U.S. patent application number 13/795279 was filed with the patent office on 2013-10-03 for planetary gear assembly, drive unit including the planetary gear assembly, and image forming apparatus including the drive unit, and installation method for planetary gear assembly.
This patent application is currently assigned to Ricoh Company, Ltd.. The applicant listed for this patent is Yasuhiro MAEHATA, Hiromichi MATSUDA, Katsuaki MIYAWAKI, Keisuke SHIMIZU, Tetsuo WATANABE. Invention is credited to Yasuhiro MAEHATA, Hiromichi MATSUDA, Katsuaki MIYAWAKI, Keisuke SHIMIZU, Tetsuo WATANABE.
Application Number | 20130260952 13/795279 |
Document ID | / |
Family ID | 47832981 |
Filed Date | 2013-10-03 |
United States Patent
Application |
20130260952 |
Kind Code |
A1 |
MATSUDA; Hiromichi ; et
al. |
October 3, 2013 |
PLANETARY GEAR ASSEMBLY, DRIVE UNIT INCLUDING THE PLANETARY GEAR
ASSEMBLY, AND IMAGE FORMING APPARATUS INCLUDING THE DRIVE UNIT, AND
INSTALLATION METHOD FOR PLANETARY GEAR ASSEMBLY
Abstract
A planetary gear mechanism includes a plurality of planetary
gears, an outer gear, a sun gear, a carrier, and a stick mount. The
outer gear meshes with the plurality of planetary gears. The sun
gear is coaxially disposed on the same axis as the outer gear and
transmits force to the planetary gears. The carrier rotatably
supports the plurality of planetary gears and is rotatably and
floatingly supported. The carrier includes a hole through which a
stick member penetrates in a direction of axis of rotation of the
carrier. The stick member penetrates through the hole and is
mounted on the stick mount. The stick mount is disposed opposite
the carrier. The outer gear and the sun gear are held such that one
of the outer gear and the sun gear does not rotate.
Inventors: |
MATSUDA; Hiromichi;
(Kanagawa, JP) ; MIYAWAKI; Katsuaki; (Kanagawa,
JP) ; WATANABE; Tetsuo; (Kanagawa, JP) ;
MAEHATA; Yasuhiro; (Tokyo, JP) ; SHIMIZU;
Keisuke; (Tokyo, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
MATSUDA; Hiromichi
MIYAWAKI; Katsuaki
WATANABE; Tetsuo
MAEHATA; Yasuhiro
SHIMIZU; Keisuke |
Kanagawa
Kanagawa
Kanagawa
Tokyo
Tokyo |
|
JP
JP
JP
JP
JP |
|
|
Assignee: |
Ricoh Company, Ltd.
Tokyo
JP
|
Family ID: |
47832981 |
Appl. No.: |
13/795279 |
Filed: |
March 12, 2013 |
Current U.S.
Class: |
475/346 ;
29/893.1 |
Current CPC
Class: |
F16H 57/08 20130101;
Y10T 29/49464 20150115; F16H 1/28 20130101; F16H 2057/0062
20130101; G03G 15/757 20130101; F16H 1/46 20130101; G03G 21/1647
20130101; F16H 1/2827 20130101; F16H 57/082 20130101 |
Class at
Publication: |
475/346 ;
29/893.1 |
International
Class: |
F16H 1/28 20060101
F16H001/28; F16H 57/08 20060101 F16H057/08 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 3, 2012 |
JP |
2012-085066 |
Claims
1. A planetary gear mechanism, comprising: a plurality of planetary
gears; an outer gear to mesh with the plurality of planetary gears;
a sun gear coaxially disposed on the same axis as the outer gear,
to transmit force to the planetary gears; a carrier to rotatably
support the plurality of planetary gears, the carrier rotatably and
floatingly supported and including a hole through which a stick
member penetrates in a direction of axis of rotation of the
carrier; and a stick mount on which the stick member penetrating
through the hole is mounted, the stick mount disposed opposite the
carrier, one of the outer gear and the sun gear being unrotatably
held.
2. The planetary gear mechanism according to claim 1, wherein the
hole of the carrier is formed at the center of rotation of the
carrier, and the sun gear includes the stick mount on a plane
facing the carrier in an axial center thereof.
3. The planetary gear mechanism according to claim 1, further
comprising a gear mount to which one of the sun gear and the outer
gear is fixed, the gear mount including a plane facing the carrier,
wherein the carrier includes a plurality of the holes evenly formed
on a circumference of a lateral surface of the carrier, wherein the
gear mount includes a plurality of the stick mounts on the plane
facing the carrier.
4. The planetary gear mechanism according to claim 1, wherein a
clearance is provided between the stick member and the hole, and
the clearance does not allow the carrier to tilt relative to a
direction of insert of the stick member.
5. The planetary gear mechanism according to claim 1, wherein one
of the stick mount and the tip of the stick member includes a
conical concavity, and another of the stick mount and the tip of
the stick member has a conical convex shape, wherein the tip of the
stick member is fitted to the stick mount.
6. The planetary gear mechanism according to claim 1, further
comprising a plurality of groups of the sun gear, the outer gear,
the planetary gears, and the carrier, wherein the plurality of
groups is disposed in series in the axial direction, wherein the
outer gears have the same number of teeth and are constituted as a
single integrated member common to each group and fixed
unrotatably.
7. The planetary gear mechanism according to claim 6, wherein the
position of the hole in the carrier is the same for all groups.
8. The planetary gear mechanism according to claim 1, wherein the
hole is formed at the center of rotation of the carrier, and the
sun gear includes the stick mount on a plane facing the carrier in
the axial center, wherein the stick member has a noncircular shape
in cross section, and the hole of the carrier has a noncircular
shape to allow the stick member to fit therein.
9. The planetary gear mechanism according to claim 1, wherein the
stick member has a rounded rectangular shape in cross section, and
the hole of the carrier has a rounded rectangular shape to allow
the stick member to fit therein.
10. The planetary gear mechanism according to claim 1, wherein the
hole of the carrier has a tubular shape extending in the direction
of insert of the stick member.
11. A drive transmission unit, comprising: a drive source; the
planetary gear mechanism of claim 1 including an output shaft; and
a shaft to support a target to be driven and transmit rotary force
output from the output shaft of the planetary gear mechanism to the
target.
12. An image forming apparatus, comprising: a plurality of targets
to be driven; and the drive transmission unit of claim 11 to drive
at least one of the plurality of targets.
13. A method for assembling a planetary gear mechanism, the
planetary gear mechanism comprising: a plurality of planetary
gears; an outer gear to mesh with the plurality of planetary gears;
a sun gear to transmit force to the planetary gears, the sun gear
coaxially disposed on the same axis as the outer gear; a carrier to
rotatably support the plurality of planetary gears, the carrier
rotatably and floatingly supported and including a hole through
which a stick member penetrates in a direction of axis of rotation
of the carrier; and a stick mount on which the stick member
penetrating through the hole is mounted, the stick mount disposed
opposite the carrier, one of the outer gear and the sun gear being
unrotatably held, the method comprising: inserting the stick member
to the hole of the carrier; mounting the stick member at the stick
mount; meshing the plurality of planetary gears with the sun gear
and the outer gear by moving the carrier along the stick member, to
mount the carrier in the outer gear; and removing the stick member
after carrier is mounted.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This patent application is based on and claims priority
pursuant to 35 U.S.C. .sctn.119 to Japanese Patent Application No.
2012-085066, filed on Apr. 3, 2012, in the Japan Patent Office, the
entire disclosure of which is hereby incorporated by reference
herein.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] Exemplary aspects of the present invention generally relate
to a planetary gear assembly, a drive unit including the planetary
gear assembly, and an image forming apparatus including the drive
unit, and a method for assembling the planetary gear assembly.
[0004] 2. Description of the Related Art
[0005] Related-art image forming apparatuses, such as copiers,
facsimile machines, printers, or multifunction printers having at
least one of copying, printing, scanning, and facsimile
capabilities, typically form an image on a recording medium
according to image data. Thus, for example, a charger uniformly
charges a surface of an image bearing member (which may, for
example, be a photoconductive drum); an optical writer projects a
light beam onto the charged surface of the image bearing member to
form an electrostatic latent image on the image bearing member
according to the image data; a developing device supplies toner to
the electrostatic latent image formed on the image bearing member
to render the electrostatic latent image visible as a toner image;
the toner image is directly transferred from the image bearing
member onto a recording medium or is indirectly transferred from
the image bearing member onto a recording medium via an
intermediate transfer member; a cleaning device then cleans the
surface of the image carrier after the toner image is transferred
from the image carrier onto the recording medium; finally, a fixing
device applies heat and pressure to the recording medium bearing
the unfixed toner image to fix the unfixed toner image on the
recording medium, thus forming the image on the recording
medium.
[0006] Known image forming apparatuses employ a planetary gear
assembly to transmit power from a drive source to a target to be
rotated, i.e., a rotary member such as a photosensitive member. An
example of the planetary gear assembly includes a carrier that is
rotatably and floatingly supported in an outer gear.
