Film winding device

A film winding device for a camera is provided in which a drive motor is housed in a film winding spool, and an output shaft of the drive motor projects from the film winding spool. A reduction mechanism is provided between the output shaft and the film winding spool to rotate the film winding spool and to thus wind film thereon. The reduction mechanism comprises a parent gear rotating with the output shaft, a planet gear provided at a position offset from the center of the parent gear, a stationary gear fixed to a camera body, and a rotational gear connected to the film winding device. The stationary gear and the rotational gear are coaxial with the parent gear and mesh with the planet gear. The rotational gear rotates relative to the stationary gear, so that the planet gear is rotated at a rotational speed dependent on the difference between the number of teeth of the stationary gear and the number of teeth of the rotational gear.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a film winding device in which rotation of 
a winding motor housed in a film winding spool is transmitted to a winding 
spool through a reduction mechanism. In particular, the present invention 
relates to the reduction mechanism of such a film winding device. 
2. Description of the Related Art 
Due to the current trend toward a miniaturization of cameras, in film 
winding mechanisms of such cameras, the drive motor is usually housed in 
the film winding spool. Conventionally, in this kind of device, an output 
shaft of the drive motor projects from the winding spool and is provided 
with a drive gear, and rotation of the drive gear is transmitted to the 
winding spool through a reduction mechanism in order to wind the film on 
to the winding spool. Conversely, when the film is to be rewound, rotation 
of the drive motor is reversed and is transmitted to a rewinding shaft 
through rotation switching mechanism, whereby a rotation of a shaft of a 
film cartridge is reversed, and the film wound onto the winding spool is 
rewound into the film cartridge. 
In this conventional device, the reduction mechanism is used to reduce the 
rotational speed of the driver motor, and to transmit the reduced 
rotational speed of the drive motor to the winding spool. Conventional 
reduction mechanisms comprise a gear train including a plurality of gears 
having a different number of teeth. Therefore, the size of the reduction 
mechanism is relatively large; and this is a disadvantage when attempting 
to reduce the size of a camera. Further, since conventional reduction 
mechanisms have many parts, the manufacturing and assembly costs are high. 
SUMMARY OF THE INVENTION 
Therefore, one object of the present invention is to provide a film winding 
device in which a reduction mechanism including a drive motor and a 
winding spool comprising of a small number of parts, so that the size of 
the reduction mechanism will be reduced and the structure thereof 
simplifieds and, further so that, the mechanism will provide a high 
reduction ratio. 
According to the present invention, a film winding device for a camera is 
provided including a winding spool rotably supported by a camera body, and 
a drive motor housed in the winding spool in such a manner that an output 
shaft of the drive motor projects from the winding spool, with the output 
shaft being connected to the winding spool through a reduction mechanism 
through which the winding spool is rotated to wind film thereon. The film 
winding device comprises a parent gear, a planet gear, a stationary gear, 
a rotational gear, and means for transmitting rotation of the rotational 
gear to the winding spool to wind film thereon. 
In the reduction mechanism according to the present invention, the parent 
gear rotates in association with the output shaft, the planet gear is 
provided at a position offset from the center of the parent gear, the 
stationary gear is provided coaxially with the parent gear and is meshed 
with the planet gear, and the rotational gear is provided coaxially with 
the parent gear and meshed with the planet gear. The rotational gear is 
rotatable relative to the stationary gear, and the number of gear teeth of 
the rotational gear is different from that of the stationary gear.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The present invention will now be described with reference to embodiments 
shown in the drawings. 
FIG. 1 shows a schematic diagram of structure by which a film in a camera 
is wound and rewound, wherein a winding spool 11 is provided in a camera 
12 in such a manner that the winding spool 11 is rotated about the axis 
thereof. A film cartridge 13, including film 14, is also accommodated in 
camera 12, and the film 14 is fed from the film cartridge 13 and extended 
to the winding spool 11, to be wound around the winding spool 11. A drive 
motor (not shown) is housed in the winding spool 11 in such a manner that 
an output shaft 15 of the drive motor projects from the winding spool 11. 
