JP3526764B2 - Image forming device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention conveys a recording medium along a plurality of photoconductors arranged in parallel, sequentially superimposes toner images formed on the photoconductors, and transfers them onto the recording medium. An image forming apparatus for obtaining an image (color image),
In particular, the present invention relates to a rotary inertia member for preventing uneven rotation of the photosensitive member, which is attached to the rotary shaft of the photosensitive member so that adjacent rotary inertia members do not interfere with each other.

[0002]

2. Description of the Related Art Generally, in an image forming apparatus for recording an image on a rotating photosensitive member by line scanning such as laser scanning, driving unevenness (rotational unevenness) is generated by a driving mechanism for driving the photosensitive member. When you recorded the image,
Since the drive unevenness remarkably appears as image unevenness (banding: band-shaped image unevenness occurring on the image), a rotary inertia body (flywheel) has conventionally been attached to one of the rotary shafts of the photoconductor.

In such a structure, since the flywheel can give inertia to the rotation of the photosensitive member, it is possible to suppress the drive unevenness generated by the drive mechanism.

However, when the means for mounting the flywheel on the rotary shaft to suppress the unevenness of driving of the photoconductor is used in a color image forming apparatus having an image forming section in which a plurality of photoconductors are arranged in parallel, the size of the flywheel ( Diameter),
The following problems have occurred in determining the distance between adjacent photoconductors.

That is, in order to increase the inertial force with respect to the rotation of the photoconductor, the diameter of the flywheel may be increased. However, a flywheel having a diameter that can give sufficient inertia to the rotation of the photoconductor is used. In this case, the distance between adjacent photoconductors must be widened. as a result,
The area occupied by the photoconductor in the image forming apparatus increases,
The image forming apparatus becomes large and hinders miniaturization.

On the contrary, if the distance between adjacent photoconductors is shortened in an attempt to downsize the image forming apparatus, the diameter of the flywheel must be reduced. However, if the diameter of the flywheel is small, sufficient inertia cannot be given to the rotation of the photoconductor, and the effect of the flywheel is reduced.

Therefore, in order to prevent the flywheels of the adjacent photoconductors from interfering with each other, the flywheels are attached to the rotation shaft of the photoconductors by alternately displacing the attachment positions in the axial direction, and the adjacent flywheels are attached. The wheels are arranged so that they overlap each other. Therefore, it is possible to make the size (diameter) of the flywheel as large as possible and to make the space between the adjacent photoconductors as narrow as possible.

The structure for alternately mounting the flywheels in the axial direction will be described in detail with reference to FIG. 6. The photoconductor drum 222 provided in the image forming section includes a gear box 2, a shaft (rotating shaft) 3, a flywheel ( (Rotary inertial body) 4.

The flywheel 4 is provided with a hole in the center for inserting and mounting the shaft 3.
Around the hole, a protrusion 4a that protrudes toward the photosensitive drum 222 is provided. The protruding portion 4a is the depth of the hole to ensure that secure the flywheel 4 to the shaft 3 (i.e., the length of the hole) is used to increase the.

The plurality of flywheels 4 are arranged so that a part of each of the plurality of adjacent photoconductor drums 222 is overlapped. Specifically, as shown in FIG. 6, the shafts 3 supporting the flywheels 4 are arranged so as to be aligned with each other, and the projections 4a are arranged.
The flywheels 4 adjacent to each other are arranged in such a state that they are superposed on each other so that the distance between them does not come into contact with each other.

[0011]

However, according to the above configuration, as shown in FIG. 6, among the plurality of flywheels 4, the flywheel 4 (104) located on the rightmost side in the figure and the flywheel 4 (104) located on the rightmost side in the figure. Flywheel 4 (2 adjacent to
04) is different from the gear box 2 in the mounting position (in the axial direction).

That is, the flywheel 4 (204) is
Since the protrusion 4a exists between the gearbox 2 and the gearbox 2, the protrusion 4a is fixed to the shaft 3 at a position with a certain distance, and the flywheel 4 (104) considers the overlap with the adjacent flywheel 4 (204). Then, the gearbox 2 must be mounted so as to have a gap of L2, and a space is required for this gap, which makes it impossible to reduce the size of the image forming apparatus.