[0007] In such a configuration in which the carrier is floatingly
supported, planetary gears may not properly mesh with the gear
teeth of the outer gear or a sun gear, and tooth meshing errors
occur. More specifically, the center tooth of the planetary gear
meshing with the sun gear among other plurality of planetary gears
is located at a position 180.degree. away from the center tooth of
the planetary gear meshing with the outer gear in the direction of
rotation of the planetary gears. When assembled properly, the
number of the center tooth of the planetary gear meshing with the
sun gear is half the total number of gear teeth of the planetary
gear when counting from the center tooth meshing with the outer
gear. By contrast, when assembled improperly, that is, when the
tooth meshing errors occur, the number of the center tooth of the
planetary gear meshing with the sun gear is not half the total
number of gear teeth of the planetary gear when counting from the
center tooth of the planetary gear meshing with the outer gear.
[0008] When such tooth meshing errors occur, the carrier supporting
the planetary gears is slightly tilted in the outer gear. In a case
in which the carrier is supported by a shaft bearing in the outer
gear, the outer circumferential surface of the carrier is fitted to
the inner circumferential surface of the shaft bearing, and hence
the carrier does not tilt in the outer gear. By contrast, when
supporting the carrier floatingly, assembly of the gear is
completed with the carrier being mounted obliquely. As a result,
tooth meshing errors occur.
[0009] When the tooth meshing errors occur, the planetary gears
receive uneven loads, hindering proper transmission of power, which
results in various problems such as degradation of imaging quality,
noise, and damage to devices.
SUMMARY OF THE INVENTION
[0010] In view of the foregoing, in an aspect of this disclosure,
there is provided an improved planetary gear mechanism including a
plurality of planetary gears, an outer gear, a sun gear, a carrier,
and a stick mount. The outer gear meshes with the plurality of
planetary gears. The sun gear is coaxially disposed on the same
axis as the outer gear and transmits force to the planetary gears.
The carrier rotatably supports the plurality of planetary gears and
is rotatably and floatingly supported. The carrier includes a hole
through which a stick member penetrates in a direction of axis of
rotation of the carrier. The stick member penetrates through the
hole and is mounted on the stick mount. The stick mount is disposed
opposite the carrier. The outer gear and the sun gear are held such
that one of the outer gear and the sun gear does not rotate.
[0011] In another aspect of this disclosure there is provided a
method for assembling a planetary gear mechanism. The planetary
gear mechanism includes a plurality of planetary gears, an outer
gear, a sun gear, a carrier, and a stick mount. The outer gear
meshes with the plurality of planetary gears. The sun gear is
coaxially disposed on the same axis as the outer gear and transmits
force to the planetary gears. The carrier rotatably supports the
plurality of planetary gears and is rotatably and floatingly
supported. The carrier includes a hole through which a stick member
penetrates in a direction of axis of rotation of the carrier. The
stick member penetrates through the hole and is mounted on the
stick mount. The stick mount is disposed opposite the carrier. The
outer gear and the sun gear are held such that one of the outer
gear and the sun gear does not rotate. The method includes
inserting the stick member to the hole of the carrier; mounting the
stick member at the stick mount; meshing the plurality of planetary
gears with the sun gear and the outer gear by moving the carrier
along the stick member, to mount the carrier in the outer gear; and
removing the stick member after carrier is mounted.
[0012] The aforementioned and other aspects, features and
advantages would be more fully apparent from the following detailed
description of illustrative embodiments, the accompanying drawings
and the associated claims.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
[0013] A more complete appreciation of the disclosure and many of
the attendant advantages thereof will be more readily obtained as
the same becomes better understood by reference to the following
detailed description of illustrative embodiments when considered in
connection with the accompanying drawings, wherein:
[0014] FIG. 1 is a schematic diagram illustrating a printer as an
example of the image forming apparatus according to an illustrative
embodiment of the present invention;
[0015] FIG. 2 is a cross-sectional view schematically illustrating
a planetary gear mechanism for rotating a photosensitive drum
employed in the image forming apparatus of FIG. 1;
[0016] FIG. 3 is a cross-sectional view schematically illustrating
a first stage of the planetary gear mechanism of FIG. 2;
[0017] FIG. 4 is a cross-sectional view schematically illustrating
a second stage of the planetary gear mechanism of FIG. 2;
[0018] FIG. 5 is a schematic diagram illustrating the planetary
gear mechanism and a supporting structure for the photosensitive
drum in a process cartridge;
[0019] FIG. 6 is a diagram illustrating an example of a design of a
planetary gear mechanism;
[0020] FIG. 7 is an enlarged diagram schematically illustrating a
configuration near a first planetary gear;
[0021] FIG. 8 is a schematic diagram illustrating inclination of
the gear upon assembly;
[0022] FIG. 9 is a perspective view schematically illustrating a
first carrier and a second sun gear;
[0023] FIG. 10 is a front view schematically illustrating the first
carrier as viewed from a first sun gear;
[0024] FIG. 11 is a cross-sectional view schematically illustrating
the first carrier and the second sun gear;
[0025] FIG. 12 is a front view schematically illustrating the first
sun gear;
[0026] FIG. 13 is a perspective view schematically illustrating the
first carrier mounted on an outer gear;
[0027] FIG. 14A is a cross-sectional view schematically
illustrating a guide stick mounted on a positioning portion
provided to the first sun gear;
[0028] FIG. 14B is a cross-sectional view schematically
illustrating a variation of the guide stick mounted on a
positioning portion provided to the first sun gear;
[0029] FIG. 15 is a perspective view schematically illustrating the
first carrier and the second carrier of a first variation of the
planetary gear mechanism;
[0030] FIG. 16 is a front view schematically illustrating the first
carrier of a second variation of the planetary gear mechanism as
viewed from the first sun gear; and
[0031] FIG. 17 is a front view schematically illustrating the first
sun gear of the second variation of the planetary gear
mechanism.
DETAILED DESCRIPTION OF THE INVENTION
[0032] A description is now given of illustrative embodiments of
the present invention. It should be noted that although such terms
as first, second, etc. may be used herein to describe various
elements, components, regions, layers and/or sections, it should be
understood that such elements, components, regions, layers and/or
sections are not limited thereby because such terms are relative,
that is, used only to distinguish one element, component, region,
layer or section from another region, layer or section. Thus, for
example, a first element, component, region, layer or section
discussed below could be termed a second element, component,
region, layer or section without departing from the teachings of
this disclosure.
[0033] In addition, it should be noted that the terminology used
herein is for the purpose of describing particular embodiments only
and is not intended to be limiting of this disclosure. Thus, for
example, as used herein, the singular forms "a", "an" and "the" are
intended to include the plural forms as well, unless the context
clearly indicates otherwise. Moreover, the terms "includes" and/or
"including", when used in this specification, specify the presence
of stated features, integers, steps, operations, elements, and/or
components, but do not preclude the presence or addition of one or
more other features, integers, steps, operations, elements,
components, and/or groups thereof.
[0034] In describing illustrative embodiments illustrated in the
drawings, specific terminology is employed for the sake of clarity.
However, the disclosure of this patent specification is not
intended to be limited to the specific terminology so selected, and
it is to be understood that each specific element includes all
technical equivalents that operate in a similar manner and achieve
a similar result.
[0035] In a later-described comparative example, illustrative
embodiment, and alternative example, for the sake of simplicity,
the same reference numerals will be given to constituent elements
such as parts and materials having the same functions, and
redundant descriptions thereof omitted.
[0036] Typically, but not necessarily, paper is the medium from
which is made a sheet on which an image is to be formed. It should
be noted, however, that other printable media are available in
sheet form, and accordingly their use here is included. Thus,
solely for simplicity, although this Detailed Description section
refers to paper, sheets thereof, paper feeder, etc., it should be
understood that the sheets, etc., are not limited only to paper,
but include other printable media as well.
[0037] Referring now to the drawings, wherein like reference
numerals designate identical or corresponding parts throughout the
several views, and initially with reference to FIG. 1, a
description is provided of an image forming apparatus according to
an aspect of this disclosure.
[0038] A description is provided of an electrophotographic color
copier as an example of an image forming apparatus. It is to be
noted that the image forming apparatus according to the
illustrative embodiment is a tandem-type image forming apparatus
using a two-component, dry developing agent.
[0039] FIG. 1 is a schematic diagram illustrating a copier as an
example of the image forming apparatus according to the
illustrative embodiment of the present invention.
[0040] The image forming apparatus receives image data including
image information from an image reading unit and performs image
forming operation. As illustrated in FIG. 1, the image forming
apparatus includes four photosensitive drums 1Y, 1M, 1C, and 1Bk
each serving as a latent image bearing member, arranged in tandem
along an intermediate transfer belt 5.
