Cylindrical rotating member having a support mechanism exhibiting little unevenness in rotation, and image forming apparatus

It is desirable if the lengthwise center axis of a cylindrical rotating member such as a photoreceptor drum is aligned exactly with the center axes of the support shafts. However, as it is impossible to eliminate manufacturing errors in components, it is unavoidable for there to be a slight angle of intersection between the center axis of the cylindrical rotating member and the center axes of the support shaft. Consequently, the object of the present invention is to provide a support mechanism for the cylindrical rotating member whereby the cylindrical rotating member exhibits little unevenness of rotation. When lengthwise axis of the cylindrical rotating member forms angle of intersection .alpha. with lengthwise axis of shaft, this angle .alpha. is absorbed by the slight space between shaft and pierced hole of a rotation transmission member, as well as by the gap between the rotation transmission member and bearing of the cylindrical rotating member, so that the center axis of the cylindrical rotating member is fixed in a set position, and the outer circumference of the cylindrical rotating member moves in a predetermined perfectly circular path.

This application is based on application No. 9-139917 filed in Japan, the 
contents of which is hereby incorporated by reference. 
BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention pertains to a mechanism that supports a cylindrical 
rotating member, e.g., a mechanism that can appropriately be used to 
rotatably support a photoreceptor drum in an image forming apparatus such 
as a copying machine based on the electrophotographic method. 
2. Description of the Related Art 
It is desirable if the lengthwise center axis of the photoreceptor drum 
mounted in an image forming apparatus such as a copying machine is aligned 
exactly with the center axes of the support shafts supporting the 
photoreceptor drum at either end of said drum. 
However, as it is impossible to eliminate manufacturing errors in 
components, including photoreceptors, it is unavoidable for there to be a 
slight angle of intersection between the center axis of the photoreceptor 
drum and the center axes of the support shafts. In particular, in a 
support mechanism in which a shaft is mounted to a member that is located 
at each end of the photoreceptor, and these shafts are inserted into 
bearing holes formed in flanges at either end of the photoreceptor, said 
discrepancy in the alignment of the center axes are so large that the 
problem arises that they become reflected in the image. 
SUMMARY OF THE INVENTION 
Consequently, the object of the present invention is to provide an image 
forming apparatus in which unevenness in the rotation of the cylindrical 
rotating member can be eliminated to the extent possible. 
Another object of the present invention is to provide a cylindrical 
rotating member that rotates based on the rotational force transmitted 
from a rotating driven shaft, wherein said cylindrical rotating member 
exhibits little unevenness, of rotation. 
Yet another object of the present invention is to provide a support 
mechanism for a cylindrical rotating member whereby the cylindrical 
rotating member exhibits little unevenness of rotation. 
In order to attain these objects, a first aspect of the present invention 
comprises an image forming apparatus having a cylindrical rotating member, 
a rotating driven shaft, a first rotation transmission member that is 
fixed to said shaft and rotates together with it, and a second rotation 
transmission member that engages with said first rotation transmission 
member and that transmits to the cylindrical rotating member the 
rotational force of the first rotation transmission member, wherein said 
second rotation transmission member has a pierced hole formed in it for 
insertion of the shaft such that there is a gap between it and the shaft 
when the shaft is inserted. 
A second aspect of the present invention comprises a cylindrical rotating 
member that rotates based on the rotational force transmitted from the 
shaft via a first rotation transmission member fixed to the rotating 
driven shaft, wherein said cylindrical rotating member has a second 
rotation transmission member that engages with said first rotation 
transmission member and that transmits to the cylindrical rotating member 
the rotational force of said first rotation transmission member, and 
wherein said second rotation transmission member has a pierced hole formed 
in it for insertion of the shaft such that there is a gap between it and 
the shaft when the shaft is inserted. 
A third aspect of the present invention comprises a support mechanism for a 
cylindrical rotating member having a transmission member that transmits to 
the cylindrical rotating member the rotational force of the rotating 
driven shaft, wherein said support mechanism is equipped with a first 
rotation transmission member that is fixed to said shaft and rotates 
together with it, as well as a second rotation transmission member that 
has a hole formed in it for insertion of said shaft, engages with said 
first rotation transmission member and transmits the rotation of said 
first rotation transmission member to said cylindrical rotating member, 
and wherein there is a gap between the shaft insertion hole and the shaft. 
In addition to the first through third aspects described above, said 
cylindrical rotating member has a pair of flanges each equipped with at 
least one bearing, and said second rotation transmission member is 
rotatably mounted in each of said bearings. 
Further, in addition to the first through third aspects described above, 
either said image forming apparatus or said cylindrical rotating member 
has a preventive member that prevents the movement of said second rotation 
transmission member along the lengthwise directions of the shaft and a 
force-applying member that applies force to said second rotation 
transmission member toward said control member. 
