Abstract:
This film sag detecting device for a sound cinecamera is provided with an opto-electronic coupler located along a film path which is formed between a means for intermittent feeding of a film for exposure and a means for continuous feeding of the same for recording sounds thereon. The opto-electronic coupler comprises a light emitting element and a light receiving element and it is placed to allow the film to interrupt a light path which bridges the two light elements exclusively when the film excessively sags, so as to detect any excessive sag of the film.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a film sag detecting device for a sound cinecamera. 
     Referring to FIG. 1 showing a typical film sag detecting device in accordance with the prior art, the sound cinecamera is provided with a motor 2 and a film advancing tool 3 for intermittent feeding of a film for exposure, a motor 5, a capstan 6 and a pinch roller 7 for continuous feeding of the film for recording sounds on it by means of a sound recording head 4 and a film sag detecting device including a detecting lever 8. The aforementioned means, in combination, performs a function of maintaining the film sag at an appropriate amount in the film path formed between the film advancing tool 3 and the capstan 6 so as to achieve the desired smooth junctioning of both the film advancing tool 3 and the capstan 6. 
     The aforementioned film sag detecting device in accordance with the prior art consists of the detecting lever 8 attached with a film sag detecting element on one end thereof and also rotatably supported by a supporting pin 10, a tension spring 9 applied to detecting lever 8, an arm branching from the detecting lever 8 and forming a blind 11 on one end thereof, and a light emitting diode 12 and a photo transistor 13 respectively placed on either side of the blind 11 within the operation area thereof. 
     Supposing an excessive sag occurs in the film path between the film advancing tool 3 and the capstan 6, the excessively sagging film 1 pushes the detecting lever 8 down to cause a clockwise rotation of said lever around the pin 10 against the tension spring 9. This action moves the arm branching from the detecting lever 8 to cause the blind 11 formed on one end thereof to interrupt the light path bridging the light emitting diode 12 and the photo transistor 13. As a result, the light beam received by the photo transistor 13 is interrupted to cause the electric circuits including the photo transistor 13 and the motor 2 to reduce the film feeding rate of the film advancing tool 3, thereby correcting the excessive sag of the film 1. 
     As mentioned above, the utilization of the photoelectric means is rather limited, and the film sag detecting device of the prior art predominantly relies on mechanical means, such as the detecting lever 8 for direct detection of excessive film sag. This causes various faults including a considerable possibility of frequent occurrence of mechanical failure and the inherent requirement for a rather large space in the camera body. Another fault to be recognized in the prior art is the inconvenience incurred when loading a camera with a film cartridge caused by the necessity to keep pushing the detecting lever 8 downwardly during the film loading operation, because the customary setup of a camera requires that it be loaded with a film cartridge from the front or downward from the front side to the back side of the page in FIG. 1. 
     SUMMARY OF THE INVENTION 
     A general object of the present invention is to provide a film sag detecting device for a sound cinecamera which is free from the aforementioned various faults recognized in the models in accordance with the prior art. 
     Another object of the present invention is to provide a film sag detecting device for a sound cinecamera which is provided with an opto electronic coupler located along a film path formed between a means for intermittent feeding of a film for exposure and a means for continuous feeding of the film for recording sounds on it, which opto-electronic coupler comprises a light emitting element and a light receiving element and is placed to allow the film to interrupt a light path bridging the two light elements exclusively when the film excessively sags, whereby a limited use of the mechanical means causes a lesser opportunity of the occurrence of mechanical failure and a lesser requirement for space in the camera body. 
     A further object of the present invention is to provide a film sag detecting device for a sound cinecamera provided with an opto-electronic coupler placed inside an L-shaped frame, in which the vertical part of the frame is fitted along the internal back surface of the camera body and in which the horizontal part of the frame extends from the internal back surface of the camera body toward the front portion of the camera body to allow the film to stay within an open space which is formed in front of the vertical part of the L-shaped frame and above the horizontal part of the L-shaped frame in a free position or without being disturbed by any other member comprising the camera, whereby it is extremely easy to load the camera with a film cartridge. 
     An additional object of the present invention is to provide a film sag detecting device for a sound cinecamera provided with an opto-electronic coupler comprising a light emitting element placed in either the vertical part of the L-shaped frame or the horizontal part of the L-shaped frame and a light receiving element placed in the other part of the frame and forming a light path inclined to the potential film surface, which film surface stays, under normal sag, at a relatively higher position and which film surface assumes a relatively lower position when the film sag exceeds a normal limit, whereby the asccuracy for detecting the film sag is extremely improved. 
     A further additional object of the present invention is to provide a film sag detecting device for a sound cinecamera provided with an opto-electronic coupler placed inside an L-shaped frame which is adjustably fitted along the internal back surface of the camera body to allow adjustment of the vertical position and inclination of the L-shaped frame in relation to the potential normal film surface and resultantly of the vertical position and inclination of the light path in relation to the potential normal film surface, whereby it is possible to adjust the accuracy or the minimum extent for detecting the film sag. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 is a schematic drawing showing principally the film sag detecting portion of a typical sound cinecamera, in accordance with the prior art. 
     FIG. 2 is a perspective view of a portion of a sound cinecamera provided with an embodiment of the film sag detecting device in accordance with the present invention. 
