sheet convey unit184and the interconnect unit185and guided along the vertical paper convey path101toward a nipping part formed between a photosensitive drum (toner image carrier)121and an image transfer roller125which will be described later.

A maintenance door19which can be opened and closed is provided on a left side of the lower body portion111and an external discharge tray152is provided immediately above the maintenance door19as illustrated. Upon completion of the print job, the printing sheet P carrying a printed image is ejected selectively onto the internal discharge tray151or the external discharge tray152.

The internal construction of the image forming apparatus10is described in greater detail with reference toFIG. 10. As depicted inFIG. 10, the aforementioned photosensitive drum121is provided approximately at a middle position of the image forming block12. While the photosensitive drum121rotates in a clockwise direction (as illustrated inFIG. 10) about a drum axis, an outer peripheral surface of the photosensitive drum121is uniformly charged by a charging unit122which is located immediately to the right of the photosensitive drum121.

The exposure unit123produces a laser beam based on image information representative of the document image read by the image reading section16. The exposure unit123radiates the laser beam onto the outer peripheral surface of the photosensitive drum121to form an electrostatic latent image thereon. As developer (hereinafter referred to as toner) is supplied from a developing unit124provided below the photosensitive drum121to the electrostatic latent image subsequently, a toner image having the same pattern as the electrostatic latent image is formed on the outer peripheral surface of the photosensitive drum121.

The printing sheet P supplied from one of the paper cassettes141of the sheet storage section14is fed along the vertically extending vertical paper convey path101up to the photosensitive drum121on which the toner image is formed through a pair of registration rollers142which together serve to feed the printing sheet P with correct timing. The toner image on the outer peripheral surface of the photosensitive drum121is transferred to the printing sheet P by the aforementioned image transfer roller125which is located to the left of the photosensitive drum121face to face therewith. The printing sheet P carrying the toner image thus transferred is fed from the photosensitive drum121into the fixing section13.

As the photosensitive drum121continues to rotate in the clockwise direction upon completion of the aforementioned image transfer process, the outer peripheral surface of the photosensitive drum121is cleaned by a cleaning unit126which is provided immediately above the photosensitive drum121. Then, the outer peripheral surface of the rotating photosensitive drum121is charged again by the charging unit122in preparation of a succeeding image forming task.

The fixing section13has a housing accommodating a fixing roller131having a built-in electric heating element, such as a halogen lamp, and a pressure roller132located to the left of the fixing roller131face to face therewith. As the printing sheet P fed from the image forming section12passes through a nipping part between the fixing roller131and the pressure roller132, the printing sheet P receives heat and, as a result, the toner image is fixed to the printing sheet P.

In the case of a single-sided print job, the printing sheet P carrying a printed image on one side is ejected selectively onto the internal discharge tray151in the sheet discharge section15or the external discharge tray152through a sheet discharge path102provided above the fixing section13.

In the case of a double-sided print job, the printing sheet P carrying a printed image on one side only is sent toward a temporary sheet accommodating space153, formed above the internal discharge tray151, through a switchback paper convey path103which is provided above the sheet discharge path102up to a point where a forward half portion of the printing sheet P sticks out into the temporary sheet accommodating space153. Then, the printing sheet P is fed in an opposite direction through a vertically extending reversing paper convey path104provided on the inside of the maintenance door19and fed again into the image forming section12with the printing sheet P reversed for printing an image on a reverse side of the printing sheet P. Upon completion of the double-sided print job, the printing sheet P carrying the printed images on both sides is discharged selectively onto the internal discharge tray151or the external discharge tray152.

The maintenance door19is provided with a cover member191which is located immediately to the right of the reversing paper convey path104, facing a left side of the image forming section12. This cover member191is held on a right side of the maintenance door19. The vertical paper convey path101for feeding the printing sheet P from one of the paper cassettes141or the manual feed tray18is configured such that part of the vertical paper convey path101is located between a right side of the cover member191and the left side of the image forming section12under conditions where the cover member191is in a closed position.

