Abstract:
A power transmission device comprises a spool gear disposed at a film take-up spool and an output gear that outputs a driving force that has been transmitted to the spool gear. The spool gear acts both to drive a take-up spool in the course of film winding and to furnish power applied thereto in the course of film rewinding to a fork gear associated with a film cartridge.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a power transmission device for winding and rewinding a film in a camera or the like, and to an apparatus using the same. 
     2. Description of Related Art 
     Among various types of photographic films, there is a type of film in which a film leader part is stowed in a cartridge until use thereof and, after the cartridge is loaded in the camera or the like, a film is thrust out from the cartridge with a spool disposed within the cartridge (hereinafter referred to as the cartridge spool) driven by a film transport mechanism disposed inside the camera or the like, as disclosed in U.S. Pat. Nos. 4,832,275 and No. 4,834,306. Such a type of film is hereinafter referred to as the thrust type. 
     Further, there have been proposed various kinds of technique for winding a film thrust out from the thrust-type cartridge onto a take-up spool disposed in the camera or the like by driving the take-up spool and for rewinding the film into the cartridge by driving the cartridge spool, as disclosed in (i) Japanese Laid-Open Patent Application No. HEI 3-206435, (ii) Japanese Laid-Open Patent Application No. HEI 3-287150, (iii) Japanese Laid-Open Patent Application No. HEI 6-265989, etc. 
     For example, in the technique disclosed in (i) Japanese Laid-Open Patent Application No. HEI 3-206435, the change-over from a film thrusting-out operation by the driving of the cartridge spool to a film winding operation by the driving of the take-up spool is smoothly performed by utilizing a one-way clutch. 
     Also, in the technique disclosed in (ii) Japanese Laid-Open Patent Application No. HEI 3-287150, two transmission route channels are arranged to be selectively used to make smooth the change-over from a film thrusting-out operation by the driving of the cartridge spool to a film winding operation by the driving of the take-up spool, without using any one-way clutch. 
     Further, in the technique disclosed in (iii) Japanese Laid-Open Patent Application No. HEI 6-265989, a sun gear is disposed at the last stage of a reduction gear train, and is provided with two planet gears. One of the two planet gears is arranged to be used for performing a film winding operation by the driving of the take-up spool, and the other is arranged to be used for performing a film thrusting-out operation by the driving of the cartridge spool, so that the change-over from the film thrusting-out operation to the film winding operation can be smoothly performed with a compact gear train arrangement. 
     However, each of the above-mentioned kinds of technique has presented a problem in that there are required at least two channels of driving power transmission for driving the cartridge spool and for driving the take-up spool, thereby disadvantageously increasing the size of the device. 
     BRIEF SUMMARY OF THE INVENTION 
     In accordance with one aspect of the invention, there are provided a power transmission device for a camera or the like and an apparatus using the power transmission device, comprising a spool gear disposed at a film take-up spool and an output gear that outputs a driving force transmitted to the spool gear, so that the spool gear is used as an intermediate gear in transmitting the driving force, thereby enabling reduction in size and cost of the device. 
    
    
     The above and other aspects and features of the invention will become apparent from the following detailed description of preferred embodiments thereof taken in conjunction with the accompanying drawings. 
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
     FIG. 1 is a perspective view showing a film transport device according to a first embodiment of the invention. 
     FIG. 2 is a perspective view showing a film transport device according to a second embodiment of the invention. 
     FIG. 3 is a perspective view showing a film transport device according to a third embodiment of the invention. 
     FIG. 4 is an exploded perspective view showing a clutch part used in each of the film transport devices in the first and third embodiments. 
     FIG. 5 is an exploded perspective view showing a clutch part used in the film transport device in the second embodiment. 
     FIG. 6 is a perspective view showing a film transport device according to a fourth embodiment of the invention. 
     FIG. 7 is an exploded perspective view showing a gear head part as viewed from the direction of an arrow A in FIG.  6 . 
     FIG. 8 is an exploded perspective view showing a clutch part in the film transport device shown in FIG.  6 . 
     FIG. 9 is an exploded perspective view showing also the clutch part in the film transport device shown in FIG.  6 . 
     FIG. 10 is a plan view showing the film transport device in FIG. 6 in the state where a film thrusting-out operation is started. 
     FIG. 11 is a plan view showing the film transport device in FIG. 6 in the state where the change-over to a film rewinding operation is performed. 
     FIG. 12 is a plan view showing the film transport device in FIG. 6 in the state where the film rewinding operation is in process. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Hereinafter, preferred embodiments of the invention will be described in detail with reference to the drawings. 