Similarly, the flywheel 4 (304) adjacent to the flywheel 4 (204) has the same arrangement as the flywheel 4 (104), and the flywheel 4 (304) adjacent to the flywheel 4 (304). (40
4) has the same arrangement as the flywheel 4 (204).

As a result, it is necessary to make the lengths of the shafts 3 provided on the respective photosensitive drums 222 different from each other. Therefore, it is necessary to use parts having the same structure for each of the plurality of photosensitive drums 222. I can't. As a result, the versatility of the parts is reduced, the manufacturing cost of the image forming apparatus is increased, and the assembly of the image forming apparatus is complicated.

The image forming apparatus of the present invention has been made in view of the above problems, and has a rotary inertia member (flywheel).
Common position the support mechanism in the rotation shaft of the photosensitive body for supporting the
It is possible to support the rotating inertia bodies that are adjacent to this support mechanism in an overlapping manner without interfering with each other and to support the entire support mechanism by installing the rotating inertia body.
Minimizing the occupied area of, it is an object of reducing the size of the entire image forming apparatus.

[0016]

In order to achieve the above object, the invention according to claim 1 forms a toner image on a plurality of photoconductors arranged in parallel, and a toner image is formed on the photoconductor with respect to a recording medium. In an image forming apparatus that forms a final image by sequentially superposing toner images, a disk-shaped rotation that is attached to the rotation shafts of the plurality of photoconductors while alternately offset from each other in the axial direction of the rotation shafts. includes an inertial body, the rotary inertial body, in its central portion, the first surface side is convex, the first
A mounting portion having a concave shape on the second surface side, which is the back surface of the surface, is formed, and at the same position of each rotation shaft of the plurality of photoconductors,
A support member for mounting each of the above-mentioned rotary inertia bodies is formed.
Is, when mounting each rotary inertial body to the rotary shaft of the plurality of photosensitive members, the surface located on the photosensitive side of the adjacent rotary inertial body, the first and second surfaces and are alternately positioned in the mounting portion It is attached to the support member of each rotary shaft such that. According to the above configuration, the first surface and the second surface of the rotary inertia body are alternately located on the photoconductor side, that is, the front and back surfaces of the rotary inertia body are alternately attached to the rotary shaft, This makes it possible to minimize the installation footprint of the rotating inertial body.

According to the second aspect of the invention, the second rotary inertia body having an opening having the size of the mounting portion of the rotary inertia body is detachably attached to the rotary inertia body. According to the above configuration, simply by attaching the second rotary inertia body to the rotary inertia body,
It is possible to increase the inertial force of the rotary inertial body.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION An outline of an image forming apparatus of the present invention will be described with reference to FIG. FIG. 1 is a front sectional view showing a configuration of a digital color copying machine which is an image forming apparatus of the present invention. On the upper surface of the copying machine body 1, a document table 11
1 and an operation panel, and the image reading unit 110 and the image forming unit 210 are provided inside the copying machine main body 1.

The upper surface of the document table 111 is supported in an openable and closable manner with respect to the document table 111, and the double-sided automatic document feeder (R) has a predetermined positional relationship with the surface of the document table 111.
ADF: Recirculating Automatic Document Fe
eder) 112 is attached.

Further, the RADF 112 first conveys the document so that one side of the document faces the image reading section 110 at a predetermined position of the document table 111, and after the image reading on this one side is completed, the other side is conveyed. The original is inverted so that its surface faces the image reading unit 110 at a predetermined position of the original table 111 and is conveyed toward the original table 111. Then, the RADF 112 discharges this document after the image reading on both sides of one document is completed, and executes the double-sided conveyance operation for the next document. The above-described operations of conveying the document and inverting the front and back are controlled in relation to the operation of the entire copying machine.

The image reading unit 110 is arranged below the document table 111 in order to read the image of the document conveyed onto the document table 111 by the RADF 112. The image reading unit 110 includes an original scanning body that reciprocates in parallel along the lower surface of the original table 111, an optical lens 115, and a CCD line sensor 116 that is a photoelectric conversion element.