A fourth aspect of the present invention comprises an image forming 
apparatus that is equipped with a cylindrical rotating member having a 
flange, a rotating driven shaft, and a rotation transmission member that 
is inserted in an insertion hole formed in said flange and transmits to 
the cylindrical rotating member the rotational force of the shaft, wherein 
said rotation transmission member is formed such that there is a gap 
between it and the insertion hole when the rotation transmission member is 
inserted. 
A fifth aspect of the present invention comprises a cylindrical rotating 
member that rotates due to the drive force transmitted from an external 
device, wherein said cylindrical rotating member is equipped with a drive 
transmission member that transmits said external drive force to said 
cylindrical rotating member and a flange that has at least one insertion 
hole for insertion of said drive transmission member, and wherein said 
rotation transmission member is formed such that there is a gap between it 
and said insertion hole when the rotation transmission member is inserted. 
These and other objects, advantages and features of the invention will 
become apparent from the following description thereof taken in 
conjunction with the accompanying drawings which illustrate specific 
embodiments of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Preferred embodiments of the present invention will be explained below with 
reference to the accompanying drawings. FIG. 1 is an example of the 
application of the present invention to the support mechanism for 
photoreceptor 10 of image forming apparatus 1 shown in FIG. 9. 
In FIG. 9, photoreceptor 10 is rotatably supported, and rotates based on 
the rotational drive force transmitted from shafts 36. When this occurs, 
photoreceptor 10 becomes charged by charging unit 3, and a latent image is 
formed by means of exposure light 4. The latent image is then developed 
into a toner image by means of developing unit 5. The toner image on 
photoreceptor 10 is transferred onto the paper supplied from paper 
cassettes 2A or 2B by means of transfer unit 6 and fused by means of fuser 
unit 8, whereupon the paper is ejected onto eject tray 9. The toner 
remaining on the surface of the photoreceptor after transfer is removed by 
means of cleaning blade 7. 
In FIG. 1, the photoreceptor indicated by the number 10 comprises cylinder 
12 having a photoreceptive layer over its outer surface and pair of 
flanges 14 (one of which is not shown in the drawing) that are fixed to 
the openings at either end of said cylinder 12. Cylindrical bearing 18 is 
formed in the flange 14 shown in the drawing using lengthwise axis 16 of 
photoreceptor 10 as its center axis. Cylindrical wall 20 is formed on 
bearing 18 such that it extends inside photoreceptor 10 with its outer 
circumference tracing the same circle as the circumference of bearing 18. 
The end of cylindrical wall 20 is closed off by end wall 22, and 
cylindrical space 24 is created inside the structure formed by walls 20 
and 22. 
Disk-shaped rotation transmission member 26 (the second rotation 
transmission member, hereinafter termed claw member 26) having a slightly 
smaller diameter than said bearing 18 is housed inside bearing 18. Claw 
member 26 has pierced hole 28 in its center, and has cylindrical boss 
member 30 located on the opposite surface from end wall 22 and aligned 
with pierced hole 28 at its center. Engaging member (claw) 32 is formed on 
the outer circumference of boss member 30. 
Spring 34 is located in space 24 so as to apply outward force to claw 
member 26. On the other hand, in order to prevent claw member 26 to which 
force is applied by means of spring 34 from separating from bearing 18, a 
member (not shown in the drawing) is formed on the outer end surface of 
flange 14 to prevent claw member 26 from moving beyond the outer end 
surface of the flange. 
Drive shaft 36 to transmit rotational force to photoreceptor 10 is 
rotatably fixed at its base end to a base plate not shown in the drawing, 
such that it transmits rotational force from a drive system not shown in 
the drawing. Rotation transmission member 38 (the first transmission 
member, hereinafter termed claw member 38) is fixed to the far end of 
shaft 36 by means of an appropriate fixing means (e.g., a pin). Claw 
member 38 has cylindrical protrusion 40 at the tip of the shaft, and 
engaging member (claw) 42 is formed on the inner circumference of said 
cylindrical protrusion 40. 
The end of the shaft 36 is inserted in pierced hole 28 in claw member 26, 
and engaging members 32 and 42 of claw members 26 and 38, as shown in the 
drawing, are engaged with each other. After the rotational force of shaft 
36 is transmitted to claw member 38, it is then transmitted to claw member 
26 by means of engaging members 32 and 42. Here, because force is applied 
to claw member 26 toward claw member 38 by means of spring 34, the 
rotational force is properly transmitted between claw members 26 and 38. 
Next, the rotational force of claw member 26 is transmitted to flange 14 
via the friction between the outer circumference of said claw member 26 
and bearing 18 with which it is in contact, and consequently photoreceptor 
10 rotates in a prescribed direction. When this occurs, because there is a 
gap between claw member 26 and bearing 18, the rotational force is 
transmitted with a slight angle between the rotational axes of claw member 
26 and photoreceptor 10. 