     FIG. 1 shows in a perspective view a film transport device according to a first embodiment of the invention. The film transport device according to the first embodiment (also, according to other embodiments of the invention which will be described later) is used for various kinds of film using apparatuses, such as cameras, film viewers, etc. 
     Referring to FIG. 1, a film cartridge  1  is of a thrust type similar to that disclosed in U.S. Pat. No. 4,832,275, U.S. Pat. No. 4,834,306, etc. Specifically, as mentioned in the foregoing, the leader part of a film  2  is stowed in the cartridge  1  until use thereof, and, after the cartridge  1  is loaded into the film transport device, the film  2  is thrust out from the cartridge  1  with the cartridge spool driven to rotate. 
     A take-up spool  3  is arranged to wind up thereon the film  2  thrust out from the cartridge  1 . The take-up spool  3  is provided with a film winding part  3   b  the surface of which is covered with an elastic rubber material for facilitating generation of a frictional force on the film  2 , and a spool gear  3   a  provided for obtaining a rotating force. A pinion gear  4  is disposed inside the take-up spool  3  and is connected directly to a motor (not shown). A first reduction gear  5  has a large gear part  5   a  which is in mesh with the pinion gear  4 . An idler gear  6  is in mesh with a small gear part  5   b  of the first reduction gear  5 . A second reduction gear  7  has a large gear part  7   a  which is in mesh with the idler gear  6  and a small gear part  7   b  which is in mesh with the spool gear  3   a . In a power transmission system composed of gears from the pinion gear  4  connected directly to the motor to the spool gear  3   a , the gears are always in mesh with one after the other, as shown in FIG. 1, and no driving change-over member such as a planet gear or the like is included. Therefore, for example, in a case where the motor is disposed inside the take-up spool  3  as shown in FIG. 1, a reduction gear train can be closely arranged only at an upper part of a spool chamber which houses the take-up spool  3  therein. 
     A planetary arm  9  is mounted on the rotating shaft of the second reduction gear  7 . A planet gear  8  which is rotatably mounted on the planetary arm  9  is in mesh with the large gear part  7   a  of the second reduction gear  7 . Incidentally, a predetermined force of turning friction is imparted between the second reduction gear  7  and the planetary arm  9  by a spring (not shown). 
     A thrust (output) gear  11  is arranged to be always in mesh with the spool gear  3   a . The thrust gear  11  is used as a member on the input side of a clutch part  12 . A rewinding gear  13  is used as a member on the output side of the clutch part  12 . 
     Here, an exploded perspective view of the clutch part  12  is shown in FIG.  4 . Referring to FIG. 4, a cam plate  17 , which is formed integrally with the thrust gear  11 , is provided with projection parts  17   a  formed at three positions in the peripheral part thereof. The rewinding gear  13 , which is shown in a sectional view in FIG. 4, is integrally provided with a bowl-shaped clutch tube  19  which is arranged to rotatably house the cam plate  17  therein. A shaft hole part  13   a  of the rewinding gear  13  and the clutch tube  19  are fitted on a rotating shaft  11   a  which is formed integrally with the thrust gear  11  and the cam plate  17 . Steel balls  18  are arranged between the inner wall of the clutch tube  19  and the cam plate  17 . 
     With the clutch part  12  configured in the above-described manner, the thrust gear  11  and the rewinding gear  13  are connected to each other when the steel balls  18  are sandwiched in between the inner wall of the clutch tube  19  and the projection parts  17   a  of the cam plate  17 , and are disconnected from each other when the steel balls  18  fall into recessed parts formed between the projection parts  17   a , depending on a relation of rotation speed between the thrust gear  11  and the rewinding gear  13 . 
     Referring back to FIG. 1, an idler gear  14  is in mesh with the rewinding gear  13 . An idler gear  15  is in mesh with the idler gear  14 . A fork gear  16  is in mesh with the idler gear  15  and is integrally attached to a fork  16   a , which engages the cartridge spool to drive the cartridge spool. 
     Next, operation of the film transport device arranged as described above will be described. In FIG. 1, arrows shown with full lines indicate driving directions in which the members mentioned above rotate for winding (thrusting out and taking up) the film  2 . Arrows shown with broken lines indicate driving directions in which the members mentioned above rotate for rewinding the film  2 . 