The original scanning body is composed of the first scanning unit 11
3 and the second scanning unit 114. The first scanning unit 113 has an exposure lamp that exposes the image surface of the original document and a first mirror that deflects the reflected light image from the original document in a predetermined direction. While reciprocating, it reciprocates in parallel at a predetermined scanning speed. The second scanning unit 114 has a first
The first scanning unit 113 includes second and third mirrors that further deflect the reflected light image from the document deflected by the first mirror of the scanning unit 113 in a predetermined direction.
And reciprocate in parallel while maintaining a constant speed relationship.

The optical lens 115 is used in the second scanning unit 1
The reflected light image from the document deflected by the third mirror 14 is reduced, and the reduced light image is reflected by the CCD line sensor 116.
The image is formed at a predetermined position above.

The CCD line sensor 116 sequentially photoelectrically converts the formed optical image and outputs it as an electric signal. The CCD line sensor 116 is a three-line color CCD capable of reading a black-and-white image or a color image and outputting line data that is color-separated into R (red), G (green), and B (blue) color components. . The document image information converted into an electric signal by the CCD line sensor 116 is further transferred to an image processing unit (not shown) and subjected to predetermined image data processing.

Next, the structure of the image forming unit 210 and the structure of each unit related to the image forming unit 210 will be described.

Below the image forming section 210, there is provided a sheet feeding mechanism 211 for separating the sheets (recording media) P stacked and accommodated in the sheet tray one by one and feeding them toward the image forming section 210. ing. The timings of the sheets P that have been separated and supplied one by one are controlled by a pair of registration rollers 212 disposed in front of the image forming unit 210, and the image forming unit 210 is imaged at the same timing as the image forming of the image forming unit 210. Is re-supplied and transported.

A transfer / conveying belt mechanism 213 is arranged below the image forming section 210. The transfer / transport belt mechanism 213 includes a driving roller 214 and a driven roller 215.
The sheet P is electrostatically attracted to and conveyed by the transfer and conveyance belt 216 stretched so as to extend substantially parallel to and between the sheet and the sheet. A pattern image detection unit is provided near the lower side of the transfer / transport belt 216.

Further, on the downstream side of the transfer / transport belt mechanism 213 in the paper transport path, a fixing device 217 for fixing the toner image transferred and formed on the paper P onto the paper P.
Are arranged. The sheet P that has passed through the nip between the pair of fixing rollers of the fixing device 217 is discharged by the discharge roller 219 onto the discharge tray 220 attached to the outer wall of the copying machine body 1 via the transfer direction switching gate 218. It

The switching gate 218 is used for the sheet P after fixing.
Is selectively switched between a path for discharging the paper P to the copying machine main body 1 and a path for re-supplying the paper P toward the image forming unit 210. The sheet P whose conveyance direction has been switched again toward the image forming unit 210 by the switching gate 218 is turned upside down via the switchback conveyance path 221 and then the image forming unit 210.
Is supplied again to.

Further, above the transfer / transport belt 216 in the image forming section 210, in the vicinity of the transfer / transport belt 216, the first image forming station Pa, the second image forming station Pb, the third image forming station Pc, and the third image forming station Pc. The four image forming stations Pd are arranged in parallel in order from the upstream side of the paper transport path.

The transfer / transport belt 216 is driven by the driving roller 214.
1 grips the paper P that is frictionally driven in the direction indicated by the arrow Z in FIG. 1 and is fed through the paper feed mechanism 211 as described above, and the paper P is transferred to the image forming stations Pa.
It is sequentially transported to Pd.

The image forming stations Pa to Pd have substantially the same structure. Each of the image forming stations Pa, Pb, Pc, Pd is a photosensitive drum 222a, 222b, 22 which is rotationally driven in the direction of arrow F shown in FIG.
2c and 222d, respectively.

Around the photosensitive drums 222a to 222d, chargers 223a, 223b, 223c, and 223d that uniformly charge the photosensitive drums 222a to 222d, respectively.
And developing devices 224a, 224b, 2 for developing the electrostatic latent images formed on the photoconductor drums 222a to 222d, respectively.
24c and 224d, and the developed photosensitive drum 222a
To 222d, transfer dischargers 225a, 225b, 225c and 225d, and cleaning devices 226a, 226b, 226c and 2 for removing toner remaining on the photosensitive drums 222a to 222d.
26d are sequentially arranged along the rotation direction of the photosensitive drums 222a to 222d.