In the support mechanism for photoreceptor 10 constructed in the manner 
described above, it is desirable for lengthwise axis 16 of photoreceptor 
10 (the axis of rotation) to be aligned exactly with lengthwise axis 44 of 
shaft 36 supporting it, but in actual practice it is impossible to achieve 
such an exact alignment, and there is normally a slight angle between 
lengthwise axis 44 of shaft 36 and lengthwise axis 16 of photoreceptor 10, 
as shown in the drawing. 
This slight angle is absorbed by said gap between claw member 26 and 
bearing 18. In order to further eliminate the rotational unevenness of 
photoreceptor 10 caused by said angle, the outer diameter of shaft 36 is 
made slightly smaller than the diameter of pierced hole 28 formed in claw 
member 26. For example, where a metal rod having a nominal diameter of 8 
mm is used for shaft 36, its outer diameter is made approximately 0.01 mm 
to 0.05 mm smaller than 8 mm. Conversely, the inner diameter of claw 
member pierced hole 28 is made approximately 0.02 mm to 0.08 mm larger 
than 8 mm. Therefore, the gap between shaft 36 and pierced hole 28 ranges 
from 0.03 mm to 0.13 mm. 
As a result, when lengthwise axis 16 of photoreceptor 10 forms angle of 
intersection a with lengthwise axis 44 of shaft 36, this angle .alpha. is 
absorbed by the slight space between shaft 36 and pierced hole 28 of claw 
member 26, as well as by the gap between claw member 26 and bearing 18, so 
that the center axis of photoreceptor 10 is fixed in a set position, and 
the outer circumference of photoreceptor 10 moves in a predetermined 
perfectly circular path. 
FIG. 2 shows a second embodiment of the present invention. In this 
embodiment, flange 54 that is located at one end of photoreceptor 50 and 
supports cylinder 52 of photoreceptor 50 has bearing 56. Pierced hole 60 
in which the shaft is inserted and engaging member 62 located outside of 
pierced hole 60 are formed in bearing 56 with their center axes aligned 
with lengthwise axis 58 of cylinder 52. 
Ring-shaped claw member 64 having essentially the same configuration as 
claw member 26 of the first embodiment is used as the second rotation 
transmission member. Claw member 64 has pierced hole 66 in its center as 
well as cylindrical boss member 68 on one end surface, and engaging member 
70 is formed around this boss member 68. 
Cylindrical member 72 is formed around the second rotation transmission 
member. Cylindrical member 72 comprises cylinder 74 and ring-shaped flange 
76 fixed to the opening at one end of said cylinder 74. Shaft 80 is 
inserted in pierced hole 78 in the center of ring-shaped flange 76, which 
is fixed to shaft 80 by means of a fixing means not shown in the drawing. 
The inner diameter of cylinder 74 is equal to or slightly larger than the 
outer diameter of claw member 64. In the second embodiment, the first 
rotation transmission member comprises cylindrical member 72 and 
ring-shaped flange 76. 
This claw member 64 is housed in cylindrical member 72 with shaft 80 
inserted in its pierced hole 66. Boss member 68 faces outside cylindrical 
member 72, i.e., toward the tip of shaft 80. Spring 82 is located inside 
cylindrical member 72 as shown in the drawing, and applies outward force 
on claw member 64. Ring 84 is placed on shaft 80, and consequently the 
movement of claw member 64 from a prescribed position toward the shaft tip 
is prevented. 
The tip of shaft 80 is then inserted into flange pierced hole 60, and 
engaging member 68 of claw member 64 engages with flange engaging member 
62. After the rotational force of shaft 80 is transmitted from cylindrical 
member 72 to claw member 64 that is in contact with the inner surface of 
said cylindrical member 72, it is transmitted to flange 54 via engaging 
members 62 and 68. 
As in the first embodiment, the inner diameter of claw member pierced hole 
66 is larger than that of the outer diameter of shaft 80 to the same 
extent as in the first embodiment. Therefore, even where lengthwise axis 
58 of photoreceptor 50 forms an angle with lengthwise axis 86 of shaft 80, 
this misalignment is absorbed by the slight space between shaft 80 and 
claw member pierced hole 66, so that photoreceptor 50 rotates around 
lengthwise axis 58 that is perfectly aligned along a predetermined axis. 
FIG. 3 shows a third embodiment of the present invention. This embodiment 
is a variation of the first embodiment, differing from the first 
embodiment only in that spring 34 is eliminated and claw member 26 extends 
to cover the tip of shaft 36, but is essentially identical to the first 
embodiment in all other respects. 
