Abstract:
A film spool has a film-unwound verifier that produces an audible indication that a particular length of a filmstrip has been unwound from the spool.

Description:
FIELD OF THE INVENTION 
     The invention relates generally to the field of photography, and in particular to a film spool with a built-in audible indicator for verifying film loading in a camera for example. 
     BACKGROUND OF THE INVENTION 
     To load most 35 mm cameras, a film cartridge is inserted in a loading chamber of the camera and the forward end portion of a film leader protruding from a light-trapping slit in the cartridge is placed over a take-up spool in the camera. In some cameras, the forward end portion of the film leader is manually attached to the take-up spool before a rear door of the camera is closed. Then, a film loading or winding operation is performed, for example, by manually pivoting a winding lever for the take-up spool and manually depressing a shutter release button several times. This is done until the entire leader is unwound from a supply spool inside the cartridge and is wound onto the take-up spool, and the first-available film frame is positioned for exposure. In other cameras, the forward end portion of the film leader is automatically secured to the take-up spool at the beginning of the film loading operation. As the take-up spool is rotated via a motor drive, for example, one or more circumferential teeth of the spool engage the forward end portion of the film leader at its perforations to wind the leader onto the spool and position the first-available film frame for exposure. A spring-like deflector or other suitable means may be provided on the rear door of the camera for pressing the film leader against the take-up spool to facilitate engagement of the forward end portion of the leader by the circumferential teeth of the spool. 
     A problem that exists in some 35 mm cameras is that even though the photographer believes the forward end portion of the film leader is secured to the take-up spool, the forward end portion may fail to be engaged with the spool or may become disengaged from the spool during the film loading operation. As a result, the film leader will not be wound onto the take-up spool and the first-available film frame cannot be positioned for exposure. However, since the rear door of the camera is closed, the photographer may not be aware of the malfunction. 
     SUMMARY OF THE INVENTION 
     A film spool comprising: 
     a film roll support rotatable to unwind a filmstrip, beginning with a film leader having several frame lengths, from the film roll support; and 
     audible verifier means for providing an audible indication only when the film roll support is rotated a sufficient number of revolutions for at least the film leader of the filmstrip to be unwound from the film roll support, whereby the audio indication will verify that enough of the filmstrip has been unwound from the film roll support to achieve film loading in a camera. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an elevation view of a film cartridge including a film spool with an audible indicator for verifying film loading in a camera, according to a preferred embodiment of the invention; 
     FIG. 2 is an elevation view of the film spool, showing the audio indicator ready for use; 
     FIG. 3 is an elevation view of the film spool, showing the audio indicator after being used; 
     FIG. 4 is an exploded elevation view of the film spool; and 
     FIG. 5 is an elevation view of an alternative embodiment of the audio indicator. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The invention is disclosed as being embodied preferably in a film cartridge. Because the features of a film cartridge are generally known, the description which follows is directed in particular only to those elements forming part of or cooperating directly with the disclosed embodiment. It is to be understood, however, that other elements may take various forms known to a person of ordinary skill in the art. 
     Referring now to the drawings, FIG. 1 depicts a film cartridge 10 comprising a known cartridge shell or housing 12 with a light-trapping film egress/film ingress slit 14 and a film spool 16 supported inside the cartridge shell for rotation about an axis X. A known 35 mm filmstrip 18 having respective edge perforations 20 is coiled about a hollow, open-end, cylindrical, film roll support 22 between a pair of disk-like end flanges 24 and 26. The pair of flanges 24 and 26 are fixed to a hollow, cylindrical, spool core 28 which coaxially extends inside the film roll support 22. Two pieces of adhesive tape 30 secure an inner end portion 32 of the filmstrip 18 to the film roll support 22. A forward end portion 34 of a film leader 36 of the filmstrip 18 originally protrudes from the slit 14. The film leader 36 is several (3-4) frame lengths long. 
     The film spool 16 in addition to the coaxial film roll support 22 and the coaxial spool core 28, as shown in FIGS. 2 and 4, includes a sound generating mechanism 38 and a trigger device 40 located inside the spool core. The sound generating mechanism 38 has a base 42 with a pair of identical metal tines 44 fixed to the flange 26 and a striker 46 rotatably supported via the base. A torsion spring 48 is originally tensioned to rotate the striker periodically into contact with the pair of tines 44 to produce a chirping or ringing sound. See FIGS. 2 and 3. The trigger device 40 has a forked end 50 normally in engagement with the striker 46. A cam follower pin 52 projects from the trigger device 40 through a motion-constraining slot 54 in the spool core 28 into a helical cam slot 56 in the film roll support 22. Location of the cam follower pin 52 in the motion-constraining slot 54 serves to prevent the striker 46 from being rotated by the torsion spring 48 as long as the forked end 50 of the trigger device 40 remains in engagement with the striker. See FIG. 2. However, when the forked end 50 is disengaged from the striker 46, the torsion spring 48 rotates the striker. See FIG. 3. 
     Operation 
     When the film leader 18 is pulled out of the cartridge shell 12 though the light-trapping slit 14, such as during film loading in a camera, the film roll support 22 is rotated about the axis X relative to the spool core 28 in a film unwinding direction U. See FIG. 2. As a result, the helical cam slot 56 drives the cam follower pin 52 from one end of the cam slot to an opposite end of the cam slot to, in turn, translate the cam follower pin from one end of the motion-constraining slot 54 to an opposite end of the motion-constraining slot. This makes the forked end 50 of the trigger device 40 disengage from the striker 46, permitting the torsion spring 48 to rotate the striker to produce the chirping or ringing sound. See FIG. 3. The chirping or ringing sound serves as an audible verification that enough of the filmstrip 18 has been removed from the cartridge shell 12 to achieve film loading in the camera. 
     Once the cam follower pin 52 is moved to the opposite ends of the motion-constraining slot 54 and the helical cam slot 56 as shown in FIG. 3, the cam follower pin causes the spool core 28 to be rotated with the film roll support 22 about the axis X in the film unwinding direction U when further lengths of the filmstrip 18 are pulled out of the cartridge shell 12 through the light-trapping slit 14. 
     Alternative Embodiment 
     FIG. 5 depicts an alternative embodiment 58 of the sound generating mechanism 38. Specifically, the alternative embodiment 58 comprises a pair of resilient switch contacts 60 and 62 which are normally held apart by the forked end 50 of the trigger device 40, a piezoelectric speaker 64, a tone generating amplifier 66, and a battery 68. When the forked end 50 is removed from between the switch contacts 60 and 62, the switch contacts spring against one another to close an electrical circuit in order for the tone generating amplifier 66 to provide a continuous tone to the speaker 66 via the battery 68. 
     The invention has been described with reference to a preferred embodiment. However, it will be appreciated that variations and modifications can be effected by a person of ordinary skill in the art without departing from the scope of the invention. 
     PARTS LIST 
     10. film cartridge 
     12. cartridge shell 
     14. light-trapping film egress/ingress slit 
     16. film spool 
     X. axis 
     18. filmstrip 
     20. edge perforations 
     22. film roll support 
     24. end flange 
     26. end flange 
     28. spool core 
     30. adhesive tape 
     32. inner film end portion 
     34. forward leader end portion 
     36. film leader 
     38. sound generating mechanism 
     40. trigger device 
     42. base 
     44. metal tines 
     46. striker 
     48. torsion spring 
     50. forked trigger end 
     52. cam follower pin 
     54. motion-constraining slot 
     56. helical cam slot 
     U. film unwinding direction 
     58. alternative embodiment 
     60. switch contact 
     62. switch contact 
     64. speaker 
     66. tone generating amplifier 
     68. battery