This output shaft 15 of the drive motor is provided with a drive gear 16 
connected to a reduction mechanism 50, and the reduction mechanism 50 is 
connected to a rotation switching mechanism 17 which selectively transmits 
rotation of the reduction mechanism 50 to the winding spool 11 or to a 
rewinding mechanism 18 connected to a rotational shaft of the film 
cartridge 13. Accordingly when the winding spool 11 is rotated, the film 
14 is pulled out from the film cartridge 13 and wound around the winding 
spool 11, and when the rotational shaft of the film cartridge 13 is 
rotated, the film 14 is rewound into the film cartridge 13. 
Thus, rotation mechanism 17, as clearly illustrated in FIG. 2, serves to 
transmit rotation of the rotational gear to the winding spool to wind film 
thereon, as indicated in the preceding paragraph; and, as is also 
indicated above, rotation switching mechanism 17 selectively transmits 
rotation of reduction mechanism 50 to either winding spool 11 or to 
rewinding mechanism 18, which is connected to a rotatable shaft of film 
cartridge 13. 
FIG. 2 shows a construction of the winding spool 11 and the reduction 
mechanism 50 according to the present invention. 
The winding spool 11 has a cylindrical shape and is rotatably supported by 
a camera body 19, and has a spool gear 11a formed on an outer surface 
thereof. A drive motor 21 is housed in the winding spool 11, and the 
output shaft 15 of the drive motor 21 extends through a hole 11b formed in 
the winding spool 11, so as to project therefrom. The drive motor 21 is 
supported by a support plate 23 fixed to the camera body 19 by a 
connecting screw 24. This support plate 23 is provided with a projection 
23a extending into the winding spool 11, and the drive motor 21 is 
provided with a recess 21a which fits over the projection 23a, at a 
position offset from the center of the drive motor 21, so that the drive 
motor 21 is fixed in the winding spool 11 in such a manner that rotation 
about the axis spool is prevented. 
A tip portion of the output shaft 15 is rotatably supported by a bearing 25 
mounted in a parent plate 26 which is rigidly connected to the camera body 
19, and a drive gear 16 is fixed to the output shaft 15. 
The reduction mechanism 50 is disposed between the parent plate 26 and the 
camera body 19, and comprises a parent gear 51, a planet gear 52, a 
stationary gear 53, and a rotational gear 54, by which the number of 
rotations of the drive gear 16 is reduced and transmitted to the winding 
spool 11 or the rewinding mechanism 18. 
The stationary gear 53 has a shaft member 55 extending between the parent 
plate 26 and the camera body 19, in parallel to the output shaft 15 of the 
drive motor 21. The end portions of the shaft member 55 are connected to 
the parent plate 26 and the camera body 19, respectively, whereby the 
shaft member 55 is fixed in such a manner that it cannot rotate about its 
own axis. The parent gear 51 is rotatably fitted to an upper portion of 
the shaft member 55 and is meshed with the drive gear 16. The stationary 
gear 53 is integrally formed with the shaft member 55 at an intermediate 
portion thereof, namely, the stationary gear 53 cannot rotate relative to 
the parent plate 26 and the camera body 19. It should be noted that the 
stationary gear 53 is coaxial with the parent gear 51, and has a diameter 
smaller than that of the parent gear 51. 
The rotational gear 54 is coaxial with the parent gear 51, and is fitted to 
a lower portion of the shaft member 55 so that it is rotatable relative to 
the stationary gear 53. The stationary gear 53 and the rotational gear 54 
have substantially the same diameter, respectively, but the number of 
teeth of the rotational gear 54 is different from that of the stationary 
gear 53. Note, although the number of teeth of the rotational gear 54 is 
larger than that of the stationary gear 53 in this embodiment, the number 
of teeth of the rotational gear 54 may be smaller than that of the 
stationary gear 53 in another embodiment. 
The planet gear 52 is provided at a position offset from the center of the 
parent gear 51, and a pin 56 is connected to a peripheral portion of the 
parent gear 51 so that the planet gear 52 is rotatably supported by the 
parent gear 51 through the pin 56. Although a single planet gear 52 is 
shown in FIG. 2, two planet gears 52' may be provided in another 
embodiment, as shown in FIG. 3, in which the planet gears 52' are 
positioned on opposite sides of the stationary gear 53 and the rotational 
gear 54. 