Further, each of the photosensitive drums 222a to 222d
Above the above is a laser beam scanner unit (LSU)
227a, 227b, 227c and 227d are provided respectively. The LSUs 227a to 227d include a semiconductor laser element (not shown) that emits dot light modulated according to image data, and a polygon mirror (deflecting device) 240 for deflecting the laser beam from the semiconductor laser element in the main scanning direction. And an fθ lens 241 and a mirror 24 for forming an image of the laser beam deflected by the polygon mirror 240 on the surfaces of the photoconductor drums 222a to 222d.
2, 243 and the like.

LSU 227a stores a pixel signal corresponding to a black component image of a color original image, and LSU 227b stores a pixel signal corresponding to a cyan color component image of a color original image.
A pixel signal corresponding to the magenta color component image of the color original image is input to the SU 227c, and a pixel signal corresponding to the yellow color component image of the color original image is input to the LSU 227d.

As a result, the electrostatic latent images corresponding to the color-converted document image information are converted into the respective photosensitive drums 222a to 222d.
Formed on. Then, the developing device 224a contains black toner, and the developing device 224b contains cyan toner.
The developing device 224c contains magenta toner and the developing device 224d contains yellow toner. The electrostatic latent images on the photosensitive drums 222a to 222d are
It is developed with toner of each of these colors. As a result, the document image information color-converted by the image forming unit 210 is reproduced as a toner image of each color.

Between the first image forming station Pa and the sheet feeding mechanism 211, a sheet suction (brush) charger 2 is provided.
28 is provided, and the paper adsorption charger 228 charges the surface of the transfer / conveying belt 216, and the paper feeding mechanism 21.
The sheet P supplied from the first sheet forming apparatus 1 is securely sucked onto the transfer / conveying belt 216 and is fed to the first image forming station Pa.
To the fourth image forming station Pd without any deviation.

On the other hand, between the fourth image forming station Pd and the fixing device 217, a static eliminator (not shown) is provided almost directly above the drive roller 214. An AC current for separating the paper P electrostatically attracted to the transfer / transport belt 216 from the transfer / transport belt 216 is applied to the static eliminator.

[0039] In the digital color copying machine having the above configuration, the cut sheet paper is used as the sheet P, the sheet P is paper feed mechanism fed et al or the sheet feed cassette 2
When fed into the guide 11 sheet transportation path, it is detected the tip portion of the sheet P by the sensor (not shown), a pair of registration rollers 212 based on a detection signal output the sensor or al Is temporarily stopped by.

Then, the sheet P is sent onto the transfer / conveying belt 216 rotating in the direction of arrow Z in FIG. 1 at a timing with each of the image forming stations Pa to Pd. At this time, since the transfer / conveying belt 216 is charged by the sheet adsorbing charger 228 as described above,
The sheet P is stably conveyed and supplied while passing through the image forming stations Pa to Pd.

In each of the image forming stations Pa to Pd, a toner image of each color is formed and superposed on the supporting surface of the sheet P which is electrostatically attracted by the transfer and transport belt 216 and is transported. When the transfer of the image by the fourth image forming station Pd is completed, the sheet P is sequentially peeled from the transfer conveying belt 216 from the leading end portion of the sheet by the discharging discharging device and guided to the fixing device 217. Finally, the paper P on which the toner image is fixed is a paper discharge port (not shown).
Is ejected onto the paper ejection tray 220.

In the above description, LSU 227a ...
Optical writing is performed on the photoconductor drums 222a to 222d by scanning and exposing a laser beam at 227d. However, a writing optical system (LED head) including a light emitting diode array and an imaging lens array may be used instead of the LSU. Compared to LSU, LED head
It is small in size and silent because there are no moving parts. Therefore, it can be preferably used in an image forming apparatus such as a tandem system (system in which a plurality of photosensitive drums are arranged in parallel) that requires a plurality of optical writing units, such as a digital color copying machine.

2 to 4 of the first embodiment of the photosensitive drum 222 of the image forming section 210 of the digital color copying machine.
It will be described based on. Photoconductor drums 222a to 222d
Includes gearboxes 2a-2d, shafts 3a-3d,
It is provided with flywheel support members 5a to 5d and flywheels (rotational inertia bodies) 6a to 6d.