A reason why the maintenance door19is provided is as follows. If a paper jam occurs in part of the vertical paper convey path101located at the left side of the image forming section12, a user (or service personnel) can flip down the maintenance door19to an open position to expose the vertical paper convey path101so that the printing sheet P which has jammed can easily be located and removed.

The photosensitive drum121of the image forming apparatus10thus configured is an example of the rotary driving device1(FIG. 1) of the present invention, and the centrifugal pendulum vibration absorber5(one of the centrifugal pendulum vibration absorbers51,52,53, hereinafter referred to simply as the centrifugal pendulum vibration absorber5collectively) is applied to the photosensitive drum121. Referring toFIG. 11and other drawings where necessary, the centrifugal pendulum vibration absorber5employed in the photosensitive drum121is now described hereinbelow.

FIG. 11is a perspective view showing an example of a driving system40of the photosensitive drum121and the centrifugal pendulum vibration absorber5applied to the photosensitive drum121. The symbols −X/+X and −Y/+Y inFIG. 11denote the same left-right and front-rear directions, respectively, as previously explained with reference toFIG. 9, −X representing the leftward direction, +X representing the rightward direction, −Y representing the frontward direction and +Y representing the rearward direction.

As shown inFIG. 11, the photosensitive drum121has a drum shaft121apassing along the drum axis so that the photosensitive drum121can rotate integrally with the drum shaft121aon a common axis. The drum shaft121ais fitted rotatably about the axis thereof between front and rear unillustrated frames provided in the lower body portion111of the main apparatus body11, whereby the photosensitive drum121is mounted at a specified position in the main apparatus body11. The drum shaft121acorresponds to the rotary shaft2of the earlier-described basic structure and the first to third embodiments shown inFIGS. 1 to 8B.

The driving system40of the photosensitive drum121includes a driving motor41supported parallel to the front-rear direction by the unillustrated frame in the lower body portion111, a driving gear42having a small diameter mounted on a drive shaft411of the driving motor41on a common axis therewith so that the driving gear42can rotate integrally with the drive shaft411, and a driven gear43having a larger diameter than the driving gear42and mounted on the drum shaft121aon a common axis therewith so that the driven gear43can rotate integrally with the drum shaft121a, wherein dimensions of the driving gear42and the driven gear43are so determined that the two gears42,43properly mesh with each other.

When the driving motor41is actuated, a driving force of the driving motor41is transmitted to the driven gear43via the drive shaft411and the driving gear42with a turning speed of the driven gear43reduced from that of the driving motor41. Consequently, the driven gear43rotates integrally with the drum shaft121aon the common axis, causing the photosensitive drum121to rotate. The driving gear42and the driven gear43together constitute a mechanism corresponding to the gear mechanism4aof the basic structure of the rotary driving device1shown inFIG. 1.

The centrifugal pendulum vibration absorber5of the present invention is mounted between the driven gear43and the driving motor41at the rear of the photosensitive drum121in such a manner that the centrifugal pendulum vibration absorber5can rotate integrally with the drum shaft121aon the common axis. The centrifugal pendulum vibration absorber5is mounted at the aforementioned location because it is preferable that the centrifugal pendulum vibration absorber5be located as close as possible to the driving system40, which is a source of vibration, for effectively producing a vibration absorbing effect. Specifically, employed as the centrifugal pendulum vibration absorber5is one of the centrifugal pendulum vibration absorbers51,52,53of the foregoing first to third embodiments shown inFIGS. 3A to 8B.

The centrifugal pendulum vibration absorber5is provided with the adjustment mechanism9on a rear side of the disk6for adjusting the radial position of each centrifugal pendulum8. This arrangement makes it possible to easily adjust the radial position of each centrifugal pendulum8by means of the adjustment mechanism9from a rear side of the lower body portion111. Specifically, employed as the adjustment mechanism9is one of the adjustment mechanisms9a,9b,9cof the foregoing first to third embodiments shown inFIGS. 3A to 8B.