     First, when the pinion gear  4  is rotated by the motor in the film winding driving direction (indicated by a full-line arrow), the gear  5  which is in mesh with the pinion gear  4 , the gears  6  and  7  and the spool gear  3   a  respectively rotate in the directions indicated by full-line arrows. The take-up spool  3  is thus caused to rotate also in the direction of a full-line arrow. In this instance, the rotation of the second reduction gear  7  causes the planetary arm  9  to turn in such a direction as to abut on a stopper  10 . As a result, the planet gear  8  is retracted to a position where the planet gear  8  transmits no power to any of other gears. 
     The thrust gear  11 , which is in mesh with the spool gear  3   a , is caused to rotate in the direction of a full-line arrow by the motor driving force received through the spool gear  3 . The rotation of the thrust gear  11  in the full-line arrow direction causes the steel balls  18  to be pushed against the inner wall of the clutch tube  19  by the projection parts  17   a  of the cam plate  17 , so that the clutch part  12  is brought into a connecting state to cause the thrust gear  11  and the rewinding gear  13  to rotate integrally. The rotation of the rewinding gear  13  is transmitted to the fork gear  16  through the idler gears  14  and  15 . The cartridge spool which engages the fork  16   a  is thus driven to rotate. As a result, the film  2  is thrust out from the cartridge  1 . 
     When the film  2  which is thrust out from the cartridge  1  reaches the film winding part  3   b  of the take-up spool  3 , the film  2  is wound on the film winding part  3   b  without slackening under a pushing action of a pushing means (not shown). The reduction ratios of the gear trains of the film transport device are set such that a peripheral velocity of the film  2  on the surface of the take-up spool  3  is always faster than the speed at which the film  2  is being thrust out from the cartridge  1 . Therefore, a portion of the film  2  wound on the take-up spool  3  causes the fork gear  16  to rotate at the faster speed in the direction of a full-line arrow. As a result, the fork gear  16 , the idler gears  14  and  15  and the rewinding gear  13  are rotated at the faster speeds in the direction of full-line arrows. When the rewinding gear  13  comes to rotate at a faster speed than the thrust gear  11  in the direction of a full-line arrow, the friction between the inner wall of the clutch tube  19  and the steel balls  18  causes the steel balls  18  to be moved into the recessed parts formed between the projection parts  17   a  of the cam plate  17 . with the steel balls  18  thus brought into the recessed part, the clutch part  12  is released from the connecting state, so that power is stopped from being transmitted from the thrust gear  11  to the rewinding gear  13 . Accordingly, after that, the film  2  comes to be wound up solely by means of the tape-up spool  3 . 
     In addition, the thrust gear  11  and the spool gear  3   a  are arranged to form a last reduction stage, excluding the reduction stage of the idler gear  15  and the fork gear  16 , for the film winding driving (the gears  13 ,  14  and  15  being arranged to make no reduction). By virtue of this gear arrangement, the gears  13 ,  14  and  15  do not generate any large load when the fork gear  16  is driven by the film  2 . Therefore, a load on the motor in canceling the connecting state of the clutch part  12  can be lessened. Besides, the change-over from the film thrusting-out driving to the film winding driving can be speedily and smoothly performed. 
     On the other hand, when the pinion gear  4  is rotated by the motor in the direction of film rewinding (in the direction of a broken-line arrow), the reduction gears  5 ,  6  and  7  and the spool gear  3   a  respectively rotate in the directions of broken-line arrows to cause the take-up spool  3  to rotate in the direction of a broken-line arrow. Then, the rotation of the second reduction gear  7  causes the planetary arm  9  to turn away from the stopper  10 , so that the planet gear  8  is brought to a position where the planet gear  8  meshes with the rewinding gear  13 . Accordingly, the rotation of the second reduction gear  7  is transmitted to the rewinding gear  13  to cause the rewinding gear  13  to rotate in the direction of a broken-line arrow. 
     Also, the thrust gear  11 , which is in mesh with the spool gear  3   a , is caused by the driving force of the motor to rotate in the direction of a broken-line arrow. Thus, the rewinding gear  13  and the thrust gear  11  both receive the driving forces to be caused to rotate in the same direction across the clutch part  12 . However, since the reduction ratio of a part from the motor to the rewinding gear  13  (the reduction ratio of the gears  4 ,  5 ,  6 ,  7   a ,  8  and  13 ) is set larger than the reduction ratio of a part from the motor to the thrust gear  11  (the reduction ratio of the gears  4 ,  5 ,  6 ,  7 ,  3   a  and  11 ), at the time of film rewinding driving, the rewinding gear  13  always rotates slower than the thrust gear  11 . Therefore, the cam plate  17  is caused to rotate in such a direction as to bring the steel balls  18  into the recessed parts formed between the projection parts  17   a  of the cam plate  17 . Accordingly, at the time of film rewinding driving, the clutch part  12  is always released from the connecting state. The driving force of the motor is thus transmitted to the fork gear  16  through the second reduction gear  7 , the planet gear  8 , the rewinding gear  13  and the idler gears  14  and  15 . 