The gearboxes 3a to 3d are equipped with gears and motors (not shown), and the photosensitive drum 222a.
~ 222d is driven to rotate. The gearboxes 2a to 2d and the shafts 3a to 3d form at least a drive mechanism for the photosensitive drums 222a to 222d. Normally, a small margin is provided between the gears in the gear boxes 2a to 2d so that they can rotate with respect to each other, but due to this margin, the photosensitive drum 22
Driving unevenness occurs in 2a to 222d, and band-shaped image unevenness called banding occurs in the image formed on the paper P.

Therefore, the photosensitive drums 222a to 222d
Of the photosensitive drums 222a to 222 by giving inertia to the rotation of
As a structure for smoothing the rotation of d, the shaft 3a
Flywheels 6a to 6d are attached to 3d. Thereby, the photosensitive drums 222a to 222d
It is possible to suppress the occurrence of drive unevenness and to avoid the occurrence of banding.

The inertia of the flywheels 6a to 6d with respect to the rotation of the photosensitive drums 222a to 222d depends on the diameter of the flywheels 6a to 6d. That is,
If the flywheels 6a to 6d have a large diameter, the inertial force applied to the photoconductor drums 222a to 222d also increases.

In order to increase the diameters of the flywheels 6a to 6d in this way, in the present embodiment, as shown in FIG. 2, the flywheels 6a to 6d have the first surface formed by press drawing the central portion thereof. The (front) side is formed in a convex shape, the second surface (rear surface) side is formed in a concave shape, and the convex portion 7a is formed on the first surface side.
Is formed on the second surface side.

First, in the flywheel 6a, the first surface side having the convex portion 7a is positioned on the flywheel support member 5a side, and the flywheel 6a is fitted and inserted into the shaft 3a.
Fix with a screw. The flywheel 6b has a recess 7
The second surface side having b is positioned on the flywheel support member 5b side, fitted into the shaft 3b, and fixed to the flywheel support member 5b with screws. The first side of the flywheel 6c having the convex portion 7a is the flywheel supporting member 5
It is positioned on the c side, fitted into the shaft 3c, and fixed to the flywheel support member 5c with screws. The second side of the flywheel 6d having the recess 7b is positioned on the flywheel support member 5d side, fitted into the shaft 3d, and fixed to the flywheel support member 5d with screws 8. The flywheel support members 5a to 5d are shuffles, respectively.
The flywheels 6a to 6d are arranged at the same positions on the toes 3a to 3b, and are formed in a triangular shape as shown in FIG.

By attaching the flywheels 6a to 6d as described above, the flywheels 6b and 6d have the recesses 7b located on the photoconductor drum 222b and 222d side, that is, on the gearboxes 2b and 2d side, and the flywheel support member. 5b and 5d are located in the recess 7b, and the flywheels 6b and 6d include the gearbox 2b and
It will be located at a position close to 2d. The flywheels 6a and 6c are connected to the photosensitive drums 222a and 22a.
2c side, that is, the convex portion 7 on the gearbox 2a, 2c side
a is positioned, and the flywheel support members 5a and 5c and the convex portion 7a come into contact with each other.
The a and 6c are located at positions apart from the gearboxes 2a and 2c.

Therefore, the adjacent flywheel 6a
~ 6d can rotate without mutual interference,
The inertia of the flywheels 6a to 6d prevents uneven rotation of the photoconductor drums 222a to 222d.

Moreover, since the flywheels 6b and 6d can be located close to the gearboxes 2b and 2d, the distance L1 between the gearbox 2 and the flywheel 6 can be reduced. That is, in FIG. 6, the interval between the flywheel 4 (204 and 404) Gagi A box 2 disposed closer to the gearbox 2 is increased, the flywheel 4 (104, 304)
Also it increases the distance between the gearbox 2, resulting in intervals L2 is large.

On the other hand, according to the present invention, since the flywheel support members 5b and 5d are located in the recesses 7b of the flywheels 6b and 6d, the flywheels 6b and 6d are not provided.
The distance between the gearbox 2 is reduced, the flywheel 6a, since the smaller spacing from gearbox 2 of 6c, distance L1 is smaller than the distance L2 in FIG. 6, in the apparatus main body of the photosensitive member The occupied area (space) can be reduced.

A second embodiment of the photosensitive drum 222 of the image forming section 210 of the digital color copying machine of the present invention will be described with reference to FIG.