[0041] It is to be noted that the suffixes Y, M, C, and Bk denote
colors yellow, magenta, cyan, and black, respectively. To simplify
the description, the suffixes Y, M, C, and Bk indicating colors are
omitted herein, unless otherwise specified.
[0042] The intermediate transfer belt 5 is formed into a loop and
entrained around a plurality of rollers including a drive roller.
The photosensitive drums 1Y, 1M, 1C, and 1Bk are arranged in tandem
along the direction of movement of the intermediate transfer belt 5
and contact the intermediate transfer belt 5. The photosensitive
drums 1Y, 1M, 1C, and 1Bk are surrounded by various imaging
equipment. For example, charging devices 2Y, 2M, 2C, and 2Bk,
developing devices 9Y, 9M, 9C, and 9Bk, cleaning devices 4Y, 4M,
4C, and 4Bk, and charge erasing lamps 3Y, 3M, 3C, and 3Bk are
respectively provided around the photosensitive drums 1Y, 1M, 1C,
and 1Bk in the order of electrophotographic process. The
photosensitive drum 1, the charging device 2, the charge erasing
lamp 3, the cleaning device 4, and the developing device 9
constitute a single integrated process cartridge detachably
attachable relative to a main body of the image forming
apparatus.
[0043] According to the illustrative embodiment, when forming a
color image, the photosensitive drum 1Y is rotated in the direction
indicated by an arrow by a photosensitive drum driving device
described later and charged uniformly by the charging device 2Y
while rotating. Subsequently, the photosensitive drum 1Y is
illuminated with a light beam LY from an optical writing unit,
thereby forming an electrostatic latent image corresponding to the
color of yellow on the surface of the photosensitive drum 1Y. The
electrostatic latent image of yellow on the photosensitive drum 1Y
is developed with yellow toner by the developing device 9Y, thereby
forming a visible image, also known as a toner image. Upon
development, a predetermined developing bias is supplied between a
developing roller of the developing device 9Y and the
photosensitive drum 1Y so that the yellow toner on the developing
roller is attracted electrostatically to the electrostatic latent
image on the photosensitive drum 1Y.
[0044] Subsequently, as the photosensitive drum 1Y rotates, the
toner image of yellow formed on the surface of the photosensitive
drum 1Y arrives at a primary transfer position at which the
photosensitive drum 1Y contacts the intermediate transfer belt 5.
At the primary transfer position, the predetermined bias voltage is
supplied to the rear surface of the intermediate transfer belt 5 by
a primary transfer roller 6Y disposed inside the looped
intermediate transfer belt 5, across from the photosensitive drum
1Y. Application of the bias voltage generates a primary transfer
electric field which causes the yellow toner image on the
photosensitive drum 1Y to move to the intermediate transfer belt 5.
This process is known as primary transfer.
[0045] Similar to the toner image of yellow, toner images of
magenta, cyan, and black are formed on the photosensitive drums 1M,
1C, and 1Bk, respectively, and transferred onto the intermediate
transfer belt 5 such that they are superimposed one atop the other.
Accordingly, a composite toner image is formed on the intermediate
transfer belt 5.
[0046] Subsequently, the composite toner image formed on the
intermediate transfer belt 5 is delivered to a secondary transfer
position facing a secondary transfer roller 7, as the intermediate
transfer belt 5 rotates. A transfer sheet such as a recording
medium is fed to the secondary transfer position by a pair of
registration rollers in appropriate timing such that the transfer
sheet is aligned with the composite toner image formed on the
intermediate transfer belt 5. At the secondary transfer position,
the secondary transfer roller 7 supplies a predetermined bias
voltage to the rear surface of the transfer sheet, thereby
generating a secondary transfer electric field. The toner image on
the intermediate transfer belt 5 is transferred onto the transfer
sheet due to the secondary electric field and pressure applied at
the secondary transfer position.
[0047] Subsequently, the transfer sheet, on which the composite
toner image is secondarily transferred, is delivered between a pair
of fixing rollers 8. The toner image is fixed onto the transfer
sheet by heat and pressure applied by the pair of the fixing
rollers 8 as the transfer sheet passes between the fixing rollers
8. After the fixing process, the transfer sheet is output outside
the image forming apparatus.
[0048] With reference to FIGS. 2 through 4, a description is
provided of a drive transmission unit that transmits rotary drive
power from a motor 60 serving as a drive source to the
photosensitive drums 1. FIG. 2 is a cross-sectional view
schematically illustrating the drive transmission unit. FIG. 3 is a
cross-sectional view schematically illustrating a first stage of a
planetary gear mechanism of the drive transmission unit. FIG. 4 is
a cross-sectional view schematically illustrating a second stage of
the planetary gear mechanism.
[0049] A planetary gear decelerator employed in the drive
transmission unit illustrated in FIG. 2 employs a two-stage 2K-H
type planetary gear mechanism. The planetary gear decelerator can
be used in the drive transmission unit for the driving roller of
the intermediate transfer belt 5, the fixing roller, and so
forth.
[0050] In the image forming apparatus, when the planetary gear
mechanism is employed as the drive transmission unit for the
photosensitive drum having a diameter approximately in a range of
from 30 mm to 100 mm, which is a typical photosensitive drum, a
deceleration ratio of approximately 1/20 is required. According to
the present illustrative embodiment, such a relatively large
deceleration ratio can be achieved by using the two-stage 2K-H type
planetary gear mechanism described above as the drive transmission
unit.
[0051] With reference to FIG. 2, a description is provided of the
planetary gear mechanism according to an illustrative embodiment of
the present invention. As illustrated in FIG. 2, the planetary gear
mechanism includes a first sun gear 12 integrally formed on a
rotary shaft M1 of the motor 60, a gear mount 24 such as a flange,
an outer gear 14, first planetary gears 15 of a first stage, a
first carrier 16 of the first stage, and so forth. The outer gear
14 is fixed to the gear mount 24. The first planetary gears 15 mesh
with the first sun gear 12 and the outer gear 14 fixed to the gear
mount 24. The first planetary gears 15 are supported by the first
carrier 16 and revolve around the periphery of the sun gear 12.
According to the present illustrative embodiment, as illustrated in
FIG. 3, at least three first planetary gears 15-1, 15-2, and 15-3
(collectively referred to as first planetary gears 15) are
concentrically disposed for rotation balance and load dispersal.
The first planetary gears 15-1, 15-2, and 15-3 are disposed at each
of three positions of an evenly divided circumference.
[0052] The number of planetary gears is not limited to three. More
than three planetary gears can be used.
[0053] The plurality of first planetary gears 15 meshes with the
first sun gear 12 and the outer gear 14 so that each of the first
planetary gears 15 rotates while revolving around the first sun
gear 12. The first carrier 16 supporting the first planetary gears
15 rotates slower than the first sun gear 12, thereby obtaining the
desired deceleration ratio of the first stage.
[0054] A second sun gear 17 serves as a sun gear for the second
stage and as an input for the second stage of the deceleration
mechanism. The second sun gear 17 is provided at the center of
rotation of the first carrier 16. It is to be noted that the first
carrier 16 does not include a rotary supporting portion, thereby
allowing the first carrier 16 to float (rotate) freely.
[0055] Similar to the first planetary gears 15, a plurality of
second planetary gears 18-1, 18-2, 18-3, and 18-4 (collectively
referred to as second planetary gears 18) serving as planetary
gears for the second stage meshes with the outer gear 14 and is
supported by a second carrier 19 of the second stage. The outer
gear of the first stage and the outer gear of the second stage are
constituted as a single integrated unit as the outer gear 14. The
plurality of second planetary gears 18 revolves around the
periphery of the second sun gear 17. According to the present
illustrative embodiment, as illustrated in FIG. 4, the second
planetary gears 18-1, 18-2, 18-3, and 18-4 are disposed at each of
four positions of an evenly divided circumference.
[0056] Alternatively, similar to the first stage, the plurality of
the second planetary gears 18 may be concentrically and evenly
disposed at each of three positions. The second carrier 19 of the
second stage which is the last stage is provided with an output
portion including a cylindrical-shaped shaft 20 serving as an
output axis, the inner surface of which includes spline teeth. The
gear of the second stage directly receives the rotational load of
the cylindrical-shaped shaft 20. In order to enhance durability, as
illustrated in FIG. 4, the number of planetary gears provided to
the second stage, that is, the number of the second planetary gears
18, is greater than the number of the first planetary gears
provided to the first stage.
[0057] As will be described later, a drum shaft 70 penetrates
through the process cartridge to support the photosensitive drum 1.
The drum shaft 70 includes a spline portion 21 serving as an output
portion having spline teeth on an outer surface thereof to mesh
with the inner teeth (spline teeth) of the cylindrical-shaped shaft
20.
[0058] According to the above-described illustrative embodiment, a
set of four kinds of parts, the sun gear, the planetary gear, the
planetary carrier for supporting revolution of the planetary gears,
and the outer gear, constitutes the 2K-H type planetary gear
mechanism.