The stationary gear 53 and the rotational gear 54 are in mesh with the 
planet gear 52, and therefore, when the parent gear 51 is rotated, the 
planet gear 52 revolves around the stationary gear 53 and rotates about 
the pin 56, so that the rotational gear 54 rotates about the shaft member 
55. The rotation speed of the rotational gear 54 depends upon the 
difference in the number of teeth of the stationary gear 53 and the 
rotational gear 54. The rotation of the rotational gear 54 is transmitted 
to the winding spool 11 or the rewinding mechanism 18 through the rotation 
switching mechanism 17, by a meshing of a gear (not shown) of the rotation 
switching mechanism 17 with the spool gear 11a or a gear of rewinding 
mechanism 18. 
The device described in the above embodiment operates as follows. 
When the drive motor 21 is rotated, the drive gear 16 on the output shaft 
15 is rotated, and this rotation of drive gear 16 is transmitted to parent 
gear 51. As a result, the planet gear 52 connected to a peripheral portion 
of the parent 51 revolves round the stationary gear 53, as a sun gear, and 
rotates about the pin 56. As the planet gear 52 meshes with the stationary 
gear 53 and the rotational gear 54, which each have a different number of 
teeth, gears 52, 53 and 54 together operate as a differential gear, so 
that rotational gear 54 is slowly rotated at a rotation speed which 
depends upon the difference between the number of teeth of the stationary 
gear 53 and of the rotational gear 54. When winding film, rotation of the 
rotational gear 54 is transmitted to the winding spool 11 through the 
rotation switching mechanism 17 and the spool gear 11a. Conversely, when 
rewinding the film, the rotation of the rotational gear 54 is transmitted 
to the rewinding mechanism 18 through the rotation switching mechanism 17. 
Assuming that the number of teeth of the rotational gear 54 is Z.sub.r and 
the number of teeth of the stationary gear 53 is Z.sub.s, and further, 
that Z.sub.r is larger than Z.sub.s, then the ratio of the number of 
rotations N.sub.l ; of the output shaft 15 of the drive motor 21 and the 
number of rotations N.sub.z of the winding spool 11 is obtained by the 
following equation. It should be noted that the rotation switching 
mechanism 17 does not reduce the rotation speed of the rotational gear 54. 
##EQU1## 
wherein Z.sub.d denotes the number of teeth of the drive gear 16, Z.sub.p 
denotes the number of teeth of the parent gear 51, and Z.sub.g denotes the 
number of teeth of the spool gear 11a. 
As understood from the above equation, the smaller the difference in the 
number of teeth denoted by Z.sub.s and Z.sub.r, the larger the reduction 
ratio. When the difference in the number of teeth denoted by Z.sub.s and 
Z.sub.r is "n", the number of planet gears 52 provided can either be "n" 
or a multiple of "n" in order to obtain a good meshing performance. In 
other words, the number of planet gears 52 is equal to, or a multiple of, 
the difference between the number of teeth in the stationary gear 53 and 
in the rotational gear 54 used to obtain a desirably high reduction ratio. 
The use of a multiple of "n" as the number of planet gears is preferable 
to using "n" gears. Note that, when the difference in the number of teeth 
of the gears 53 and 54 is 1, by taking into consideration deviations in 
the parent gear 51 due to meshing thereof with the planet gear 52, a pair 
of planet gears 54 may be provided around the stationary gear 53 and the 
rotational gear 54 at a spacing of 180 degrees from each other, as shown 
in FIG. 3. 
Note that, if the number of teeth of the rotational gear 54 is smaller than 
that of the stationary gear 53, the direction of rotation of the 
rotational gear 53 is the reverse of that given in the above description. 
As described above, film winding devices according to the present invention 
have a simple construction and require a relatively small space when 
mounted in a camera. Therefore, these film winding devices allow reduction 
of the size of a camera, and further, since the number of parts required 
for the devices is reduced, the manufacturing and assembly costs are 
correspondingly lowered. 
Although the embodiments of the present invention have been described 
herein with reference to the accompanying drawings, obviously many 
modifications and changes may be made by those skilled in this art without 
departing from the scope of the invention.