In the second embodiment, in order to increase the inertial force of the flywheels 6a to 6d, the projections 7a and the recesses 7b formed on the flywheels 6a to 6d are formed.
An open flywheel 9 which is a second rotary inertia body having an opening formed in a portion corresponding to the region where the is formed is detachably attached to the flywheels 6a to 6d by screws or the like.

The flywheels 6a to 6d are provided with projections and screw holes for positioning, and the opening flywheel 9 is provided with holes and screw holes for positioning, and the projections of the flywheels 6a to 6d are provided. After positioning with the holes of the opening flywheel 9 and the holes of the opening flywheel 9, the opening flywheel 9 is attached to the flywheels 6a to 6d by screws, so that the area occupied by the photoconductor (space) is not increased so much. The inertial force of 6a to 6d can be increased.

[0056]

According to the first aspect of the present invention, the photosensitive drum has a first surface (convex surface) and a second surface (concave surface) of the rotary inertia member which are adjacent to each other.
By alternately mounting the shafts at the same mounting position, it is possible to minimize the installation occupation area of the rotary inertia body, save space, and reduce the size of each shaft.
It is possible to use photoconductors of the same shape with the same length of chaft , and it is possible to reduce the manufacturing cost.
The assembly of the image forming apparatus can be simplified.

According to the second aspect of the present invention, the second rotary inertia body is simply attached to the rotary inertia body, and the inertia force of the rotary inertia body is increased without increasing the installation occupation area of the rotary inertia body. You can

[Brief description of drawings]

FIG. 1 is a front sectional view showing a configuration of a digital color copying machine of the present invention.

FIG. 2 is a cross-sectional view showing a state before attachment of a flywheel in the first embodiment of the photosensitive drum of the image forming unit of the digital color copying machine of FIG.

FIG. 3 is a cross-sectional view showing a state after the flywheel is attached in the first embodiment of the photosensitive drum of the image forming unit of the digital color copying machine of FIG.

FIG. 4 is a plan view of FIG. 3 viewed from the flywheel side.

5 is a cross-sectional view showing a state before attachment of a flywheel in the second embodiment of the photosensitive drum of the image forming unit of the digital color copying machine of FIG.

6 is a sectional view showing a mounting state of the flywheel in the photosensitive drum of the image forming unit of a conventional digital color copying machine.

[Explanation of symbols]

2 ... gearbox 3 ... shaft 5 ... flywheel supporting members 6 ... flywheel 7a ... protrusion 7b ... recess 9 ... opening flywheel

Front Page Continuation (72) Inventor Norio Tomita 22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka Prefecture, Sharp Corporation (72) Inventor Takasuke Kyosuke 22-22 Nagaike-cho, Abeno-ku, Osaka City, Osaka Prefecture (72) ) Inventor Manabe Shinsei 22-22 Nagaike-cho, Abeno-ku, Osaka City, Osaka Prefecture (56) References JP-A-6-332289 (JP, A) JP-A-9-90698 (JP, A) JP 4-147279 (JP, A) JP-A-7-281500 (JP, A) JP-A-11-119593 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) G03G 15 / 01-15/01 117 G03G 21/00 350 G03G 15/00 550

Claims (2)

(57) [Claims] 1. An image forming apparatus for forming a final image by forming toner images on a plurality of photoconductors arranged in parallel and sequentially superposing the toner images on the photoconductors onto a recording medium, The rotary shafts of the plurality of photoconductors are provided with disc-shaped rotary inertia bodies that are attached while being alternately displaced in the axial direction of the rotary shafts.
Its central portion, the first surface side is convex, a second surface side as the back side of the first surface is attached portion is formed as a concave, and the
At the same position on each rotation axis of multiple photoconductors,
A support member for attaching a body is formed, and when each rotary inertia body is attached to the rotation shafts of the plurality of photoconductors, a surface of the adjacent rotary inertia body located on the photoconductor side is attached to the attachment portion. first surface and a second surface on each rotary shaft so as to be positioned alternately
An image forming apparatus characterized by being attached to a supporting member . 2. The image forming apparatus according to claim 1, wherein a second rotary inertia body having an opening having a size of a mounting portion of the rotary inertia body is detachably attached to the rotary inertia body. .