[0059] One of three elements of rotation, that is, one of rotation
of the sun gear, revolution of the planetary gear (rotation of the
carrier), and rotation of the outer gear, is fixed, and remaining
two gears are each connected to the input and the output. With this
configuration, the deceleration ratio and the direction of rotation
can be switched between different deceleration ratios and
directions of rotation depending on designation of each element,
that is, according to which gear is fixed and which gear is
connected to the input or the output.
[0060] The two-stage 2K-H type planetary gear mechanism is
classified as a composite planetary gear mechanism including at
least two sets of 2K-H type planetary gear mechanisms. In the
composite planetary gear mechanism, among three elements, the gears
having the same element are either connected or fixed. The
remaining two elements are each connected to the input and the
output.
[0061] The planetary gear mechanism of the illustrative embodiment
is a planetary type mechanism in which the outer gear is fixed, the
sun gear serves as the input axis, and the carrier serves as the
output axis. The direction of rotation of the input axis is the
same as that of the output axis.
[0062] More specifically, power from the motor 60 is transmitted
from the motor shaft M1 to the first sun gear 12, thereby rotating
the first sun gear 12. Due to rotation of the first sun gear 12,
three first planetary gears 15-1, 15-2, and 15-3 engaging the first
sun gear 12 themselves rotate while revolving around the first sun
gear 12. Due to revolution of the first planetary gears 15-1, 15-2,
and 15-3 around the first sun gear 12, a decelerated driving force
is transmitted to the first carrier 16, thereby rotating the first
carrier 16 and hence causing the second sun gear 17 provided to the
first carrier 16 to rotate. Subsequently, power is transmitted to
the four second planetary gears 18-1, 18-2, 18-3, and 18-4 engaging
the second sun gear 17. Accordingly, the second planetary gears
18-1, 18-2, 18-3, and 18-4 themselves rotate while revolving around
the second sun gear 17. Due to revolution of the second planetary
gears 18-1, 18-2, 18-3, and 18-4, the driving force is decelerated
and transmitted to the second carrier 19 and then to the
photosensitive drum 1 via the cylindrical-shaped shaft 20 and the
drum shaft 70 provided to the second carrier 19. Accordingly, the
photosensitive drum 1 is rotated at a predetermined speed.
[0063] The deceleration ratio of a single-stage planetary gear
mechanism is expressed by the following equation:
Deceleration Ratio=Za1/(Za1+Zc1),
where Za is a number of teeth of the sun gear, Zb is a number of
teeth of the planetary gear, and Zc is a number of teeth of the
outer gear. In the equation, "1" represents the first stage.
[0064] The deceleration ratio of a planetary gear mechanism having
two stages is a product of the deceleration ratio of the first
stage and that of the second stage. Both the first and the second
stages of the planetary gear mechanism of the illustrative
embodiment are the planetary type. Thus, the deceleration ratio is
expressed by the following equation:
Deceleration Ratio=Za1/(Za1+Zc1).times.Za2/(Za2+Zc2)
[0065] In this equation, "1" represents the first stage and "2"
represents the second stage.
[0066] It is to be noted that the rotary shaft M1 of the motor 60
is supported by a motor mount 13 via two shaft bearings. The motor
mount 13 may be a flange.
[0067] By supporting the rotary shaft M1 of the motor 60, an outer
rotor of a brush-less direct current (DC) motor is also supported.
A stator core of the motor 60, a motor driving circuit, and so
forth are also disposed on the motor mount 13.
[0068] The first sun gear 12 is formed on the rotary shaft M1 of
the motor 60 by cutting. In order to secure coaxial accuracy of the
shaft of the first sun gear 12 and the shaft of the outer gear 14,
the outer gear 14 and the motor mount 13 are positioned in place by
being fitted together. Furthermore, the motor mount 13 is
positioned in place by being fitted to the gear mount 24.
[0069] An end cap 22 is fixed to one end portion of the outer gear
14 opposite the motor mount 13. The end cap 22 is used to prevent
the first planetary gears 15, the second planetary gears 18, the
first carrier 16, the second carrier 19, and the cylindrical-shaped
shaft 20 from falling off from the outer gear 14 when the planetary
gear decelerator is mounted on a lateral plate 127 at the motor
side. There is a clearance between the end cap 22 and the
cylindrical-shaped shaft 20 of the second carrier 19. More
specifically, the end cap 22 does not rotatably support the second
carrier 19 but instead allows the second carrier 19 to float
(rotate) freely.
[0070] With reference to FIG. 5, a description is provided of
support of the photosensitive drum 1 in the process cartridge
detachably attachable relative to the main body of the image
forming apparatus. FIG. 5 is a cross-sectional view schematically
illustrating the photosensitive drum 1Y as a representative example
of the photosensitive drums and the planetary gear decelerator
supporting the photosensitive drum according to the illustrative
embodiment of the present invention.
[0071] It is to be noted that the photosensitive drums 1Y, 1M, 1C,
and 1Bk all have the same configuration as all the others,
differing only in the color of toner employed. Thus, the
description is only provided of a driving device for the
photosensitive drum 1Y. The driving device may be applied to the
driving roller of the intermediate transfer belt 5, the fixing
roller, and so forth.
[0072] As illustrated in FIG. 5, a rear drum flange 115 and a front
drum flange 114 are fixed to each end portion of the photosensitive
drum 1Y in the axial direction thereof. The drum shaft 70 disposed
at the main body side penetrates through the rear drum flange 115
and the front drum flange 114 so that the flanges 114 and 115 are
supported by the drum shaft 70. The rear drum flange 115 is
connected to the drum shaft 70 by a serration coupling 116. The
photosensitive drum 1Y rotates in sync with rotation of the drum
shaft 70. The serration coupling 116 has a male end at the drum
shaft side and a female end at the drum flange side (the rear drum
flange 115). The serration coupling 116 tapers toward the drum
flange 115.
[0073] A housing 117 that supports the photosensitive drum 1Y
houses the photosensitive drum 1Y, the charging device 2Y, the
developing device 9Y, the cleaning device 4Y, and the charge
erasing lamp (not illustrated), and so forth. As illustrated in
FIG. 5, the rear side (right side in FIG. 5) of the housing 117 is
supported by a shaft bearing 123a which is one of the shaft
bearings 123a and 123b (collectively referred to as shaft bearings
123) fixed to the drum shaft 70 interposing a collar 124
therebetween. The rear drum flange 115 is also supported by the
shaft bearing 123a. In this configuration, the rear side of the
housing 117 and the rear drum flange 115 are supported by the shaft
bearing 123a so that the photosensitive drum 1Y is aligned with the
housing 117. The front drum flange 114 includes a boss 128
rotatably fitted with the housing 117 at the front side thereof
(left side in FIG. 5).
[0074] The shaft bearing 123b is provided to the drum shaft 70 at
the place at which the drum shaft 70 is fitted to a main-body rear
lateral plate 119. Accordingly, the drum shaft 70 is aligned with
the rear lateral plate 119. A main-body front lateral plate 110
includes a notch at which a face plate 111 is fixed. The front end
of the drum shaft 70 is rotatably supported by the face plate 111
via a shaft bearing 112.
[0075] The process cartridge can be detached by removing the face
plate 111. In an installed state in which the process cartridge is
mounted, the photosensitive drum 1Y is pressed in the direction of
the drum shaft by a pressing spring 113 disposed between the shaft
bearing 112 fixed to the face plate 111 and the boss 128 of the
front drum flange 114. Accordingly, the rotation direction and the
thrust direction of the photosensitive drum 1Y are positioned in
place at the tapered serration coupling 116. The housing 117
includes two positioning pins 118 at the rear side thereof. The
positioning pins 118 are fitted into holes formed in the main-body
rear lateral plate 119 so that the process cartridge in the
direction of rotation is positioned in place.
[0076] Still referring to FIG. 5, a description is provided of
installation of the planetary gear mechanism.
[0077] The lateral plate 127 of the motor side is attached to the
main-body rear lateral plate 119 via studs 126. The gear mount 24
that supports the planetary gear mechanism is fixed to the lateral
plate 127 at the motor side. The planetary gear mechanism is
positioned in place by fitting the outer gear 14 into a hole formed
in the lateral plate 127. Alternatively, the planetary gear
mechanism is installed such that the lateral plate 127 serves also
as the gear mount 24. As the planetary gear mechanism is attached
to the lateral plate 127 at the motor side, the output side of the
outer gear 14 becomes free and therefore easily deformed.
Alternatively, the outer gear 14 may be fixed to the motor mount 13
without the gear mount 24.
[0078] Precise control of rotation speed of the photosensitive drum
1 and the intermediate transfer belt 5 is required. More
specifically, the photosensitive drum 1 and the intermediate
transfer belt 5 are rotated at a precise constant speed. If the
speed of rotation of the photosensitive drum 1 and the intermediate
transfer belt 5 fluctuates, imaging failure such as jitter and
unevenness of image density occurs. Furthermore, if the rotation
speed continues to fluctuate at a certain frequency, unevenness of
image density appears periodically over the entire image as banding
or stripes on an output image.