     Further, in rewinding the film  2 , both the fork gear  16  and the take-up spool  3  are driven in the film rewinding direction. However, since the rewinding speed of the film  2  on the surface of the take-up spool  3  is set always faster than the rewinding speed of the film  2  on the surface of the cartridge spool which is rotated by the fork gear  16 , the film  2  is brought into a loosely coiled state within the spool chamber, so that the film  2  can be prevented from being stretched. 
     As described above, in the film transport device according to the first embodiment, the spool gear  3   a  is used not only as a gear to which the driving force of the motor for driving the take-up spool  3  is inputted, but also as an idle gear for transmitting the driving force of the motor to the thrust gear  11  which is arranged to input the driving force of the motor to a cartridge-spool driving system composed of gears from the rewinding gear  13  to the fork gear  16 . This arrangement permits reduction in number of gears required in the film transport device, so that efficiency of driving force transmission to the cartridge-spool driving system can be enhanced. 
     Further, the spool gear  3   a  is disposed at the perimeter of the spool chamber and is arranged to be relatively large in size. Therefore, the output of the spool gear  3   a  can be taken out from any direction. In other words, the setting position of the thrust gear  11  is selectable with a wide range of latitude. 
     Further, in the film transport device according to the first embodiment, the driving action for winding the film is performed by causing the planet gear  8  to mesh with the rewinding gear  13  for power transmission. Therefore, even if the location of the rewinding gear  13  (determined by the location of the thrust gear  11 ) is relatively far from the second reduction gear  7  (a sun gear for the planet gear  8 ), the distance can be easily covered by changing the size of the planet gear  8 . 
     The above arrangement of the film transport device according to the first embodiment thus permits the relatively thick clutch gear train ( 11 ,  12  and  13 ), the planet gear train ( 8  and  9 ) and the reduction gear train ( 5 ,  6  and  7 ) to be closely arranged above the spool gear  3   a . The gears  14 ,  15  and  16  which follow the clutch gear train ( 11 ,  12  and  13 ) can be arranged in a relatively thin space extending to the fork gear  16 . In other words, although the film transport device includes the clutch part  12 , it can be arranged without setting any bulky gear part within a thin space available above a cartridge chamber in which the film cartridge  1  is to be placed and also within a thin space available between the cartridge chamber and the spool chamber. Therefore, wider spaces other than these thin spaces can be used for members other than the film transport device. The arrangement described above, therefore, permits effective utilization of spaces within the apparatus using the film transport device. 
     In addition, since the clutch gear train ( 11 ,  12  and  13 ), the planet gear train ( 8  and  9 ) and the reduction gear train ( 5 ,  6  and  7 ) can be closely arranged above the spool gear  3   a , they can be formed into one unit. Such a unit can be also used in various kinds of apparatuses. 
     Further, in the first embodiment, the moving range of the planet gear  8  is limited to two positions, i.e., the position where the planet gear  8  is in mesh with the rewinding gear  13  and the position where the planet gear  8  is away from the rewinding gear  13 . Therefore, compared with a case where the planet gear  8  is arranged, for example, to selectively mesh with two gears, the planet gear  8  can be arranged to have a smaller moving range. Hence, the first embodiment permits reduction in size of the film transport device in this respect. 
     Incidentally, in the first embodiment, the planet gear  8  may be arranged to come to mesh, for example, with the idler gear  15  instead of with the rewinding gear  13  at the time of film rewinding. Such a modification can be made without difficulty as long as the clutch part  12  can be released from the connecting state for film rewinding. 
     FIG. 2 shows in a perspective view a film transport device according to a second embodiment of the invention. In FIG. 2, all component elements that are in common with the first embodiment shown in FIG. 1 are indicated by the same reference numerals, and the details of these elements are omitted from the following description. The second embodiment differs from the first embodiment in that the spool gear  3   a  is provided with an internal gear part  3   c , the small gear part  7   b  of the second reduction gear  7  is in mesh with the internal gear part  3   c , and the thrust gear  11  is arranged to engage with the spool gear  3   a  (external gear part) through an idler gear  20 . 
