thus resulting in a complex construction. In addition, a fourth type of mechanism uses a coil spring through which the film windup member and the film takeup shaft are drive coupled to transmit power from the film wind-up member to the film takeup shaft through the action of the tightening of the coil spring to advance the film, and to open or cut off the drive transmission through the loosening of the coil spring when a predetermined length of film has been advance, i.e., when a film frame advance has been completed, thus preventing an excess of film advancing. This type of mechanism is advantageous in that the film advance is stopped without restraining the movement of the film wind-up member to thus provide smooth film advance operation,the power or drive transmission or cutoff can be controlled through the tightening or loosening of the coil spring to assure functional stability, and only a coil spring is required as the power transmission or cutoff controlling means permitting a very simple construction.
The present invention relates to improvements in the above-identified fourth type of film advance mechanism or device, which type is described in Japanese Utility Model Publication No. 45-9355 issued on May 1, 1970. The device described in the above publication employs a construction in which a coil spring is wound around a film-advance shaft integrally rotatable with a wind-up lever, one free end of the coil spring being fixed to a spool shaft and the other end to a stop gear rotatably fitted to the shaft