The photosensitive drum121of the image forming apparatus10is an example of the rotary load body3shown inFIG. 1, and the photosensitive drum121and the centrifugal pendulum vibration absorber5together constitute the rotary driving device1of the present invention.

Since the photosensitive drum121is provided with the centrifugal pendulum vibration absorber5of this invention, vibration produced by the driving system40when the same is operated is effectively absorbed by the centrifugal pendulum vibration absorber5. Also, even if the mounting holes7deviate from intended positions due to errors in design or manufacture or the driving system40vibrates in a state different from what has been expected due to local conditions, for instance, pendular motion of the centrifugal pendulums8fitted in the mounting holes7can be properly controlled by finely adjusting the positions of the centrifugal pendulums8in radial directions by means of the adjustment mechanism9. Thus, the centrifugal pendulum vibration absorber5can produce a sufficient vibration absorbing effect. Accordingly, the aforementioned arrangement of the invention makes it possible to effectively prevent the occurrence of such an inconvenient situation that an image can not be properly formed on the outer peripheral surface of the photosensitive drum121due to vibration thereof.

It should be recognized that the invention is not limited to the foregoing embodiments but includes various modifications and variations thereof as described hereinbelow, for example.

While the rotary driving device1shown inFIG. 1includes the driving motor4and the gear mechanism4amounted on one end of the rotary shaft2and the centrifugal pendulum vibration absorber5mounted on the other end of the rotary shaft2, the driving motor4, the gear mechanism4aand the centrifugal pendulum vibration absorber5may be mounted on the same end of the rotary shaft2. In this variation, the source of vibration and a vibration absorbing part are located closer to each other, making it possible to obtain a greater vibration absorbing effect.

The centrifugal pendulum vibration absorbers51,53of the first and third embodiments include the adjuster613mounted between the stationary disk element611and the movable disk element612and between the thick-walled disk63and the positioning disk94, respectively. The adjuster613is not absolutely necessary, however. It is possible to eliminate the adjuster613if the movable disk element612or the positioning disk94is reliably mounted at a fixed position on the rotary shaft2by securely tightening the screw B.

While the four mounting holes7are formed in the disk6(one of the disks61,62,63of the first to third embodiments), the number of the mounting holes7is not limited to four but may be less than or more than four.

While the invention has been described with reference to the illustrative embodiment in which the image forming apparatus10having the photosensitive drum121applied with the centrifugal pendulum vibration absorber5is a copying machine, the image forming apparatus10of the invention is not limited to the copying machine but may be a printer which simply performs a print job based on image information fed from an external apparatus like a computer or a facsimile machine which performs a print job based on image information fed through a communications line, for example.

While the printing sheet P used as an image carrying medium in the image forming apparatus10of the foregoing embodiment is a sheet of paper, the image carrying medium is not limited to the sheet of paper in this invention. For example, the image carrying medium may be a transparent plastic sheet used in an overhead projector or an image transfer belt to which toner images of different colors once formed on the outer peripheral surface of the photosensitive drum121are transferred for color printing. In the latter case, the color images transferred to the image transfer belt one on top of another are eventually together retransferred to a sheet of paper or a transparent plastic sheet.

While the invention has thus far been described with reference to the illustrative embodiments thereof, principal arrangements and features of the invention can be summarized as follows.

In one preferable form of the invention, a rotary driving device includes a rotary shaft supported rotatably about an axis thereof on a predetermined supporting member, a rotary load body mounted on the rotary shaft to project radially outward from the rotary shaft in such a manner that the rotary load body can rotate integrally with the rotary shaft about the axis thereof, a driver for rotating the rotary shaft about the axis thereof, a disk mounted on the rotary shaft coaxially therewith for integral rotation with the rotary shaft, the disk having a mounting hole formed therein, a pendulum loosely fitted in the mounting hole, and an adjustment mechanism for adjusting a relative position relationship between a central axis position of the mounting hole and a center of gravity position of the pendulum under conditions where the disk is rotating.