     In the film transport device according to the second embodiment, too, when the pinion gear  4  is rotated by the motor in the direction of film winding (in the direction of a full-line arrow), the driving force of the motor is transmitted to the spool gear  3   a  through the reduction gear train ( 5 ,  6  and  7 ) to cause the take-up spool  3  to rotate also in the direction of a full-line arrow. In this case, the internal intermeshing of the small gear part  7   b  of the second reduction gear  7  with the internal gear part  3   c  of the spool gear  3   a  gives a wider meshing range to make the driving action on the spool  3  more stabilized by as much as the increase in the meshing range than a case where the small gear part  7   b  is externally in mesh with the spool gear  3   a  as in the case of the first embodiment. 
     The spool gear  3   a  transmits the driving force of the motor to the thrust gear  11  through the idler gear  20  to cause the thrust gear  11  to rotate in the direction of a full-line arrow. In this instance, the rotation of the second reduction gear  7  causes the planetary arm  9  to turn in such a direction as to abut on the stopper  10 , so that the planet gear  8  is retracted to a position where the planet gear  8  does not mesh with any gear. 
     As shown in FIG. 5, a clutch part  12 ′ disposed between the thrust gear  11  and the rewinding gear  13  differs from the clutch part  12  in the first embodiment (see FIG.  4 ), in the shape of projection parts  17   a ′ of a cam plate  17 ′, i.e., in the biting-in direction of the steel balls  18  into the projection parts  17   a ′ and the clutch tube  19 . More specifically, when the thrust gear  11  rotates in the direction of a full-line arrow in FIG. 2 in thrusting out the film from the cartridge, the cam plate  17 ′, which is formed integrally with the thrust gear  11 , pushes the steel balls  18  against the inner wall of the clutch tube  19 . Therefore, the clutch part  12 ′ comes into a connecting state to cause the rewinding gear  13  to rotate at the same speed as the thrust gear  11 . After that, when the film  2  is taken up to be wound on the take-up spool  3  and the rewinding gear  13  comes to rotate in the direction of the full-line arrow at a speed faster than the thrust gear  11 , the inner wall of the clutch tube  19  moved the steel balls  18  into the recessed parts formed between the projection parts  17   a ′ of the cam plate  17 ′, so that the clutch part  12 ′ is released from the connecting state. After that, the winding driving of the film  2  is performed solely by means of the take-up spool  3 . 
     On the other hand, when the pinion gear  4  is rotated by the motor in the film rewinding direction, i.e., in the direction of a broken-line arrow, the driving force of the motor is transmitted to the spool gear  3   a  through the reduction gear train ( 5 ,  6  and  7 ) to cause the take-up spool  3  to rotate also in the direction of a broken-line arrow. Further, the spool gear  3   a  transmits the driving force of the motor also to the thrust gear  11  through the idler gear  20  to cause the thrust gear  11  to rotate in the direction of a broken-line arrow. In this instance, the rotation of the second reduction gear  7  causes the planetary arm  9  to turn away from the stopper  10 . As a result, the planet gear  8  comes to mesh with the rewinding gear  13  to cause the rewinding gear  13  to rotate in the direction of a broken-line arrow. 
     Both the rewinding gear  13  and the thrust gear  11  thus rotate in the same direction with the clutch part  12 ′ interposed between them. However, the reduction ratio of a part from the motor to the rewinding gear  13  (the reduction ratio of the gears  4 ,  5 ,  6 ,  7   a ,  8  and  13 ) is set larger than the reduction ratio of a part from the motor to the thrust gear  11  (the reduction ratio of the gears  4 ,  5 ,  6 ,  7 ,  3   a ,  20  and  11 ). Therefore, in driving for film rewinding, the rewinding gear  13  rotates always slower than the thrust gear  11 . Hence, the cam plate  17 ′ then rotates in such a direction as to moved the steel balls  18  into the recessed parts formed between the projection parts  17   a ′, thereby releasing the clutch part  12 ′ from the connecting state at the time of driving for film rewinding. In this instance, therefore, the driving force of the motor is transmitted to the fork gear  16  through the second reduction gear  7 , the planet gear  8 , the rewinding gear  13  and the idler gear  14 . 
     With the film transport device according to the second embodiment arranged in the above-described manner, the same advantageous effect as that of the first embodiment can be attained. 