FIG. 4 shows a fourth embodiment of the present invention. This embodiment 
is a variation of the second embodiment, wherein cylindrical member 72 and 
spring 82 are eliminated. In addition, for a first rotation transmission 
member, instead of cylindrical member 72, pins 90 are fixed to shaft 80. 
On the other hand, notches 92 are formed in claw member 64 so as to 
perfectly house pins 90, such that pins 90 engage with these notches 92 
and the rotational force of shaft 80 is transmitted to claw member 64. 
In the third and fourth embodiments as well, the pierced holes in claw 
members 26 and 64 have a diameter that is slightly larger than the outer 
diameter of shafts 36 and 80 that are inserted in these pierced holes, and 
as a result the photoreceptor rotates around its center axis that is 
perfectly aligned along a predetermined axis. 
In the first and second embodiments, a spring is used as a means to apply 
force to the claw member, but a different force-applying means (such as a 
sponge) may be used as long as it can apply force to the claw member. 
The present invention is explained above with regard to a situation in 
which it is applied in a mechanism to support a photoreceptor in an image 
forming apparatus, but the present invention may also be applied in any 
device that supports a cylindrical rotating member. 
The support mechanism described above may be applied at either one end of 
the cylindrical body or at both ends of said body. 
Using the photoreceptor supported by means of the support mechanism of the 
first embodiment, as shown in FIG. 5, an original document (sample image) 
having dots aligned into columns in the middle and at the edges of the 
paper and located at a prescribed distance from each other (25 mm) was 
copied, the dot spacing in the copied image (corresponding to distance A 
on the document) was measured, and the amount of distortion 
[100.multidot.(distance A in original document image/distance A in copied 
image)(%)] was sought. In addition, the distance from the leading edge of 
the copy paper to the first copy dot (corresponding to distance B on the 
original document) was measured and the amount of blurring [distance B in 
the original document image-distance B in copied image (mm)] was sought. 
In the experiment, three types of photoreceptors (100 mm, 80 mm, 60 mm) 
were used. The spring constant of the spring used was 35 g/mm. For a 
control, the same photoreceptors were supported by shafts fixed to the 
copying machine main unit using a conventional support mechanism and the 
amount of distortion was measured in the same way. 
As a result, as shown in the table in FIG. 6, in the images created using 
photoreceptors supported by any of the support mechanisms pertaining to 
the present invention, the amounts of pitch distortion and edge distortion 
were considerably less than those in the images created using 
photoreceptors supported by the conventional fixed-type support mechanism 
(the control units). 
Next, the spring force of the spring in the support mechanism of the 
embodiment shown in FIG. 1 containing a spring was changed and the amount 
of pitch distortion was measured. The amount of pitch distortion was also 
measured using the support mechanism of the embodiment shown in FIG. 3 in 
which the spring is eliminated. For a control, the amount of pitch 
distortion was measured using the conventional fixed-type support 
mechanism. As a result, the desirable setting for the spring force of the 
spring was determined to be 300 gf, as shown in FIG. 7. Even where there 
was no spring, the amount of pitch distortion was reduced to the same 
extent as when there was a spring. However, it was confirmed that the 
amount of pitch distortion was larger with the conventional fixed-type 
support mechanism than with the support mechanisms pertaining to the 
present invention. 
Next, a prescribed number of copies were made of the original document 
using the support mechanism of the first embodiment, the support mechanism 
of the second embodiment, and the conventional fixed-type support 
mechanism, and the distribution of pitch distortion amounts was examined. 
As shown in FIG. 8(A), FIG. 8(B), FIG. 8(C), it was consequently 
determined that the pitch distortion using the support mechanism in which 
a spring is located on the photoreceptor flange side was the smallest and 
that the pitch distortion using the support mechanism in which a spring is 
located on the shaft side was the next smallest, while the pitch 
distortion using the conventional fixed-type support mechanism was the 
largest. 
Using the support mechanisms described above, where the center axis of the 
shaft is not aligned exactly with the center axis of the rotating member, 
since the pierced hole into which the shaft is inserted of the second 
rotation transmission member of said support mechanism is slightly larger 
than the shaft, this misalignment is absorbed by the space between said 
pierced hole and the shaft, and as a result the center axis of the 
rotating member is corrected to be in the position where it should be, and 
the rotating member can be rotated without unevenness. 
Further, the second rotation transmission member may be used either in the 
photoreceptor bearing or around the shaft. It is also desirable for the 
support mechanism of the present invention to include a control member 
that controls the movement of the second rotation transmission member 
located around the shaft such that it extends along its length and an 
elastic means that applies force to the second rotation transmission 
member toward the control member. 
Although the present invention has been fully described by way of examples 
with reference to the accompanying drawings, it is to be noted that 
various changes and modification will be apparent to those skilled in the 
art. Therefore, unless otherwise such changes and modifications depart 
from the scope of the present invention, they should be construed as being 
included therein.