According to the rotary driving device thus configured, the disk rotates about the rotary shaft concentrically therewith when the driver is actuated, so that vibrational energy of the rotary driving device is absorbed by pendular motion (oscillatory motion) of the pendulum fitted in the mounting hole formed in the disk. This serves to suppress vibration of the rotary driving device. If the oscillatory motion of the pendulum does not produce an initially intended level of vibration absorbing effect, the relative position relationship between the central position of the mounting hole and the center of gravity of the pendulum is varied by manipulating the adjustment mechanism and the vibration absorbing effect thus produced is reconfirmed repetitively on a trial-and-error basis. By this adjustment process, it is possible to make the frequency of vibration of the rotary driving device equal to the natural frequency of vibration of the pendulum, so that oscillatory motion of the rotary driving device is effectively absorbed.

Also, even after the disk having the mounting hole in which the pendulum is loosely fitted is once mounted on the rotary shaft, it is possible to effectively suppress vibration of the rotary driving device by manipulating the adjustment mechanism if the desired vibration absorbing effect is not obtained. Therefore, unlike the case of a conventional arrangement, it is not necessary to replace the disk or the pendulum with new ones when the desired vibration absorbing effect is not obtained. This makes it possible to effectively prevent the occurrence of such an inconvenient situation that replacement of components results in a cost increase. Additionally, as one can quickly enhance vibration absorbing performance according to the structure of the invention, it is possible to ensure that the rotary driving device constantly produces the desired vibration absorbing effect.

In the rotary driving device of the above structure, preferably, the central axis of the mounting hole is set to be parallel to the axis of the rotary shaft, the pendulum is caused to move radially outward within the mounting hole due to a centrifugal force produced by rotary motion of the disk, and the adjustment mechanism adjusts the relative position relationship between the central axis position of the mounting hole and the center of gravity position of the pendulum under conditions where the pendulum is moved radially most outward in the mounting hole.

In the rotary driving device of the above structure, preferably, the adjustment mechanism goes into contact with the pendulum to regulate the amount of radially outward movement of the pendulum within the mounting hole, thereby adjusting the relative position relationship between the central axis position of the mounting hole and the center of gravity position of the pendulum.

The following description deals with specific arrangements for adjusting the relative position relationship between the central axis position of the mounting hole and the center of gravity position of the pendulum.

In the rotary driving device of the above structure, preferably, the disk includes a stationary disk element fixedly mounted on the rotary shaft and a movable disk element slidably mounted on the rotary shaft, the mounting hole is made of a first mounting hole formed in the stationary disk element and a second mounting hole formed in the movable disk element so as to accommodate the pendulum between the first and second mounting holes, the pendulum is a spherical body having a diameter larger than a minimum diameter of the mounting hole and the spherical body is fitted in the mounting hole while being sandwiched between the stationary disk element and the movable disk element, and the adjustment mechanism includes the movable disk element sliding on the rotary shaft to go into contact with the pendulum through the second mounting hole and a locking member keeping the movable disk element from moving.

According to the rotary driving device thus configured, the distance between the stationary disk element and the movable disk element varies when the movable disk element is moved back and forth along the rotary shaft. It is therefore possible to vary the distance between the central axis of the rotary shaft and the center of gravity of the pendulum under conditions where the centrifugal force produced by rotation of the rotary shaft is exerted on the spherical body sandwiched between the stationary and movable disk elements. It is possible to improve the vibration absorbing effect by adjusting the distance between the two disk elements in the aforementioned fashion.

In the rotary driving device of the above structure, preferably, the movable disk element includes a facing surface facing the stationary disk element, an opposite surface opposite to the facing surface and a protrusion part protruding from the opposite surface in a direction in which the rotary shaft extends, the projecting part has a slot so formed as to extend in the direction in which the rotary shaft extends, the rotary shaft has a peripheral surface formed with a threaded hole corresponding to the slot, and the locking member is a screw screwed into the threaded hole through the slot.