     FIG. 3 shows in a perspective view a film transport device according to a third embodiment of the invention. All the component elements of the third embodiment that are in common with those of the second embodiment are indicated by the same reference numerals, and the details of them are omitted from the following description. The third embodiment differs from the second embodiment in that the spool gear  3   a  and the thrust gear  11  are arranged to intermesh directly with each other, and an idler gear  21  is interposed in between the planet gear  8  and the rewinding gear  13  which are arranged to engage with each other in driving for film rewinding. 
     In the film transport device according to the third embodiment, too, when the pinion gear  4  is rotated by the motor in the direction of film winding, i.e., in the direction of a full-line arrow as shown in FIG. 3, the driving force of the motor is transmitted to the spool gear  3   a  through the reduction gear train ( 5 ,  6  and  7 ). The take-up spool  3  then also rotates in the direction of a full-line arrow. 
     Further, the spool gear  3   a  transmits the driving force of the motor also to the thrust gear  11  to cause the thrust gear  11  to rotate in the direction of a full-line arrow. In this instance, the rotation of the second reduction gear  7  causes the planetary arm  9  to turn in such a direction as to abut on the stopper  10 . As a result, the planet gear  8  is retracted to a position where the planet gear  8  does not mesh with any gear. 
     The clutch part  12  disposed between the thrust gear  11  and the rewinding gear  13  is the same as the clutch part in the first embodiment (see FIG.  4 ). When the thrust gear  11  rotates in the direction of a full-line arrow in FIG. 3 in thrusting out the film from the cartridge, the cam plate  17 , which is formed integrally with the thrust gear  11 , pushes the steel balls against the inner wall of the clutch tube  19 , so that the clutch part  12  is brought into a connecting state. The rewinding gear  13  thus rotates at the same speed as the thrust gear  11 . After that, when the film  2  is taken up to be wound on the take-up spool  3  and the rewinding gear  13  comes to rotate in the direction of the full-line arrow at a speed faster than the thrust gear  11 , the inner wall of the clutch tube  19  moved the steel balls  18  into the recessed parts formed between the projection parts  17   a  of the cam plate  17 , so that the clutch part  12  is released from the connecting state. After that, the winding driving of the film  2  is performed solely by means of the take-up spool  3 . 
     On the other hand, when the pinion gear  4  is rotated by the motor in the film rewinding direction, i.e., in the direction of a broken-line arrow, the driving force of the motor is transmitted to the spool gear  3   a  through the reduction gear train ( 5 ,  6  and  7 ) to cause the take-up spool  3  to rotate also in the direction of a broken-line arrow. Further, the spool gear  3   a  transmits the driving force of the motor also to the thrust gear  11  to cause the thrust gear  11  to rotate in the direction of a broken-line arrow. In this instance, the rotation of the second reduction gear  7  causes the planetary arm  9  to turn away from the stopper  10 . As a result, the planet gear  8  comes to engage with the rewinding gear  13  through the idler gear  21  to cause the rewinding gear  13  to rotate in the direction of a broken-line arrow. 
     Both the rewinding gear  13  and the thrust gear  11  thus rotate in the same direction with the clutch part  12  interposed between them. However, the reduction ratio of a part from the motor to the rewinding gear  13  (the reduction ratio of the gears  4 ,  5 ,  6 ,  7   a ,  8 ,  21  and  13 ) is set larger than the reduction ratio of a part from the motor to the thrust gear  11  (the reduction ratio of the gears  4 ,  5 ,  6 ,  7 ,  3   a  and  11 ). Therefore, in driving for film rewinding, the rewinding gear  13  rotates always slower than the thrust gear  11 . Hence, the cam plate  17  then rotates in such a direction as to moved the steel balls  18  into the recessed parts formed between the projection parts  17   a , thereby releasing the clutch part  12  from the connecting state at the time of driving for film rewinding. In this instance, therefore, the driving force of the motor is transmitted to the fork gear  16  through the second reduction gear  7 , the planet gear  8 , the rewinding gear  13  and the idler gears  14  and  15 . 
     With the film transport device according to the third embodiment arranged in the above-described manner, the same advantageous effect can be attained as in the cases of the first and second embodiments. 
     FIG. 6 shows in a perspective view a film transport device according to a fourth embodiment of the invention. FIG. 7 is an exploded perspective view showing a gear head part of the film transport device as viewed from the direction of an arrow A in FIG.  6 . In FIGS. 6 and 7, all component elements that are in common with the above-described embodiments are indicated by the same reference numerals, and the details of them are omitted from the following description. 