[0079] Fluctuation of the rotation speed of the photosensitive drum
1 in particular causes an optical writing system sub-scanning
exposure misalignment. At the same time, the fluctuation of the
rotation speed of the photosensitive drum 1 causes deviation of the
sub-scanning position on the intermediate transfer belt 5 at
primary transfer. Fluctuation of the rotation speed of the
intermediate transfer belt 5 in return causes deviation of
sub-scanning position both at the primary transfer and the
secondary transfer. The banding derived from such fluctuation of
the rotation speed degrades imaging quality significantly.
[0080] An allowable range of speed fluctuation based on banding of
an image is equal to or less than approximately .+-.0.3%
Peak-to-Peak in a bandwidth between 0 and 200 Hz to achieve precise
operation, which is higher by one digit than a known planetary gear
decelerator for a positioning purpose. In view of the above, a
module of each gear constituting the planetary gear mechanism is
0.3 (approximately 0.9 mm for one tooth pitch). In this
configuration, a gear mesh frequency can be 200 Hz or higher,
thereby making the speed fluctuation of the gear mesh frequency
within the allowable range.
[0081] As a high-precision gear with a small gear module such as
0.3 and 0.4, a plastic gear manufactured by injecting a molten
resin into a mold is used. As compared with a metal gear, the
plastic gear itself has lubricating properties, hence generating
less noise during operation, and it is lightweight. Furthermore,
the plastic gear is highly resistant to corrosion and easy to
mass-produce.
[0082] Although advantageous, the plastic gear has some
disadvantages in terms of its durability, stiffness, and
tolerances. Thus, as will be described in detail later, according
to the illustrative embodiment, the planetary gear decelerator is
used to enhance durability and stiffness of the drive transmission
unit using the plastic gear. More specifically, the planetary gear
mechanism can increase durability and stiffness of the drive
transmission unit because output shaft rotational road is dispersed
and transmitted by a plurality of planetary gears. Furthermore,
employing the planetary gear mechanism as the drive transmission
unit can reduce gear size compared with a gear assembly using a
gear train.
[0083] FIG. 6 is a diagram illustrating an example of a design of
the planetary gear of the present illustrative embodiment.
[0084] The first sun gear 12 is formed on the motor shaft at the
center of the outer gear 14 which is unrotatably held. The first
planetary gears 15-1, 15-2 and 15-3 are disposed at each of three
positions equally spaced around the first sun gear 12. Each of the
first planetary gears 15-1, 15-2, and 15-3 is rotatably supported
by a carrier pin 16a fixed to the carrier 16.
[0085] Due to rotation of the first sun gear 12, the first
planetary gears 15-1, 15-2, and 15-3 engaging the first sun gear 12
themselves rotate while revolving around the first sun gear 12.
[0086] Revolution of the first planetary gears 15-1, 15-2, and 15-3
is output by the carrier 16. According to the present illustrative
embodiment shown in FIG. 6, the number of teeth Za of the first sun
gear 12 is 30 (Za=30), the number of teeth a of the first planetary
gears 15-1, 15-2 and 15-3 is 60 (Zb=60), and the number of teeth Zc
of the outer gear 14 is 150 (Zc=150), and the deceleration ratio is
1/6.
[0087] In the present illustrative embodiment, two planetary gear
mechanisms having the same configuration described above are
connected to constitute the planetary gear decelerator for driving
the photosensitive drums as illustrated in FIG. 2. Downsizing and
increased accuracy of the planetary gear decelerator can be
achieved by employing the gear module of 0.3. A known single-stage
gear decelerator uses a gear with a diameter of approximately 100
mm. By contrast, in the present illustrative embodiment, the pitch
diameter of the outer gear 14 is approximately 45 mm which is
approximately the same diameter as that of the photosensitive drum.
In this configuration, interference with other parts is
insignificant, and hence downsizing can be achieved.
[0088] In a standard image forming apparatus, when an image
formation process linear velocity is 360 mm/sec and the diameter of
the photosensitive drum is 60 mm, the number of rotations of the
shaft of the photosensitive drum (the output shaft of the planetary
gear mechanism) is 2 rotations per second. In this configuration,
the number of teeth of the outer gear 14 is 150, and the planetary
gear rotates twice per second while revolving. Accordingly, the
mesh frequency is 300 Hz. In this configuration, visibility of
banding in accordance with the mesh frequency is low and impact on
the image quality is insignificant.
[0089] However, the planetary gear mechanism with the carrier
supported floatingly and holding a small module gear, for example,
a gear having the gear module of 0.4 (tooth pitch=approximately 1.3
mm) and 0.3 (tooth pitch=approximately 0.9 mm) is difficult to
assemble. For example, when the carrier holding the plurality of
the planetary gears is mounted on the outer gear which has been
assembled with the sun gear, it is necessary to make sure that the
outer gear and the planetary gears, and the planetary gears and the
sun gear mesh properly. In a case in which the small-module gear
such as the one with the module of 0.4 (tooth pitch of
approximately 1.3 mm) and 0.3 (tooth pitch of approximately 0.9 mm)
is employed, if the carrier itself is inserted obliquely into the
outer gear, the teeth of gears do not mesh properly, that is, tooth
meshing errors occur.
[0090] With reference to FIG. 7, a description is provided of an
example of tooth meshing errors of the first planetary gear
15-1.
[0091] FIG. 7 is an enlarged diagram schematically illustrating a
configuration near the first planetary gear 15-1.
[0092] As illustrated in FIG. 7, the first planetary gear 15-1
meshes with the outer gear 14 at a mesh A (on a broken line) and
meshes with the sun gear 12 at a mesh B (on a broken line). The
mesh center of the mesh B is located precisely 180 degrees from the
mesh center of the mesh A. More specifically, in a case in which
the first planetary gear 15-1 meshes properly with the outer gear
14 at the mesh A and meshes properly with the sun gear 12 at the
mesh B, when a tooth of the first planetary gear 15-1 (having 60
teeth) at the center of the mesh A on the broken line in FIG. 7 is
presented as a first tooth (tooth 1) and each tooth is given a
consecutive number in the clockwise direction, the tooth of the
first planetary gear 15-1 at the mesh B on the broken line is the
31st tooth (tooth 31). However, tooth meshing errors occur due to
various reasons. The tooth of the first planetary gear 15-1 to mesh
with the tooth of the sun gear 12 may be the 30th tooth (tooth 30)
or the 32nd tooth (tooth 32). In this case, the planetary gear 15-1
is displaced by one tooth relative to the sun gear 12. This tooth
meshing error is hereinafter referred to as one-tooth shift.
[0093] Once assembled with one-tooth shift, the position of the
planetary gear 15-1 cannot be corrected to a proper meshing
position. In a case in which more than three planetary gears are
employed as in the present illustrative embodiment, if the
planetary gear 15-1 is assembled with one-tooth shift and other two
planetary gears 15-2 and 15-3 are mounted properly, adjustment of
only the planetary gear 15-1 by moving in the revolution direction
cannot be performed because the carrier 16 restricts relative
positions between the planetary gears.
[0094] Only the planetary gear 15-1 which is assembled with
one-tooth shift receives or does not receive transmission load. If
the planetary gear 15-1 does not receive transmission load, the
planetary gear 15-1 becomes an idle gear. As a result, load is
dispersed unevenly to each of the planetary gears. Furthermore, the
opposite side of the meshing tooth of the planetary gear 15-1
meshes with the sun gear 12, causing significant irregular rotation
and vibration. Furthermore, it results in degradation of
durability. In the image forming apparatus, such a power
transmission error causes various problems such as degradation of
imaging quality, noise, and damage to the planetary gears.
[0095] There are four known causes that lead to improper assembly
or the one-tooth shift of the planetary gears.
[0096] 1. Amount of backlash (backlash between the outer gear and
the planetary gear, between the planetary gear and the sun gear, a
sum of two mesh portions).
[0097] 2. Rattling of the planetary gear shaft (a clearance between
an internal diameter of the planetary gear and a carrier pin)
[0098] 3. Shape variations of parts (e.g., tooth profile deviations
and displacement of shafts)
[0099] 4. Inclination of a gear upon assembly (e.g., Inclination of
the carrier holding the planetary gear)
[0100] In the present illustrative embodiment, each of the sun
gear, the planetary gear, and the outer gear is made through
injection molding with precision so that the causes 1 through 3
alone cannot cause the one-tooth shift. Therefore, it is understood
that the one-tooth shift is mainly due to the inclination of a gear
described below.
[0101] First, in a case in which each gear with the module of 0.3
is made with an accuracy grade of Japan Industrial Standard
(hereinafter, JIS) 7 and JIS 8, the amount of backlash (i.e., the
cause No. 1 described above) between the outer gear and the
planetary gear is in a range of from approximately 70 .mu.m to
approximately 100 .mu.m. The amount of backlash between the
planetary gear and the sun gear is in a range of from approximately
50 .mu.m and approximately 80 .mu.m. The total amount of backlash
is in a range of from approximately 120 .mu.m and approximately 180
.mu.m.