According to the rotary driving device thus configured, the movable disk element can be moved back and forth along the rotary shaft upon loosening the screw screwed into the threaded hole through the slot formed in the projecting part of the movable disk element. Then, the movable disk element is set at a fixed position on the rotary shaft if the screw is tightened after adjusting the distance between the stationary d is k element and the movable disk element.

As the screw is used as the locking member as discussed above, the locking member can be made in an extremely simple structure and the distance between the stationary disk element and the movable disk element thus adjusted can easily be maintained.

In the rotary driving device of the above structure, the disk has one and the other surfaces facing in opposite directions, the pendulum is a truncated conical body having a tapered peripheral surface that has a diameter gradually decreasing from the one surface toward the other surface, the disk has a cutout space formed therein by cutting out a portion of the disk from an outer peripheral surface thereof toward the mounting hole, and the adjustment mechanism includes an adjusting tab mounted in the cutout space and going into contact with the tapered peripheral surface of the truncated conical body and a moving member moving the adjusting tab back and forth along a thickness direction of the disk.

According to the rotary driving device thus configured, a contact point of the adjusting tab on the tapered circumferential surface of the truncated conical body varies if the adjusting tab is moved back and forth along the axial direction of the rotary shaft (that is, along the thickness direction of the disk) by manipulating the moving member due to the centrifugal force produced by rotation of the disk about the rotary shaft. As a result, the center of gravity position of the truncated conical body moves along a radial direction of the disk and the distance between the center of gravity position of the truncated conical body and the central axis of the rotary shaft varies. This makes it possible to finely adjust the vibration absorbing effect of the rotary driving device.

In the rotary driving device of the above structure, preferably, the moving member is an adjusting screw passing through the disk from the one surface to the other surface while passing through the adjusting tab mounted in the cutout space.

According to the rotary driving device thus configured, the adjusting tab can be moved back and forth along the thickness direction of the disk by turning the adjusting screw clockwise and counterclockwise about an axis thereof. It is possible to make the moving member in a simple structure by using the adjusting screw as the moving member as mentioned above.

In the rotary driving device, preferably, the disk has first and second surfaces facing in opposite directions, the mounting hole is a conical hole having a diameter gradually increasing from the first surface toward the second surface, the pendulum is a spherical body having a diameter larger than both a minimum diameter of the conical hole and the thickness of the disk, and the adjustment mechanism includes a positioning disk arranged in face to face relation with the second surface and slidably and coaxially fitted on the rotary shaft and a locking member keeping the positioning disk from moving.

This configuration serves to keep the spherical body from coming off the conical hole with the aid of the positioning disk mounted face to face with the first surface of the disk where the conical hole has the minimum diameter. In this condition, part of the spherical body protrudes from the conical hole toward the positioning disk.

The amount of projection of the spherical body from the conical hole in the disk can be varied by moving the positioning disk along the axial direction of the rotary shaft. Thus, when the disk is caused to rotate about the rotary shaft integrally therewith, the distance between the center axis of the rotary shaft and the center of gravity position of the spherical body varies according to the amount of projection of the spherical body. This makes it possible to finely adjust the vibration absorbing effect of the rotary driving device.

In the rotary driving device of the above structure, preferably, the positioning disk includes a facing surface facing the disk, an opposite surface opposite to the facing surface and a protrusion part protruding from the opposite surface in a direction in which the rotary shaft extends, the projecting part has a slot so formed therein as to extend in the direction in which the rotary shaft extends, the rotary shaft has a peripheral surface formed with a threaded hole corresponding to the slot, and the locking member is a screw screwed into the threaded hole through the slot.

In the rotary driving device thus configured, it is possible to affix the positioning disk to the rotary shaft and thereby set the spherical body in position by tightening the screw fitted in the threaded hole in the rotary shaft. Since the screw is screwed into the threaded hole in the rotary shaft through the slot in the projecting part of the positioning disk, it is possible to move the positioning disk back and forth along the axial direction of the rotary shaft. As the screw is used as the locking member as discussed above, the locking member can be made in a simple structure.