     Referring to FIGS. 6 and 7, a pinion gear  4  is connected directly to a film transport motor (not shown). A reduction gear  5  has a large gear part  5   a  which is in mesh with the pinion gear  4 . A planet gear  22  is arranged to have the reduction gear  5  as a sun gear and to revolve around the reduction gear  5 . A large gear part  22   a  of the planet gear  22  is in mesh with a small gear part  5   b  of the reduction gear  5 . A planetary plate  23  is arranged to cause a small gear part  22   b  of the planet gear  22  to be selectively come to mesh with the internal gear part  3   c  of the take-up spool  3  or with a sun gear  25 . A planet shaft  24  is arranged to rotatably carry the planet gear  22  through a spring (not shown). The sun gear  25  is arranged to rotate in a fixed position where the sun gear  25  never meshes with the internal gear part  3   c  of the take-up spool  3 . A planetary clutch gear  26  is arranged to be always in mesh with the sun gear  25  and a large gear part  29   a  of a transmission gear  29  and to turn around the sun gear  25 . A planetary thrust gear  27  is arranged to turn around the sun gear  25  between a position where the planetary thrust gear  27  meshes with the internal gear part  3   c  of the take-up spool  3  and another position where the planetary thrust gear  27  does not mesh with the internal gear part  3   c , while carrying out a clutching function between the planetary thrust gear  27  and the planetary clutch gear  26 . A clutch shaft  28  acts as a rotating shaft for the planetary clutch gear  26  and the planetary thrust gear  27 . The clutch shaft  28  has an end projection  28   a  which engages a cam part  23   a  of the planetary plate  23 , so that the position of the clutch shaft  28 , i.e., the revolving position of the planetary thrust gear  27 , is controlled by the planetary plate  23 . 
     FIGS. 8 and 9 are exploded perspective views showing a clutch part composed of the planetary clutch gear  26  and the planetary thrust gear  27  shown in FIG.  6 . Referring to FIGS. 8 and 9, a sun-gear rotation sleeve  31  is caulked integrally with the planetary plate  30  and is fitted in the sun gear  25 . The planetary clutch gear  26  is provided with slanting claw faces  26   a  on its lower side as shown in FIG.  9 . The planetary thrust gear  27  is also provided with slanting claw faces  27   a  as shown in FIG.  8 . The clutch shaft  28  is carried by the planetary plate  30  while compressing a coil spring  32  to push the planetary clutch gear  26  against the planetary thrust gear  27 . 
     Next, operation of the film transport device arranged as described above according to the fourth embodiment will be described. FIG. 10 is a plan view showing the state of the film transport device at the time when the operation of thrusting out the film from the cartridge is started. Referring to FIG. 10, the reduction gear  5  which is driven by the pinion gear  4  (not shown in FIG. 10) rotates in the direction of an arrow. The planet gear  22 , which is in mesh with the reduction gear  5 , receives a revolving force which is exerted on the planet shaft  24  in the direction of an arrow. The planet gear  22  is thus brought into a position where the planet gear  22  is held in a state of meshing with the internal gear part  3   c  of the take-up spool  3 . In this position, the planet gear  22  is out of mesh with the sun gear  25 . Then, the take-up spool  3  is caused by the planet gear  22  to rotate in the direction of an arrow, i.e., in the film winding direction. In this instance, since the internal gear part  3   c  of the take-up spool  3  has a large diameter, a sufficient amount of speed reduction is possible, despite the fact that there are only a few number of gear stages between the pinion gear  4  and the internal gear part  3   c  of the take-up spool  3 . 
     Further, the end projection  28   a  of the clutch shaft  28  is restricted to be on the side of the internal gear part  3   c  of the take-up spool  3  by the action of the cam part  23   a  of the planetary plate  23 . By virtue of this action, the planetary thrust gear  27  is kept in a state of meshing with the internal gear part  3   c  of the take-up spool  3 . Since the planetary thrust gear  27  is rotated in such a direction that the slanting claw faces  27   a  of the planetary thrust gear  27  shown in FIG. 8 mesh with the slanting claw faces  26   a  of the planetary clutch gear  26 , the planetary clutch gear  26  rotates integrally with the planetary thrust gear  27 . The power of the planetary clutch gear  26  is thus transmitted to the large gear part  29   a  of the transmission gear  29 . In other words, the planetary thrust gear  27  is arranged such that the power of the internal gear part  3   c  of the take-up spool  3  which is driven by the rotating force of the planet gear  22  is extracted from a different part of the internal gear part  3   a  and transmitted to the fork gear  16  by the planetary thrust gear  27 . 
