Machine element or mechanism – Gearing – Teeth
Reexamination Certificate
2001-04-06
2004-06-22
Fenstermacher, David (Department: 3682)
Machine element or mechanism
Gearing
Teeth
C074SDIG001
Reexamination Certificate
active
06752035
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a gear made of a resin widely used in a power-transmitting mechanism such as a duplicator, a printer, a facsimile, an automobile part and the like, and an image-forming device providing an enhanced image quality, such as a duplicator, a printer and the like, which is designed to drive a photoconductor through such gear made of the resin.
The present invention also relates to a gear made of a resin and a pulley made of a resin as a rotation-transmitting means made of a resin.
BACKGROUND OF THE INVENTION
A gear made of a resin is conventionally used in a power-transmitting mechanism such as a duplicator, an automobile part and the like for the purpose of reducing the cost and the weight of the part and reducing an operational sound. Such a gear made of a resin is formed into a predetermined shape by an injection molding, and the shape is contrived to provide a tooth-profile accuracy and a strength suited for the purpose of use.
For example, in an image-forming device such as a color duplicator, a gear made of a resin adapted to be meshed at a high contact rate with a gear made of a resin for driving a photoconductor is used and the shape of this gear is contrived for forming a distinct color image having a high quality. The gear made of the resin is connected to a photoconductor-driving motor (a drive means), so that the rotational force of the photoconductor-driving motor is transmitted smoothly through the gear made of the resin to a photoconductor to turn the photoconductor smoothly and with a high accuracy, thereby effectively preventing a printing failure such as a color shift.
(First Prior Art)
For example, a gear
150
made of a resin shown in
FIGS. 1 and 2
is formed into such a shape that an annular toothed portion
152
having teeth
151
formed thereon and a boss (shaft-supporting section)
154
fitted over a shaft
153
are connected to each other by a thin plate-shaped web
155
. The web
155
connected to the toothed portion
152
is thinner and hence, the amount of radially inward contractive deformation (shrinkage transformation) of a connection between the web
155
and the toothed portion
152
after the injection molding and a portion in the vicinity of the connection is smaller, whereby a tooth profile can be formed with a higher accuracy. When the thickness of the web
155
connected to the toothed portion
152
is larger, the volume of the web
155
is larger, and the amount of radially inward contractive deformation of the web
155
after the injection molding is larger. For this reason, the connection between the web
155
and the toothed portion and the portion in the vicinity of the connection are deformed in such a manner that they are pulled in a direction of contraction of the web
155
and hence, the amount of toothed portion
152
deformed is larger, resulting in an increased reduction in accuracy of formation of the teeth
151
.
On the other hand, when the gear
150
made of the resin as shown in
FIGS. 1 and 1
transmits a power in a state in which it has received a radial load WR as shown in
FIG. 3
, the web
155
is deformed elliptically in an increased amount, as shown by a dotted line in
FIG. 3
, resulting in a decreased accuracy of transmission of the rotation, because the web
155
receiving the radial load WR has a smaller thickness and a lower strength. When the gear
150
having a sectional shape as shown in
FIG. 2
is a helical gear, a thrust load WS is applied to the toothed portion
152
and the web
155
and hence, the web
152
is deformed in a flexed manner in an increased amount in a direction of application of the thrust load WS, as shown by a dotted line in
FIG. 4
, resulting in a reduction accuracy of transmission of the rotation, because the thickness of the web
155
is smaller.
(Second Prior Art)
Therefore, to eliminate such a disadvantage, a gear
157
made of a resin has been considered which includes radial ribs
156
formed on a side of a web
155
to connect a boss
154
and a toothed portion
152
to each other, as shown in
FIGS. 5
to
7
, so that the rigidity of the web
155
is increased, and the accuracy of transmission of the rotation is enhanced. In the gear
157
in which the boss
154
and the toothed portion
152
are connected directly to each other by the radial ribs
156
, however, the following new disadvantage is brought about: A connection between the radial ribs
156
and the toothed portion
152
and a portion in the vicinity of the connection are contractively deformed radially inwards in an increased amount (shown by a dotted line in each of FIGS.
5
and
6
), thereby generating a phenomenon of the falling of the teeth
151
as shown in
FIG. 8
, resulting in a reduced accuracy of a tooth profile.
(Third Prior Art)
A gear
200
made of a resin as shown in
FIGS. 9 and 10
has been developed by the present applicant, wherein such disadvantages associated with the prior arts can be overcome.
The gear
200
made of the resin shown in
FIGS. 9 and 10
includes a shaft-supporting section
203
having a shaft hole
202
fitted over a photoconductor driving shaft
201
for rotation in unison with each other, a rim
205
having teeth
204
and located radially outside the shaft-supporting section
203
, and a thinner web
206
which connects the shaft-supporting section
203
and the rim
205
. In order to prevent the deformation of the web
206
due to a thrust load, this gear
200
made of the resin has first and second annular circumferential ribs
207
and
208
formed inside the rim
205
and on opposite sides of the web
206
, diametrical ribs
210
formed radiately on opposite sides of the web
206
between the shaft-supporting section
203
and the second circumferential rib
208
to connect the shaft-supporting section
203
and the second circumferential rib
208
to each other, and diametrical ribs
211
formed radiately on the opposite sides of the web
206
between the first and second circumferential rib
207
and
208
to connect the first and second circumferential rib
207
and
208
to each other.
In the gear
200
made of the resin and having such configuration, the diametrical ribs
210
and
211
are not connected to the rim
205
and hence, the rigidity of the web
206
can be increased without detraction of the roundness of the rim
205
having the teeth
204
. The gear
200
made of the resin is formed into a shape shown in
FIGS. 9 and 10
by an injection molding and hence, as the thickness of the resin is larger, a longer time is taken to cool the resin within a cavity, and the amount of resin contractively deformed is increased more. Therefore, in the gear
200
made of the resin having such shape, if the thickness of the web
206
is larger, the thickness of the connection between the web
206
and the rim
205
is larger, and the amount of radially inward contractive deformation of the connection between the web
206
and the rim
205
is larger than those of other portions, resulting in a degraded tooth profile accuracy. If the diametrical ribs
212
are connected to the rim
213
, as shown in
FIG. 11
, the thickness of the connection between the diametrical ribs
212
and the rim
213
is larger, and the amount of radially inward contractive deformation of the connection between the diametrical ribs
212
and the rim
213
is larger than those of other portions (see a portion shown by a dotted line in FIG.
11
), resulting in a reduced roundness. Therefore, the conventional gear
200
made of the resin shown in
FIGS. 9 and 10
is formed so that the thickness of the web
206
is decreased as much as possible to provide a desired accuracy of the teeth
204
, and the lack of the rigidity of the web
206
can be compensated for by the first and second circumferential ribs
207
and
208
and the diametrical ribs
210
and
211
.
In recent years, in an image-forming device such as a color printer, a color duplicator and the like, a small error of the rotation-transmitting accuracy of each of the gears
157
and
200
Noguchi Kouji
Sakamaki Kazuyuki
Enplas Corporation
Fenstermacher David
Koda & Androlia
LandOfFree
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