[0102] Next, as for the clearance of the shaft of the planetary
gear (i.e., the cause No. 2), when the shaft bearing is made of
resin having a relatively large mold variation, the shaft clearance
of the planetary gear is in a range of from approximately 50 .mu.m
to 70 .mu.m. In a case in which the planetary gear shifts towards
one side relative to the shaft with the mesh-A side as a reference,
the amount of shift at the mesh-B side is in a range of from
approximately 100 .mu.m to approximately 140 .mu.m.
[0103] As for the shape variations of parts (i.e., the cause No.
3), due to cumulative pitch deviations and displacement of the
carrier pin when using the gears with the module of 0.3 made with
accuracy grade JIS 7 and JIS 8, the positional deviation at mesh
positions is in a range of from approximately 80 .mu.m to
approximately 100 .mu.m. In total, a deviation of 420 .mu.m at
maximum occurs at the mesh positions.
[0104] To produce the one-tooth shift, a deviation of one-tooth
pitch (approximately 900 .mu.m for Module 0.3) is required.
Therefore, it is understood that the inclination of the gear (i.e.,
the cause No. 4) upon assembly is most likely the main reason for
the one-tooth shift when a deviation of approximately 500 .mu.m or
greater occurs.
[0105] With reference to FIG. 8, a description is provided of
inclination of the gear, which is the main cause of the one-tooth
shift upon assembly. FIG. 8 is a schematic diagram illustrating the
inclination upon assembly.
[0106] As illustrated in FIG. 8, the position of the edge of teeth
deviates in accordance with an amount of inclination when
assembling the planetary gear 15 and the sun gear 12 by moving
these gears in the direction of arrow. When the gears tilt upon
assembly, the mesh position of the edge of the gear changes easily
in accordance with the amount of inclination, resulting in the
one-tooth shift.
[0107] In the present illustrative embodiment, the carrier 16 is
supported floatingly. In a case in which the sun gear 12 is
inserted into the fixed outer gear 14 to which the planetary gears
15 and the carrier 16 supporting the planetary gears 15 have been
mounted, the carrier 16 tilts easily together with the planetary
gears 15 because the carrier 16 is floatingly supported. In a case
in which the carrier 16 supporting the planetary gears 15 is
inserted to the fixed outer gear 14 to which the sun gear 12 has
been mounted, because the shaft bearing is not provided to the
carrier 16, the carrier 16 is inserted without its position being
held in place. In other words, the position and the orientation of
the carrier 16 are not determined, and hence the tilted carrier 16
is inserted, resulting in the one-tooth shift.
[0108] In view of the above, according to the illustrative
embodiment, the carrier 16 is guided by a stick-type guide member
33 (hereinafter referred to simply as guide stick) as illustrated
in FIG. 13 when the carrier 16 is mounted on the outer gear 14.
[0109] FIG. 9 is a perspective view schematically illustrating the
first carrier 16 and the second sun gear 17. FIG. 10 is an
elevational view schematically illustrating the first carrier 16 as
viewed from the first sun gear 12. FIG. 11 is a cross-sectional
view schematically illustrating the first carrier 16 and the second
sun gear 17.
[0110] According to the illustrative embodiment, the second sun
gear 17 and the first carrier 16 are constituted as a single molded
resin member through injection molding or the like. With this
configuration, the center of rotation of the first carrier 16 and
the center of rotation of the second sun gear 17 are coaxial,
thereby securing coaxial accuracy and increasing transfer
stiffness.
[0111] The first carrier 16 consists of two lateral plates 16c and
three supports 16d disposed equally spaced around the circumference
and between the lateral plates 16c, thereby connecting the lateral
plates 16c. The first planetary gears 15-1, 15-2 and 15-3 are
disposed between the supports 16d, and both ends of the carrier pin
16a supporting the planetary gear 15 are supported by the lateral
plates 16c of the carrier 16. The lateral plates 16c include holes
through which the carrier pins 16a are inserted. The first
planetary gears 15-1, 15-2 and 15-3, and the first carrier 16 are
assembled such that the first planetary gears 15 are disposed
between the supports 16d and then the carrier pins 16a are inserted
from the holes of one of the lateral plates 16c through the first
planetary gears 15 into the holes of the other lateral plate
16c.
[0112] To facilitate assembly of the first planetary gears 15-1,
15-2 and 15-3 and the first carrier 16, the first carrier 16 may be
constituted of two separable parts, that is, the lateral plate
including the second sun gear 17 and the lateral plate at the first
sun gear side. The lateral plate and the second sun gear 17 may be
constituted as a single molded member. In this case, after one end
of the carrier pin 16a constituted as a single integrated unit with
the first sun gear 15 is fitted into the hole of one of the lateral
plates 16c, the other end of the carrier pin 16a is fitted into the
hole of the other lateral plate 16c, connecting the first and the
second lateral plates via the supports 16d. Accordingly, the first
planetary gears 15 and the first carrier 16 are assembled.
[0113] As illustrated in FIG. 9, a single integrated body T
consisting of the second sun gear 17 and the first carrier 16
includes a tubular member 31 penetrating through the center of
rotation of the single integrated body T. As illustrated in FIG.
11, the tubular member 31 is supported by the second sun gear 17
via a rib 31a. As will be described later in detail, the internal
diameter of the tubular member 31 is slightly larger than the
diameter of the guide stick 33 inserted thereto, thereby preventing
the first carrier 16 from getting tilted (inclination in the
direction of assembly of the first carrier 16) due to a gap between
the guide stick 33 and the tubular member 31. The length of the
tubular member 31 (the length in the horizontal (left-right)
direction in FIG. 11) is equal to or greater than the tooth width
of the second sun gear 17, thereby suppressing, if not preventing
entirely the first carrier 16 from getting tilted due to a gap
between the guide stick 33 and the tubular member 31. Furthermore,
use of the guide stick 33 and the tubular member 31 upon assembly
of the second carrier 19 can prevent inclination of the second sun
gear 17.
[0114] FIG. 12 is a front view schematically illustrating the first
sun gear 12 according to the illustrative embodiment of the present
invention.
[0115] As illustrated in FIG. 12, the center of rotation of the
first sun gear 12 includes a guide positioning portion 32 including
a conical concavity (also shown in FIG. 14) to which the guide
stick 33 is fitted. In FIG. 12, the outer gear 14 is fixed to the
motor mount 13. Alternatively, the outer gear 14 may be fixed to
the gear mount 24.
[0116] Next, with reference to FIGS. 13 and 14, a description is
provided of assembly of the first carrier 16 (the single integrated
body T constituted of the first carrier 16 and the second sun gear
17).
[0117] FIG. 13 is a cross-sectional view schematically illustrating
the first carrier 16 being mounted in the outer gear 14. FIG. 14A
is a cross-sectional view schematically illustrating the guide
stick 33 fitted to the positioning portion 32 of the first sun gear
12.
[0118] First, as illustrated in FIG. 12, the outer gear 14 is fixed
to the motor mount 13 using screws 40. The first sun gear 12 is
inserted to the through hole formed at the center of the motor
mount 13. Subsequently, the motor 60 including the first sun gear
12 is screwed to the opposite side of the motor mount 13 to which
the outer gear 14 is fixed as illustrated in FIG. 2.
[0119] Next, the motor mount 13 to which the first sun gear 12 and
the outer gear 14 are fixed is set to a jig. Subsequently, as
illustrated in FIG. 14A, the guide stick 33 is inserted through the
tubular member 31 formed at the center of rotation of the first
carrier 16 and the second sun gear 17. As illustrated in FIG. 14A,
the guide stick 33 has a conical convex or pointed tip. The conical
convex or pointed tip of the guide stick 33 penetrating through the
first carrier 16 is mounted on the positioning portion 32 provided
at the center of rotation of the first sun gear 12.
[0120] According to the present illustrative embodiment, as
described above, the positioning portion 32 includes a conical
concavity, and the guide stick 33 has a conical pointed tip. With
this configuration, even if the tip of the guide stick 33 is out of
the center of rotation of the first sun gear 12 when the guide
stick 33 is mounted on the positioning portion 32, the tip of the
guide stick 33 contacts an oblique surface of the positioning
portion 32 which guides the tip of the guide stick 33 to the center
of rotation of the sun gear 12. Accordingly, the conical pointed
tip of the guide stick 33 is fitted reliably to the conical
concavity of the positioning portion 32, and the tip of the guide
stick 33 is positioned coaxially on the same rotation axis of the
first sun gear 12. The opposed end of the guide stick 33 is
supported by the jig such that the guide stick 33 is concentrically
disposed on the same axis of the outer gear and the sun gear placed
at the predetermined location of the jig.