     In the state shown in FIG. 10, the individual gears rotate in the direction of full-line arrows, and the film  2  is driven by the fork gear  16  to be thrust out from the cartridge  1 . The film  2  which is thrust out is taken up to be wound on the take-up spool in a state of being pushed by an elastic member  33  against the take-up spool  3 . Then, since the film winding speed of the take-up spool  3  is set faster than the film thrusting-out speed of the fork gear  16 , the film  2  is pulled out from the cartridge  1  at a speed faster than the film thrusting-out speed of the fork gear  16 . Therefore, a tensile force of the tape  2  caused by the rotation of the take-up spool  3  is transmitted to the fork gear  16 . Then, since the planetary clutch gear  26  is caused to rotate in the direction of a full-line arrow at a speed faster than the planetary thrust gear  27 , the engaging connection between the planetary clutch gear  26  and the planetary thrust gear  27  is canceled, so that the film  2  is wound up solely by the rotation of the take-up spool  3 . Incidentally, in this instance, since the sun gear  25  is always in mesh with the planetary clutch gear  26 , the sun gear  25  is driven to rotate by the planetary clutch gear  26 . However, the rotation of the sun gear  25  is nothing but an idle rotation. Therefore, the film  2  can be thrust out and wound up without hindrance. 
     FIG. 11 shows in a plan view the state of the film transport device obtained immediately after the change-over from the film thrusting-out and winding-up operation to a film rewinding operation. Referring to FIG. 11, the reduction gear  5 , which receives power from the pinion gear  4  (not shown in FIG.  11 ), is driven in the direction of an arrow indicated by a broken line. The small gear part  22   b  of the planet gear  22  is then released from its state of meshing with the internal gear part  3   c  of the take-up spool  3  by the turning of the planetary plate  23  in the direction of an arrow indicated by a broken line, so that the planet gear  22  moves in such a direction as to mesh with the sun gear  25 . At the same time, the end projection  28   a  of the clutch shaft  28  is caused by the motion of the cam part  23   a  of the planetary plate  23  to move in the direction of a broken-line arrow to a position where the planetary thrust gear  27  never meshes with the internal gear part  3   c  of the take-up spool  3 . 
     FIG. 12 shows in a plan view the state of the film transport device where the film rewinding operation is in process. In this state, the small gear part  22   b  of the planet gear  22  is in mesh with the sun gear  25  to impart a turning force in the direction of a broken-line arrow. The planetary clutch gear  26 , while receiving a force of revolving around the sun gear  25 , is kept by the position restricting action of the cam part  23   a  of the planetary plate  23  in a position where the planetary thrust gear  27  never meshes with the internal gear part  3   c  of the take-up spool  3 . A film rewinding driving force in the direction of a broken-line arrow is thus transmitted to the fork gear  16  through the sun gear  25 , the planetary clutch gear  26 , the transmission gear  29  and the idler gears  14  and  15 . Therefore, the take-up spool  3  is allowed to rotate, free from the driving force of the motor, following a force of rewinding the film wound on the film winding part  3   b . Then, the presence of the elastic member  33  (a leaf spring or the like) shown in FIG. 6 ensures that the film  2  can be transported without slackening its coiled state on the film winding part  3   b  of the take-up spool  3 , even if the film winding operation and the film rewinding operation are repeatedly performed. 
     With the film transport device according to the fourth embodiment arranged as described above, the same advantageous effect can be attained as in the cases of the above-described embodiments. 
     The individual components shown in schematic or block form in the drawings are all well-known in the camera arts and their specific construction and operation are not critical to the operation or best mode for carrying out the invention. 
     While the invention has been described with respect to what is presently considered to be the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. To the contrary, the invention is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions. 
     For example, while the spool gear disposed at the film take-up spool is used as an intermediate gear for transmission of a film transport driving force in each of the embodiments disclosed, the invention is not limited to the arrangement disclosed. The spool gear may be used as an intermediate gear for transmission of a driving force other than the film transport driving force, such as an optical system driving force. 
     The invention may be carried out by combining as necessary the embodiments or their technological elements described in the foregoing. 
     The invention applies to cases where either the whole or a part of claims or the arrangement of each embodiment described forms an apparatus or is used in combination with some other apparatus or as a component element of an apparatus. 
     Further, the invention is applicable to cameras of various kinds, such as a single-lens reflex camera and a lens-shutter type camera, and apparatuses other than cameras, such as a film viewing apparatus, a film using apparatus, a power transmission apparatus, etc.