Machine element or mechanism – Gearing – Plural power paths to and/or from gearing
Reexamination Certificate
2000-09-26
2002-07-16
Marmor, Charles A (Department: 3681)
Machine element or mechanism
Gearing
Plural power paths to and/or from gearing
C074S66500G
Reexamination Certificate
active
06418816
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a power transmission device for transmitting the rotational force of a motor to a driven member. In particular, the present invention relates to a power transmission device adapted to be used in a film transport device for an optical apparatus, such as a camera or a film viewing apparatus.
2. Description of Related Art
Hitherto, an automatic-winding-type camera has a film transport device in which the rotational speed of a motor is reduced by a plurality of gears so as to rotate a film winding spool by a large rotational force.
Recently, the rotational forces of motors have been reduced as the motors and batteries have been reduced in size due to reduction in sizes of cameras. Therefore, the speed of the motors must be reduced at a large reduction ratio so as to rotate spools by a desired rotational force. In order to reduce the rotational speed of a motor, a plurality of two-stage gears, each of which is composed of two gear parts coaxially integrally formed to have different numbers of teeth, are generally used. The following methods using the two-stage gears to obtain a large reduction ratio are known.
(i) A method in which a large number of two-stage gears are used.
(ii) Another method in which a relatively small number of two-stage gears are used, each having gear parts differing greatly from each other in the number of teeth.
In power transmission through gears, power loss during transmission generally occurs at engaging parts of the gears. Therefore, as the number of engaging parts, that is, the number of gears, increases, the efficiency in power transmission decreases. Accordingly, in the method (i) described above, there is a problem in that although a large reduction ratio can be obtained, the efficiency in power transmission is lowered due to the large number of two-stage gears, the rotational force transmitted to a spool thereby becoming small. In order to overcome this problem, the reduction ratio may be further increased. However, when the reduction ratio is excessively large, even if the desired rotational force is transmittable to the spool, the rotational speed of the spool becomes very low, so that the film winding speed would be lowered.
On the other hand, in the above method (ii), if the number of gears used is reduced by using the two-stage gears having a large difference in the number of teeth between the two gear parts constituting each two-stage gear, the efficiency of power transmission can be prevented from being lowered. However, the larger gear part of the two gear parts constituting the two-stage gear must be made sufficiently large to provide such a large difference in the number of teeth, whereby the distance between axes of the two-stage gears is increased, thereby increasing the space as viewed in a direction of the axes of the gears. Then, power transmission devices described below have been proposed in order to overcome these problems.
FIGS.
3
(
a
) and
3
(
b
) show one of the power transmission devices as proposed. In the power transmission device shown in FIGS.
3
(
a
) and
3
(
b
), the rotational force of a motor
11
is transmitted by a pinion gear
12
fixed thereto to an internal gear
13
a
which is the larger gear part of an intermediate two-stage gear
13
. Then, the rotational force of a gear
13
b
which is the smaller gear part of the intermediate two-stage gear
13
is transmitted to an internal gear
14
a provided at a spool
14
.
The power transmission device is provided with only two engaging parts of the gears, thereby significantly reducing power loss during transmission. In the power transmission device, with the internal gears used, the distance between axes of the gears does not need to be large, as compared with a case where external gears having the same number of teeth are used. As shown in FIG.
3
(
b
), the intermediate two-stage gear
13
can be disposed close to the pinion gear
12
as viewed in a direction of the axes of the gears.
However, with the arrangement described above, although the arrangement offers an advantage regarding the winding of film by the spool
14
, since the rotational force of the motor
11
in a forward or backward direction is transmitted to the spool
14
as it is, a configuration of the spool
14
must be devised, for example, to be divided into two pieces with regard to the rewinding of film.
FIGS.
4
(
a
) and
4
(
b
) show another proposed power transmission device. In the power transmission device shown in FIGS.
4
(
a
) and
4
(
b
), the rotational force of a motor
21
is transmitted by a pinion gear
22
fixed thereto to an internal gear
25
a
provided at a spool
25
, while, during transmission, the rotational speed of the motor
21
is reduced by a two-stage sun gear
23
and, then, by a two-stage planet gear
24
.
In FIG.
4
(
b
), with a connecting arm
26
connecting the two-stage sun gear
23
and the two-stage planet gear
24
and a friction spring
27
used, the two-stage planet gear
24
revolves clockwise and counterclockwise around the two-stage sun gear
23
.
When the two-stage planet gear
24
revolves clockwise and engages with the internal gear
25
a
of the spool
25
, the winding of film can be performed, and when the two-stage planet gear
24
revolves counterclockwise and engages with a rewinding gear
28
, the rewinding of film can be performed.
With this arrangement, although one gear is added to the configuration shown in FIGS.
3
(
a
) and
3
(
b
), the winding and rewinding of film can be performed by using a simple planetary mechanism.
With the above-described arrangement, a gear part of the two-stage planet gear
24
engages with the internal gear
25
a
of the spool
25
by revolving at the time of the winding of film, so that the two-stage planet gear
24
can be disposed approximately inside the internal gear
25
a
as viewed in a direction of the axis thereof, as shown in FIG.
4
(
b
). That is, if an engaging gear of the spool is disposed at the outer periphery thereof, the two-stage planet gear
24
must naturally revolve in the outer area of the spool so as to engage with the external gear of the spool. Therefore, the space for the gear train must be enlarged for the revolving area for the two-stage planet gear
24
. With the arrangement described above, the space can be reduced due to the provision of the internal gear
25
a
of the spool
25
.
In the conventional power transmission devices shown in FIGS.
3
(
a
) and
3
(
b
) and FIGS.
4
(
a
) and
4
(
b
), the rotational force of the motors can be amplified and transmitted to the spools while maintaining transmission efficiency by reducing the number of gears used. However, there are the following problems regarding the “breadth” as viewed in a direction of the axes of the gears, as shown in FIGS.
3
(
b
) and
4
(
b
), and regarding the “thickness” as viewed in a direction perpendicular to the axes of the gears, as shown in FIGS.
3
(
a
) and
4
(
a
).
The thickness of the power transmission device shown in FIGS.
3
(
a
) and
3
(
b
) is the minimum required for a two-stage gear, which is the sum of thicknesses “A” and “B” required for two engaging parts, as shown in FIG.
3
(
a
).
However, as is understandable from FIG.
3
(
b
), the internal gear
13
a
of the intermediate two-stage gear
13
protrudes from the periphery of the spool
14
by an amount “C”, thereby increasing the breadth by the amount “C”.
Further, in the power transmission device shown in FIGS.
4
(
a
) and
4
(
b
), the two-stage planet gear
24
does not significantly protrude from the spool
25
, as shown in FIG.
4
(
b
). The power transmission device shown in FIGS.
4
(
a
) and
4
(
b
) offers an advantage regarding the space as compared with that shown in FIGS.
3
(
a
) and
3
(
b
).
However, the thickness of the power transmission device shown in FIGS.
4
(
a
) and
4
(
b
), which is the sum of thicknesses “D”, “E” and “F” required for three engaging parts as shown in FIG.
4
(
a
), is greater than that of the device shown in F
Canon Kabushiki Kaisha
Marmor Charles A
Parekh Ankur
Robin Blecker & Daley
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