[0121] In the configuration described above, the guide stick 33
which has been assembled together with the first carrier 16 is
fitted to the positioning portion 32 of the first sun gear 12 so
that the first carrier 16 and the first sun gear 12 are reliably
positioned in place. Alternatively, after the guide stick 33 is
positioned in place on the positioning portion 32, the first
carrier 16 is assembled with the guide stick 33.
[0122] According to the present illustrative embodiment, the
positioning portion 32 includes a conical concavity, and the guide
stick 33 includes a conical pointed tip that is fitted to the
conical concavity of the positioning portion 32. The shapes of the
positioning portion 32 and the guide stick 33 are not limited to
this. Alternatively, as illustrated in FIG. 14B, the tip of the
guide stick 33 has a planar surface, and the positioning portion 32
may have a circular concavity 32a in cross section having a similar
or the same diameter as that of the guide stick 33. The tip of the
guide stick 33 is fitted to the concavity 32a of the positioning
portion 32. Similar to the foregoing embodiments, by forming a
surface 32b of the positioning portion 32 at the carrier side
oblique such that the internal diameter thereof decreases towards
the concavity 32a or the sun gear side as illustrated in FIG. 14B,
the oblique surface 32b of the positioning portion 32 guides
reliably the tip of the guide stick 33 to the concavity 32a of the
positioning portion 32.
[0123] After the guide stick 33 is positioned in place, the first
carrier 16 is slidingly moved along the guide stick 33 to the first
sun gear side, thereby inserting the first carrier 16 in the outer
gear 14. The first planetary gears 15-1, 15-2 and 15-3 held by the
first carrier 16 are meshed with the first sun gear 12 and the
outer gear 14. According to the present illustrative embodiment,
the outer gear 14 is common to the first and the second stages.
Thus, the tooth width of the outer gear 14 is wider than that of
the first sun gear 12. With this configuration, first, while the
guide stick 33 regulates the position of the first carrier 16, the
first planetary gears 15-1, 15-2 and 15-3 of the first carrier 16
inserted to the outer gear 14 mesh with the outer gear 14.
[0124] As the first carrier 16 with the first planetary gears 15-1,
15-2 and 15-3 meshing with the outer gear 14 is inserted further,
the first planetary gears 15-1, 15-2 and 15-3 mesh with the first
sun gear 12. At this time, the guide stick 33 regulates the
position of first carrier 16 so as to be parallel to the shaft of
the outer gear 14 and the first sun gear 12. With this
configuration, the first planetary gears 15-1, 15-2 and 15-3 mesh
with the first sun gear 12 properly without the one-tooth
shift.
[0125] Preferably, the second carrier 19 is assembled in a similar
manner as the first carrier 16. In this case, the
cylindrical-shaped shaft 20 formed with the second carrier 19 as a
single integrated member has spline teeth, and cylindrical internal
spline teeth are formed on the drum shaft 70, which is a
configuration in which a male coupling member and a female coupling
member are reversed as compared with the configuration shown in
FIG. 2. Accordingly, the cylinder portion that extends to the
external teeth of the spline teeth is formed.
[0126] After the first carrier 16 is mounted, the guide stick 33 is
inserted to the cylinder portion of the second carrier 19 and the
second carrier 19 is slidingly moved to the outer gear 14 along the
guide stick 33 while the guide stick 33 regulates the position of
the second carrier 19. Accordingly, the second planetary gears
18-1, 18-2, 18-3, and 18-4 supported by the second carrier 19 mesh
with the outer gear 14 and the second sun gear 17. At this time,
the guide stick 33 regulates the position of second carrier 19 so
as to be parallel to the shaft of the outer gear 14 and the second
sun gear 17. With this configuration, the second planetary gears
18-1, 18-2, 18-3, and 18-4 mesh with the second sun gear 17
properly without one-tooth shift.
[0127] Preferably, the tooth width (the length in the direction of
insert of the carrier) of the outer gear 14 extends beyond the tip
portion of the tooth of the second sun gear 17. Similar to assembly
of the first carrier 16, the planetary gears and the sun gear mesh
after the outer gear 14 and the planetary gears mesh with each
other. Furthermore, the gears can be assembled reliably and
smoothly as compared with meshing the outer gear and the sun gear
with the planetary gears simultaneously.
[0128] In a case in which the cylindrical-shaped shaft 20 including
the internal spline teeth is formed on the second carrier 19, the
portion of the second carrier 19 through which the guide stick 33
penetrates cannot have a cylinder shape, but it is a through-hole.
Because the thickness of a plate member constituting the second
carrier 19 is relatively thin, if there is a slight gap between the
guide stick 33 and the through hole, the second carrier 19 is
tilted. However, if the through hole has the same diameter as that
of the guide stick 33 to eliminate the gap therebetween, the guide
stick 33 does not move smoothly in the second carrier 19, hindering
assembly of the second carrier 19.
[0129] Thus, in this case, preferably, the first carrier 16 and the
second carrier 19 are assembled together using the guide stick 33.
More specifically, after the first carrier 16 is inserted to the
guide stick 33, the guide stick 33 is inserted to the through hole
of the second carrier 19. Subsequently, the second carrier 19 is
slidingly moved so that the second planetary gears 18-1, 18-2,
18-3, and 18-4 supported by the second carrier 19 mesh with the
second sun gear 17 formed with the first carrier 16 as an
integrated member. At this time, the center of the first carrier 16
and the center of the second carrier 19 are aligned by the guide
stick 33, thereby allowing the second planetary gears 18-1, 18-2,
18-3, and 18-4 to mesh smoothly with the second sun gear 17.
Similar to the foregoing embodiments as described above, the tip of
the guide stick 33 is positioned on the positioning portion 32, and
the other end of the guide stick 33 is positioned in place on the
jig. Subsequently, the second planetary gears 18 mesh with the
second sun gear 17, and in the state in which the first carrier 16
and the second carrier 19 are assembled, the first carrier 16 and
the second carrier 19 are inserted to the outer gear 14.
[0130] As described above, the position of the first carrier 16 is
regulated by the guide stick 33 and the tubular member 31, thereby
allowing the first carrier 16 to be assembled without one-tooth
shift. As for the second carrier 19, the second carrier 19 is
assembled with the first carrier 16, and the second planetary gears
18 mesh with the second sun gear 17. In this configuration, the
second carrier 19 is supported by the guide stick 33 inserted to
the first carrier 16 and the through hole of the second carrier 19.
Similar to the configuration with the tubular portion, the
supported portion of the second carrier 19 supported by the guide
stick 33 in direction of insert is long enough to prevent
inclination of the second carrier 19 in the axial direction of the
outer gear 14.
[0131] In view of the above, the cause of one-tooth shift of the
secondary planetary gears 18 relative to the outer gear 14 includes
backlash, rattling of shafts, and the shape variations.
[0132] According to the present illustrative embodiment, the mesh
error (positional error) upon assembly can be approximately 420
.mu.m or less, which is less than the mesh error of approximately
900 .mu.m (Module 0.3) that generates the one-tooth shift. The
second carrier 19 can be assembled without the one-tooth shift.
[0133] According to the present illustrative embodiment, the first
planetary gears 15 and the second planetary gears 18 are assembled
properly without the one-tooth shift, thereby providing good
transmission of rotation force and hence preventing degradation of
imaging quality and noise. Furthermore, damage of the planetary
gears is prevented.
[0134] With reference to FIG. 15, a description is provided of a
variation of the illustrative embodiment of the present
invention.
[0135] [Variation 1]
[0136] FIG. 15 is a perspective view schematically illustrating a
first variation of the planetary gear mechanism.
[0137] In the first variation, as illustrated in FIG. 15, the
tubular portion of the first carrier 16 through which the guide
stick 33 penetrates and the shape of a through hole 34 of the
second carrier 19 has a substantially oval shape with at least one
corner, and the guide stick 33 has a substantially oval shape with
at least one corner in cross-section. With this configuration, by
rotating the guide stick 33, the first and the second carriers can
be rotated.
[0138] When meshing the carriers with the outer gear and the sun
gear, the mesh position of mating gear teeth can be found easily by
rotating slightly the carriers themselves, thereby shortening
assembly time. In the first variation, the guide stick 33 has a
rounded rectangular shape in cross-section, and the hole of second
carrier 19 and the tubular portion 31 of the first carrier 16 has
also a rounded rectangular shape. By rotating the guide stick 33,
the first and the second carriers are rotated, thereby shortening
the assembly time.
[0139] According to the above example, the guide stick 33 has a
substantially oval shape with at least one corner in cross-section,
and the shape of the hole of second carrier 19 and the tubular
portion 31 of the first carrier 16 has also an oval shape with at
least one corner. However, the shape is not limited to a
substantially oval shape with at least one corner. The shape may be
elliptical, square, and noncircular.
