In general, this invention relates to photographic film cassettes and, more particularly, an improved pressure pad spring and cassette arrangement therefor which avoids diminishing spring effectiveness and improves overall cassette assembly.
Multipurpose film cassettes have been developed in which a strip of photographic film is operated so as to be exposed, processed and projected without leaving the cassette. Film cassettes of this type are disclosed in several U.S. patents assigned in common with the present invention.
In film cassettes of this category, a supply of light sensitive photographic film can be selectively exposed in a camera particularly adapted to receive and operate the cassette. To process or develop the exposed film, the cassette is removed from the camera and placed in a player or processing and viewing apparatus capable of activating a cassette contained processor for depositing a desired uniform layer of processing fluid on the film's exposed emulsion surface. During such processing a conventional series of successive, positive transparent images on the exposed film is developed. Following processing in the manner indicated, the player apparatus is operated as a projector. During projection, the film is incrementally advanced, frame-by-frame, past a light source. Accordingly, the series of positive transparent images of the scenes to which the film were exposed are capable of being successively viewed while being projected onto a screen.
Towards the end of achieving the desired and critical fluid thickness on the film strip, as well as for avoiding blemishes in the developed transparent images, the cassette contains a spring-biased pressure pad yieldably supporting the film strip between the pad and a fluid processor nozzle structure.
The current state-of-the art with respect to achieving this uniform and substantially blemish free coating is represented by the disclosure of U.S. Pat. No. 3,951,530 issued Apr. 20, 1976 to Frank M. Czumak, Paul B. Mason and Joseph A. Stella, which patent is commonly assigned with the present invention. In the disclosure of this patent, the film's emulsion surface is yieldably urged into sliding engagement with the processor nozzle so that a uniform and predetermined gap exists between the emulsion surface and a doctoring surface formed on the nozzle. Formation of the desired fluid thickness is effected after the fluid has been deposited onto the film and passes the doctoring surface positioned downstream, in the direction of film advancement during processing, of a nozzle opening. This formation is facilitated by the doctoring surface being configured to develop positive hydrodynamic pressures in the deposited fluid which force the film strip into sliding engagement with the pressure pad. To resist this tendency, the pressure pad spring must be constructed to retain the desired gap spacing despite the presence of these hydrodynamic pressures. Also, the biasing force of the spring is selected to provide a net balance of forces on the film strip. This is accomplished by selecting the spring biasing force to be substantially equal and opposite to the hydrodynamic pressures. As a result foreign particles, such as dust or the like, on the emulsion surface of the film will effect a slight instantaneous increase in the gap between the doctoring surface and such emulsion surface and be permitted to pass therebeneath. Consequently, foreign particles will not be trapped and the possibility of blemishes occurring on the developed film is substantially eliminated, it being understood that these particles, in themselves, are inconsequential to either processing or developing because of their minute size. It will be appreciated, therefore, the spring force of the spring must be carefully controlled, otherwise the foregoing functions of the spring will result in significant operational problems. The type of spring described in the foregoing identified patent, which is the kind typically used in cassettes of this category, is a thin leaf spring having one end staked to the cassette, and the other end contacting and biasing the pressure pad. While the leaf spring performs satisfactorily there is potential for problems arising from the fact that the spring can be overstressed and thereby have adversely altered the noted preselected biasing force. Usually the problems of overstressing arise by virtue of the cassette assembly operations wherein an operator must periodically bend and thereby possibly overstress the spring in order to produce the completed film cassette. Aside from this potential problem use of the conventional leaf spring in its present embodiment necessitates relatively costly assembly procedures because of the staking operation.
It follows, therefore, that avoidance of overstressing the spring biasing the pressure pad during assembly is a major focal point of attention to overall film cassette development.
Moreover, the potential of the foregoing problems is further compounded by the requirement the cassette and its components including the pressure pad spring must be capable of mass production manufacturing techniques as well as be within tolerance levels incident to such techniques for the system to be acceptable in a competitive commercial market. Accordingly, the structural organization of components by which the film is supported in predetermined relationship to the doctoring surface is important to the overall system.