     FIG. 3 is a schematic view of a portion of FIG. 2. 
     FIG. 4 is an enlarged sectional view of an embodiment of film sag detecting device in accordance with the present invention shown in FIG. 2. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The following description concerns the portions which are novel or different and distinctive from the corresponding portions of models in accordance with the prior art. The same reference numbers are given to the same portions, parts or members throughout the description for both the prior art and the present invention. 
     FIG. 2 through 4 show an embodiment of the present invention. 
     Referring to FIG. 2, a bracket 14 supports a pinch roller 7 and a spring 15 urges the bracket 14 to press the pinch roller 7 against a capstan 6 which extends across a film 1. Both of these are known in the prior art, though they are not shown in FIG. 1. 
     Indicated as 17 is a film sag detecting device in accordance with the present invention, more specifically the frame of the film sag detecting device. The film sag detecting device 17 is placed ahead of a sound recording head 4 in the film path between the film advancing tool 3 and the capstan 6. The frame 17 of the film sag detecting device is formed of an L-shaped member consisting of a vertical part fitted along a supporting member 16 (FIG. 4) which is further fitted along the internal back surface of a camera body. The frame 17 includes a horizontal part extending from the internal back surface of the camera body toward the front portion of the camera body. The frame 17 is fitted along the supporting member 16 in such a manner that the vertical part of the L-shaped member is placed at the back of the film path, leaving an open space for the film to pass through and that the horizontal part of the L-shaped member extends toward the front portion of the camera body also leaving an open space, above the horizontal part of the L-shaped member, for the film to pass through. Accordingly, it is extremely easy to load the camera with a film 1. 
     Referring to FIG. 4, the frame 17 has two openings 28 and 29, respectively, on the vertical part and the horizontal part. A light emitting element 20, specifically a red visible ray emitting element, is placed in the opening 28 together with a condensing lens 19. A light receiving element 21, specifically a silicon photo transistor, is placed in the opening 29. These light elements form an opto-electronic coupler. The light emitting element 20 and the photo transistor 21 are placed to face each other, forming between them a light path 22 which is inclined relative to the surface of the film 1 at an angle of about 45 degrees. A transparent L-shaped plate 18 is placed across the internal corner of the frame 17 at which the vertical part and the horizontal part thereof join with each other in order to protect the elements 20 and 21 from being polluted by dust. Therefore, the aforementioned light path 22, starting at the light emitting element 20, passes through the vertical part of the transparent plate 18, the open space outside the frame 17 and the horizontal part of the transparent plate 18, before it arrives at the photo transistor 21. Since the film 1 stays at a relatively higher position above the horizontal part of the frame 17, as shown by the chain-dotted line in FIG. 4, when it has a normal amount of sag, it does not interrupt the light path. However, when the film 1 excessively sags, the film 1 occupies a relatively lower position above the horizontal part of the frame 17, as shown by the solid line in FIG. 4, and consequently, the magnetically coated stripe 23 formed on one edge of the film 1 interrupts the light path 22. The reason why one edge of the film 1 is magnetically coated to interrupt the light path 22 is to prevent the film 1 proper from being exposed to the light emitted from the light emitting element 20. If an infrared ray emitting element, rather than a red visible ray emitting element, is used, such danger could be effectively avoided. In this manner, it is possible to detect whether the film sag is in the normal and allowable state or in an excessive and abnormal state. 
     Also referring to FIG. 4, indicated as 24 is a screw penetrating the vertical part of the frame 17 around the center thereof. The screw 24 contacts the internal surface of the supporting member 16 at one end thereof and is adjustable for adjusting the position of the frame 17 back and forth. Screws 26 fit the frame 17 on the supporting member 16, and a compression spring 25 lies between the head of the screw 26 and the frame 17. Therefore, the relative adjustment of the screwing extent between the pair of screws 26, in combination with the adjustment of the length of the screw 24 extending from the frame 17, is effective to adjust the position and the inclination of the light path 22, resulting in an effective adjustment of the minimum extent and the full range of the film sag requiring detection. 
     When the film 1 excessively sags as shown by the chain-dotted line in FIG. 3, the film 1 approaches the horizontal part of the frame 17 as shown by the solid line 1 in FIG. 4, allowing the magnetically coated stripe 23 to interrupt the light path 22 of the opto-electronic coupler. This interruption of the light path 22 causes the pertinent electric circuits to function for reducing the film feeding rate by means of the film advancing tool 3 driven by the motor 2, resulting in the appropriate correction for an excessive sag of the film 1. When the sag of the film 1 is corrected to the normal extent, the film 1 returns to the relatively higher position above the horizontal part of the frame 17 as shown in the chain-dotted line in FIG. 4, resulting in termination of the interruption of the light path 22, causing the motor 2 to revert to the normal operation for allowing the film advancing tool 3 to maintain the normal film feeding rate. 
     Since the film sag detecting device of the present invention uses mechanical means to an extremely limited extent, the opportunity for the occurrence of mechanical failure, as well as the requirement for space in a camera body, are extremely reduced from the models in accordance with the prior art. 
     Although a particular preferred embodiment of the invention have been disclosed in detail for illustrative purpose, it will be recognized that variations or modifications of the above disclosed devices, including the arrangement of parts, lie within the scope of the present invention.