[0140] [Variation 2]
[0141] With reference to FIGS. 16 and 17, a description is provided
of a second variation of the planetary gear mechanism. FIG. 16 is a
front view schematically illustrating the first carrier 16 of the
second variation of the planetary gear mechanism as viewed from the
first sun gear 12. FIG. 17 is a front view schematically
illustrating the first sun gear 12 of the second variation of the
planetary gear mechanism. In the second variation, the planetary
gear mechanism does not include the gear mount 24, and the outer
gear 14 is fixed to the motor mount 13. However, the second
variation is applicable to a configuration including the gear mount
24 to which the outer gear 14 is fixed.
[0142] In the second variation, as illustrated in FIG. 16, the
first carrier 16 includes three through holes 41 provided equally
spaced in the circumferential direction of the first carrier 16.
The guide sticks 33 are inserted to the through holes 41. More
specifically, the first carrier 16 is provided with three planetary
gears 15, and the through holes 41 are provided between each of the
planetary gears 15. As illustrated in FIG. 17, the bottom of the
outer gear 14 or the motor mount 13 includes three positioning
portions 42 at which the guide sticks 33 are positioned in
place.
[0143] In the second variation, each of the guide sticks 33 is
inserted to the through holes 41 and positioned in place at the
positioning portions 42. The first carrier 16 is moved into the
outer gear 14 while the position thereof is adjusted by the guide
sticks 33 (in this example, three guide sticks 33), thereby
mounting the first carrier 16 in the outer gear 14. With this
configuration, a plurality of guide sticks 33 (in this example,
three guide sticks 33) maintains the position of the first carrier
16 parallel to the axis of outer gear 14 and the first sun gear 12
when meshing the planetary gears 15-1, 15-2, and 15-3 with the
outer gear 14 and the first sun gear 12. The teeth of the planetary
gears 15-1, 15-2, and 15-3 can mesh with the proper mating teeth of
the outer gear 14 and the first sun gear 12 without meshing errors
such as the one-tooth shift.
[0144] In the second variation, three second planetary gears 18 are
provided, and the second carrier 19 includes through holes. The
through holes are formed in the second carrier 19 at the same
position as the through holes in the first carrier 16. In this
configuration, after installation of the first carrier 16, the
second planetary gears 18 supported by the second carrier 19 can
mesh with the second sun gear 17 and the outer gear 14 while the
position of the second carrier 19 is adjusted by three guide sticks
33, similar to the first carrier 16.
[0145] In the second variation, the position of the first carrier
16 is adjusted by three guide sticks 33. With this configuration,
even when the supported portion of the carrier supported by the
guide stick 33 is not relatively long in the direction of insert of
the guide stick 33, the carrier does not tilt relative to the
direction of insert. Therefore, this configuration is effective
when the carrier pin 16a is cantilevered by the carrier.
[0146] In the above example, the outer gear 14 is fixed. However,
the present invention is not limited thereto. The present invention
is applicable to a configuration in which the sun gear is fixed,
and the carrier is floatingly supported. Similar to the foregoing
embodiments, the planetary gears supported by the carrier can mesh
with the outer gear and the sun gear without mesh errors while the
position of carrier is adjusted by the guide sticks.
[0147] Although the embodiment of the present invention has been
described above, the present invention is not limited to the
foregoing embodiments, but a variety of modifications can naturally
be made within the scope of the present invention.
[0148] According to an aspect of the disclosure, a planetary gear
mechanism includes a plurality of planetary gears, an outer gear, a
sun gear, a carrier, and a stick mount. The outer gear meshes with
the plurality of planetary gears. The sun gear is coaxially
disposed on the same axis as the outer gear and transmits force to
the planetary gears. The carrier rotatably supports the plurality
of planetary gears and is rotatably and floatingly supported. The
carrier includes a hole through which a stick member penetrates in
a direction of axis of rotation of the carrier. The stick member
penetrates through the hole and is mounted on the stick mount. The
stick mount is disposed opposite the carrier. The outer gear and
the sun gear are held such that one of the outer gear and the sun
gear does not rotate. With this configuration, the planetary gears
held by the carrier mesh with the outer gear and the sun gear
properly without one-tooth shift.
[0149] According to an aspect of the disclosure, in the planetary
gear mechanism the hole of the carrier is formed at the center of
rotation of the carrier, and the sun gear includes the stick mount
on a plane facing the carrier in an axial center thereof. With this
configuration, the planetary gears held by the carrier mesh with
the outer gear and the sun gear properly without one-tooth shift
while the stick member adjusts the position of the carrier.
[0150] According to an aspect of the disclosure, the planetary gear
mechanism includes a mounting portion to which one of the sun gear
and the outer gear is fixed. The mounting portion includes a plane
facing the carrier. The carrier includes a plurality of the holes
evenly disposed on a circumference of a lateral surface thereof.
The mounting portion includes a plurality of the stick mounts on
the plane facing the carrier. With this configuration, the
planetary gears held by the carrier mesh with the outer gear and
the sun gear properly without one-tooth shift while the stick
member adjusts the position of the carrier.
[0151] According to an aspect of the disclosure, in the planetary
gear mechanism a clearance is provided between the stick member and
the hole, and the clearance does not allow the carrier to tilt
relative to a direction of insert of the stick member. With this
configuration, the stick member can regulate the position and
orientation of the carrier.
[0152] According to an aspect of the disclosure, in the planetary
gear mechanism one of the stick mount and the tip of the stick
member includes a conical concavity, and another of the stick mount
and the tip of the stick member has a conical convex shape.
Accordingly, the tip of the stick member is reliably fitted to the
stick mount. With this configuration, even when the tip of the
stick member is offset from the center of rotation, the tip of the
stick member is guided to the stick mount.
[0153] According to an aspect of the disclosure, the planetary gear
mechanism includes a plurality of groups of the sun gear, the outer
gear, the planetary gears, and the carrier. The plurality of groups
is disposed in series in the axial direction. The outer gears have
the same number of teeth, and are constituted as a single
integrated member and fixed so as not to rotate. With this
configuration, a large deceleration ratio can be obtained. The
outer gears having the same number of teeth allow the carrier to be
inserted therein while the position of the carrier is adjusted by
the stick member.
[0154] According to an aspect of the disclosure, in the planetary
gear mechanism the position of the hole in the carrier is the same
for all groups. With this configuration, the stick member can be
inserted to the carriers of different groups, and the carriers are
inserted to the outer gear. Alternatively, the carriers are
assembled on the stick member and then inserted to the outer
gear.
[0155] According to an aspect of the disclosure, in the planetary
gear mechanism the hole is formed at the center of rotation of the
carrier, and the sun gear includes the stick mount on a plane
facing the carrier in the axial center. The stick member has a
noncircular shape in cross section, and the hole of the carrier has
a noncircular shape to allow the stick member to fit therein. With
this configuration, the carrier is rotated by rotating the stick
member and mounted in the outer gear. Proper meshing positions of
the planetary gears meshing with the sun gear and the outer gear
can be found easily, thereby reducing assembly time.
[0156] According to an aspect of the disclosure, in the planetary
gear mechanism the hole of the carrier has a tubular shape
extending in the direction of insert of the stick member, thereby
preventing the carrier from getting tilted due to the clearance
between the stick member and the hole.
[0157] According to an aspect of the disclosure, a drive
transmission unit includes a drive source, the planetary gear
mechanism including an output shaft, and a shaft to support a
target such as a photosensitive drum to be driven and transmit
rotary force output from the output shaft of the planetary gear
mechanism to the target. With this configuration, rotation force is
properly transmitted and noise is prevented.
[0158] According to an aspect of the disclosure, an image forming
apparatus includes a plurality of targets to be driven and the
drive transmission unit to drive at least one of the plurality of
targets. With this configuration, rotation force is properly
transmitted and noise is prevented.
[0159] According to an aspect of the disclosure, a method for
assembling a planetary gear mechanism includes inserting the stick
member to the hole of the carrier; mounting the stick member at the
stick mount; meshing the plurality of planetary gears with the sun
gear and the outer gear by moving the carrier along the stick
member, to mount the carrier in the outer gear; and removing the
stick member after carrier is mounted.
[0160] According to an aspect of this disclosure, the present
invention is employed in the image forming apparatus. The image
forming apparatus includes, but is not limited to, an
electrophotographic image forming apparatus, a copier, a printer, a
facsimile machine, and a multi-functional system. Furthermore, it
is to be understood that elements and/or features of different
illustrative embodiments may be combined with each other and/or
substituted for each other within the scope of this disclosure and
appended claims. In addition, the number of constituent elements,
locations, shapes and so forth of the constituent elements are not
limited to any of the structure for performing the methodology
illustrated in the drawings.
[0161] Still further, any one of the above-described and other
exemplary features of the present invention may be embodied in the
form of an apparatus, method, or system.
[0162] For example, any of the aforementioned methods may be
embodied in the form of a system or device, including, but not
limited to, any of the structure for performing the methodology
illustrated in the drawings.
[0163] Example embodiments being thus described, it will be obvious
that the same may be varied in many ways. Such exemplary variations
are not to be regarded as a departure from the scope of the present
invention, and all such modifications as would be obvious to one
skilled in the art are intended to be included within the scope of
the following claims.
* * * * *